CRT freaks out.

[Vincent Vega]

88. Sometimes the CRT starts getting weird. screen rolls. Turns off Radio. Once the Phone-in-use screen came up(no phone option). The Service manual has a chart to use to troubleshoot. Seems the culprit is 12v from the CPS. Sometimes it's 12v and things are OK. I suspect it drops below that when it freaks out. I did check it when it was misbehaving and it was 10.4 volts. pulled the fuse, checked again, and it was 11.7v. So, sometimes it works sometimes not. Nothing seems to trigger the drop. Yes, when it is bad the "electrical problem" displays on the IPC. Any ideas? I tried a different CPS. Same problems.

[KDirk]

Are you certain your battery and alternator are both good? Also, make sure the main grounds block is clean and tight (near battery, in engine bay) and that both battery terminal connections are tight. I recently had strange problems on one of my 88's due to the negative battery cable coming slightly loose as the bolt was worn (threads were visibly bad). Replacing the bolt solved that problem.

 

If a substitute CPS behaved the same way, I'd be looking for an external cause beyond the CPS. Also possible that one of any number of other loads (hvac blower, cooling fans, A/C compressor clutch among others) may be failing and drawing much greater than normal current momentarily causing a voltage drop. Tracking that down will require a planned, sequential troubleshooting approach to eliminate possible causes one at a time until the culprit is identified.

[Vincent Vega]

I'll check the grounds again. Do you know if the grounds for this circuit go under the seat where the notorious bad grounds are located?  One other weird thing it did was the high beam indicator would turn on and off. I did not have the headlights on.

[KDirk]

I don't think any of the underseat grounds are directly involved in the CRT/CRTC/IPC circuits, as they all come from the the fuse block or the BCM up inside the dash. Now, some of the circuits at the rear of the car (fuel pump and level, trunk light and release, ABS,  etc.) may run in the floor race, and could be causing issues related to voltage drop (short circuits perhaps).

 

The hi-beam indicator is driven by the BCM when it senses the hi-beams are called for,  so low voltage causing odd behavior from the BCM could easily account for that. 

Edited March 30, 2018 by KDirk (see edit history)

[RetroJohnny]

I had similar issues, but my screen would only show up in like a 3 inch area. Very weird. My issue was my battery, I had blown a fuse while changing tail lights, and everything kinda went downhill from there, but I noticed my battery was only giving me about 10-11.5 Volts. So possibly a new battery? Becuase when I put a new battery in the screen shined like it was new, very bright. and the voltage pumped up to about 14.