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Post by husker on Oct 5, 2008 0:07:38 GMT -5
Ok guys.. I went to use SSB on my D201a and I have audio, but no transmit. So I tried replacing v701 just to see if it could be going bad..no help. So I replaced my Balanced Modulation brd with my spare and it works great again. Now I want to fix my spare just in case I have another failure. Any one have any ideas on where I should start?  ? Bob |
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Sandbagger
Administrator/The Boss 
Posts: 6,247 
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Post by Sandbagger on Oct 6, 2008 7:18:04 GMT -5
Ok guys.. I went to use SSB on my D201a and I have audio, but no transmit. So I tried replacing v701 just to see if it could be going bad..no help. So I replaced my Balanced Modulation brd with my spare and it works great again. Now I want to fix my spare just in case I have another failure. Any one have any ideas on where I should start? ? Bob Well, the BM board is responsible for both AM and SSB transmit. If Am is working and only the SSB part is inop, then part of the RF chain is still working. Is both SSB modes out or just USB? If USB only, then I'd look at the USB carrier oscillator crystal (X200) and associated circuitry. If both SSB modes are out, then you have two paths to look at. Check for the presence of audio along Q204 and Q206 including the coupling capacitors. You should have microphone audio up to the junction of D212 and D214. If audio looks good, then the problem is likely in the RF path. On AM, the RF is bypassed around the balanced modulator, the crystal filter and Q201, so check along that path in SSB mode. Trace the signal with a scope probe or RF voltmeter. The schematic gives approximate signal levels. Also check D.C. voltages on the various stages. |
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Post by husker on Oct 6, 2008 10:23:47 GMT -5
Both USB and LSB are dead, I have no transmit, no audio no nothing. The only thing I did was replace all the E-caps on that specific brd. I went back through it and checked all the solder joints etc.. I will check voltages next
thanks!!!
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Post by 2600 on Oct 6, 2008 20:29:52 GMT -5
It transmits with your spare BM board.
And it won't with the one you reworked.
Compare the polarity of the three 1uf capacitors on the working BM board to the ones on the reworked board. We know that they are turned around the right way on the board that works.
My prediction is that you will find one or more of these caps turned the wrong way on the board you updated.
This is all it takes.
You'll never guess how I know this.
Odds are that the old parts were marked with a "+" on one end. The pc board is NOT marked this way. The new ones probably have the negative end marked "-" on them. This creates an opportunity for confusion, even if you have practice doing this.
I suggest that you not molest parts on your spare board until the 'reworked' one is talking like it should.
73
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Post by husker on Oct 6, 2008 23:27:16 GMT -5
That was actually the first thing I checked. I am in Washington DC now, butI will certainly look again. That is why I keep a spare for everything I work on  The best way to learn is to dig right in! |
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Post by Marc on Oct 6, 2008 23:27:25 GMT -5
2600 dont the newer caps have a longer lead on the + leg
and the - pole have markings on the side??
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Post by husker on Oct 7, 2008 11:37:49 GMT -5
2600 dont the newer caps have a longer lead on the + leg and the - pole have markings on the side?? yup, the ones I got are exactly that way |
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The best way to learn is to dig right in!