d0pefish's Amiga 600/030

hi Dale,
No mate - it's the other side. You can see the Thyristor that was shorted on my monitor in the 2nd pic, it's inbetween the 2 capacitors.

I'm with you now - cheers :)

Well, I somehow found the courage to go for it. :ninja:

https://lh5.googleusercontent.com/_k...0/CIMG0165.JPG

https://lh4.googleusercontent.com/_k...0/CIMG0164.JPG

So far so good. I'll see about removing the board from the tray and giving it a nice clean up.

Does anyone have a service manual and/or schematics for the Mk II? I see plenty of CM8833 Mk I service manuals around the net, but not for the Mk II. :unsure:

@Mods: probably a good idea to split the last set of posts about the monitor fault into a new topic if possible; perhaps call it "Philips CM8833 Mk II repair"? :)

I have it somewhere but can't find it at the moment. have a search around for cm11342, thats the alternate model code for this monitor

Cheers Hikey - that did it, I have a manual now. :)

I've already noticed a couple of concerns.

This wire has a dry joint and is just freely wiggling around in the hole - it's the lower grey wire of the flyback, soldered to the tube daughterboard. Just above the "S" of the sticker:
https://lh6.googleusercontent.com/_k...0/CIMG0166.JPG

And the solder joints on the flyback itself aren't fantastic, there evidence of some fractures in at least one of the legs' joints:
https://lh4.googleusercontent.com/_k...0/CIMG0167.JPG

Not sure if this is enough to cause my symptoms, or just coincidental.

After I re-do these, I'm thinking of desoldering the components you mentioned, and testing them individually.

Is there any way to test the health of the flyback if it was to be removed from the board?

Cheers :)

Well, I re-did the poor joints in question, and I also removed and tested the thyristor, transistor and the various diodes around that area - they all seemed to be behaving fine, though all I can do is some basic multimeter tests, here.

I couldn't make the thyristor latch with just the resistance test on the multimeter, but it wasn't open circuit, at least.

So far nothing's changed, no power LED, and whining. The tube doesn't get seem to get fired up at all or anything.

Can you remember which component is the fusistor on this board hikey?
I wish I had more knowledge on how to fault-find circuits like these :(

At least the board and the monitor's other internals are now meticulously clean! :lol:

Hi Dale,
Good work so far.
There are quite a few fusible resistors on this board. They look like regular resistors but are stood away from the board. The silkscreen symbol for them is like a regular resistor but with a horizontal line above and below. The fusible resistor for the HOT is located quite near the brightness/contrast controls.

Thanks hikey, your description of the fusible resistors was spot on:
https://lh6.googleusercontent.com/_k...0/CIMG0169.JPG

I went round and used the diode test function on all of the fusible resistors I could see, especially the ones around the transformer/power supply area. They all buzzed out - though I'm not sure an in-circuit test is good enough. Should I desolder them all and test their resistance against the parts list in the Philips service manual?

Also, is this the HOT?
https://lh4.googleusercontent.com/_k...0/CIMG0170.JPG

Can I test it like a regular transistor? Shall I remove it and see?

Thanks for your help mate :)

Remove the transistor to check, it may buzz OK on transistor checker.

BTW: from the second shot on the page#7 I can tell the flyback is shot.

Thanks, I'll pull it out tonight and see how it meters.

I've ordered the flyback regardless :) CPC.co.uk, a division of Farnell, carries the HR replacement transformer for a reasonable price, so I've gone for it and should have it this week, maybe even tomorrow going by Farnell's history! :D

If you think it's shot, then I'll put it in and cross my fingers. Is is the discolouration to the casing that's telling you it's broken (combined with the symptoms in general)?

If the transformer fixes the screen, I'll do a huge capacitor list/order and re-do the entire board to try and keep it going. :thumbsup:

Replacing the electrolytic capacitors on old hardware is always a good idea.

I spotted a black carbonization on the top of the ferrite of the flyback, that give the problem away.

Sack it out and smell it: you sense the burn "essence". Don't sniff it in place! The tube may still have charge and a discharge on your nose will be not funny at all.