[Jerry Simcik]

I'm hoping to hear from the expert on this, but any and all advice is welcome.

I recovered an Infinity IV from a local junk yard in good physical condition.

Upon plugging it into a vehicle to test (no bench setup here unfortunately) the tuner works, and the cd player works. The volume control and balance/fader is laggy, though this is expected.

What is puzzling to me is that I have no illumination or display whatsoever. No backlighting of any kind. I do, however, have 5 bright LEDs for the equalizers.

What would cause a no-light condition like this? Again, no illumination, no display, but all 5 amber LEDs on the equalizer function, and the tuner and CD player are working fine.

Thanks for any and all replies...

 

[Oklahoma Wolf]

It's a common problem with these units. Basically, the most likely cause is a large surface mount resistor on the upper circuit board in the deck that has gotten hot enough to de-solder itself. The board will be discolored around it, making it easier to spot.

The fix is to reflow the solder joints on it.

 

[Jerry Simcik]

Well, on this unit I have the large green resistor (like the one in the tear-down), but I see no discoloration. Is this still the most-likely culprit?

If so, is it best to solder it from the top or remove the panel and come from the bottom?

 

[Oklahoma Wolf]

In that case, you'll have to go through it carefully looking for bad joints. It's possible the display itself has failed... let's hope it's not that.

Beyond that, if it's not soldering issues, you'd have to trace the circuit to find the problem. Without access to schematics, it will be very difficult.

On that deck, you have to go top down to get it apart. The bottom PCB will be a real pain to get out of there, but that's only used for the CD player section anyway. It's the top board that handles the display.

 

[Jerry Simcik]

Sounds like fun...

Would you say that this circuit is the most likely culprit for both the display and illumination failures? If so, that's where I'll start.

If there is something else that they share, (like a ground circuit or something?) I'd like to check that too.

I removed the front panel last night as well, everything there looked fine (bulbs still had their fillaments, solder joints looked good, no broken/missing pins on the connectors, etc.), is there anything on there worth inspecting again?

Thanks for the advice thus far...

 

[Oklahoma Wolf]

Sounds like issues in the power supply section, if the illumination bulbs test good.

 

[Jerry Simcik]

I've been doing some continuity testing. I have no continuity between the illumination input pin and the panel lamp pins elsewhere throughout the radio, though I have yet to find the break in the circuit. It is hard to trace at some points... The large green resistor is fine and fully connected to the circuit. I wish there was a schematic for these circuits. I may have to remove the large metal panel on the bottom of the top board to gain some more access...