Received from Spain this Cadash PCB (it turned out to be an undumped Spanish version)

Board was stuck on a garbage screen :

A clicking sound suggested that the watchdog circuit was active, infact both /HALT and /RESET lines of 68000 main CPU were going LOW and HIGH in an endless loop.At first glance I thouhgt the Taito custom ‘TC00220IOC’ (responsible of generating the master reset for whole system) was faulty since this is a very prone to failure part :

But I was wrong since I replaced it with no changes.Probing the 68000 CPU I found that data line D0 (pin 5) was stuck low, using a multimeter revealed it was shorted to ground:

Looking at solderside I traced the pin back also to pin 25 of a Fujitsu MB8422 Dual-Port SRAM (part of linking mode circuit)

I cut the trace and the short was cleared (so the I/O pin of the MB8422 was internally shorted).Finally board booted into game:

But I noticed two problems : the buttons of the Player 1 were not responding and sound had rustles, you can hear it from this video :

As for first issue, using a logic probe revealed the relevant pins of JAMMA edge connector were stuck LOW :

Inputs of an arcade board  must be HIGH when not activated, they are usually pulled in this state by resistors.Indeed, tracing back the pins of the three P1 buttons from JAMMA connector lead me to some custom resistor network:

The array @RRC1 was the one involved so I removed and replaced it, this fixed the controls issue.As for sound, using an audio probe I figured out that the bad audio was coming out from the TL074 OP-AMP from Texas Instruments (which are really prone to failure, have replaced tons of them) 

Replacing it restored a crisp sound.End of job

Received from Austria this pretty mint Xexex PCB:

According to the owner the board had only faint sound but actually it was not booting for me resetting on attract mode:

At a closer inspection I found some lifted pins of the custom ‘053250’ which I promptly reflowed :

Finally the board successfully booted but, as expected, with very low sound , you could barely hear it with volume set at maximum level though:

Obviously the culprit was the ‘054544’ hybrid audio module:

I removed it and changed all the electrolytic capacitors (repainting it as well)

This restored full sound.Then I thought this was the right chance to try out my reproduction:

Testing was successful :

Received today from Germany some faulty PCBs for repair, there was this Dragon Breed boardset (on Irem M72 hardware)

Sprites were glitched with jailbars thru them:

Sprites data are stored in four 28 pin 1Mbit MASK ROMs (Toshiba TC531000) located on top board:

Due the fragile nature of these devices I was pretty sure that there was a faulty one but I was wrong since dumps turned out to be good.Analysing them with a logic probe I noticed that data line D0 (pin 11) of the MASK ROM @IC49 was stuck low, measuring its resistance to GND gave me only few Ohms:

Since device was good there was clearly something forcing the pin low, most likely a short (not ‘dead’ though).I traced the involved pin back until I came across to this scenario:

Here’s a close-up under a microscope:

The capacitor @C62 was bended and its terminal connected to GROUND  was accidentally lented on the pad of the trace tied to the data line.I straightened the capacitor, this cleared the short and hence sprites issue, simple but effective!Job done.