Commodore 1960 monitor

[kirk_m]

I have a 1960 monitor that still works, but, it's seemingly getting glitchy.  It makes a popping/whining noise on powering on and video mode switches.  Not terribly loud, but, noticeable enough to make me think there is a problem.  What typically goes bad on these?  I can bring it to a TV repairman for a once over, but, I'd like to get an idea on what I might be facing before bringing it over there.

Thanks!

Kirk

[kirk_m]

https://flic.kr/p/23mz5c5



OK, a few days after posting this, the monitor stopped working.  Even the power LED doesn't illuminate.  I had it on, and, suddenly, a bunch of random colors and such appeared on the screen and then it all faded away.  After letting it sit the last few weeks, unplugged, I opened up the case to have a look.  I didn't see any obvious expansion in any of the capacitors, and the only suspect area on the PCB was under the tube.  It looked to be burned, and, there was some corrosion on the part.  The white cylindrical component above has the burns around it.

[kirk_m]

sadly 50% of these monitors could be saved if people would quit using them when they first show symptoms and fix them.

Bad solder joints happen so often on them,and when you beat on them often its enough to make contact,but the joints carrying high current get hot due to the resistance and run until they arc and burn.

Bad solder on the flyback causes arcing and just does damage the longer you run it.

the last 1960 i was given the guy ran it until the FET fried itself and burned legs off and burned a hole in the pcb.

Is this unfixable?  I can take it all apart and look, but, need to know what I am looking at first.  What is the white cylindrical component that has the burns around it?

[kirk_m]

Sorry to resurrect this thread, but I think it is time to try and repair   this monitor.  For the last few years, I've been more into arcade cabinets than Amiga.  I've repaired quite a few arcade monitors during this time.   This monitor is different, though, since it has its own SMPS versus relying upon an isolation transformer built into a cabinet.

Several times in this  thread, @mechy mentioned the FET being an issue in the ones he's repaired.   @mechy , are you referring to Q403 (a 2SC4123 located on the heatsink/shield immediately next to the flyback transformer)?  Is this transistor the HOT?   I've pulled this transistor and tested it via a diode test on my multimeter, and it is shorted.  What I've learned from arcade monitors is that if the HOT is shorted, there's a problem somewhere else that is causing it.  Where to look next?  I plan on first recapping things,  but, if it's the flyback that's out, is that an unobtainable part?

Thanks!

[kirk_m]

Bump... no monitor gurus here?

[kirk_m]

I've got a new flyback on order as well as a replacement HOT (ordered it a few days ago from that particular supplier).  I've checked all the diodes on the board, and none are bad.  I'm very familiar with monitor voltages, I've repaired 20-30 arcade monitors in the last few years.  I still have to make a cap list and perform a recap.  I'll update the thread as I move forward with the repairs, and I hopefully have a lead on an original copy of schematics, versus all the poor quality scans of them on the web.

[kirk_m]

Swapped out the FBT and the HOT today...no change.  The power LED blinks quickly, and, I have no B+ voltage at TP4.    What else should I be looking at?

[kirk_m]

I am recapping the monitor...so I compiled a list of all 54 caps as I removed them from the main chassis and the neck board.  Maybe this might help someone else resurrect one of these monitors.  The list is attached to the post.

[kirk_m]

Recapping  didn't fix the problem, neither did replacing the HOT or flyback.  Likely,   these parts were all still good, unfortunately.   I should  have  known that the issue was with the SMPS, because  even with the old components, the power led would flash on and off rapidly,  and a very, very  faint  ticking could be heard if  I were to  work on it in an extremely  quiet  room.  I began  checking the DC lines and eventually found that D805 was shorted.  Replacing it  with an identical fast recovery diode of required  rating brought it back to life.  HV immediately appeared, and I adjusted the B+ trim pot, now have a solid 86V B+.  Just a few tweaks to focus and screen controls were all that were needed.  The monitor lives again after nearly 6 years of being dead.