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Author Topic: Hantarex MTC-900 (DB-2 variant) arcing at neckboard (spark gaps?)  (Read 218 times)

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itsdanik

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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!

grantspain

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Re: Hantarex MTC-900 (DB-2 variant) arcing at neckboard (spark gaps?)
« Reply #1 on: July 13, 2018, 05:01:40 pm »
or 200v video b+ missing, that would cause max output on all colours and the tube would not been to keen on that

itsdanik

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Re: Hantarex MTC-900 (DB-2 variant) arcing at neckboard (spark gaps?)
« Reply #2 on: July 13, 2018, 06:29:10 pm »
or 200v video b+ missing, that would cause max output on all colours and the tube would not been to keen on that

Thanks for replying. How would I proceed on checking that? I'm not very experienced with arcade monitors.

grantspain

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Re: Hantarex MTC-900 (DB-2 variant) arcing at neckboard (spark gaps?)
« Reply #3 on: July 13, 2018, 06:40:38 pm »
so first you should be looking for bad solder joints on the chassis, in particular around the flyback- secondly the caps on there will be over 30 years old, change them all- then check b+ at one of the centre two pin of deflection yoke connector(should have a wire link on pins 3,4) b+ should be about 130vdc, possibly 120vdc if usa spec (use heatshield as ground), lastly I will dig out the manual and locate the safety resistor on the video b+ circuit, this will be the main cause of the bright white screen(most likely)
this is a real old chassis, they were in service when I first started work in the coin op industry in 1986, I think they date from around 1982/1983- this is one of the few chassis that I do not repair

itsdanik

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Re: Hantarex MTC-900 (DB-2 variant) arcing at neckboard (spark gaps?)
« Reply #4 on: July 13, 2018, 06:56:49 pm »
so first you should be looking for bad solder joints on the chassis, in particular around the flyback- secondly the caps on there will be over 30 years old, change them all- then check b+ at one of the centre two pin of deflection yoke connector(should have a wire link on pins 3,4) b+ should be about 130vdc, possibly 120vdc if usa spec (use heatshield as ground), lastly I will dig out the manual and locate the safety resistor on the video b+ circuit, this will be the main cause of the bright white screen(most likely)
this is a real old chassis, they were in service when I first started work in the coin op industry in 1986, I think they date from around 1982/1983- this is one of the few chassis that I do not repair

Wow, it must be older than me. I have already recapped the chassis. Good news is, I have another one, exactly the same, which has really a beaten up neckboard (probably dead for good) that I can use for spare parts.

Thanks for the tips, I'll do the measurements tomorrow and report back

princess prin prin

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Re: Hantarex MTC-900 (DB-2 variant) arcing at neckboard (spark gaps?)
« Reply #5 on: July 13, 2018, 10:38:22 pm »
That's not the correct CRT socket for that neckboard. How the hell did they fit it?? That needs to be corrected asap.

Practically all these chassis are now in bad or even terrible condition. They need to be fully rebuilt by someone skilled enough and willing to put a lot of time into it. If you just want a working monitor get a newer chassis.

itsdanik

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Re: Hantarex MTC-900 (DB-2 variant) arcing at neckboard (spark gaps?)
« Reply #6 on: July 14, 2018, 03:26:15 pm »
You are right. All three are pretty beaten up and must have been repaired / modded multiple times. Every neckboard is somehow modded (cables were not put through the holes, but soldered directly on the inner pads).
That's weird because the Kortek monitor worked wonderfully after recapping. Oh well. I might as well give up on these.
Luckily there's a local guy that still runs a CRT repair shop and is an ex Hantarex service employee, so I'll give them to him to take a look and tell me if it's worth restoring. :)

In the meantime, are these Chinese universal chassis any good or should I just get a bunch of 21" TV's with RGB scart input for these cabs? :)

  
 

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