Since 20EZ posts are popular these days...

modessitt

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Got two problem chassis:

1) B+ is at 22.8vdc. The 180-ohm pot gets smoking hot. I've swapped out IC601, IC401, the 180-ohm, the one below it, the current limiter, the HOT, the flyback, reflowed every single thing, and VR451, and still get this issue. The B+ pot is measuring properly, but I haven't tried replacing it yet.

2) B+ is at 140.1vdc. Reflowed everything. Swapped all the same parts as above. Tried turning both the B+ pot and VR451 counter-clockwise, but that didn't make any change.

Both monitors were working prior to coming to me. The owner installed a cap kit on one (#2), and it died not long after. The other (#1) had a horizontal hold issue, and was dead after the cap kit.

Any ideas? I've been checking trace continuity but I'm not finding any issues.

Here's something of interest on #1. I have a working 20EZ to compare to, and when I use the diode test and measure the filter cap (black on negative lead) I can watch the reading climb as the cap charges. That's normal. On #1, it only climbs to about .336 and stops. If I remove the fuse, then it climbs all the way like it should. I've traced it as far as the flyback pin, and if I cut that trace right before the flyback pin, then it charges like it should. Obviously something on this chassis is not working like it does on the working one....
 
Geez Mod I feel for ya. If you can't fix it they have to be hosed. Maybe you should think about carrying a few Wei-Ya chassis on hand huh? Yank the old - slap in the new chassis and either fix the original chassis at a later date (and resell it) or pitch it. By freeing up your time how much more money could you make in a day if you did this ;)
 
Damn Steve, nothing is easy with you is it?

Check diodes D601-D604 on both and see what you get.

I did that, comparing them against the working one, and I get the same readings.

BTW - If I measure the resistance between pins 1 and 2 on the flyback, I get different readings between the working one and the #1. I know I have other parts in parallel, but obviously this probably means something in that circuit is screwing everything up. What I don't understand is why I get such a big voltage drop on the 180-ohm. Something in parallel with it must not be working properly, making the 180-ohm take it all, right?

Let me ask you this: What all needs to be hooked up to get this chassis to turn on?

Normally, if I'm working on a G07 or something, I can stick the anode cup in the hole (to keep from being electrocuted accidentally by it), hook up the power through my test bench iso, then sit there with it upside down and trace voltage through the chassis. When i tried this with the working 20EZ, it didn't work. No spark at the anode cup, B+ about 137. Hooked it all up normally and B+ was at 108 and a perfect pic.

I'd like to be able to test things easier while it's powered up. It might help me figure these out faster...
 
It would seem that everything needs to be hooked up on both the Sanyo's and Sharp's. I have yet to find a way to test them in any "easy" way.

Do you have a flyback tester?
 
Put another cap kit in number 2, unless you can verify where the guy got the cap kit from. He may have got one of those cheap shitty cap kits that are out there.
 
Got two problem chassis:

1) B+ is at 22.8vdc. The 180-ohm pot gets smoking hot. I've swapped out IC601, IC401, the 180-ohm, the one below it, the current limiter, the HOT, the flyback, reflowed every single thing, and VR451, and still get this issue. The B+ pot is measuring properly, but I haven't tried replacing it yet.

2) B+ is at 140.1vdc. Reflowed everything. Swapped all the same parts as above. Tried turning both the B+ pot and VR451 counter-clockwise, but that didn't make any change.

Both monitors were working prior to coming to me. The owner installed a cap kit on one (#2), and it died not long after. The other (#1) had a horizontal hold issue, and was dead after the cap kit.

Any ideas? I've been checking trace continuity but I'm not finding any issues.

Here's something of interest on #1. I have a working 20EZ to compare to, and when I use the diode test and measure the filter cap (black on negative lead) I can watch the reading climb as the cap charges. That's normal. On #1, it only climbs to about .336 and stops. If I remove the fuse, then it climbs all the way like it should. I've traced it as far as the flyback pin, and if I cut that trace right before the flyback pin, then it charges like it should. Obviously something on this chassis is not working like it does on the working one....


Since they both worked before the caps kits were done I'd triple check the cap work and look for solder bridges. Sounds like the "human" factor to me.

Matt
 
Believe me, I've thought that, too.

The guy is a friend and fellow KLOVer. He got his caps from Bob Roberts.

The first monitor had a horizontal hold issue that had a warped picture that wouldn't adjust. He had changed out VR451 but that didn't help. I had him swap out IC401, and then he was stuck with this. I replaced IC401 again, but still nothing. I've gone over everything he did, and have done continuity checks, but found no suspects.

The second monitor was working with jailbars. He put a cap kit in and had a perfect picture. he took it to use as a test monitor on a dead Donkey Kong, and it worked for a bit, but then he said there was "smoke" and it stopped working. I haven't found any burnt or popped parts, or any indication where this smoke came from, and he doesn't really know where it came from, but now I have a high B+. I asked if he accidentally plugged it into the wrong outlet in the DK bottom, and he said no.

So, perhaps some more testing this weekend will help find something. I've been thinking about just doing a complete cap kit again.


One question - as I don't have an ESR meter (yet), will pretty much all 'good' caps charge up on the screen if using a DMM on diode test with the black lead on the negative leg and red lead on the positive leg? I have some that do, and some that don't...
 
Sorry Mod, it is not worth my time to test caps. A complete cap kit including the audio section is roughly $7. If they are suspect, I just replace them to save both time and money.
 
I know, that's why I haven't spent the bucks on an ESR meter yet. Still, I hate doing an entire recap only to find that the problem doesn't change, but at least I save the new caps I take out for reuse...
 
I asked if he accidentally plugged it into the wrong outlet in the DK bottom, and he said no.

I recently plugged a working Sanyo EZV into my wall outlet....as an experiment, to see what actually gets killed. No isolation transformer and 120VAC pumping into it (actually, my walls pump out almost 135VAC). I had a Donkey Kong motherboard running into it, so I could have visuals. I fired it up, let it run for approximately twenty minutes....no issues. I powered it down. I proceeded to do this four more times....each time letting it run 20, 30, 45 minutes before powering it down. Well, at the fifth power up....she was dead. The only casualty...R609. The big 180 ohm 20W resistor. That was (probably) ten months ago....it's been running fine ever since.

Also, in a factory machine....both outlets are isolated.

Edward
 
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