Thanks for that suggestion Martin, that sounds like A Cunning Plan! I shall do just that. VERY much a newbie with an Oscilloscope, so will read up about changing the vertical sensitivity and the timebase first. The Rigol seems to have a pretty decent manual fortunately.The TDA1541A dac is current-output, so you won't see AC voltage on its outputs; that's the job of the I-V converter on each channel, which is the pair of OP42 opamps immediately adjacent to the dac - with a very handy ground point adjacent were several wires meet.
The output signal voltage appears on pin 6 of each - counted relative to the notch on the opamp body:
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So - clip the scope probe ground wire to the ground point, checking you get continuity onto the bare wire stub
If so - then the dac is working, and the problem lies downstream; since the problem affects both channels, it's the muting relay/ its drive circuit.
- Set the scope to a vertical sensitivity of something like 1V ac / division and a timebase of maybe 1mS/ horizontal division
- Set a CD playing
- Carefully with the probe set at' x1' - probe pin 6 on each of the two opamps.
- Check to see if you are getting music out of the dac..! which will be a recognisable jumble of waveforms of nearly 3v pk-pk.at each .
Feint hope, but I wouldn't want you to tear-into removing the dac without testing it is not delivering first. The PCB tracks on these are getting fragile.
Find the data sheet for the reed relays and just bypass the audio switch pins with a bit of wire from above the pcb ,they are trouble some, when you get it working bob some new ones in as part of the service.
Thanks for that suggestion Martin, that sounds like A Cunning Plan! I shall do just that. VERY much a newbie with an Oscilloscope, so will read up about changing the vertical sensitivity and the timebase first. The Rigol seems to have a pretty decent manual fortunately.
Thanks Martin - that looks like a perfect primer! Ta muchlyJohn,
A great Primer on learning what you can do with an oscilloscope, remains Tektronix' classic ' XYZs of oscilloscopes'
I've posted a copy here:
ATB!
Rip test CD with sine waves from youtube . It's easier to test than with music signal. Less confusing.( taking a break from re-caping Ole Nait 5![]()
Good point - I've generated a range of test tones at -10dB which form a compact zip archive I can post if anyone wants to write themselves a test CD.
do'h _ I'd somehow skipped past those, sorry!
Were those taken with a disc playing..?
Right-o, will have a think later... though I don't think its shows anything much like good news (initial impression, sadly - but yet to get my head around the Rigol screen display and markers; I'm still a 'reach for the Tek 475A' sort of person...)
Thanks for the pointer, but, I don't see enough space around the TDA for such a large heat sink. The D/A chip measures 14 x 35 mm and there is no room for so much overhang. This rectangular seems fit better: https://uk.rs-online.com/web/p/heatsinks/7500932