Good news guys! I have bought another 6BX81, one with the integrated ESS Solo 1 sound card this time. I had to replace 8 caps and a missing coil, but now it's running again AND it keeps the BIOS settings. So I have a working board to compare the other one to 😀. Yay!

I will be back with some more stuff on the topic, hopefully soon! Thank you all for your help so far!

_ar wrote on 2024-10-06, 16:26:

The attachment Screenshot 2024-10-06 at 18.13.46.png is no longer available

There are two separate zener diodes basically, which all test fine in circuit and according to these measurements work fine as well. D1 had some corrosion on (mould) but it easily came off with IPA.

That are normal diodes, not zener diodes.
Normal diodes pass volts from Plus to Minus.
Zener diodes do the same thing, and do additionally pass volts in the opposite direction when reaching the zener diode's breakthrough voltage. But that makes absolutely no sense in that circuit (at best, it would be good for assisting to recharge or explode the non-rechargeable battery).

nocash wrote on 2024-10-27, 21:59:

That are normal diodes, not zener diodes. Normal diodes pass volts from Plus to Minus. Zener diodes do the same thing, and do ad […]
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_ar wrote on 2024-10-06, 16:26:

The attachment Screenshot 2024-10-06 at 18.13.46.png is no longer available

There are two separate zener diodes basically, which all test fine in circuit and according to these measurements work fine as well. D1 had some corrosion on (mould) but it easily came off with IPA.

That are normal diodes, not zener diodes.
Normal diodes pass volts from Plus to Minus.
Zener diodes do the same thing, and do additionally pass volts in the opposite direction when reaching the zener diode's breakthrough voltage. But that makes absolutely no sense in that circuit (at best, it would be good for assisting to recharge or explode the non-rechargeable battery).

Thanks for the info, I'm sure you're right. I just saw the glass packages and went with zener. The 440BX schematic has schottky diodes in those places, tho. I thought only zeners have glass packages, but apparently it is not so.

I took some pictures of the same components on the working board. The only difference I can see is that the solder joints look good on this one, while the joints on the non-working one look corroded. As you guys have already pointed out. I'll reflow the joins and see if things improve.

EDIT: Reflowing the joints did not help. I have smelled a fishy smell when reflowing D14 and C149. There's no electrolytic cap around these components, tho. Also took some measurements and C149 has a capacitance around 5.7nF in circuit on the good and about half of that on the bad board. Other components measure about the same on both boards.