I don't know really. I've never dug in that direction.
If you want to replace the optocouplers, type TLP521 on Aliexpress, you'll find them.
You can either take 4x TLP521-1, or 2x TLP521-2 or 1x TLP521-4 to replace 4 optocouplers. Sega populated differently from one Driveboard to the other as you can see:

Thanks. I thought I might be able to use some of the resources I have. I've already ordered the new TLP521-1.

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.

Waoh, you fixed quite a few
Thanks a lot for sharing this, I hope this will help areni2002 and many others

Hello after a long break. I finally managed to get this unfortunate board working. Although IC2, IC5, and IC18 were fine on the tester, I replaced them with brand new ones. The feedback loop started working, albeit with minor issues. After a while, an Err 24 error was displayed. Another board in the same machine worked fine. After a quick inspection, I fixed one solder joint and tested it in a different machine. It's working so far, so I'll keep testing. Thank you all for your help. In total, I've now brought six boards to life 😃

That'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've never seen error 03. However, on my ER 24 board, it reappeared 😥. This happens after the game has been running for a while. I'd also appreciate any suggestions.

Magnifique ce sera parfait pour mon Model 3 step 1.5 !

Hello. Repairs to the 7-segment display boards are going quite well, although one is resisting However, I have several servo boards from various machines (Scud Race, Sega Rally 2, Club Kart - MIDI) that aren't working. Has anyone had any success repairing them? The MOSFETs seem fine to me. I've also checked the diodes and various passive components. I'd appreciate any suggestions.

Hi Tibal

Have you seen this error before?

When I power it up, I do not get any segments on led2
But led3 is powering up, missinig a segment and shows 22 at the end.

What I have done so far
Swaped the borads with a working one - the error follows the board
Swaped GAL16V8 with a working one - the error follows the board

I have removed IC26 - and tested it, it where bad - so I have put in a new good 74HC373, but it is still the same error.

What to you think that causes the missing segment display?

A small video of the error here:

Hi,
I don't think you can rely on the Er22 info as your display is messy. You should start by testing/replacing all your 245 and 238 chips.

Citation de: Tibal le Dimanche 22 Février 2026, 13:09:23 PMHi,
I don't think you can rely on the Er22 info as your display is messy. You should start by testing/replacing all your 245 and 238 chips.

Thanks for fast reply, I will try that 😊👍

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?

That's interesting, thanks for the report.

In the meantime, I noticed something trying to fix my Er03 board:
- a working Driveboard reads about 1,5k ohms between +5V and GND on the power connector, when totally unplugged
- my Er03 Driveboard reads 5 ohms

So it looks like there is some kind of short somewhere, but loose enough not to burn the board or my PSU.
I tried to find a hot chip when the board was powered, with no luck.

Given that I replaced most of the chips on that board, that the display works fine, and from what you say about peripherals, I wonder if the culprit could be the OKI chip...

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.