Pincushion adjustment - admiral tv

[maxhifi]

I have posted this tv before, SAMS has no info on how to adjust the pincushion, and it looks kind of bad. There's no control for pincushion... Any advice on how to fix this? At first I thought it wS capacitors but it's too symmetrical

[marty59]

To me, the lack of horizontal towards the bottom looks more like a slight "keystone" than pincushion, although you may be able to do something about it vertically. What is the Sam's listed for this set?

[DaveWM]

B&W has magnets in the yoke, color uses active circuits. Assuming its a BW set I would look for magnets in the yoke that may have fallen out or become weak.

It does not look that bad, back in the day you did not have black bars on top and bottom for wide screen format to show minor defects like this. (I was looking for classic pin cushion defect this is opposite of what you would expect, like too much pincushion correction).

after looking again I think I see what the prob is the bottom looks a tad pulled in on the right. If it was a color set I would look to see if there is a connection from the screen of the horz out to the vert, this was how some zeniths corrected pin cushion but again only on a color set. the pic is in BW so I assume its BW, pin cushion effect should be the opposite.

check B+ and try new horz sweep tubes.

[maxhifi]

Sams is SET 778 Folder 1
TV is a 19" Admiral B&W G310, series string B&W TV set. I haven't replaced any capacitors, it's all original. Other issues are vertical linearity is really touchy, it seems to vary with line voltage sometimes, and I often have to re-adjust it to make circles look round. I also haven't tested the tubes... the only thing I did to this TV is clean it up really well inside and out, and replace a defective speaker. The picture tube isn't super strong so I don't want to put a lot of money into the set, but it's a decent bedroom TV - way better than the RCA/Sharp I posted about recently. I am scratching my head over the linearity and pincushion problems though. While bad filter capacitors are possible, the distortion seems symmetrical, and there is no hum at all in the audio.

I should also mention that when I cleaned up the TV (it had been in a shed for a long time), I removed the yoke from the CRT. Could I have installed it too far forward or back, and this is responsible for the problem? I didn't know about magnets in the yoke, it makes sense though. The rings around the CRT neck are for adjusting horizontal centering, not pincushion.

Attached is the schematic diagram from Sams.

[DaveWM]

bw set yokes are alway pushed as far forward as possible, should fit up snug to the jug.

is C61 a disc cap?

[maxhifi]

Originally Posted by DaveWM

bw set yokes are alway pushed as far forward as possible, should fit up snug to the jug.

is C61 a disc cap?

I am pretty sure when I reinstalled the yoke I did just that, pushed it right up as far as it would go. C61 is a white tubular capacitor, see attached image copied from Sams. The capacitors in the TV itself look identical but everything says "made in Canada" rather than "made in usa"

[DaveWM]

If it was my set I would replace both those tubular caps. They are too high a voltage rating to test with my cap tester (450v max) for leakage, and I am pretty sure they are just paper caps in a ceramic tube. Not saying this will fix the problem, but if I can't test it I replace it, esp since one of them seems tied into the yoke and vert height control. the other is a boost cap, and again not one that you would want to leak and drag down voltages from the flyback.

[maxhifi]

Originally Posted by DaveWM

bw set yokes are alway pushed as far forward as possible, should fit up snug to the jug.

is C61 a disc cap?

Originally Posted by DaveWM

If it was my set I would replace both those tubular caps. They are too high a voltage rating to test with my cap tester (450v max) for leakage, and I am pretty sure they are just paper caps in a ceramic tube. Not saying this will fix the problem, but if I can't test it I replace it, esp since one of them seems tied into the yoke and vert height control. the other is a boost cap, and again not one that you would want to leak and drag down voltages from the flyback.

There's more similar caps on the top side of the circuit board, and very very few electrolytic capacitors in this TV. OK you have me convinced, I better change them before proceeding with more troubleshooting.

[DaveWM]

those lower voltage ones like the 400-600vdc I would have no problem lifting a leg and checking with old school cap tester. I have found some of them to be just fine, others test leaky. I think it has to do with the enviroment the set was stored in.

looking it over maybe C45 if you have trouble with vert setup, If the the pic looks ok other than vert sweep and that pull in at the bottom, I doubt those other caps on the top of the pcb will make any change. I am not a fan of wholesale replacement unless there is a symptom. If I check a couple and they all tested leaky I prob would assume they rest will be, but with those I would say better that 50/50 they are ok. If they were wax paper then I would not even test, just replace on sight as prob more then 90% will test bad.

of course shot gun of all those white ceramic tube caps will not hurt anything, just make sure you replace with the correct value.

[maxhifi]

Problems with the pic are to do with vertical linearity, which changes as the set warms up, and the pincushion setting looking distortion. Sound is good, but focus is a bit soft, and it's hard to find the ideal settings for brightness and contrast, it seems to vary by program material which is the best setting. Picture dynamic range is kind of bad, things will either look washed out, or everything will be lost in darkness, the correct setting for the contrast knob seems to be elusive. When I am just watching it though and not analysing it, the TV makes a decent enough picture, and it's perfect for watching some talking heads at bed time.

[DaveWM]

a LOT of problems trace back to a weak CRT, if the CRT is weak you will never get good results. Have you tested it? good cut off and emissions will be needed to deal with varying content.

[maxhifi]

Originally Posted by DaveWM

a LOT of problems trace back to a weak CRT, if the CRT is weak you will never get good results. Have you tested it? good cut off and emissions will be needed to deal with varying content.

I don't have a CRT tester, only an EICO 667 and TV-7C for the little tubes. I suspected the same, which is why I was hesitant to order parts for the TV. The poor contrast especially made me think the CRT may be tired. It also loses focus when brightness/contrast are increased, which to me is a clear sign the CRT is weak. Still doesn't explain the bad linearity and pincushion issues though. Maybe it's better to put this one out to pasture and find a TV with a better tube?

[DaveWM]

I would just do those 3 caps, see how it looks. check C18, maybe a bit lossy.

[Electronic M]

You may have dirty brightness/contrast pots.

[DaveWM]

there is a lot of ways to approach this. replacing caps is one. diagnosing and replacing in the offending area is another. Tube subbing (like the video out) and the CRT, is a way. Using a scope to see the signal is good. there are so many ways its just you need to decide what your end game is.

If you just want to watch a tv, I would start with shot gun of caps, they are not expensive,there are not a lot, and it may help.

If you want to learn to diagnose, then I would get the scope out and look at the wave forms while replacing caps/making sure tube sockets are clean/pots are clean and look to see whats going on with each change. I think of TVs as a learning tool, so a few problems are a good thing. If you are getting a good signal to the CRT and good HV, and it still looks bad, then its prob a weak CRT that is having to be driven to hard. But remember this is a low end set, no DC restoration so black levels will be all over the place.