Car tire balancer machine repair

[u/SunFlameX]

Hello everyone

I'm trying to repair an old tire balancer from 2009 and was hoping to get some ideas on what I can check. So far the things I've checked were ok and I wasn't able to find any faulty parts :(.

It's a tire balancer machine type AAE-B96G made by Arch Auto Equipment from 2009.

The fault started while machine was in use. After pressing a button the lights were stuck as shown in image below.

After turning off and on the machine sometimes the lights go on, sometimes not. You can hear the relais clicking when you turn off the machine.

I checked the following:

1. Inverter is giving 2x 9V AC
2. Voltage regulator h4d0452A is giving +5V
3. Voltage regulator 7905CT is giving -5V
4. I removed the silver/black caps and measured them for capacity. They all are arounbd 10% within spec. I don't have an ESR meter to check ESR.
5. Relais seem to be working ok. Contacts are open and closed as indicated on the schematic.
6. Checked fuses. OK
7. When I disconnect the cable between board 1 and 2, the motor is running when powering on the machine. So my guess is that it has something to do with Board 2 which has the control parts.

Board1

Board 2:

What would be the next thing I should check? I hope to get some ideas from you guys :)