Taito AA017751 cocktail power supply repair

I am very slowly restoring a Taito black & white Space Invaders in between other projects. The time has come to rebuild the power supply, I fully recapped it including all the tantalums. One of the resistors was burnt out but there's no documentation online for this exact power supply, so I had to hope that the reading of 33 ohms was correct and replaced it with another 33 ohms.

I then tested it in the cabinet and the 12v, 18v and -5v were all spot on but the 5v was putting out 8.5v! luckily I didn't have the board hooked up at the time or it would have gone up in smoke.

Adjusting the 5v pot made no difference to the voltage. I went looking for documentation online again, backflipper on ukvac pointed me to a schematic in the moon alien manual but after looking it over my power supply is very different.

Then I found a very old newsgroup post by John from John's Jukes (www.flippers.com) that mentioned he had schematics for the AA017741 power supply. I sent an email and got a reply and a copy of the schematics almost instantly, thanks again John. The layout is slightly different but otherwise looks the same as the 51 version.

I looked over both the schematics and the board again and I narrowed the problem down to the TA7089P voltage regulator. A chip that hasn't been made for years and can be hard / expensive to find.

For a new old stock one anyway, I went the utsource route which basically means used pulls that have had their legs sanded and dipped in solder to make them look new again. I don't like this as it makes the legs extremely fragile but they are cheap and everything I've had from them has always worked.

The TA7089's arrived after about two weeks, I fitted a 'new' one to the power supply fired it up, 5.05v on the 5v line, success!.

I replaced the 555 timer too as chances are the 8.5v killed it.

Next the monitor speaking of which, TC if you're reading this I might have a spare chassis available at the end of this project.

My cap map is famous.

 

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