Need some electronics help!

[hairy]

hi ra-clan

as you may have guessed from the MAX680 datasheet, its purpose is to get dual power from +5V which is probably forwarded into op-amps and other analog circuitry.

Have you tried, referring to the pinout on the datasheet, to measure the +10V/-10V output from that chip using a multimeter?

IMHO the hum in the headphones seems to suggest that the power amp is not dead, have you tried the line output jack also?

After you finished with cleaning with a toothbrush, as someone already suggested, and rechecking the thing, if still no dice AND you feel brave enough, you could also attempt to temporarily feed +10V/-10V from some external power supply and at least have confirmation if the problem lies in that regulator chip.

P.S.: I have a working QY20, but it's one of the few lucky devices that escaped the "peek inside the belly" treatment :razz: So I can't say I know the circuitry very well. Also, samples from that specimen were used in the very first release of GMPlay.

[hairy]

Am I correct in that, with the device powered on, I would touch one multi-meter probe to the circuit leg, and the other to ground to test if the proper voltage is coming out of that leg?  The multimeter would be set to measure DV voltage.  Is this correct?

Yes, that's correct.

Unless your multimeter is NOT a digital one, don't worry too much about range and polarity, it will simple display opposite sign or display over voltage. Nevertheless, try to use the black probe on GND and the red one on V+ and V- pins. Mine has ranges like 200mv, 2V, 20V, etc., in this case the correct range would be 20V. Just choose the first available range that's higher than the voltage you're going to measure.

Just looked at the datasheet again, we're lucky since all three pins are located on three corners, this way even if the chip is SO package, it should be farly easy to push probes over the pins from the respective outer side, without the risk of making shorts.

This is the complete pinout:

1 C1-
2 C2+
3 C2-
4 V-     <= red probe here should read something near -10
5 GND   <= black probe here for both measures
6 Vcc
7 C1+
8 V+     <= red probe here should read something near +10

The line on the chip is the "front" of it. Looking toward the front, pin 1 is the top-left one, pin 4 the bottom-left, 5 bottom-right, and 8 top-right.

Sorry if it's a bit pedantic, but at least I hope it's understandable!

[hairy]

One last detail crossed my mind: due to the way those kind of regulators work internally (by slicing the 5V power and then rectifying/multiplying to both polarities), the external capacitors play a fundamental role in obtaining correct DC levels on the outputs.

If you're going to replace both the caps and the IC, you could start with the caps and recheck the voltages before replacing the IC also.

Being able to check caps in circuit was suggested, and that would be really cool, maybe for the display issue too.
But I don't have the faintest idea on how that ESR meter works. The only thing you could try with a simple multimeter would be to check if any capacitor failed to "short", though I think it's very rare: I had many of them blown on a PC gfx card, and the thing still worked albeit much more unstable, sign that they were failing to "open".