Electrical Engineering

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Shalvenay

04:31

@rdtsc thou shalt measure voltages

9 hours later…

Bartek Banachewicz

13:36

No schematics, unfortunately, but I'm preparing to draw them.

The PSU is on a separate board. It has a 5-pin connector from the main transformer with 2 AC inputs; they get rectified, one of them is fed to a bunch of linear regulators and powers digital stuff, the other is filtered and fed directly to the TDA - no issues here, straight +/- 40V.

When working with the board I'm either powering it via a bulb current limiter or symmetric DC directly.

With the TDA removed there's +7V on standby and mute, and everything else looks fine. With the TDA in standby and mute become quite weird, and there's a -30V DC bias at the output. I haven't yet looked at that with the scope, it might be oscillations as well.

it's been hard for me to test anything with the TDA in because they kept burning too easily; this one seems fine for at least a couple seconds when i power it in via the limiter, but the bulb is certainly showing some abnormal current so I'm not risking powering it for more than a couple seconds

rdtsc

13:53

Do a google search for "XYZ amplifier schematic", perhaps there is already one out there. If there are any tantalum caps nearby, suspect one or more could be shorted (common failure mode of tantalums.)

2 hours later…

Bartek Banachewicz

15:38

@rdtsc no tantalum caps afaict, i have the reference schematic from the datasheet and it's very similar

there's no schematic available for this specific amplifier

i know that this power amp IC is very picky and needs everything to be "just right"...

rdtsc

15:59

Numerous TDA datasheets here; perhaps probe yours against reference (with load lamp) and see which pin voltage(s) seem "off."

4 hours later…