98vettetorchred

I have an issue after replacing the incandescent bulbs for the back light display. I used 70mA bulbs after reading on here that they are the "right" ones. After I got them all soldered in I tested them by plugging in the unit while still apart and all the lights came on, very bright! I reassembled the unit and installed it, then while re-testing it to make sure it still worked good before putting everything back together, I now have the issue of the lights only come on intermittently. What's happening is when I first turn on the lights the unit lights up, but quickly goes dark. All 14 bulbs light up but then go out quickly. If I play with the dimmer **** sometimes it will flash back on for a few seconds and go out again. After reading a bunch more threads about this I thought maybe the 70mA bulbs were too much current, so I ordered 50mA ones. After I got these all soldered in I tested the unit again while apart. Now the lights will stay on for a bit longer around 5 sec but then go off. Again playing with the dimmer **** turning it all the way off and back to full brightness the bulbs will come on but then go out quickly. I have had a few times where the lights stayed on for over a minute, during that time I adjusted the dimmer **** and the lights dim as they should. In one case I got the lights to stay on for about 30 min while i was driving on the freeway. Next time I drive the car lights go out after a few seconds. Very intermittent issue. I suspected the dimmer itself but all other lights work and dim properly every time, only the HVAC has problems. After looking through wiring diagrams I suspect the BCM may be the issue since from what I saw it sends the signal to the HVAC on a separate line than the other dimming circuits. I plan on busting out my O-scope to check that signal soon, I tried checking with a DVM but the diagram says it's a PWM signal so the meter prob wasn't reading it correctly . The only other thing I can think of is maybe I blew one of the other components on the board when I was soldering the 241's or the backlight bulbs. I looked the board over and no burnt traces, damaged components, checked all resistor readings and made sure the 2 big caps weren't' blown. I didn't see anyone else post about this kind of issue so I figured I would and see what suggestions come in. If anyone has more detailed wiring diagrams or schematic for the HVAC unit that would def help. Thanks in advace, Joe

dadaroo

I don't know anyone with the HVAC board(s) design. Sure sounds like a bad solder/connection issue that heats up and increases the circuit resistance. However that would assume they are all in series which I doubt since you can turn some on or off with the buttons. Would have to be a overall power feed for everything to be affected maybe. Does the actual unit seem to work otherwise in controlling everything?

With that said, were all the lights out before you started? I have worked on an issue for a friend where they would not dim. It turned out to be the head unit and not the BCM.

Strange they worked until you put it all back together. Maybe a bad connector pin in reassembly?

I have my console off now. Worse case you could ship it to me and I could see if it does the same thing for me. I don't want you to replace a BCM just to try a theory. I could return it very quickly for you after testing.

I'm in SC. Mr. Sam

mrr23

he is referring to the back lighting for each button as seen here:

https://www.corvetteforum.com/forums...acklights.html

bjones7131

What a great offer you are making Mr Sam, Good for U, thanks for all the help U provide to us less knowledgable vette guys.

98vettetorchred

thanks for the offer dadaroo, but the unit itself works fine and I need it so I can use cooling and heating in the mean time. and yes i'm referring to the 14 backlight bulbs not the 5 LED's that light when you push the buttons. The current state is that I can't get it to light up at all. only the digital display and 5 LED's light. When I get a chance i'm going to pull it back out, dis-assemble and check all solder connections, components, etc there has got to be a bad component or solder joint somewhere. I am thinking about bench testing the unit with a DC power supply I have. I'm a little unsure of the signal from the BCM to the unit for back lighting but I will try just supplying a little less than 12V and see how it goes. It's upsetting to me that so many other people replaced these bulbs and didn't report an issue like this. I must have messed something up haha

65GGvert

Be very careful connecting a 12v supply to the unit out of the car. Don't reverse the +- leads. I did and the hvac unit no longer worked at all, no display, no functions. The button lights did work though. I ended up replacing it with a used unit.

martysauto

Sounds like overload protection. If you still have a functional o.e. bulb, measure the resistance and compare it to your replacements. If the replacement value is lower try using different bulbs with the same or slightly higher resistance.
You could also power up the old and new bulbs threw an ammeter. This way you know if the new 50 ma bulbs are 50ma or not. If the o.e. bulbs are pulling less than 50ma, order bulbs that match.

dadaroo

Here are the pin outs in case you need them.





HVAC Part 1





HVAC Part 2

98vettetorchred

My issue is solved!! thanks everyone who chimed in. In case someone else ever has the issue of no backlight on the HVAC only but every other light works off the dimmer including the LCD display, the problem was no voltage on pin C16 of the HVAC connector shown in the above pinout. Well it would get 10V but quickly go down to near zero. After I got the guts to connect the HVAC unit to my hobby power supply and provided the 12V bat on pin C12 and 12V on pin C16 (and of course ground on pin C1), the backlights lit up and stayed on. I traced pin C16 from HVAC connector to pin B2 of connector 3 to BCM (green one). No signal coming out there, so again got some guts and opened up the BCM. I removed and re-flowed solder to all the caps connecting to the pins for connector 3 as well as touched up a few solder joints I didn't like the look of. For added comfort I re-did solder for pins B1,B2, and B6 which all concern Instrument panel lamp feeds. Put it all back together and to my surprise it worked the a champ, first time every time. There are so many components on that board I thought for sure I was going to have to use a heat gun and just re-flow the whole board haha. If anyone has an issue similar let me know and I'll help with the knowledge I've gained on the way.

dadaroo

Excellent diagnostics. You must have a very small tipped soldering iron and a steady hand.

zdeckich

Im having the same problem. Do you have pics of what you had to resolder?