PET flyback lines

[razza]

I had flyback lines that my brightness pot couldn't resolve. I have a 'mismatched' driver PCB and monitor (M24-302-GH). I followed Mr Holden's guide (section 9 - page 13) linked here and it worked a treat!

I have gone from...


to...


Mine is not quite as neat yet!


Thank you so much!

 

[razza]

Now I have the CRT section mostly working, I thought I would give the CRT, PCB and case a clean. Should the EHT cap connector just pull off with minimal effort?
Mine feels like it's hooked on and I am scared of wrecking it with force - sorry for such a dumb question but I have looked on YouTube etc. but not seen anything for a PET/CBM 9"

 

[razza]

For any newbies interested, the EHT cap connector is like a 2 prong clip that needs to be squeezed together to release it.

 

[Hugo Holden]

I have been removing and re-fitting these CRT clips since the early 1970's.

For those it is best fold back the rubber cap edges, reach under the cap first, with thin long nosed pliers to squeeze the two pins together. Though if you understand the arrangement you can put force on the cap along the axis of the two spring pins, to compress them together, that way and aid the release of one of the side clips first.

Though I don't use any ordinary pliers, I always coat the metal of the pliers with plastic tape, the reason is you don't (ever) want a metal tool touching the glass-work of a CRT as it can scratch the glass.

 

[Hugo Holden]

Those brown deposits on the Black EHT cap...What do you think it is ?

 

[razza]

Those brown deposits on the Black EHT cap...What do you think it is ?

I have no idea. Rust?

 

[Hugo Holden]

I have no idea. Rust?

Yes.

You could do a taste test on it, tastes very much like blood (Hemoglobin), not that I am a Vampire, but Iron does have a very characteristic metallic taste. I know this because I have spent many years restoring various rusted items on vintage electronic gear and vintage cars, and in the end have got some of that rusty particulate matter in my mouth and noticed the similarity of it to the taste of blood from accidentally biting the inside of my mouth....... too much information maybe.

The metal PET VDU housing; it was only lightly over-sprayed unlike the outer surface. So what happened was the inside of it rusted. By electrostatic attraction many of those fine rust particles became airborne and transferred to the anode cap.

To fix the rust on the inside of the metal cabinet, brush it with Fertan organic rust converter solution. It will turn the rust in the metal pits into a harmless blue-black organic compound. Once that is done re-spray paint the inside of the cabinet.

Clean the rust particles off the anode cap.

 

[razza]

Hi Hugo, I am most certainly going to do the inside, as you describe in your document I used to fix the low voltage issue on my mismatched CRT/PCB.
Having sorted out the EHT coil, it appears I now have some logic issues affecting the display (hopefully, 2114 RAM), cosmetics are next on the list.

What is the best way of cleaning some really dirty PCBs (monitor and mainboard)? I have done some extensive scrubbing with an anti-static brush also brush with alcohol, but it feels like progress is poor.

 

[Hugo Holden]

Once pcb's have been cleaned with alcohols and or contact cleaners, they can end up not looking particularly cosmetically good and have a flat looking irregular surface devoid of any gloss.

Assuming the board has been well cleaned and there is no remaining dirt, one way to fix that appearance is to use a lint free cloth with the product Inox MX-3 applied. And rub that into the board surface. It is a high purity long lasting oil. Then with a dry cloth, keep rubbing it off until the appearance no longer changes. The microscopic amount of it remaining in surface irregularities of either a conformal coating or bare fiberglass solves the cosmetic issue. The method seems long lasting, I have some pcb's I did this to a few years ago and they still appear good. You can also use the MX-3 as a lubricant for IC sockets and it helps prevent future corrosion on IC pins that have lost their original electroplating.