Electronics > Repair

Help with diagnosing faulty LCD on Becker CDR-220 car radio/CD player

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Valden:
Thanks for taking a look at this.

My 21 year old Becker CDR-220 suddenly stopped displaying all characters on the LCD of the removable faceplate. Other than this, the faceplate and body work properly. The buttons on the faceplate, the LED backlights, radio, CD - everything.

All contacts cleaned. No change.

All faceplate circuit board components checked. Seem OK. One dodgy-looking solder joint for a capacitor re-soldered. No change.

The pictured PCF8578 LCD driver IC seems OK when probed for appropriate terminal voltages and frequencies and continuity with the board, but with one possible anomaly. Column driver output 30 is inconsistent. All other row and column outputs show 2.4V (below VDD supply voltage of 4.6) and 2.25kHz. Column 30 is 0.08V and 0Hz. Perhaps it’s not connected? I’m checking.

This fault was instant and complete, so I don’t think the elastomeric connector strip between the board and the LCD is the cause. It’s been cleaned (problematic, I realise). No change.

What should I do next?

Replace the PCF8578? Or should I remove the radio from the dash and look for a fault in it? It could be that I2C bus data is not reaching the faceplate.

Also, how are these LCDs grounded? Via contact with the bezel? Or not at all? I can’t identify a path to ground, though there is a contact pad on the board for one of the bezel’s twist tabs, which is connected.

Thanks for clues and advice. Please don’t say, ‘Get a new radio.’ Heresy! 😄

cantata.tech:
It's going to be a challenge.

I guess you could look up some of daves old videos and try to bypass the chip entirely and see if you can operate the actual display directly from a uC.

I'd be looking for spare parts about now on an online marketplace.

Valden:
You’re right Cantata. It is proving to be a challenge.

I’ve continued with checking the circuit board of the removable faceplate and everything seems fine.

I found the contact pad that delivers I2C data from the radio and probed for frequency. It’s intermittent and variable, which might be OK, or might not be. I think it’s time to pull the radio out of the dash and start looking inside.

I’m going to start a separate thread, seeking help with identifying another IC on the faceplate board; a 36 pin IC (18 pins each side), marked NEC 1299 662, then 0128K3006. It’s shown in the full board pic, above. I can’t find anything on this. Strange. Clues appreciated.

Rgds, Valden.

Runco990:
I'm afraid this may not help much, but download a service manual for it or similar Becker.  I have 2 traffic pro's.  The displays began to fade away some time ago.  What I found out is that the LCD bias voltage was faulty or no longer enough.  There is a resistor on the faceplate that sets it.  In my case, I breathed new life into it by jumpering it to get a crisp display again.

If nothing else, you can try that to diagnose if you lost the driver IC or just the bias voltage.

And yes..... Nice Radios. 

Valden:
Thanks for your suggestion. I will follow up on this.

From the photo of the whole board in my first post (I can take a better one if needed, along with the other side), can you point to which resistor you think might be the one to focus on? Am I right in thinking you bypassed it, to raise the voltage going to the LCD?

Some extra information from tests yesterday. If I put the LCD glass on a light box, I can see that segments of the display are activated by using my multimeter probes in resistance test mode. This works with the red probe on the left-most contract and moving the black probe over others. Then I noticed segments would activate by using only the black probe. Very little voltage is needed, it seems. Fascinating.

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