EDIT: I gave up on this model and moved on to another, just kept this thread instead of making a new one. Please go to last post for current issue.
Original post below this line
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Hello there!
I have recently bought in "as-is/unknown" condition a bunch of really beat-up and poorly stored cabinets for next to nothing.
I am now checking/repairing the monitors one by one. All of them are 21" (I think they're called 19" in the US becase in Europe we count the "bezel", as well. Correct me if I'm wrong). The first one was a Kortek w/ Samsung tube. Had a vertical collapse due to snapped off coil (!) at the yoke. Luckily I was able to repair it, did a cap replacement and it now works.
Now the second one. Very weird model (the board reads "Hantarex DB-2" and the neckboard "HFB - S4" - this cabinet was definitely made in Greece during the 80s and is not original, probably had some bootleg game installed).
It is a Hantarex MTC-900 monitor with the East/West correction board installed and a very weird flyback. After some reading, I found out that this is a flyback that produces unrectified 8kV output and then a cascade rectifies and multiplies that voltage, right before the anode cap (and also feeds focus voltage to the neckboard). I have attached some photos of the board in the state I first found it. It was already repaired in '89 (had a sticker on it from the tech guy).
When I first powered it up, it acted as if it was working normally. The raster lines came on, but then it kept getting brighter and brighter, I was scared it would burn the phosphors and I turned it off. There is no screen and focus controls on the flyback, due to the nature of the flyback that I mentioned earlier, so there are two pots in the neckboard for these adjustments. I dialed them down, tried again, no difference. The tube was getting full-white (with no RGB connected). The next day I tried one more time before I dismantle it for inspection and this time (and ever since) upon power up, I can hear the coil whine normally (coming from the yoke), but I can hear zaps that are in a fixed frequency (about 3-4 per second). On the screen with each zap I see some random bright lines (much like these you get when you turn off the TV). When I turn off the monitor, the zaps get scarcer until they stop. Upon further inspection I noticed that the arcing sounds are coming from the socket of the neckboard, and upon further reading, I found out there are intentional "spark-gaps" in the neckboard to prevent arcing in the tube in case there is an excess in B+ voltage. Seems like there would be overvoltage in the B+ line if some component has failed?
Am I going in the right direction? How do I safely measure B+ voltage?
PS: Sorry for the long post!