Ok, it's 2, 3 months later. I've no idea what I'm looking at or what advice I already gave, and I'm loathe to spend the time and research to do it all over and reacquaint myself once again with the whole thing. And why are you checking continuity between 8-11, did I ask you to do that previously, and how did you do that, details matter, they really do. And I can already see that the measurements you gave this time around are different than last time, which is that your pins 8 and 11 voltages are about 1/2v lower than supply (pin 10) which is what I mentioned to you last time was suspect since you gave the same readings for pins 10 and 8. And did you remove and reinstall the amp chip? Or else how are you comparing the old chip and the new spares? One in circuit and the other out of circuit? And if you are getting audio out, then that generally indicates that the amp chip is fine, but that is a dual channel amp and you are only checking one channel. Are you just going to presume that the other channel is good because one is good? Sometimes, amps act up after they've had a chance to heat up, so keep that in mind too. Oh and if you don't know what a zener diode is, then you are going to have to educate yourself on that. There is no way that I'm going to be able to give you an education on every single component in your boombox, nor am I going to study, research and tell you where each and every component is located. You are going to have to do some work. The zener diodes are different from regular diodes because they restrict reverse current (like any regular diode) up until the zener voltage, in which case, then it breaks down and allows current to flow. That's why when you check the voltages (based on schematic specs), it will tell you alot and this characteristic is also why they are frequently used in voltage regulators. On the schematic, it looks like a regular diode except instead of a straight bar perpendicular to the arrow, it has a squigly one. As for output caps, they are exactly what I described them, which is that they are directly in series with the speaker outputs. In general, they are typically 1000uf or thereabouts. Large ones. Oh and did you check for DC at the outputs? The outputs are the 2 leads from the amp that are connected to the speakers (outputs). If you put a DC voltmeter across those leads when they are operating, they should not have any significant DC. If they do, you are likely going to toast any speakers connected to it. Do not measure AC, because it will show a reading. I'm concerned only with DC. They should read low mv if anything. If more than 50mv, I would replace the amp module and any associated electrolytic capacitors in amp circuit.
Now with all that being said, I will just give you some general troubleshooting tips. IF you conclude that the amplifier portion is working fine, then you need to work backwards using the schematic as a guide. Map the signal path from (i.e. aux input jack) to the amplifier input (pins 3/5 of connector 7). Work your way backwards probing point by point until the signal breaks in which case, you have likely found the problem circuit source. Keep in mind that it is normal for volume to change, possibly increasing as you work your way backwards, especially before/after a transistor which may be amplifying the signal.
I will also tell you that if the amp is working while disconnected to everything else, but you smell smoke or burning when it is connected back up again, something is definitely not connected right. Or is your speaker outputs shorted? Check the speaker harness too to make sure it is not shorted. The service manual has a wiring diagram and it is quite tedious to check each and every wire hookup, but that's something you will have to do if it was messed with before and can potentially be mis-wired.
