More B+ woes on a Sanyo Monitor

LyonsArcade

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Hi guys;
I have a nintendo Sanyo 20EZ monitor that I keep having trouble with. I've replaced all the caps, the flyback, the hot, the voltage regulator (IC601) and the current limiter, Q901. I also had a broken resistor, the BIG one right next to the B+pot that I replaced with a in spec one from a parts board.

Anyways, the problem I'm having is that the monitor will come up and look great, with the B+ sitting at about 107.6. If you leave it on for a while, eventually it goes into overcurrent protection and the B+ rises to 135 or so, and can't be adjusted. If you turn the monitor back off and then back on, it'll half and half come back up with the right B+, and half the time it'll come up in over current protection.

Everything meters out making good contact in the 600 section, is there another section of the board that could cause it to do that? Per Dokert's Flow Chart suggestions, I've got the three brightness controls centered and the picture looks pretty good.

One thing I've noticed is that the resistor directly beneath the White ceramic resistor in this section of the board (it looks like about a 5W) is slightly higher in resistance (10%) than the one in my parts board, could that have anything to do with it?
 
Check the 3k Horizontal pot on the board, switch the monitor on and try to adjust it slowly and see if it makes it go into HVS.
 
I don't really have time, now it's going into shutdown about 5 seconds after coming on. The B+ will be at about 107.8, then jump to 135 or so and shutdown. I've checked everything in the 600s, and all the resistors check out fine. I tried checking them soon after unplugging it to make sure something wasn't opening up under heat, everything checked out great. All my traces are checking out fine with continuity between everything that's supposed to be connected, and no solder splashes shorting anything out. I replaced the voltage regulator, and just now re-replaced the limiter. The limiter tested fine once out of circuit, so I don't think it's blowing that transistor or anything. I also replaced the two electrolytics in that area again just to be sure.

If I turn the b+ pot and the sub brightness pot all the way counterclockwise, I can get the monitor to come on, if the screen is on a bright screen. As soon as it switches to a dark screen (This is in a playchoice 10!), the B+ rises and the monitor goes into Shutdown.

Diodes and everything checked out over by the a/c, and I would assume everything's working in that area or I wouldn't be getting voltage over to where I am. I'm also getting 139v on both sides of the large 180ohm resistor, (one side is the B+) but the resistor is fine. Since that 'feeds' the circuit off of the fuse, is my problem that I'm getting too much voltage before that fuse?
 
Try replacing both the B+ pot and the sub-brightness pots. Hell for another $1 I would even do the H hold pot at the same time.
 
Alright, I'll see if I can get my hands on those, but I've ohm'd them all out and they work great.

If they work great that's not it, it was a long shot but I have one that did the same thing but after I adjusted it out of its bad area it works fine, touch the pot and it goes into HVS every time.

I have another one that's in HVS that I suspect the same pot, I pulled the pot and one leg is jacked up and only works part of the time.

3k pots are really hard to find, I hope you have a packrat buddy like I do. :)
 
3k pots are really hard to find, I hope you have a packrat buddy like I do. :)

Muahahahaha ..... wait.... "packrat" ? ..... these pots are new.
Where they came from and why I have them, who knows. ;)

His symptoms do seem near exactly what we had going on on that other monitor huh?
 
Muahahahaha ..... wait.... "packrat" ? ..... these pots are new.
Where they came from and why I have them, who knows. ;)

His symptoms do seem near exactly what we had going on on that other monitor huh?

I don't care how they came about, just that they did.. :)

Yeah, that problem seems nearly exact.
 
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