IBM 5151; Power but no video

[Ioncannon]

Got a IBM 5151 that I've been trying to figure out. The CRT has power, but no video shows up on the screen (setting the brightness to max shows raster lines).

• Tried replacing the 7406 chip.
• Checked the contrast pot and it goes from 0ohms to 500ohms
• Checked against a IBM 5150 first (MDA and Hercules card; though this card beeps a video error code) and then a Tandy 1000 SL in monochrome mode. The former did nothing; the latter showed a flash for a moment before also showing nothing.
• Checked continuity from the pin on the chassis to the pin in the connector.

Any idea where the problem might lie?

 

[Ioncannon]

Well, I found the issue! The video line had burnt off on the board side (the wire that goes to the neckboard). However putting the chassis back in now the display won't power on .

When removing the main power cable to the chassis the thing was mighty stuck, so I thought I may have broken something but there is conductivity and 24v AC (shouldn't this be higher?). Back to the drawing board sigh.

 

[Ioncannon]

Fixed the IBM 5151! Seems when I reconnected the video wire the bipolar cap had killed itself. It became disconnected from the two terminal pins. I wonder if the cap was what caused the wire to melt in the first place?

Anyways, recapping the whole board + replacing the bipolar with a film cap had done the trick and this 5151 is back to life!