CRT monitor display distortion problem - Page 1
Forum section: electronics / repair

author: Serge125
author_rank: Regular Contributor
timestamp: October 31, 2018, 05:28:33 pm
content: 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!!

author: floobydust
author_rank: Super Contributor
timestamp: October 31, 2018, 05:42:56 pm
content: 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=1630641.3.6

author: Serge125
author_rank: Regular Contributor
timestamp: October 31, 2018, 07:01:45 pm
content: Quote from: floobydust on October 31, 2018, 05:42:56 pmHi 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!!!! ;-)

author: floobydust
author_rank: Super Contributor
timestamp: November 01, 2018, 12:38:22 am
content: Is this theschematic 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 problemMario gets pretty big jumping

author: Serge125
author_rank: Regular Contributor
timestamp: November 01, 2018, 01:20:01 am
content: Quote from: floobydust on November 01, 2018, 12:38:22 amYep 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!!!

author: floobydust
author_rank: Super Contributor
timestamp: November 01, 2018, 02:35:03 am
content: See if you can find C506 (C306?) 47uF and C307 1000uF 25V at IC301 pin 12.

author: xavier60
author_rank: Super Contributor
timestamp: November 01, 2018, 03:43:37 am
content: 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.

author: Serge125
author_rank: Regular Contributor
timestamp: November 01, 2018, 08:02:33 pm
content: Quote from: floobydust on November 01, 2018, 02:35:03 amWill 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!!!

author: floobydust
author_rank: Super Contributor
timestamp: November 02, 2018, 01:20:13 am
content: 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...

author: Serge125
author_rank: Regular Contributor
timestamp: November 02, 2018, 08:54:00 am
content: Quote from: floobydust on November 02, 2018, 01:20:13 amHi 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!!!

author: andy2000
author_rank: Frequent Contributor
timestamp: November 02, 2018, 02:38:08 pm
content: Quote from: Serge125 on November 02, 2018, 08:54:00 amR103 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.

author: Nusa
author_rank: Super Contributor
timestamp: November 02, 2018, 05:04:09 pm
content: Is that brown stuff next to the large electrolytic in your pictures from a leaking capacitor? If so, that needs cleanup and replacement.

author: Serge125
author_rank: Regular Contributor
timestamp: November 02, 2018, 05:13:43 pm
content: Quote from: Nusa on November 02, 2018, 05:04:09 pmYeah 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.

author: Serge125
author_rank: Regular Contributor
timestamp: November 02, 2018, 05:19:20 pm
content: Quote from: floobydust on November 02, 2018, 01:20:13 amBeen 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? ;-)

author: xavier60
author_rank: Super Contributor
timestamp: November 02, 2018, 09:09:34 pm
content: Where the yellow glue turns brown, it can cause problems because it becomes conductive.

author: james_s
author_rank: Super Contributor
timestamp: November 02, 2018, 10:25:28 pm
content: Quote from: Serge125 on November 02, 2018, 05:19:20 pmYes 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.

author: Nusa
author_rank: Super Contributor
timestamp: November 02, 2018, 10:54:59 pm
content: Quote from: Serge125 on November 02, 2018, 05:13:43 pmMaybe, 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.

author: Serge125
author_rank: Regular Contributor
timestamp: November 03, 2018, 01:10:35 am
content: Quote from: Nusa on November 02, 2018, 10:54:59 pmI 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!!!

author: andy2000
author_rank: Frequent Contributor
timestamp: November 03, 2018, 03:11:17 pm
content: Quote from: Serge125 on November 03, 2018, 01:10:35 amThat 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.

author: james_s
author_rank: Super Contributor
timestamp: November 03, 2018, 05:24:37 pm
content: 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.

author: Serge125
author_rank: Regular Contributor
timestamp: November 04, 2018, 12:58:29 pm
content: Quote from: james_s on November 03, 2018, 05:24:37 pmSo 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:0Thanks!!

author: Serge125
author_rank: Regular Contributor
timestamp: November 04, 2018, 01:06:37 pm
content: 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!!!

author: james_s
author_rank: Super Contributor
timestamp: November 04, 2018, 06:02:39 pm
content: 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.

author: Serge125
author_rank: Regular Contributor
timestamp: November 09, 2018, 09:44:52 pm
content: 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

author: james_s
author_rank: Super Contributor
timestamp: November 10, 2018, 01:45:56 am
content: 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.

author: Serge125
author_rank: Regular Contributor
timestamp: December 17, 2018, 08:22:14 pm
content: Hi allWell decided to get an ESR meter for my Christmas present!! Got it today and can't wait to try it out. Again THANKS for all the help and my little monitor is still running like new THANKS to ALL for your HELP!!! Merry Christmas to all and HAVE A HAPPY NEW YEAR!!!!Serge

author: Cargo Cult
author_rank: Newbie
timestamp: December 03, 2020, 12:44:03 am
content: I'm writing to say thanks to those that posted to this topic and to leave additional information for those who find themselves here in the future.I was having the same issue--vertical stretch commensurate with a degraded right triangle waveform controlling V-Lin. This is the only place on the internet I could find actual detail around the cause of the non-uniform stretch. It's fairly obvious once you've seen the waveforms, but this is the only place it's explained and which there is a reference image of the actual problem, on-screen.I've just completed the teardown of my beloved 1084s-d and I can confirm the same exact failure. It appears that the glue that was put in place to minimize component movement/drop damage was excessively applied at C306. It also appears to be the only place where the glue is directly in contact with the capacitor leads. After removing the glue with a pick, I found that the C306 capacitor leads were corroded fully through. The glue must be highly corrosive in direct contact with the leads. Fortunately, most of the capacitors on the board which are glued in place (except for C306) are so close to the pcb, the glue is only in contact with their plastic casings--not the leads. They appear to be safe.I would note for future reference that the schematic supplied, while incredibly helpful, has C306 incorrectly labeled as C506. Floobydust correctly stated "C506" in his message, as it is labeled that way on the schematic--however, the board is stenciled C306--which is in line with the numbering for components in that physical location. I would figure that C306 is in fact the correct label, given how the numbering of components is laid out. I suppose we've discovered a typo in the original documentation--ironic given that it's the part that failed.I also discovered during the teardown that C116, one of the two large 100uF capacitors on the isolated side of the transformer--and filtering a 320Vpp signal--was leaking gel from the top (though I seemed to have no other issue with the monitor). Every other capacitor on the board looks pristine. The same is true for my Amiga 500 rev. 5 and the power supply it came with. I suppose the Daewoo (in this monitor) and the Nichicon capacitors of the late 80s are just solidly made components. I can't say so much for the adhesives of the time.Due to other demands, I've yet to replace the capacitor (planning on doing the entire board), but will report back what I expect to be success when I'm finished.In the meantime, if you find yourself here troubleshooting the 1084s-d, I would expect C506 (or C306 depending on what you're looking at) will need to be replaced regardless of other issues you are having if that glue is present and in contact with the capacitor leads--come to think of it, anywhere that glue is in contact with capacitor leads (or other metallic portions of components), remove the glue and replace the component.Cheers,Cargo

author: helius
author_rank: Super Contributor
timestamp: December 03, 2020, 01:48:33 am
content: Had the glue turned a nice toasty shade of brown? That stuff is indeed corrosive; it was used in a lot of phenolic 1-sided boards in 1980s Japan, and causes similar problems in stereos and computers. Good to see you found the cause of the issue.

author: Cargo Cult
author_rank: Newbie
timestamp: December 03, 2020, 02:59:54 am
content: Exactly that shade--like overly toasted toast. Some of it--where it was very brittle, was an almost burnt color. I spent some extra time chipping away anywhere the glue came in contact with leads, and lo and behold, corrosion. I'll be cleaning the entire board with "safe" flux remover tomorrow.Best,Cargo

author: james_s
author_rank: Super Contributor
timestamp: December 03, 2020, 03:45:36 am
content: I remember repairing quite a few monitors in the late 90s-early 2000's with that same fault. The glue would turn brown and become conductive and then it caused all sorts of problems.