Hard buttons around CRT don't light up

[Trey]

The labels for the the hard buttons around the CRT do not light up. They did one time, so I know they have the capability - but most of the time they do not work. I remember what the buttons do (usually) - but still, I wonder why they do not light up when all of the other lights do work (my fuse # 2 is working). Note that the dimmer switch is working.

[Guest Mc_Reatta]

If the switches in your console accessory switch pod light you either have a bad connection to the CRT or the inverter inside the CRT has burned out.

[Trey]

I just tried it again, and now the labels for the six buttons around the CRT light up again. Note that the CRT is fine - it is just the labels for the 6 hard push buttons around the CRT. I don't know why they sometimes work and sometimes not. Were you thinking that the whole CRT was not working MC_Reatta?

[harry yarnell]

There's an inverter in the CRT?

[Guest Mc_Reatta]

Yes, per the discussion that Kdirk and I had about this, we determined that the dimming signal from the BCM goes into the CRTC and from there connects up to the CRT where an inverter built into the circuit board powers the EL strips behind the labels on the hard switches. So if the switches in the console accessory switch pod are lit up, then the dimming signal from the BCM is working (photocell, dimming slider etc are OK) and the problem is either the signal is not getting to the CRT, the inverter in the CRT isn't working or the internal connections to the EL strips is broken.

[KDirk]

Harry,

MC_Reatta and I recently had some discussion here on that subject. There is apparently an inverter circuit within the CRT. This is based on the following known facts:

1) The hard button legends on the CRT frame are illuminated by EL back lighting, just as with the door/mirror/headlamp/wiper switches and the gear position indicator.

2) The CRT has no connection on it's harness to the EL inverter circuits from either of the two stand alone inverters (black one in the dash, pink one in the console)

3) The CRT edge lighting works when testing the CRT attached to the Kent-Moore CRT tester tool, and not connected to the vehicle harness. Thus, the 12VDC input is being internally routed to an in-board inverter circuit to power the EL back lighting on the CRT frame for the hard button legends.

I looked at the main circuit board of a CRT I had disassembled here and have found that it contains components very similar to those contained in the two stand alone converters. With that and the other points above, I surmised that the CRT had it's own small inverted circuitry.

An additional point of confusion is that the 88 and 89 FSM show the EL back lighting on the circuit diagrams as being represented by the schematic symbol for a conventional light bulb. This makes it appear that the CRT (as well as mirror/window switches) are lit by 12V lamps, when in fact they are not. Add to that the fact that the CRT is simply represented by a nondescript box with a picture tube shaped icon inside of it, and no detail of the internal circuitry is represented; as is the case with all modules of course.

The good news is that the failure of the CRT edge lighting appears to be a very uncommon occurrence based on the historical lack of posts here about it. The bad news is that to repair this failure requires dis-assembly and component level repair of the inverter circuit on the CRT circuit board. In the case of the current problem posted by Trey, it may be as simple as a loose connection internally within the CRT, or a bad solder joint, and not necessarily bad components since it appears to be an intermittent failure.

There are two small harnesses inside the CRT that connect the frame with the hard buttons to the rest of the module. The hard button back lights, 6 amber LED's for each hard button, and the 6 switch outputs are routed through these two harnesses. There is also a separate mylar flex harness that connects the touch screen membrane to the side mounted switch matrix decoder circuit board, however that one has nothing to do with the hard buttons or the back lighting.

Since the internal design and circuitry of the CRT is undocumented, and I'd guess Reatta most owners have not bothered to tear into a CRT module to see what makes it tick, most of this information has never been aired out for discussion. As these cars age, those with proficiency in electronics will be needed to keep these parts in working order. Figure these cars were built for a reliable life of 10 or so years. At almost 25 years, the electronic modules on these cars have proven remarkably solid, but age is now starting to show it's effects.

KDirk

[Trey]

As a follow-up to this thread, when I replaced the blower control module (ACDelco 15-72530 ) the lights for the labels around the hard buttons around the CRT started to work better and no longer flicker on and off. Is this a coincidence?

[KDirk]

I'd say it is a coincidence. Given that your problem with the hard button back light is intermittent, I would more suspect the ipc dimmable lighting input lead on the CRT harness is loose, or the pin for that lead within the harness connector is not "making" properly with the connector in the CRT socket 100% of the time. If you are so inclined, you might pull the CRT, use a good non-residue electronic contact spray cleaner (NOT WD-40!) and seat/reseat the connector a few times. This would be the big rectangular connector with several wires on it, not the small rust colored one with two leads (that one is the video and horizontal sync lines for the CRT display).

Also inspect the connector where the wires go into the plastic shell and make sure all the internal pins are fully seated and tight. It is unusual for these to come loose (they have a retaining latch that keeps them in the plastic shell) but not impossible. If one or more seem not to be fully seated inside the plastic shell, try gently pushing them back in. After all this, if you still have intermittent problems with the button labels not lighting up, I'd expect the problem will be in the CRT assembly itself, thus requiring component level troubleshooting and repair to be done.

KDirk