If you're referring to the OKI M6253 - ADC chip, I haven't seen a faulty one yet, even though I've suspected it
a few times (it's hard to remove), but in the end it was fine. Check the protective diodes at the CN5 connector
I've replaced them there several times.
I think that if there's only 5 ohms at the power connector, something must be getting very hot, and it will show up on
a thermal camera. Or you can track it down by checking for voltage drops (in millivolts) on individual chips
or other components like EMF filters, etc., from the CN8 connector all the way to the ADC.

Citation de: Tibal le Mardi 09 Septembre 2025, 22:18:12 PMThat's great! Thanks for the report!

While I'm at it, if you @areni2002 , @Sillicon or anyone have spotted chips that may be responsible for an Error 03, I would love to know

I finally found a note from when I was trying to disassemble the program to figure out what was causing error 03, and I finally found the answer.

Error Er03 is triggered by an NMI interrupt. Part of the NMI interrupt handler routine is checking whether another interrupt arrives while this handler is still executing, i.e., before the routine has finished. If this happens, error Er03 is triggered.

After power-up, the program performs a ROM and RAM check (about 2 seconds). If error Er03 appears immediately before these tests, when the system is not yet initialized (RAM initialization after the test, peripheral setup, etc.), the response to the NMI may not be correct, and the problem is likely related to the peripherals?

When I repaired several drive boards for a friend in February (see below) ;-), one behaved similarly.
If IC28 is working as you write, then check the activity IC28 on pins 1 and 19, if it is not there,
then if I remember correctly, the cause is IC18 or then IC2 and IC5.
I have repaired many of these boards and there has never been a faulty optocouplers or output drivers TD62384 and ADC M62353.
Note, the optocouplers inputs are powered from the CN1 and CN3 connectors.