g07 cbo picture is vertically shrunk at power up then ...

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g07 cbo picture is vertically shrunk at power up then ...

After a few minutes it's perfect again.

It is roughly 1/2" shrunk on both the top and bottom.

IN my wacko, so it's a vertical size problem if you want to call it that.

This chassis had an issue with white horizontal diagonal lines when I received it.

I did the full rebuild and then narrowed it down to several resistors that were bad.
R517, R512, R522, but replacing them didn't fix the lines. R526 was the culprit.

Anyway, I don't remember having any issue with the chassis, not powering up to full screen size prior to installing R526.

It is cold here, so I wonder if that could be an issue.
I think even though I replaced them already, I am going to go in and change out both 200ohm vert. pots on the chassis and see what happens.

I'm just documenting this in case I need help (or anyone else) in the future on a similar issue.

Input welcome.
 
Doubt the cold is the issue. I have operated GO7's in a lot colder temperatures then what you are having right now with no problems.

Check the voltage on the cathode of D508. It should be 12 volts DC. Check at initial power up and after warming up. Both times it should be at 12 volts DC. If low I believe it could cause a partial vertical collapse.

I have never seen this problem. Can't wait to hear what the fix is.

Guessing R526 was way out of tolerance not open.

Ed
 
Doubt the cold is the issue. I have operated GO7's in a lot colder temperatures then what you are having right now with no problems.

Check the voltage on the cathode of D508. It should be 12 volts DC. Check at initial power up and after warming up. Both times it should be at 12 volts DC. If low I believe it could cause a partial vertical collapse.

I have never seen this problem. Can't wait to hear what the fix is.

Guessing R526 was way out of tolerance not open.

Ed

R526 was burnt up, cracking apart and measured nothing.

Changed both (new), 200 ohm pots, no change.

B+ doesn't seem to be fluctuating at all. It's solid. It's a new flyback, but I did not install it.

I hate to call this vertical collapse. It's 1/2-1" short at power up and continues to drift into vertical largeness. I need to watch it for several hours I suppose and see if it gets infinitely bigger.

I'll check your suggestion and report back.
 
It was about 12.5vdc



Not sure that it matters but the HOT was replaced with an NTE89
 
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Thanks for posting the fix. I have a completely different monitor that was slightly off like that as well and making very slight adjustments to the vertical hold allowed me to fill in the screen.
 
Well , I am still looking for a cure actually.

I flip it on. Screen is vertically too short at both the top and bottom by an inch or so.

If I adjust it to proper sizing, it takes about 10 minutes and it stretches vertically too large.
10-15 minutes in and I lose vertical hold. I can adjust it to a stop, but the screen is far too vertically large at this point.

If I leave it alone, it eventually stretches vertically and looks jumpy along the way as it grows vertically larger.

Feels like a cap issue , but I don't know. I use 10,000 and 15,000 hour, high quality caps (panasonic and nichicon).

All caps are installed correctly and of proper value.
The flyback is new, though I didn't install it.

B+ never seems to vary.
 
I found a bad trace or lack of continuity coming from the 100uf 250v cap (C411 maybe I forget), now at power up it is normal size, not shrunken at all.

It does continue to grow larger (vertically in horizontal mode).

I went through, check all of my work.

I thought maybe it is a vertical sync problem on some level, so I pulled and tested everything I could in that circuit:
X302, R305, r306, r304, R319, C304 (not shorted)
X306, R315, R317, R316

everything tested good.

If I sit there and watch the screen, I can see it struggling to bulge larger.

It acts like a capacitor issue to me. Though I am not an expert. Guess I can pull out the caps and test them 1 by 1 ?
 
There is a tantalum capacitor underneath the metal shield next to the integrated circuit which could be going bad or becoming temperature sensitive. I believe it's C402 (2.2 uf @ 16v) and probably blue in color.
 
There is a tantalum capacitor underneath the metal shield next to the integrated circuit which could be going bad or becoming temperature sensitive. I believe it's C402 (2.2 uf @ 16v) and probably blue in color.

Ha, well I pull it and replace it with one from a parts chassis-now I have jumpy vertical collapse.

So
I put a freaking 2.2uf50v electrolytic cap in there and it's holding pretty steady, 10 minutes in.

I'm cautiously optimistic at this point and will report back in a bit. It should only take a few minutes to exhibit the same old behavior or (hopefully) not.
 
Well it hasn't messed up yet!

Thanks once again, Ken.

Problem solved.
 
Ah the infamous Tantalum cap at C402 again. That's twice now. Never seen this problem with it. Good to know what the fix was.

I bet you will be replacing it now when doing the caps (lol). Most cap kits should have that cap in them.

Ed
 
Ah the infamous Tantalum cap at C402 again. That's twice now. Never seen this problem with it. Good to know what the fix was.

I bet you will be replacing it now when doing the caps (lol). Most cap kits should have that cap in them.

Ed

Is it safe/long term fix to place an electrolytic in that location
 
In the hundreds of monitors I've repaired over the years, I have seen that particular tantalum capacitor go bad. I've seen it cause vertical collapse too.

Usually a capacitor ESR testing meter will spot it.
 
Ah the infamous Tantalum cap at C402 again. That's twice now. Never seen this problem with it. Good to know what the fix was.

I bet you will be replacing it now when doing the caps (lol). Most cap kits should have that cap in them.

Ed

Zanen Electronics did have that capacitor included in their kits a long time ago, but no longer do. Due to the age of this monitor, I believe capkit suppliers should include this capacitor.
 
Ah the infamous Tantalum cap at C402 again. That's twice now. Never seen this problem with it. Good to know what the fix was.

I bet you will be replacing it now when doing the caps (lol). Most cap kits should have that cap in them.

Ed

Yeah Ed helped me fix one a couple of weeks ago that had vert. Collapse (same cap).

Guess I better start stocking and changing these.
 
Yeah Ed helped me fix one a couple of weeks ago that had vert. Collapse (same cap).

Guess I better start stocking and changing these.


i should probably throw one in with your order...;)
 
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