Re: This can't be right...

Wow, I am really grateful for how helpful you're being. Thank you.

Yes, fault was present before recapping. The recapping was just a stab in the dark. The picture is at least sharper now following the recap so it wasn't in vein.

Will check those transistors as suggested.

SAMS for the monitor is here:

[url]https://tinyurl.com/3npws544[/url]Re: This can't be right...<br /> <b...recapping. The

Re: This can't be right...

The raster seems to shrink from both directions at once, and when power is disconnected a brief vertical line blinks on the screen (which would only happen if HV were still present?).

I've never worked on anthing like this before, I'm not sure what freezer spray or a heat source would show me?

There's a really good SAMS for this monitor thankfully, showing me what voltages and resistances I should expect to see at key probe points and what signal patterns an ossiloscope should show me at certain points too so I guess I'll go down...

Re: This can't be right...

Well I've replaced every electrolytic in the monitor except for the Horizontal drive big boi.

Unfortunately I still get the same symptoms - raster collapsing after two minutes of being powered on from cold (less if warm):

[url]https://youtu.be/jPryi-k_XXY[/url]

I think it might be time for me to buy an oscilloscope...Re: This can't be right...<br /> <b...ptoms - raster

Re: This can't be right...

Marvellous, thanks guys, will reinstall the old one!

Re: This can't be right...

Yeah, I've zoomed out on the SAMS for this monitor and you can see that C505 is positioned between the flyback and the horizontal deflection coil.

You can also see that it's referenced to the HV output of the flyback, it's not galvanically isolated.

I really feel like we are missing some kind of special characteristic that this capacitor exhibits... Either that or the voltage rating on the old cap is just plain wrong on the label?

Probably not given the collector of that tranny is rated 14.63v on the diagram... But...

Re: This can't be right...

But how would you explain the physical size difference?

That's what I'm alarmed by, the old cap is a lower capacity same voltage as the replacement capacitor so why is it 20x the size?

I really feel we are missing something here...

None of the other replacement capacitors have shrunk in dimensions by anywhere near that magnitude, the others are maybe 10-20% smaller, not 2,000+% smaller.

So I'm here repairing an old IBM 5151 monitor, and I've ordered replacements for all the electrolytic capacitors.

I've found like for like replacements for each one except weird one which, according to the circuit diagram sits at a centre tap of the flyback and the collector of the horizontal output transistor?

It's C505.

Non polarized, 18uF, 25v. Apparently.

So the replacement caps arrive, I've had to obtain a 22uF 25v NP cap as there weren't any 18uF 25v available, not sure what the consequences of this might be.

But...

Re: New Members - please post your introductions here

Good morning all!

Great to encounter a forum dedicated to capacitors, I've just started a hobby of repairing old electronics and I'm starting with an IBM PC, already recapped the motherboard now working on the 5151 monitor which has some anomalies in it I'm hoping your expertise can assist with.

Peace out y'all