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Vertical collapse on IBM 5153

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First post, by geiger9

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Hey all. Looking for help troubleshooting vertical collapse with a CRT monitor. It's an IBM 5153 so a fair bit old. Here's what I've done so far:

- looked for cracked solder joints and broken traces
- removed the v.hold and v.size pots from PCB and tested them
- tried injecting a vertical signal directly into the sync processor
- replaced the sync processor IC (Q402)
- recapped the board
- removed the three transistors in the vertical circuit and tested them
- checked resistor R312 which, according to one forum user, caused his vertical collapse.

The most recent thing I did was check the voltages on the three transistors in the vertical circuit while the monitor was running:

Q301
b 0V
e 0V
c 48.5V

Q302
b 48.5V
e 49V
c 120V

Q303
b 48V
e 49V
c 0V

I don't know what these values can tell me or what my next steps should be. Hoping someone can help.

Reply 1 of 3, by MagefromAntares

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Hi,

While unfortunately I personally don't own a 5153 monitor, as I intend to add one to my collection in the future(If I find one that seems to be in at least in "fixable" condition and not insanely overpriced) I already checked for the availability of the service manual and it is on archive.org:
https://dn721801.ca.archive.org/0/items/sams- … 05153%20VDU.pdf
It might contain enough information to help debug this issue.

"A process cannot be understood by stopping it. Understanding must move with the flow of the process, must join it and flow with it." - Dune

Reply 2 of 3, by geiger9

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MagefromAntares wrote on 2026-07-01, 19:13:
Hi, […]
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Hi,

While unfortunately I personally don't own a 5153 monitor, as I intend to add one to my collection in the future(If I find one that seems to be in at least in "fixable" condition and not insanely overpriced) I already checked for the availability of the service manual and it is on archive.org:
https://dn721801.ca.archive.org/0/items/sams- … 05153%20VDU.pdf
It might contain enough information to help debug this issue.

Hey thanks for checking out my post. I've already been looking at the service manual and I've followed the steps in the troubleshooting section for no vertical deflection.

Reply 3 of 3, by geiger9

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Turns out I didn't have vertical collapse but rather loss of vertical deflection (the majority of it, but not full collapse. I used the wrong terminology). There were two issues:

1. The service mode switch was corroded. I tried adding dexoit but it couldn't save it. I ended up desoldering it completely and just bridging the pins that enabled normal mode.

2. There was a copper winding that had broken just outside the yoke. Upon closer examination of the yoke, I found a little green crusty area and when I picked at it, that's when I saw the copper wire was broken. I just had to burn off some enamel and carefully solder the two broken pieces together and it worked, I had full vertical deflection again. The monitor looks great too!

This 5153 was handled very roughly and was stored for years in the cab of an old truck that had it's windows beat out and it's still alive.

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