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Author Topic: Sanwa 27Z21C Display problems  (Read 316 times)

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Sanwa 27Z21C Display problems
« on: June 06, 2019, 04:57:58 pm »

First off, I am a complete beginner when it comes to working with CRTs and troubleshooting them.

I have an Dance Dance Revolution/Dancing Stage Euromix 2 machine with a Sanwa 27Z21C CRT, which is the same as the Sanwa PM1745 apparently. According to the previous owner, the monitor was working up until late April when the flyback transformer started arcing. I ordered a new one and replaced it. It worked ok for a couple of minutes (the image was "buzzing"/was a bit fuzzy from time to time, but was definitely very readable and working seemingly fine) and suddenly started doing what is shown in the two videos when I was trying to calibrate the colours.

A couple of the transistors have been replaced before it seems, back in 2008 I believe (according to a label on the heatsink).

Apologies for lack of photos, I can take some pictures of the mainboard later this weekend.

Possible problems:
  • Flyback solder points were bad, so I scraped the traces to get the solder to flow properly over the traces. Bad soldering?
  • Flux causing shorts?
  • I found a 7W cement resistor (R803) that was cracked, so I've ordered a replacement of that part. Possibly something to do with the power supply?
  • Some random cap dead?
  • After I turn off the machine, I hear some pops/crackles for a second of seconds. Something shorting?
  • I heard something starting up and failing a couple of times (like when you first turn on a CRT). Something shorting?
Here is the service manual (page 119 and onwards) for the chassis if someone knows a bit more about this stuff than me. There's a lot of troubleshooting info there that I'll probably try, but if anyone knows the reason for the specific behaviour in the video that'd help a ton.