Re: I broke it, but it's not the finals

James Daldry W4JED

Hi, Jeffrey

If you have 9 volts on IC3 pin 3 at all times, that voltage has to come from the +12 in some way. The logical place would be by way of a punctured gate on Q1, 2, or 3, combined with a shorted always-on Q6. If you pull out Q1 thru Q3  or Q6 I bet the 9 volts goes away. Sounds like the standard Q1, 2, 3, 6 fix.



On 6/29/19 6:52 AM, JH via Groups.Io wrote:


I neglected the troubleshooting page on the website and was instead going through the schematic and the chip datasheet. Comparing the expected voltages with mine reveal they are not ok. Pins 1, 2 are +5V, pin 3 is +9V. In transmit I get this modified square on pins 1, 2:

On pin 3 transmit I get +6.5V DC. Pin 4 looks normal. Pin 5 has +5V DC on Rx and Tx, with a tiny voltage change. Pin 6 goes from +5V DC to the modified square as in pin 1 (makes sense, pin 6 feeds both pins 1, 2).

Pin 8 goes from +5V DC to this ringing pattern on Tx:

Pins 9, 10 look normal. Pin 11 is also +5V DC on Rx and Tx. Pins 12, 13 drop from +5V DC to +4V DC on Tx.

I suspect I may have a short somewhere downstream from pin 3, given it has high voltage in Rx. I will need to double-check traces around Q1-Q3. I also started looking at the PA section of the troubleshooting page, but it's getting late and a more thorough investigation will take some time to figure out.

Thanks for pointing me in a direction. Since this is my first transceiver kit (and my first failure, hihi) I would like to learn as much as possible from it.

73 Jeffrey

On 6/25/19 1:31 PM, Alan G4ZFQ wrote:
IC3 seems to be functioning (I see logic high on the input pairs and see logic high on the outputs).


And you get 5V squarewave (meter usually reads 2.5V) on pin 6 as described on the troubleshooting page?

(Q5) seems to pass a basic mosfet test, but then I found the gate never drops voltage when I key down.

Possibly, but this is not really a PA check, it is isolated by C33.
Check all IC3 voltages according to that page.
There has been one case that a PA fault went right back to the 328 but you need to follow the sequence of checks.

73 Alan G4ZFQ

??The manual's circuit overview states that
Tx is low while Rx is high. In fact, in Rx it reads about 4.6-4.7V relative to the regulator's ground, and in Tx it goes /up/ to about 4.8-4.9V. Does this mean the 328 is not bringing the pin down?

So the switch never turns to Tx mode, so wouldn't that mean it's stuck in Rx mode? No, because I don't get any Rx audio, and if I key down I get a signal in my nearby SDR (but the amp transistors don't turn on, so my tuner's deflection meter doesn't move).

At this point my limited knowledge has reached an end. I've switched out the the transistors enough times to lift traces (due to one of my original mistakes of using lead-free solder, doh!) and it's getting to the point where I can't mess with it any more, lest I completely trash the PCB. The whole unit has been relegated to the cannibalism pile, but I would still like to know what exactly went wrong. I have a project in need of some parts, so I would be willing to tear it apart for other tests, unless someone knows what's up and how to fix it ;)

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