Replacing Backlighting in Sys 9000 Control Heads?

Leadenwah · Post by **Leadenwah** » Wed Jan 10, 2007 9:47 am

It looks like the backlighting in the Systems 9000 control heads is some sort of Surface Mounted Device.

Is there a way to replace the backlighting in these heads or does that simply mean a whole new board?

kb0nly · Post by **kb0nly** » Wed Jan 10, 2007 9:59 am

The backlighting is just small through hole LED's.. I can't think of the package style/name but its a small rectangular LED with a flat back and the leads come out of each end and go through the board.

If you have the clear rubber key membrane you have to pull that off to get to them underneath. If you have the white rubber membrane than there is just holes cut for them to poke through.

Just desolder the leads and remove the LED. Might need a tweezers or needle nose pliers, on some i have done they appeared to have a small drop of red colored glue in the center of them to keep them in place on the board for soldering.

Leadenwah · Post by **Leadenwah** » Wed Jan 10, 2007 10:17 am

Good news.

I'll try to rundown the part number for those LED's.

Thanks

kb0nly · Post by **kb0nly** » Wed Jan 10, 2007 10:31 am

Item Number. 4880246K04
DIODE LE 46K04 TAPE GRN AXIAL
Unit of Measure: 5 PK $6.35

Axial is the word i was trying to think of earlier.. That's the package they are in.

Another note, if you have a control head where the entire keypad lighting is out grab a voltmeter and start checking the diode leads from the back with the head powered and flipped open. They are in series, so one goes out and they all go out.

I had one like that a couple months back, the first led in the chain was burnt out, replaced that and nothing, traced the voltages on the board and found another one that was burnt out, replaced that and they all came back on. Then about an hour later they died again, the cause was another one that died.

Replacing the dead ones caused the already weakened ones to die. So moral of the story, if you replace one put a mark by it on the back of the board with a sharpie marker or something so when it dies again you remember which ones were already replaced.. lol

Almost forgot..

I also had one that the transistor used to turn on the backlighting died..

Q120 is turned on which then turns on Q105-Q109...

So if you have a batch of LED's that are out make sure you have voltage on the output, emitter, of those transistors. They are just standard 2N3904's also.

If you need the number for any of the other LED's in the head let me know, i have them all written down on a cheat sheet for quicker ordering.

jmr061 · Post by **jmr061** » Wed Jan 10, 2007 10:48 am

It depends on what style control head you have, the newer systems 9000 heads have surface mount leds, not through hole ones.

Jason

kb0nly · Post by **kb0nly** » Wed Jan 10, 2007 11:09 am

Can you tell me which ones??

I have a 1073 SMD head here, the LED's are NOT surface mount. They are small axial lead packaged even on the newer heads i have worked on.

I haven't seen one yet with SMD led's in them.

jackhackett · Post by **jackhackett** » Wed Jan 10, 2007 11:15 am

Are you sure it's the LEDs that are bad?

kb0nly · Post by **kb0nly** » Wed Jan 10, 2007 11:17 am

jackhackett wrote:Are you sure it's the LEDs that are bad?

He's right, there can be other things wrong, including the transistors and such that power them.

Leadenwah · Post by **Leadenwah** » Wed Jan 10, 2007 10:30 pm

This is great help. I will order a set of these.

I have 10 Sys 9000 heads. The back light is dim on some, but on others certain areas are out while other areas are lit.

I had not thought about other components which may have failed.

Is the leaky capacitor issue a probably cause? I've seen no sign of corrosion or leakage in the head I just took apart.

Thanks again

kb0nly · Post by **kb0nly** » Thu Jan 11, 2007 8:57 am

If you have heads with one area out and the other is lit then you have either a bad led or a bad transistor. If you have the keypad area out i would almost bet its a bad led because they are in series, think of the old christmas lights where one bulb goes out and the whole string of lights is dead.

If the backlighting on the entire head is dim than you got other problems. The power source for the backlighting is to blame.

On the display board check to make sure you have 5v at Q120, and check the value of the 10k resistor, R133, across its base and collector leads. There is also R104, 4.7k, from the emitter to ground on Q120. I have had a few of them where that transistor or one of those resistors crapped out.

Also check for the control voltage to the base of Q120, it comes from U3 pin 14 on the controller board, rear board of the control head. I had one with a problem i never did figure out, i just assumed it was U3 that was causing it, and you couldn't get the backlighting to turn on though the head worked perfectly otherwise. So i just cut the trace from pin 20 of the interconnect ribbon to the base of Q120 and used a small trimpot and used it to supply power from 5v to the base of Q120, which let me manually set the brightness level to whatever i wanted.

That actually brings up a good way to test the backlighting, you can supply 5v to the base of Q120 and see if the backlighting comes on if it won't otherwise. If it still doesn't replace Q120 or start tracing out where the problem is.

Leadenwah · Post by **Leadenwah** » Thu Jan 11, 2007 9:26 am

Very good suggestions there.

I have all of the above, that is, I've got 6 very good Sys 9000 heads, but 6 others with only the keypad out then some of the other keys totally out then also a head which has uniform dimness. So, I can use all of those ideas.

I did not know that the keypad LED's were in SERIES. Not many of the younger members will remember those maddening Christmas tree light stings which were in series. I do and I was a kid then. It drove my father crazy having to try each bulb. I don't want to second guess Motorola, but in series LED's seem like a bad idea to me.

Thanks again for the very detailed suggestions.

kb0nly · Post by **kb0nly** » Thu Jan 11, 2007 9:41 am

I'm not really sure about why they would put them in series...

I can say one thing, the first one in the chain gets hot and usually is the one i find dead. Because of course the voltage has to be higher there than at the last one to provide uniform brightness.