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  NinoTNC N9600A4 Assembly

page modified May 22, 2024
Specifications may change without notice.
Do not use this device in any situation where loss of life or property would be the result of the device missbehaving or failing. If you go beyond this rule, you are self certifying this device. This device is built by hobbyists for a hobby project. We do not certify that this design, or any particular unit, is sound. Use at your own risk.

Feel free to use all of the images on this page for publicity or articles!

NinoTNC A4 built with the Mouser bill-of-materials, February 2022
Note: The Mouser BOM (and these instructions) does not include the socket for the op-amp. Nino put a socket down on his unit for the op-amp to allow for easy experimentation with alternative op-amps. The CPU was not installed for the photo to show that the CPU socket is a machined socket instead of the usual.

These are the assembly instructions for the N9600A4r2 blue-board. Make sure the silkscreen information on the board you are assembling matches this. The bill of materials linked below is specific to the N9600A4r2 board.


From Oct 2021, Digikey ran out of stock of the IRLD120, our choice for Q1 PTT switch. We substituted the IRFD123 in the bill of materials on this webpage, not knowing that the drive voltage requirement for the MOSFET was different than the IRLD120.
This will cause a problem for some radios, but not all, and possibly not even most. The failure symptom is that some radios will not go into transmit when they should because PTT isn't driven close enough to ground.
Anybody who has NOT soldered down the IRFD123 should seek the IRLD120 part.
As I edit this web page (in early February 2022) the correct part for this board, IRLD120, is available at Mouser.
On February 8, 2022 we switched our recommended parts source on this webpage from Digikey to Mouser as Mouser has better stock of some of the less-widely-sourced components.

First Time Kit Builders

People who are unfamiliar with kit building may approach this as their first kit but there are a few caveats.
  1. Be careful. While this kit is one of the easier and better documented kits, and building a kit is pretty easy, a cavalier attitude will result in hard-to-diagnose failures.
  2. Have an experienced hand available for guidance and troubleshooting. Building a kit is much easier than fixing a kit. It is possible to reverse a soldering mistake, but it is definitely much harder than doing it right the first time. If you have any doubts, send a message to [email protected] and we'll try to help you out.
  3. If you find anything in the instructions which is unclear, write us. We'll try to fix it.
  4. If you are a first time kit builder, please consult your local experienced builder for help in reversing any mistake.
  5. #4 is important.
  6. Adafruit has some excellent tutorials on soldering.

  Order the Parts

It is important that once you load your shopping cart with parts on the Mouser website that you verify that all of the parts say "In Stock" for shipping.

Load the latest bill of materials from this page. If you have fetched this page before, make sure you refresh your browser and get the latest bill of materials.

Mouser deals with many different manufacturers of parts. If a part is out of stock, we can select a part from a different manufacturer, or, in some cases, a part with a slightly different value. Whenever a part is backordered, we can select a different part and update the BOM. This happens about three times a month.

If you see a part is backordered from the CURRENT Bill of Materials, start a new thread on ninotnc @ groups.io
Make your subject line the word "BACKORDER" the reference designator, and the BOM filename:
For Instance:

SUBJECT: BACKORDERED C7 in n9600a4f_bom_m426
Almost everything is available from a second source right on Mouser.
We'll fix it and send a reply.
If you go ahead and let it be backorded, Mouser may charge you postage twice, or delay your shipment.
If everything is available, do checkout and pay for your order. with a SUBJECT containing backordered, the Part designator (i.e. C7), and the BOM file name. We'll try to take care of it really quickly and reply to that email.
example subject:backorder C7 in N9600a4f_bom_m426


Bill Of Materials Right-click on this link and save the n9600a4 m029 bom XLSX spreadsheet file to your computer.
This is the Mouser shopping list for the NinoTNC.
Find the n9600a4f XLSX file on your computer (it will be named starting with n9600a4 and will be a XLSX, Excel Spreadsheet, file)
Go to Mouser website Click on this link: Mouser. You might as well register at Mouser because they're going to get your delivery information and whatnot anyway. Registering and logging-in means that your shopping cart is retained through separate sessions, on separate computers, and they will provide you with a history of your orders.
Shopping Cart Click on the shopping cart. If there are already items in your cart, you can click on View cart and then New Cart.
Upload CSV There is an Upload A Spreadsheet field in the middle of the form.
Drag the XLSX file from your Finder/Explorer into that field,
or click on Browse your files,
and then navigate to the XLSX file.
Price Availability Assistant The web page will now want you to specify what the columns in the spreadsheet represent.
By adjusting the drop-down menus at the top of each column, you can tell Mouser that you have
Mouser OR Mfr. #, then
Qty. 1, then
Customer #, and then leave the rest of the field headings blank.
The Line items begin on row# should be set to 1.
Click on Next
USB cable? If you need a USB A male to USB B printer cable, better shop someplace else as Mouser doesn't seem to be the cheap place to go. You should be able to find a half-meter printer cable (1 foot or so) for under $5. In quantity I've gotten them for 50 cents on eBay.
Short is better for RF immunity but it does have to make it from the host computer (Raspberry Pi) to the NinoTNC.
Checkout Inspect the list
1 Ships Now or something like that means good.
If anything is On Order, stop and send an email to [email protected] email reflector.
Make your subject line the word "BACKORDER" the reference designator, and the BOM filename:
For Instance:

SUBJECT: BACKORDERED C7 in n9600a4f_bom_m426
Almost everything is available from a second source right on Mouser.
We'll fix it and send a reply.
If you go ahead and let it be backorded, Mouser may charge you postage twice, or delay your shipment.
If everything is available, do checkout and pay for your order.

What you will need

⇒  All parts are inserted from the silk-screened side of the board, i.e. from the side on which the white writing is printed.
⇒  Except where specifically noted, all two pin components are non-polorized so you can put the part onto the board with the pins in either hole.

Soldering tips

Insert the component so it is flush without breaking the part.
Splay the wire-leads out to keep the part in the board while you invert the board to solder.
Solder the leads at the hole.

Inspect the leads to make sure the solder comes up over the lead for a visible amount. Cut the lead at the point where the lead meets the solder, but don't cut the solder. The solder is your friend. What you do NOT want is a lead which is not making good electrical contact with the hole.

When debugging the NinoTNC because something went wrong, it is nice to have a clear image of the naked printed circuit board (PCB). Here you go:

A4r2 board:
Click either to enlarge

The ground plane and power plane on our printed circuit board (PCB) are not visible on the top and bottom becuase this is a four layer board. The ground and power are pretty much everywhere except near where wires pass through.

Here's the A4 PCB's schematic. Click to load the PDF.

Circuit description

The NinoTNC has an audio output, TXA, to drive a radio transceiver, an audio input, RXA, to be fed by the radio transceiver's receiver, and a PTT output which pulls to near ground in order to key up the radio transceiver. The main components of the NinoTNC are the connector to the transceiver, the connector to the host computer, the processor, the displays and controls, a USB interface, and a quad op-amp audio amplifier.

The USB host connection, a MCP2221 USB to serial interface, takes USB host signals, at multiple megabits/second, converts it to serial data to the CPU at 57600 bits/second, and takes serial data from the CPU, and pushes it to the host computer's USB.

The quad op-amp, an MCP6004, is 4 separate operational amplifiers which are used in two capacities. First, it is a transmit audio buffer and filter which takes the simulated analog output from the CPU and smooths it and filters it to generate the best transmit audio wave-form we can for the given packet radio transmission, while keeping the impedance of the radio's input from affecting the fidelity of the CPU's analog output. Second, it is a receive audio buffer to allow the CPU to read the received audio, without the CPU screwing up the impedance on the receive audio signal and thus affecting the voltages, or audio fidelity, on the receive signal. One of the four op-amps, connected by pins 8, 9 and 10, is left unused in this version of the NinoTNC.

The CPU's purposes are

The transmitted packet starts with the CPU driving Q1 to pull PTT to near ground, then a preamble bit stream is sent, followed by the synchronization word, and then the packet described by the host computer. Finally, the CPU stops driving Q1 allowing the PTT line to be pulled high by the transceiver, unkeying the transmitter.

The LEDs and controls have several functions as well.

Assembly Instructions

Some of the images on this page can be enlarged and opened in a new browser tab by clicking on them.

Install parts in this order:

1 Y1 7.3728 MHz crystal
The crystal will have some lettering on it containing 7 and 3, in order. It may say 037 or 7.37 or something like that.
The crystal and two capacitors, C4 and C5, form an oscillator to provide clocking for the CPU's digital circuits.
y1 after install

2 R4, R15, R16, R17 100 k Ω 5% 1/4 W resistor
R4 is part of the output impedance/level control, along with RV1 - TX Deviation Adjust. R4 is bypassed by the Mic/Data DIP switch. R4 attenuates the TXA signal to support low-volt, high sensitivity microphone inputs to use NinoTNC

R15, R16 and R17 are a filter in the receive circuit.

Note: the color codes on the 1% resistors are pretty hard to use. If you are receiving your resistors in a mixed bag of parts, you probably want to do all of the remaining resistor steps before soldering the resistors so you can double check the color codes before you solder and cut. I recommend using a VOM to prove that each 1% resistor is what you think it is, and not one of the other values.

3 R10 7.87 kΩ 1% 1/4 W resistor
7.87kohm resistor
This resistor is in the input and feedback loop for the 2nd op-amp stage in the TX-data/audio path.

4 R11 47 kΩ 5% 1/4 W or 1/8 W resistor
1/8 W shown
brown or blue body is ok. The stripes are how the part is identified.
R11 turns off the MCLR input to the CPU in the normal case when a PIC-Kit programmer tool is not attached to the ICSP connector (J4). The PIC-Kit uses this input to reset the CPU as needed when programming or debugging. If this resistor is missing, the MCLR line would float across many voltage levels, causing intermittent CPU resets.
r11 after install
r11 after install closeup

5 R12 4.75 kΩ 1% 1/4 W resistor
4.75kohm resistor
This resistor is in the audio path between the 1st and 2nd op-amp stage in the TX-data/audio path.
after r12 install closeup

6 R13 7.15 kΩ 1% 1/4 W resistor
7.15kohm resistor
This resistor is in the input and feedback loop for the 1st op-amp stage in the TX-data/audio path.
after r13 install closeup

7 R14 14.7 kΩ 1% 1/4 W resistor
14.7kohm resistor
This is part of the filter circuit for the 1st op-amp stage in the transmit data circuit.
after r14 install

8 R18 15 kΩ 5% 1/4 W resistor
15 k ohm resistor
R18 is part of the amplification circuit for the Receive audio op-amp.
after r 18 install
after r18 install

9 R19 150 kΩ 5% 1/4 W resistor
150 k ohm resistor
R19 is part of the amplification circuit for the Receive audio op-amp. One of the SIGNALS switches, 1x/11x, bypasses this resistor. If this resistor is bypassed by the switch in the UP (toward edge of the PCB) position, then the gain of the amp is 11x. If this resistor is in circuit, switch in the DOWN (toward the TARPN logo) position, then the gain of the amp is 1x, which is also unity gain.
after r 19 install
after r 19 install

10 C4 and C5 18 pF 5% 50 V Ceramic capacitor (may be 100 V)
marked 18 with a following letter.
A substitute part may be blue.
C4 and C5 are part of the crystal oscillator circuit

11 C8, C12, C13 0.1 µF 10% 50 V Ceramic capacitor
0.1uF c8
These ceramic radial capacitors provide power supply filtering and glitch reduction on the CPU’s main power input and two other places on the board.

Be careful here. Starting now we'll be installing components which are polarized. That means you have to get each pin in the correct hole.

12 Q1 MOSFET 100v 1.3amp 4-pin DIP      PTT driver.
Metal Oxide Semiconductor
Field-Effect Transistor

q1 back of the board
Warning - from October 2021 to end of January 2022 the BOM had the wrong part!
The IRFD123 is not a good part for Q1.

Install so the two shorted-leads (see images) are away from the TARPN Logo. The two independent leads are nearest the Q1 symbol. You'll have to squeeze the pins across the chip so they line up with the holes. You can test insert on the bottom of the board where there are no part-neighbors.
Once you have the chip inserted in from the top of the board, go back to the bottom of the board and spread two corner pins out so the part is held in place. See images.

This four-pin device is driven by a GPIO on the CPU and is responsible for pulling the PTT line to ground when the NinoTNC wants to send a packet. The device takes a turn-on signal, in the form of very little current at 3.3v, from the CPU. If no turn-on current is present, the output of the MOSFET is allowed to float. The radio will provide a pull-up voltage.

When used with a microphone, the measured voltage on the PTT wire is whatever the radio generates. When the microphone button is squeezed, the PTT wire is grounded to the radio ground, bringing the voltage to a relative 0 V.

When used with NinoTNC A4, the PTT wire is fed into, or out of, the TNC through the DE9 connector, directly to the MOSFET pins 3 and 4. If the CPU is not asserting its turn-on signal to pin 1 of the MOSFET, pins 3 and 4 are dragged up by the radio's PTT voltage. When the CPU asserts 3.3 volts onto its GPIO output, wired directly to pin 1 of the MOSFET, the MOSFET shorts pin 3 and 4 through its internal diode to pin 2, which is ground on the NinoTNC and ground on the DE9 connector.

When the CPU is asserting the PTT as active, the 3.3v also drives LED D1 to turn on. Note that the LED can function even if the MOSFET is completely missing, so D1 illuminating is not a sign that the MOSFET is installed correctly or working.

The other design consideration is that we want to prevent leakage between the PTT wire from the radio into the CPU. With the TNC we started with, the TNC-PI, it was possible for the CPU to power itself from the leakage through the NPN transistor. This is still an uncertainty because, though we saw the CPU do some bad things, we never proved it was powering from the PTT leakage.
We went with the MOSFET, instead of the NPN transistor, just to be sure.

Q1 after install

13 XU3 28 pin DIP IC socket for U3
closeup of pins
This is the socket for the CPU.
  • Make sure all pins are straight before you insert the socket.
  • Use long-nose plier to fix any that need fixing.
  • Carefully insert into the board with the round half-moon end pointing to match the board. -- That will be up from the perspective of this image.
  • Once all 28 pins are showing through the board, bend the corner leads outward to keep the socket from falling out as you invert the board to solder.

pcb looking down after ux3 socket install

14 U2 MCP1702 3.3 V or
MCP1700 3.1 V
250 mA
TO92 case regulator
This part takes the 5 V DC from the USB connector and regulates it down to 3.3 V or 3.1 V, to fall within the 3.0 to 3.6 V operating range of the dsPIC CPU.
Align flat edge with the board silkscreen
pcb looking down after u2 install
u2 close up after install

Here is the schematic showing the regulator and its two caps. I talk about this circuit fragment again in the step where you add the two capacitors.
regulator schematic

15 RN3 5 resistor 180 Ω resistor network
Substitute may be a 220 Ω resistor network
schematic for RN3
bent leads on bottom of board
Orientation is important!
Pin 1 is identified by the square around the hole on the PCB and an interesting symbol near the end pin on the component. See schematic symbol below.
I had good luck by folding two of the leads in opposite directions to hold the part in place before soldering. Once you fold the two pins, align the part upright, then solder.
This five-resistor network provides an in circuit resistance to limit the LED current for each of the 5 LEDs
RN3 after install
RN3 closeup
RN3 closeup

16 C17, C18 1 µF
[metal] film capacitor
radial leads
c1 1uF capacitor
C17 is part of a receiver filter between the DE9 and the CPU.
C18 is capacitive coupling just before the DE9 on the TXA circuit. C18 is bypassed by SIGNAL switch SW3. Capacitive coupling has the effect of moving AC (audio) waveforms such that they are relative to the recipient's own neutral. The input to C18, in NinoTNC's TXA output circuit, is alternating current audio wich is relative to the final op-amp's output. In this case the output is all elevated by 1.65 volts, so the negative going side of a sine wave could be just barely above 0 volts, where the positive going side is nearly at 3.3v. This 1.65 volts is called a DC offset. If DC/AC switch is off, i.e. AC, the TXA output goes through C18 and the DC offset is removed from the signal. Having the DC/AC switch set to off is the prefered mode of operation of the NinoTNC, at least at this time.
after c17 and c18 -install
c17 c18 closeup

17 C2, C3, C11, C15 10 µF 10% 16 V
tantalum dipped capacitor
10uF Tantalum
Carefully observe values and polarities. Positive side is marked with a very small plus sign on the part, or a red stripe, and goes into the square solder pad/hole on the PCB. The silk-screen actually + sign.
C2 is 5v filter on the input to the regulator.
C3 is the 3.3v filter on the output from the regulator.
regulator schematic
C11 is vcap input to the CPU on one side and ground on the other. VCAP is a pin on the Microchip CPU used for an internal filter. I'm guessing it is to make the Analog to Digital converter input more stable.
C15 is part of a receive filter circuit, along with C1 R15 R15 R17, between the DE9 and the first receive op-amp stage.
10uF Tantalum
10uF closeups C2 and C3
Click to zoom. The above image shows the positive + stripe on the capacitor lining up with the + on the PCB for C2 and C3.
As an aside, you can critique the soldering on this board. Notice how both sides of C2 and the + of C3 are well soldered and the - side of C3 isn't? The solder should be heated for long enough for it to flow through along the pin to show on the top side of the board. This is a technique that is really hard to be perfect at, but it's worth noting. Perfect soldering leads to the light side of the board.
10uF closeups C11 and C15
The above images show the positive + stripe on the capacitor lining up with the + on the PCB for C11 and C15.
10uF closeups C15
better image of c15. Again with the soldering

18 RV1 and RV2 10 kΩ 1/2 W cermet 1-turn side adjusted trimmer potentiometers. Label="103"
10 * 10**3 = 10000 Ω.
two potentiometers, rv1 and rv2
Notice the arrow on one of the legs of the yellow cross. It is pointing down in this image.
If necessary, RV2 (TXDELAY) can be a larger value, up to 100 kΩ.
Place the two parts side by side in the appropriate holes. The yellow screwdriver adjustable end faces the edge of the board.
Solder one pin on each part.
Hold each part with a finger while heating the one pin so the solder melts and the part can be pressed flat to the board.
Let the solder harden, and then solder the other two pins.
Finally, go back and wet the original pin and let the solder reflow around the pin.
TXLEV RV1 adjusts the Tx Audio level at the output of the TXA op-amp pair.
TXDELAY RV2 adjusts an input to the CPU and is used by the program to set the transmit preample duration. This preamble compensates for the time needed for the transceiver to switch from receive to transmit.

19 C6 3300 pF
[metal] film capacitor
radial leads
3300pf capacitor
This is part of the feedback loop in the 2nd stage of the transmit data output.
c6 closeup

20 C9 1500 pF
[metal] film capacitor
radial leads
1500pF capacitor
This capacitor looks just like another of your capacitors.
Look at the label carefully!
c9 part
This is part of the feedback loop in the 1st stage of the transmit data output. A wrong value here would make your packets hard to decode while the loopback test might pass!
c9 after install
c9 closeup

21 C7, C10 1200 pF 50v capacitor
light-yellow polyester-film
or blue ceramic
In the transmit Op Amp chain, these two capacitors are across the input on each of the first two stages.

There is one capacitor left over, marked 15J100 0.15uF. . We'll use it in one of the last steps.

22 J3 USB-B socket
This socket has 6 solder points, two of which look like they'll get in the way when you insert them. They don't. But they will hold this connector onto the PCB. Solder all 4 pins and the 2 support items.

Test #1 -- Regulator Test

Now that the USB connector is on the board, 5 V will get to the board. It will be regulated down to 3 V by U2 and will show up at the CPU socket at pins 27 and 28.

If this test fails, inspect the USB connector, U2, C2, C3, socket U3. Also look for any solder bridges (smudge between two solder points) or insufficient solder on a pin.
23 SW1 and SW3 4 position dip-switch
package with 4 white switches
May be black or red
Install each switch so the label 1 2 3 4 is toward the TARPN-logo edge of the board.
Each switch is a separate circuit. SW1's four switches pull four separate CPU inputs on the CPU to VCC, and are used to select options. SW2 has four different circuits... more coming. One switch bypasses a resistor which, if the switch is off, reduces the output drive level such that a microphone input radio can be used.
Important: If the switch is installed upside down, all of the photo references and instructions will be backwards. Take care in installing the swiches so the label 1234 is toward the TARPN-logo edge of the board!!
SW1 board placement
SW1 board placement
SW3 board placement
red SW3 board placement

24 SW2 side facing push button switch labelled TEST TX
Mount so switch button faces off the edge of the board, directly away from the J3-pins in step 24. Solder one of the smaller pins (not the switch shell), then, while pressing the switch into the board, wet the pin's solder again and make sure the switch is fully flush to the board.
This switch will tell the NinoTNC to send a transmit-audio-calibration tone and also generate a transmit packet from the saved callsign and to "CQ". The transmit packet is held until the switch is released.
While the switch is held the NinoTNC will send one of 4 calibration tones which can be used for setting TX-LEV.
On release, the NinoTNC sends a KISS frame back to the host with diagnostic data, and the NinoTNC also transmits the queued packet.
Electrically, pressing this button connects a GPIO input on the CPU to VCC.
Releasing lets the GPIO input be pulled to ground by the CPU's internal configurable "weak pulldown".
sw2 board location
sw2 txtest closeup
sw2 txtest closeup

In the next steps you'll be soldering 5 LEDs onto the PCB. When you cut the leads, save the trimmings for use as scope test loop wire in a later step. You only need 3 longish thick wire leads for the scope test loops, but save as many as you can for practice purposes.

25 D1, D3, D4, D5, D6 LED installation

In this step you are going to bend the leads of all 5 LEDs.
What we need is a fixture to allow all 5 LEDs to be bent the same so they point out the end of the board. It is only critical that the LEDs be perfect lengths and all the same direction if you intend to ever show this NinoTNC to anybody. It's even more critical if you obtain a housing for the NinoTNC made with the LED positions in mind. The leads need to be just long enough before the bend such that the LED lays over the end of the board and just misses the end of the board.

We're going to use a USB connector for a guide. It happens to be exactly the correct size. Grab a USB A connector, just like the kind on a keyboard or mouse cable where it plugs into the Raspberry Pi.
Put the LED so the short lead is toward the cable side of the connector and the long lead is toward the plug.

The LED body's base will be against the wide side of the plug and the wires lay around the short side of the plug.

Now fold the wires over the wide side of the plug making a 90 degree bend.

Here is the result we want:

Notice the short wire and the long wire on the LED. The short wire goes in the hole showing the square pad.

After bending all 5 LEDs, solder them in by color, then clip and save the trimmings for later use.

D1 Red LED
TX - This LED is illuminated when the NinoTNC is keying the radio through the opto-isolator.
D3 Yellow LED
Data Carrier Detect. This LED will illuminate during radio received when several zero crossings occur in the wave-form (noise) which match the selected bit rate.
D4 Green LED
Last RX packet was decoded properly. This LED remains illuminated until a short time expires, or a packet is not decoded properly.
D6 Blue LED
TX message is queued. The Pending LED illuminates when the NinoTNC has a message ready to transmit but hasn't had the opportunity to get rid of it yet.
D5 Red LED CRC error on receive packet, This LED illuminates when a valid callsign field is received but the checksum/CRC on the packet doesn't match the rest of the packet and error correction either couldn't be applied, or didn't fix the problem.

26 U3 Microchip dsPIC33EP256GP502 CPU
To make the chip fit into the socket easily, place the leads on one side against a hard flat surface and push on the package to bend the leads. Then turn the IC over and do the same thing on the other side. The pins themselves should be straight, but not splayed out like they are when the IC shipped.
Make sure the half moon on the IC matches the half moon on the socket and on the PCB.
As you insert the chip for the first time, don't push it all the way in.

Get all of the leads to go into the 28 holes, then reverse and pull the chip back out. It may be advisable to use a screw driver to gently lift one end a little, then the other.
Once the chip is removed, inspect the leads and make sure none of the bent while inserting. Fix any needing fixing and then insert the chip again, paying attention to the half-moon end as per the photo. If all goes well, push it in all the way.

Test #2 -- CPU Clock, LEDs, and TEST TX Button

If all 5 LEDs were made to illuminate independently, and if the MODE dip switch caused the 4 LEDs to cycle, skip to the next step. You are done with LEDs.

There are features in the A4 firmware, engaged by holding the red TEST-TX button for seconds, which can leave the CPU "stuck" in a test mode (A4 Operations, chapter 19) which could create a confusing LED display. These test-modes are sticky and survive through reset and power cycling. To exit a test mode, simply press the TEST-TX button for a short period (1 second or less), and then release.

If the LEDs did not perform as described, check the CPU for bent pins.
Failing that, inspect the LEDs carefully, as well as the soldering around the CPU socket, the MODE switch, the RN3 resistor array. One or more LEDs might have been installed backwards -- that's not uncommon. Installing one LED backwards should not affect the other LEDs. Rarely a problem is caused by incomplete soldering of crystal Y1 or capacitors C4 and C5 near Y1.

Notice the shape of the metal inside the LEDs. The LED face toward the top of the board is a mirror of the face toward the bottom of the board. Look in the parts of the metal which are in the bulb of the LED.
In addition, for all but the blue/clear LED, there is a difference in the shape of the legs near the bottom of the LEDs. The thicker part, where it joins the plastic part of the LED, is in the square hole.
The tops of the LEDs should look like this:                Back of board view should look like this:

Closeup of top of silkscreen side of PCB with LED. Notice the shape of the metal inside the bulb.

Closeup of top of back side of PCB with LED. See here that there appears to be a slot between metal pieces inside the bulb. Now check the photos up above and see if you can tell that the LEDs match on the top photo and on the back photo.

If your inspection shows the LEDs are installed correctly, reapply power and use your VOM to measure the DC voltage of pins 27 and 28 of the CPU.
These are the pins closest to RV2 potentiometer in the corner of the board.
You should see 3.3 V. If not, check for shorts or badly inserted pins on the CPU.
If you do see 3.3 V, we have a problem that might take an oscilloscope to check.
Try swapping CPUs with another board if one is available.
Even a CPU from an A2 board would at least light the LEDs.
Look for 7.3 Mhz sine wave on pin 9 and 10 of the CPU.
If 7.3 Mhz is present, then its possible your CPU is not programmed.

27 Test points GND, TXA, RXA These are loops of scrap wire bent around the blade of a long-nose-plier.
Test points for receive audio, transmit audio and ground. Uses these to connect a high-impedance input audio amp to listen to packets, receive or transmit. Or connect an oscilloscope to observe the receive voltage or wave form quality.
See pix below for installation.
ground test loop img-1972
rxa and txa loops img-1971

The integrated circuits installed in the next two steps are exactly the same size. They are of completely different function and if you put the wrong one in, thinking you only have one to go, you will have quite a bit of work removing it! Be careful that you grab the correct chip for this next step!

28 U1 MCP6004 quad op-amp
may substitute MCP604 or MCP6284
Install the quad op-amp Integrated Circuit without a socket. The pins will have to be bent a little to fit. See step 30. Since the PCB is now rather crowded, and since the pin bending requirements and limits have no calibration, I recommend test-fitting the IC on the back of the PCB, and then when you get the pins bent as needed, move around to the front of the PCB and insert the op-amp where it needs to be.
This is a quad-package op-amp (operational amplifier) used to buffer the receive AF data signal from the radio and to condition and buffer the transmit AF data signal to the radio.
The quad op-amp has 4 separate amplifier sections. 2 of these are used in the transmit AF signal processing. 1 in the receive.
Make sure the half-moon shaped end lines up with the PCB as shown in the photos.
29 U4 MCP2221 or MCP2221A
USB interface chip
u4 part
Install the MCP2221A USB-serial interface Integrated Circuit without a socket.
Make sure the half-moon shaped end aims toward the USB-B socket.

Note the extra header pins, J5, underneath where U4 MCP2221 is installed. These pins are for an optional header to be used if the NinoTNC will have a TTL interface and separate 5v source. This could be handy for an embedded project where USB interconnect would be inefficient. If you intend to use a TTL interface to the NinoTNC, don't install U4.
u4 header
u4 header

30 C16 CAP FILM 0.15UF 5% 100VDC 
c16 part
This capacitor looks just like C9. Look at the label carefully!
c16 part

This capacitor is in the receive audio and serves to remove DC offset from the received audio. If this part is missing, there won't be any receive audio. See schematic below.

31 J1 DE9 connector
This connector is the interface to the transceiver from the NinoTNC.
TXA data, PTT, RXA data, and ground are connected to pins 1, 3, 5 and 6 respectively.
Solder a center pin first, then squeeze the connector into the board and then reheat the center pin.
Now solder the remaining 8 pins and then the two outer fingers in 3 places each.
de9 j1 installed

Test #3 -- Op Amp and Full Cycle NinoTNC Loop Back Packet Exchange

This procedure will show that the op-amp is soldered in correctly and that the support components for the transmit and receive audio paths are installed, by actually sending a packet out through the transmit audio path and back through the receive audio path, demonstrating that most of the components must be working. It is our expectation that if a NinoTNC passes loopback test for 9600 baud, it should work correctly with a 9600 capable radio.
Note that the GREEN LED is the sign of a passing test. The Yellow LED does not illuminate on some versions of firmware.
Here's a video of the loopback test run at 1200 and 9600 baud. Note that this video shows the yellow LED coming on. In some versions of the firmware the yellow LED does NOT activate during the operations of a well built NinoTNC. This is a firmware thing, not a mark of bad parts or assembly.

The green light is the 'good' sign that the unit is passing the tests.

TARPN NinoTNC N9600A4 loopback test-demo [rumble.com]

Test #4 -- USB Driver

This test procedure shows that you are getting a USB connection from the computer to the NinoTNC.

To test the host-computer to USB connection, you will need a computer whose OS lets you see when a new USB device is attached.

    Test Procedure for MSWindows XP, 7, Vista, 8, 10:
  • Attach the USB-A end of a USB cable to a computer and set up the computer to show you what USB devices are attached.
  • Find and open the Device Manager on MSWindows. It is available from Start and then right-click on "Computer" and then click on Device Manager. Note that this varies by MSWindows OS version. If you can generate screen shots detailing this, I would love to have copies and make a separate web page per OS version.
  • Attach the USB-B end of the USB cable to the NinoTNC.
  • Observe that a new item appears in the Device Manager. It may be in "Other" or in "Universal System Bus Controllers" and it will have the text "MCP-2221 USB-I2C/UART Combo". That's the NinoTNC.
  • If the computer offers to get a driver for this unit, let it download it from the Internet. The good news about using an obscure combo USB chip is that nobody is cloning it, yet, or that Microchip is defending itself from.
  • Now download and run PUTTY, terminal program. Here's a movie by K4FD showing the procedure.
    TARPN NinoTNC USB testing by K4FD Here's a PDF by AL0I showing how to test the NinoTNC USB/serial operation if the driver does not automatically install.
    Test Procedure for MacOSX:
  • Attach the USB-A end of a USB cable to a computer.
  • Launch the Terminal application
  • Type (or paste) this command ls -lrats /dev/*usbmodem*
  • The ideal response would be ls: /dev/*usbmodem*: No such file or directory
  • Now plug the USB-B end of the cable into the NinoTNC.
  • Now repeat the command ls -lrats /dev/*usbmodem*
  • The ideal response would be
    macmini:tadd$ ls -lrats /dev/*usbmodem*
    0 crw-rw-rw-  1 root  wheel   13,   0 Jun 13 10:30 /dev/tty.usbmodem14601
    0 crw-rw-rw-  1 root  wheel   13,   1 Jun 13 10:30 /dev/cu.usbmodem14601
  • Hopefully you have a program which can talk to a KISS TNC and demonstrate that this works. An important detail you may need is that the NinoTNC appears to be a 57600baud serial connection.
    Test Procedure for Linux:
  • Attach the USB-A end of a USB cable to a computer.
  • Launch the Terminal application
  • Type (or paste) this command ls -lrats /dev/ttyACM*
  • The ideal response would be ls: /dev/ttyACM*: No such file or directory
  • Now plug the USB-B end of the cable into the NinoTNC.
  • Now repeat the command ls -lrats /dev/ttyACM*
  • The ideal response would be
    pi@raspberrypi:~ $ ls -lrats /dev/ttyACM*
    0 crw-rw---- 1 root dialout 166, 0 Jun 13 10:58 /dev/ttyACM0

See the Operations page for more info
© Tadd Torborg, 2019↝2024 -- all rights reserved