I think you could ground the input of CF1 and injecting the signal between F1 and F2 would be easier imo.Actually I think this pioneer sx-550 would be easier? Seems to have the same flow. The proper tie in point would be pin 1 of the HA1137 chip, correct?
if you measure DCV across R115 and divide by the R value you can calc the bias I and compare against the data sheet spec.There is a resistor in series with the supply pin, R115. I bet if you measure on the input side of R115 the voltage will be closer to 12V.
Agree, rather moot point as too doing the cross injection testing, but it is something you can try as a learning experience if you so choose to learn more about tuner troubleshooting. I have used this technique to even troubleshoot HP RF signal generators and other gear. Nothing better than having the same working unit to compare against.I think the fact that you could see the signal on pin 1 of IC102 changing when you tune the dial, and that pin 8 has a lower signal level pretty much clinches it, IC102 is bad.
The reading of 1.5V on pin 5 of the AN377 may be significant. I don't read Japanese, but the test circuits in the datasheet have pin 5 grounded. I think that a positive voltage on that pin might be causing the chip to go into muted mode.
Edit: here's the AN377 schematic from the the SA-700 service manual. The freebie SA-800 schematic doesn't appear to show the voltages, this one does show the expected voltages.
The IC102 should still work with 10V on the supply. There is a resistor in series with the supply pin, R115. I bet if you measure on the input side of R115 the voltage will be closer to 12V. If so, that's another indication IC-102 is bad and drawing too much current, dropping the voltage across R115. I think the fact that you could see the signal on pin 1 of IC102 changing when you tune the dial, and that pin 8 has a lower signal level pretty much clinches it, IC102 is bad.
if you measure DCV across R115 and divide by the R value you can calc the bias I and compare against the data sheet spec.
Get the ones from Ceitron. they have been around a long time and seem to be reliable. I doubt anything internal killed that IC, it might have had a ESD hit or powerline spike. If that's the case there may be more damaged ICs. In the days when this was built there was little knowledge of proper ESD precautions in manufacturing, so the IC may have had some latent damage that caused eventual failure or a wire bond could have let go.OK so I see two at the same price. Recommendations of one over the other?
https://www.ebay.com/itm/AN377-Orig...820286&hash=item43da7989f1:g:I4cAAOSwcwhVJsBk
https://www.ebay.com/itm/AN377-IC-D...RsAAOSw4DJYmN-e:sc:USPSFirstClass!21784!US!-1
Also - with the old one out of circuit and before I put the new one in - What should I check for to make sure there isn't a circuit problem causing the chip to fail? Hate to blown up the new one!
telemedicine by a real doctor...dr*audio!Sort of like telemedicine for audio equipment!