X-Ray protection, Commodore 1084S-D1 CRT

[G6ONEDave]

A1 and 'screen' are the same in this context. I've tried to only use the word screen (A1) as the adjustment, as opposed to the front displayed image. The front displayed image can also be called 'screen' just to add confusion, that's why Ive tried to refer to it as display. Hope that has helped a bit.

It will be interesting to see what the monitor displays with the correct computer input.

Re the squealing and possible spark noise, visibly check all the ceramic capacitors in both the power supply and line output stage. Do this with the monitor off first. You are looking for any cracks and or burn/flash marks in the capacitor insulation. It will be obvious if there is one. If you can't see anything obvious, then try powering up the monitor in a darkened room and and look for any flashes in the same 2 areas. If that doen't reveal any culprits, check the crt base pcb and crt socket. There could be a capacitor or a spark gap breaking down on it.

Dave

[Overkill]

Originally Posted by G6ONEDave

A1 and 'screen' are the same in this context. I've tried to only use the word screen (A1) as the adjustment, as opposed to the front displayed image. The front displayed image can also be called 'screen' just to add confusion, that's why Ive tried to refer to it as display.

Should I leave the brightness and contrast half way while adjusting the flyback?
Do I need to adjust it to a very dark grey?

[Maarten]

I always adjust it so that with max brightness, zero contrast and no signal, the screen is grey without flyback lines visible. The proper procedure will be in the service manual. It might be called G2 instead of A1. The former meaning second grid, the latter first anode. The construction is neither a grid nor an anode, but we have to call it something...

[Overkill]

I shouldn't have listened to Google, everywhere it said "high-pitch whine = bad flyback", but the original flyback was fine

So, it turned out to just be that transistor in the EW circuit and the diode in the HOT circuit

It sounds like I could have used the new flyback, but I would have had to change the value of the tuning capacitor in the HOT circuit.

Thanks for all the help, it's much appreciated

[Maarten]

Given the almost 10% difference in the +15V measurement and the activation of the protection circuit, it's likely some tuning would have been necessary.

[Overkill]

Looks like I need to find VR323

[sexton_mallard]

A great result! I followed this thread with interest as I have a much older late 50s TV set also with an EHT fault like your monitor. I also tried a replacement LOPT (flyback transformer) like you did here but the actual apparent fault was a high voltage breakdown in the scan coils killing the EHT. A similar set of replacement scan coils were kindly donated to me by forum member Heatercathodeshort which solved the EHT problem.

[Sideband]

There is a lot of mis-information on Google....usually because of inexperienced people reading theoretical faults from different sources and then getting it all mixed up....plus there are a lot of 'Americanisms' being used that cause confusion to us Brits (as no doubt our terminology does to Americans)! There are a lot of well-meaning people who try to help but in themselves are 'successful dabblers' with limited formal training. There are also some very good to excellent ones out there....it's a question of sorting out the good from the bad.

Looks like you got a good result in the end so well done for persevering.

[Overkill]

I'm not quite there yet The pincushioning trim does nothing and I get intermittent screen rolling, but H-Hold trim does nothing

I'm going to try another video source.

[Welsh Anorak]

Don't forget rolling would require adjustment of the V-HOLD preset.

[Overkill]

Thanks sexton_mallard & Sideband for following and your congrat's, but still a little way to go.

Originally Posted by Welsh Anorak

Don't forget rolling would require adjustment of the V-HOLD preset.

I don't see a V-Hold adjustment. the rolling seems intermittent , so I think I might start a new topic to deal with the pincushioning first.

[Station X]

Please don't start a new thread. It can all be dealt with in this one.

[Overkill]

Originally Posted by Station X

Please don't start a new thread. It can all be dealt with in this one.

OK, I'll see how it goes here

[Overkill]

Pincushioning: Adjusting does nothing!

I think I might be close to finding something, but too much electronics hurts my head

So far:
>I removed C312 just to see if the circuit was doing anything, but the picture looked the same.
>I found that R332 was a 75K, not a 47K that the diagram said, I thought maybe someone in the past had fitted the wrong value.
>Now here's the thing that makes me think I've missed a faulty component, with R320 and R332 removed, I get a 1.5K reading (1.9 with MM probes reversed) between the pads where they were connected (obviously not the end where they joined). I had already replaced Q301 and because H.size works I assumed Q302 must work. I also think I tested C333, but maybe I should check it again. Q301 went short, so it makes sense something else near may have got damaged.

[Overkill]

1.65K with MM probes reversed, not 1.9k

[Overkill]

I checked the parts list, R332 should be a 75K, it's just wrong on the diagram.

[Overkill]

Got to be Q302 short I'm thinking

[Overkill]

See the attached photo of Q302 transistor in my component tester, fingers crossed

[Maarten]

That would explain a lot. Just to make sure, did you test or replace Q301 as well / previously?

[Overkill]

Originally Posted by Maarten

That would explain a lot. Just to make sure, did you test or replace Q301 as well / previously?

Yes, it was Q301 and a diode that caused the original fault.