Question/help on CR-220 Lighting Issue

I bought some replacement lamps (14V, 80mA) for my CR-220, which has a meter light out and the dial light on the pointer is dim.

Well, when I looked inside, someone had cut and spliced the two lamps to different voltage sources and neither of them are 14V anymore.

The meter lamp is being fed by a 20V supply, and the dial lamp is being fed by a supply that's 6.5V or so (I guess that's why it's dim).

Looking at the schematic, these lamps are supposed to be fed by L1/L2 and L3/L4. See green boxes in attached picture.

I can see cut wires on L2 and L3, no longer being used.

When I probe voltage between L1/L2 and L3/L4, I get 20V initially, but the voltage bleeds down to zero over time.

I thought perhaps a leaky cap, so I desoldered the cap in red box that is common to L2/L3 and put a new cap there, but I still get the 20V initial and bleed down to zero.

Any idea what's going on?

Whoever was in there before must have found a stable 20V supply and connected the meter light to that source, and found a lower voltage supply for the dial lamp.

I am thinking that trying to use 14V lamps with a 20V source is a bad idea and I'll burn them out (if not immediately, then quickly).

So ideally I'd like to find out why the voltages aren't correct on the Lx terminals and why they're bleeding down just by my measuring them.

Any ideas on where to check next?

Nope. Use the 14v lamps. There is a resistor in series with the lamps to drop the voltage and establish the correct current once you reinstall the good lamps. Otherwise measuring the unloaded voltage source will read a little funky:thmbsp:

Thanks Avionics. But how about the fact that when I read voltages from the correct terminals (L1-L4), the voltage bleeds down to zero. That's not normal is it?

captouch said:

Thanks Avionics. But how about the fact that when I read voltages from the correct terminals (L1-L4), the voltage bleeds down to zero. That's not normal is it?

Click to expand...

With or without the new lamps installed ?

Kind of both. Without them, I measured the higher value, but then they bled down to zero. Then I decided to just clip lead the new lamps in, but they didn't illuminate. When I measured again after that, the voltage was basically zero.

Seems like once it bleeds off, it takes some time to "recharge".

For now, I just installed the new lamps with the "alternate" voltage sources that the hacker used. It seems fine, with the only issue being that the FM stereo red light is constantly illuminated like the Power red light.

There's some interaction between the alternate voltage sources and this FM stereo light. If I remove the new lamps, it seems the FM stereo light never wants to come on.

captouch said:

Kind of both. Without them, I measured the higher value, but then they bled down to zero. Then I decided to just clip lead the new lamps in, but they didn't illuminate. When I measured again after that, the voltage was basically zero.

Seems like once it bleeds off, it takes some time to "recharge".

For now, I just installed the new lamps with the "alternate" voltage sources that the hacker used. It seems fine, with the only issue being that the FM stereo red light is constantly illuminated like the Power red light.

There's some interaction between the alternate voltage sources and this FM stereo light. If I remove the new lamps, it seems the FM stereo light never wants to come on.

Click to expand...

Check that resistor , for the correct resistance,that's in series with that cap you highlighted in the schematic. That no one can read.

If the resistor is within 5%. Then you most likely have a bad capacitor tied to the +20v power source/supply circuit. Smaller sized caps.. Not the two biggin's.

Have a good at that first cap thats right off the + and - of the bridged rectifier in the regulated supply.