Help me talk thru this WG 49xx/55xx repair...

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Help me talk thru this WG 49xx/55xx repair...FIXED!

I need to talk this through while I think about it. Perhaps someone else has an idea or has encountered something like this.

I'm working on a 5515, which is the 25" medium-res version of the K4900. Most of the chassis is the same, so repairs between them should be fairly similar.

Anyway, I got a chassis of undetermined status (I can't remember if it worked or not). I inspected it and found a crack in the neckboard that had been repaired well, a big epoxy blob on the flyback, and old caps. I installed a new cap kit and cleaned up some solder, checked the HOT and VR, fired it up and got HV static on the tube and neckglow, so I shut it down right away so I could hook up a video signal. I hooked up the video, turn it on, and about 2 seconds later flames came thru the epoxy. Okay. I had a new flyback, so I put that in. Found the fuse and HOT was blown, so I replaced them. Hooked it all back up, fired it up, got the HV static and neckglow - but no picture. I can't even get raster by turning up the screen control or black level pot. I did notice that it was missing a cap betweeen the +185 line and ground, and I installed it, but it's not helping. My +185 is measuring +175, and the voltages at the drive transistors is incorrect, which I've found can cause no picture (remember my red G07 thread?). +130 line and +15 line is spot on. I can hear the hum of the chassis running and I get a big spark when I discharge.

It just so happens that I have a 100% working K5515 right here, also. I've been doing some bench voltage checks, and everything seems to measure the same between the two while it's on the bench. But if I connect them to the tube (same tube for both), I get different voltages at the drive transistors - and I'm not sure why.

Just for kicks, I replaced the VR. It's an STR381. The parts listing says it should be STR380, but the schematic lists STR381, and the working chassis also has an STR381.

I also thought maybe the new flyback could have a problem, so I swapped in an old working flyback and still get the same result.

This is going to turn out to be some stupid resistor that is out of value like the G07 was.

Anyone got any bright ideas?
 
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did you check for blown or cracked traces after the epoxy fire?

Yeah. The epoxy was on the top corner and the flames spouted out the top for just a second. Just for kicks I did continuity checks all over the damn thing and can't find a problem that way.

I may swap the neckboard just for the hell of it, just in case the repairs isn't as perfect as it looks, even though i can't find a problem with it...
 
B+ holding steady at 145, which is supposed to be a problem with the voltage regulator circuit, but the VR has been replaced, as have the caps, and no cold solder or broken traces have been found. I guess I'll look through that circuit some.

Also, noticed some resistance differences around the sync amp (Q301) between the good and bad chassis. Noticed that the good chassis had R379 cut off, while the bad chassis did not. I removed it from the bad chassis, but it didn't help.

I'm going to put the new flyback back on and see if the B+ stays at 145...
 
What's the voltage look like going into the regulator? (pin 1)

It's weird. On my bench, I have perfect B+. Hook up the yoke and it jumps to 145. Disconnect the yoke, and it goes to 160. Shut it off and turn it back on, and it's back to 130.

The flyback starts up and is sparking good, then starts sputtering and then goes out.

I've swapped in new HOTs, VRs, and flybacks with no change. Swapped the 'auto protect' board - no change. I'm going to do the damn IC301 chip next, but I anticipate no change because it seems to be reading the same as on the good chassis.

I'm almost to the point where I just start swapping parts between them one at a time until it starts working...
 
Update:

Perfect B+, no picture. Swapped neckboards and now have raster with vertical collapse, so I'll look into the neckboard more. It had a crack that was repaired and I seem to have continuity everywhere, but somethings messed up. Perhaps a bad socket?

As for the vertical collapse, I found one of the vertical yoke pins wasn't making contact to it's trace, so I fixed that and now have deflection to about 2/3's of the screen. I can adjust the size, but no bigger than that. I'm going to swap out the vert transistors with new ones first to see where I'm at. Once I get the full raster, then I can concentrate on fixing the neckboard...
 
As for the vertical collapse, I found one of the vertical yoke pins wasn't making contact to it's trace, so I fixed that and now have deflection to about 2/3's of the screen. I can adjust the size, but no bigger than that. I'm going to swap out the vert transistors with new ones first to see where I'm at. Once I get the full raster, then I can concentrate on fixing the neckboard...

Don't forget that there are two kinds of 4900, with two different yokes.

We had a 55xx series that you could get a widescreen type picture but no wider. It turned out to be a cap (not an electrolytic) that went out of spec. I do not know which, sorry.
 
Don't forget that there are two kinds of 4900, with two different yokes.

Yes, I am aware of that, although I don't think this is true of the 5515's, and it's not foldover. Just a size issue.

We had a 55xx series that you could get a widescreen type picture but no wider. It turned out to be a cap (not an electrolytic) that went out of spec. I do not know which, sorry.

Yeah, kinda looks like a widescreen image on a standard tube. Do you at least know if it was in the vertical section?
 
Sorry, I do not. This repair was done by Al of New England Coin Op. He no longer works there, but does it freelance. I don't know how to get in contact with him.
 
I hate crappy monitor repairs. :mad:

So My vertical deflection was fine, hooked it up to a signal and I was getting a scrambled pic. Couldn't dial the image in. I just get a double-image, like maybe I was displaying a standard-res signal on a medium-res screen. Double-checked that I had my settings on medium-res, then wondered if perhaps I was misinformed and this was actually a 5501 and not a 5515. There are slight differences between this one and the other working 5515. Tried it with a 5501 yoke and standard signal, but got the same type of pic (albeit a lot darker as usual when trying to test a medium-res chassis with a standard-res yoke). So, verified as a 5515. Hooked it back up as a 5515 and got the same double image.

So, I tried going to the outer ranges of my horizontal hold pot to see if perhaps I hadn't found the proper "lock-in" spot yet. Going all the way to the right makes the chassis squeal and the image get screwy. Started going to the left, and as I get towards the left limit, the image started to pulse, then the fuse blew. Found the HOT was blown.

Now - it keeps blowing HOT's, even though I've turned the horizontal hold pot back to the center. (Yes, they have insulators.)

So far (before the blowing HOTs thing) I've installed a new flyback, caps, VR, IC301, Q301, vert defl transistors. I noticed that R353 and R352 (connected to the Horiz Osc pin of IC301) were the wrong value from the schematic and the good one (47k vs 39k and 3.3k vs 4.3k), plus the working one had R379 removed but the bad one didn't. But changing the bad one to the same as the good one hasn't helped.

I'm wondering if perhaps this could be a problem with the new flyback? It has the same number as the parts listing, so I expect it is right, but perhaps it has a problem? I'm thinking about pulling one from another chassis and tossing it in to see what happens.

Anyone have any bright ideas as to why this keeps blowing HOTs? I can't find anything in that circuit with a short. I've put my circuit breaker on to save fuses...
 
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Well, I solved the puzzle.

First off, there were a few things that helped screw this up:

1) I was working on a chassis that I don't see very often.

2) I was working on a chassis that looks almost exactly like two other versions of the same chassis but operate completely differently.

3) I was starting from a point based on an assumption based on incorrect information provided by a customer who bought it non-working from someone else who misidentified it.

Got all that? Whew.

Okay - short story: It's not a 5515. It's a 5501.

So, I was wondering why I was blowing HOT's. Since I was told it was a 5515, and it looked like a 5515, I thought it was a 5515. The original flyback had blown up, and the customer had provided a new 5515 flyback with it. I installed it and couldn't get it to sync and kept blowing HOT's. Since I couldn't find anything specific that could be causing my problems (after many, many, many hours of troubleshooting), I decided to look at the possibility that the new flyback was the problem (even though it tested okay with my ring tester).

As I knew that the 4900 flyback had been reproed not long ago, I didn't figure a specific 5515 flyback was available. The manual for the 4901, 4915, 5501, and 5515 all have different WG part numbers for the flyback, but the description for them all say M-11. So, I assumed they all used the same flyback. Well, they don't. I checked Arcadecup's site, and found that they 4901/4915 uses a different flyback than the 5515. So, I pulled the blown flyback out of the trash and tried to decipher the dirty label on it. I came up with a part number, and looked through the manuals I have to find that it's the part number from the 4901/4915, not the 5515.

AHA! So, now I'm thinking it must be a 4915. I track down a used-but working flyback with the proper number, and install it. I pull out my 4915 tube/yoke for testing, and am about to fire it up - but wait! Maybe it's a 5501 instead of a 4915? After all, I know for a fact that the 5501 has that little input protection board (ipb) that the 4915/5515 uses. But does it use the same flyback as the 19"? Well, it just so happens that I have a 5501 in my Lethal Enforcers, so I dig it away from the wall, open it up, and start checking stuff out. Not only does it use the same flyback as the 19", but had the same linearity coil under the ipb as the 19", and different than the 25". I also noticed right away that it was missing the big mylar cap on the top right wall that the 4915/5515 has. The chassis I was fixing also had that cap missing.

So, now that I am pretty sure it's a 5501, I pull off the 5515 yoke, put on the 5501 yoke, hook up the chassis (with new HOT) - AND IT WORKS!!!!

I only blew 5 HOT's in the process of fixing it ($$$), and a few times considered throwing it out in the parking lot and running it over a few times. I will be extremely happy to ship this damn thing out....
 
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