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Compaq Portable CRT board - removal/service

PhilipA

Experienced Member
Joined
Aug 4, 2013
Messages
476
Location
Larose, LA, USA
All,

With my Portable getting some good use, it's coming to the point where the screen drive board is beginning to act up. The image wavers around on the screen, most noticeably in 320x200 graphics mode. I've read elsewhere from the vintage TV guys that this is particularly common to bad power smoothing capacitors, of which there are several on the board.


20130826_211821 by renault9gta, on Flickr

The innards of the VDU show an interesting thing. Running diagonally across the yoke in that image is a second high voltage wire, with a tubular section under heat-shrink rubber.
The HT wiring is connected from the flyback, to the anode, then out through that wire to the chassis ground.

Is that a HT bleeder resistor? I don't want to start poking around in there without first making sure everything's discharged- but that should discharge the tube overnight if it's still in working order?

--Phil
 
All,

With my Portable getting some good use, it's coming to the point where the screen drive board is beginning to act up. The image wavers around on the screen, most noticeably in 320x200 graphics mode. I've read elsewhere from the vintage TV guys that this is particularly common to bad power smoothing capacitors, of which there are several on the board.


20130826_211821 by renault9gta, on Flickr

The innards of the VDU show an interesting thing. Running diagonally across the yoke in that image is a second high voltage wire, with a tubular section under heat-shrink rubber.
The HT wiring is connected from the flyback, to the anode, then out through that wire to the chassis ground.

Is that a HT bleeder resistor? I don't want to start poking around in there without first making sure everything's discharged- but that should discharge the tube overnight if it's still in working order?

--Phil

I'm not that familiar with the portables CRT chassis, I never had mine apart, but even if its got a bleeder I wouldn't trust that its working, I wouldn't touch a thing without manually grounding the anode with a bleeder (homemade or purchased).
 
Got a bit of experience discharging these things now, it's not as bad as I had feared. I think I'll be good to pull the board :)

--Phil
 
What's your procedure for discharging these tubes? I'm sure mine will need to be recapped eventually, so a howto would be most helpful.
 
Well, would you believe it... I actually managed to order the parts for this, recapped it and it's now back working again.

Discovered that one of the address decoders on the expansion board is going funny when it's hot. For now a heatsink and stationary fan has remedied the crashing.

It's nice to have it back.
 
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