Old Commodore CRT with possible vertical deflection issue?

Thread Starter

joelgraff

Joined Dec 24, 2018
10
Hi,

I have an old Commodore 1802 (Goldstar) CRT that has a funny problem... Someone suggested it might be a vertical deflection issue, but that seems to consist of distortion of the image vertically, whereas it appears, here, the image is undistorted, but drawn in the lower three quarters of the screen, and wrapped around.

The vertical hold knob on back seems a bit suspect (there's some damage on the case surrounding it), but I've yet to open it to see. Before I go tearing into things, I thought maybe I'd post to see if anyone recognizes this issue and can help provide a little scope...

20181224_151644.jpg
 

spinnaker

Joined Oct 29, 2009
7,835
Welcome to the forum. Wow it must be a million years since I worked on a television CRT. If I had to rack my brain and remember this issue, I would take a guess and say it is some kind of vertical sync issue.

I found this this.

http://kibaro.blogspot.com/2008/03/tv-vertical-section-problems-and.html

Look in the squashed video section.

The thing is very old. A bad cap is a good guess. I would open it up and take a look. Take a close look at the vertical control. If I am remembering correctly I have seen this issue when the control is not adjusted correctly. The pot may simply be smashed or disconnected entirely.

Do you happen to have a schematic? Where is Sam's photo facts when you need them? :)
 

MrChips

Joined Oct 2, 2009
24,415
It does look like a problem with the vertical drive or the power supply.
If you have an oscilloscope, examine the signal at test point 20 going to the vertical deflection coil.

Possible suspects are:
C308 100μF 35V
C318 470μF 35V

Try adjusting:
R305 V-HOLD
R309 V-LINE
 

Thread Starter

joelgraff

Joined Dec 24, 2018
10
I found this this.

http://kibaro.blogspot.com/2008/03/tv-vertical-section-problems-and.html

Look in the squashed video section.

The thing is very old. A bad cap is a good guess. I would open it up and take a look. Take a close look at the vertical control. If I am remembering correctly I have seen this issue when the control is not adjusted correctly. The pot may simply be smashed or disconnected entirely.

Do you happen to have a schematic? Where is Sam's photo facts when you need them? :)
I'm starting to discover that this monitor was previously manufactured under a completely different model number, but is otherwise identical. I found a schematic for that. The only 1802 reference documentation I found was the user's manual. Caps are definitely part of the plan to replace.

What does the audio sound like? Do you hear a 60 cycle hum (buzzing)?
No buzzing or humming that I can detect. Just that usual CRT high-pitched squeal that always drove me nuts as a kid. Would be nice if getting old meant I couldn't hear that anymore... :)

I think it is just a monitor, no audio.

Believe it or not.... Service manual at http://www.schematicsforfree.com/archive/file/Video/Monitors - CRT/Commodore 1802 Monitor.pdf
There were two 1802 monitors. The GoldStar one (which I have) is a bit rarer. The other was the DaeWoo one. Pretty sure this manual is for the DaeWoo, because it shows a monochrome RCA jack on the input panel, which doesn't exist on the GoldStar. I did discover that the GoldStar was previously made under a completely different model number, CM-141, but was supposedly otherwise identical in the 1802 revision. The pictures I found certainly look nearly identical. I managed to find a schematic for that, at least, but still no service manual. :/

It does look like a problem with the vertical drive or the power supply.
If you have an oscilloscope, examine the signal at test point 20 going to the vertical deflection coil.

Possible suspects are:
C308 100μF 35V
C318 470μF 35V

Try adjusting:
R305 V-HOLD
R309 V-LINE
Wish I had an oscilloscope. Should have asked for that for Christmas. But I'm sure it would have been trumped by the Nintendo Switch the kids got, anyway. :)

Anyway, your responses have given me some direction to start investigating. I'll definitely be taking it apart in the next few days to see if I can learn anything more.
 

spinnaker

Joined Oct 29, 2009
7,835
It does look like a problem with the vertical drive or the power supply.
If you have an oscilloscope, examine the signal at test point 20 going to the vertical deflection coil.

Possible suspects are:
C308 100μF 35V
C318 470μF 35V

Try adjusting:
R305 V-HOLD
R309 V-LINE

Wow you are good. Not sure I would have been able to find those. I still can't find r305 or R309 on the schematic. Am I just completely out of practice in TV troubleshooting and reading a schematic or is that a horribly drawn schematic? I don't remember them being that hard to floow.

What is this?
upload_2018-12-25_11-34-11.png

Is that the deflection yoke?
 

ian field

Joined Oct 27, 2012
6,539
Hi,

I have an old Commodore 1802 (Goldstar) CRT that has a funny problem... Someone suggested it might be a vertical deflection issue, but that seems to consist of distortion of the image vertically, whereas it appears, here, the image is undistorted, but drawn in the lower three quarters of the screen, and wrapped around.

The vertical hold knob on back seems a bit suspect (there's some damage on the case surrounding it), but I've yet to open it to see. Before I go tearing into things, I thought maybe I'd post to see if anyone recognizes this issue and can help provide a little scope...

View attachment 166371
Quite a few monitors of that era had non polar electrolytic coupling for the vertical scan, so its worth checking for that before getting too into difficult stuff. They tend to be not much bigger than about 3.3uF - not all THAT difficult to find metalised foil types that big these days.
 

ian field

Joined Oct 27, 2012
6,539
I repaired dozens of monitors and small TV with same issue. In 90% instances the electrolytic caps around the vertical amp were bad
Electrolytics can certainly be a PITA, if they're all getting on a bit I'd expect the linearity seen in the picture to be further off.
 

Thread Starter

joelgraff

Joined Dec 24, 2018
10
Quite a few monitors of that era had non polar electrolytic coupling for the vertical scan, so its worth checking for that before getting too into difficult stuff. They tend to be not much bigger than about 3.3uF - not all THAT difficult to find metalised foil types that big these days.
Ok, it seems like the capacitors are the place to start, assuming no issues with the vertical pots (apparently, there's an internal one as well...)

On the topic of capacitors, I've always assumed electrolytics were the major capcitor type to be most concerned about (given that there's no paper / wax caps in the design, of course :) ), but as I reviewed the parts list for the monitor, I saw a wide variety of capacitor types. Specifically,

  • Ceramic (Hi-K and TC)
  • Electrolytic (chemical)
  • Polypropylene (MPP and PP)
  • BiPolar
  • Mylar
  • Polyester
  • AC
  • TANIAL
I'm familiar enough with them to know ceramic and mylar are fine, and I was under the impression the poly types were as well, but being an electronics guy more by necessity than personal interest, I can't really claim to know much, honestly.

Also, there's a few types I'm not familiar with. There's a couple "BP" (bi-polar / non-polarized) caps - no idea what type that could be until I open it up I guess. Then there's "AC" and "TANIAL" - no idea at all what those are.

Incidentally, a link to the parts list. The caps start at the end of page 5:

http://www.bombjack.org/commodore/commodore/1802_Color_Monitor_Goldstar_Replacement_Parts_List.pdf
 

ian field

Joined Oct 27, 2012
6,539
Ok, it seems like the capacitors are the place to start, assuming no issues with the vertical pots (apparently, there's an internal one as well...)

On the topic of capacitors, I've always assumed electrolytics were the major capcitor type to be most concerned about (given that there's no paper / wax caps in the design, of course :) ), but as I reviewed the parts list for the monitor, I saw a wide variety of capacitor types. Specifically,

  • Ceramic (Hi-K and TC)
  • Electrolytic (chemical)
  • Polypropylene (MPP and PP)
  • BiPolar
  • Mylar
  • Polyester
  • AC
  • TANIAL
I'm familiar enough with them to know ceramic and mylar are fine, and I was under the impression the poly types were as well, but being an electronics guy more by necessity than personal interest, I can't really claim to know much, honestly.

Also, there's a few types I'm not familiar with. There's a couple "BP" (bi-polar / non-polarized) caps - no idea what type that could be until I open it up I guess. Then there's "AC" and "TANIAL" - no idea at all what those are.

Incidentally, a link to the parts list. The caps start at the end of page 5:

http://www.bombjack.org/commodore/commodore/1802_Color_Monitor_Goldstar_Replacement_Parts_List.pdf
Ceramic can fail in horizontal flyback - but not usually a problem in vertical.
 
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