CRT monitor display distortion problem

[Serge125]

Hi all! Ok got my little 1084 monitor fixed and powers up nicely BUT now the display is kinda distorted. Half of the screen is kinda pinched at the middle to the bottom of the screen while it get's bigger from middle to top. Before I saw this I had a screen that the top menue bar was way up in the screen that I couldn't see it so I checked if I could adjust the V-Size and the V-Position that kinda corrected the problem but now I have this screen distortion problem and need advice on how to correct this (if I can).

THANKS!!

[floobydust]

I would adjust the "vertical linearity" trimpot 3573, inside on the main board. You really adjust all three together: height, centering, linearity until the picture is good.
Some CRT's have vertical lin accessible on the back.

How much did you adjust your (front panel) vertical size and position controls?
If it was a huge shift, or a pot is near the end then I would suspect a problem in the vertical deflection circuitry. But your pic does not show a big problem.

I refer to Commodore 1084S-P1 Service Manual: http://atariage.com/forums/index.php?app=core&module=attach&section=attach&attach_id=163064 1.3.6

[Serge125]

How much did you adjust your (front panel) vertical size and position controls?
If it was a huge shift, or a pot is near the end then I would suspect a problem in the vertical deflection circuitry. But your pic does not show a big problem.

I refer to Commodore 1084S-P1 Service Manual: http://atariage.com/forums/index.php?app=core&module=attach&section=attach&attach_id=163064 1.3.6

Hi and thanks for the info, I have a 1084S-D monitor and I don't see any adjusting controls on the board as in the manual but I do have the adjustments at the back. I have the V-Size and a V-Pos and that's it and then I have a H-Position in the front panel. I have turned them to a point that I could see the top menu bar (V-Size) while doing this there was a black bar at the bottom getting bigger so adjusted the V-Pos until there was just a wee bit of black at the bottom of the screen and then this is what I saw that the display is kinda distorted as you see in my pics. BTW If you need more pics while the cover is still off let me know.

Thanks for any help!!!!  ;-)

[floobydust]

Is this the schematic  for Commodore 1084S-D ?
Your vertical linearity is bad, however I don't see a V-LIN trimpot adjustment, so it can also be caused by bad electrolytic capacitors.
C506 47uF and C307 1000uF 25V by (vertical) IC301 would be my guess, I would replace them.
Can you post a picture of the board by the IC301, that helps.

Someone else has the same problem  Mario gets pretty big jumping

[Serge125]

Is this the schematic  for Commodore 1084S-D ?
Your vertical linearity is bad, however I don't see a V-LIN trimpot adjustment, so it can also be caused by bad electrolytic capacitors.
C506 47uF and C307 1000uF 25V by (vertical) IC301 would be my guess, I would replace them.
Can you post a picture of the board by the IC301, that helps.

Someone else has the same problem  Mario gets pretty big jumping

Yep you got it!!! Small at bottom and big on top. As for the schematics yep that's the one! I confirm that there isn't any V-LIN pot at the back of the board. Ok here are some pics it's the best I can do. Hope it helps a bit. Let me know.

Thanks!!!

[floobydust]

See if you can find C506 (C306?) 47uF and C307 1000uF 25V at IC301 pin 12.

[xavier60]

R308 and R309 take the place of where the linearity Pot would have been. The problem is more likely to be caused by the capacitors  mentioned in the previous post.

[Serge125]

See if you can find C506 (C306?) 47uF and C307 1000uF 25V at IC301 pin 12.

Will do!! When I find them can I just replace them without discharging everything and if I have to discharge what must I do? Just discharge the fly and there's a big cap C109 too? I can do this I know (changing caps) I got my tools for this and Digi Key for the parts I just need to know if I must discharge it first or just change the caps and that's it.

Thanks for all the infos!!!

[floobydust]

I'd just leave the monitor off overnight. It has a focus/screens resistor-divider which will discharge the CRT on its own.
Main filter cap C109 also has a bleeder resistor. You can measure with a multimeter C109 and C309 (24V) to be sure. Careful with polarity on the new caps and don't hit the CRT neck! I wear safety glasses and move slowly...

[Serge125]

I'd just leave the monitor off overnight. It has a focus/screens resistor-divider which will discharge the CRT on its own.
Main filter cap C109 also has a bleeder resistor. You can measure with a multimeter C109 and C309 (24V) to be sure. Careful with polarity on the new caps and don't hit the CRT neck! I wear safety glasses and move slowly...

Hi and THANKS for the reply!!! How do you know that there's a bleeder resistor and where is it on the schematics (just want to learn question)? BTW I saw that C308 +C309 is 35V on the schem.

THANKS!!!

[andy2000]

Hi and THANKS for the reply!!! How do you know that there's a bleeder resistor and where is it on the schematics (just want to learn question)? BTW I saw that C308 +C309 is 35V on the schem.

THANKS!!!

R103 is in parallel with C109 and will gradually discharge it.  It's still a good idea to check the voltage on that cap before you stick your hands in there!

You don't have to worry about discharging the CRT unless you need to removed the HV connection from the side of the CRT.  Also, this design uses the focus and screen controls as a bleeder resistor.

If you ever do need to discharge the CRT, it's simple to do.  Just ground a screwdriver to the grounding strap for the conductive coating that's on the outside of the CRT with a clip lead.  Then, slip the screwdriver under the rubber cup until it touches the metal contact.  If you hear a snap, then leave it connected for a few minutes so all the charge bleeds off. 

[Nusa]

Is that brown stuff next to the large electrolytic in your pictures from a leaking capacitor? If so, that needs cleanup and replacement.

[Serge125]

Is that brown stuff next to the large electrolytic in your pictures from a leaking capacitor? If so, that needs cleanup and replacement.

Yeah I saw it too when I took the pics but I thought it was glue. They guy who fixed it would of seen this and replace it but it works.

[Serge125]

I'd just leave the monitor off overnight. It has a focus/screens resistor-divider which will discharge the CRT on its own.
Main filter cap C109 also has a bleeder resistor. You can measure with a multimeter C109 and C309 (24V) to be sure. Careful with polarity on the new caps and don't hit the CRT neck! I wear safety glasses and move slowly...

Been off for a few days now and I just checked C109 and I get 0 volts on the meter so now I can play in it, RIGHT?  ;-)

[xavier60]

Where the yellow glue turns brown, it can cause problems because it becomes conductive.

[james_s]

Been off for a few days now and I just checked C109 and I get 0 volts on the meter so now I can play in it, RIGHT?  ;-)

Yes you'll be fine, honestly a couple of minutes is probably enough. If in doubt, test the voltage across the larger capacitors to confirm as you have.

[Nusa]

Is that brown stuff next to the large electrolytic in your pictures from a leaking capacitor? If so, that needs cleanup and replacement.

Yeah I saw it too when I took the pics but I thought it was glue. They guy who fixed it would of seen this and replace it but it works.

Maybe, I don't know how good the guy is. Some guys stop when they get it to work, not when they've actually fixed all the problems. That cap doesn't look recently replaced, in any case, but the picture could be fooling me.

I suspect that big one is C307, with C306 being the smaller one next to it. I see a 306 label peeking out from under the crud.

[Serge125]

Is that brown stuff next to the large electrolytic in your pictures from a leaking capacitor? If so, that needs cleanup and replacement.

Yeah I saw it too when I took the pics but I thought it was glue. They guy who fixed it would of seen this and replace it but it works.

Maybe, I don't know how good the guy is. Some guys stop when they get it to work, not when they've actually fixed all the problems. That cap doesn't look recently replaced, in any case, but the picture could be fooling me.

I suspect that big one is C307, with C306 being the smaller one next to it. I see a 306 label peeking out from under the crud.

I have removed the C306 and C307 and I do conform that it was some kind of glue that was there and not a cap leak. When I removed the caps the glue was very dry and came off with the caps so WOOHOO!! Cleaned up the holes to accept the new caps. I would like to check my removed caps but there is so many explanations on the web that I don't know which one is the right one. Up to now I see that a multimeter isn't the best tool to use to test caps and that I need a special tool just for caps. I do have a digital and analog meters that I can use. I'm still gonna change the caps to new ones but I just want to learn the "good way" on how to check 'em with what I have now. I even have a very OLD oscilloscope can this be used to test them? Again THANKS for all your help AND explanations!!!

[andy2000]

I have removed the C306 and C307 and I do conform that it was some kind of glue that was there and not a cap leak. ..

That type of glue has caused more trouble over the years than you would believe.  In the 80's they would glop it all over everything.  Within a few years it turns conductive and corrosive causing all kinds of weird problems.  By the 90's they mostly stopped using it, but it still shows up occasionally on newer things.  Always remove as much as possible if you see it.

Just this week the power brick for one of my computer monitors died.  Inside I found that glue used to secure the transformer and a large cap.  Eventually it corroded through a wire which caused the power MOSFET to fail and take out the driver IC.  After that, I preemptively cleaned up an identical power brick which was still working.

[james_s]

To properly test the capacitors you really need an ESR meter, those $10 Chinese component testers will do a passable job if you don't have a proper capacitor tester. Another thing you can do is just replace the caps and see if the performance changes, if it fixes the problem then you know the capacitor was bad.

[Serge125]

To properly test the capacitors you really need an ESR meter, those $10 Chinese component testers will do a passable job if you don't have a proper capacitor tester.

So those Chinese $10 testers aren't reliable that much then. What is a "proper" capacitor tester that I can get? This is one that I was interested in and it's not a $10 Chinese tester (even though it still comes from China) what do you think about this one?

https://www.ebay.ca/itm/MESR-100-ESR-Capacitance-Ohm-Meter-Cap-Resistance-Capacitor-In-Circuit-Tester/361399064189?hash=item542510167d:g:VLUAAOSwsW9Y3grF:rk:8:pf:0

Thanks!!

[Serge125]

Hi all!!

  I ordered the parts needed and I was able to test them with an analog meter and that small 47uf (c306 or c506) is dead, no activity with the needle and the 1000uf just seems to be ok but changed it anyway so it's gonna be all brand new! I should get the parts by Thursday and will get back to you with an update!

THANKS!!!

[james_s]

Those $10 component testers are really quite good, especially for what they are. They're not as good as a purpose built capacitor analyzer but they're impressive and good enough for hobby use.

[Serge125]

Hi all!!!

   UPDATE!!! Well got the caps as said on Tuesday and changed them today and I am VERY HAPPY to report that every thing is WORKING, IT'S FIXED WOOHOO!!!!! I'm so overwhelmed about this fix all THANKS TO ALL OF YOU!!!!! I AM GRATEFUL for all of your input and HELP!!! THANKS THANKS THANKS THANKS!!!!

Like I said before I wished that I was able to find and fix problems like all of you out there, that is what I wanted to do when I was teen but at school I needed good math and well wasn't good enough to be able to take the course so..... here I am today STILL having this wish at 51!!! AGAIN THANKS!!!!

PS: THANKS!!!!!!!!!!!!!!!!!!!!!

Serge

[james_s]

Nice job! Do a few more and you'll be on a roll. I always enjoyed repairing CRTs, it was always a rush to hear the HV come up after a monitor had been dead. They're fun to work on, you tend to see the same 5-10 faults in most of them.