MC 2155 Backlighting Issue

[62caddy]

This morning I noticed the all the lamps on the lower panel of the MC 2155 began flickering in unison- and also the left green PG indicator was out. About a half hour later, I just happened to be looking at it when the PG indicator suddenly lit back up. I'll check it again when I get home but it's probably not something that's going to get any better. :sigh:

Any ideas?

 

[damacman]

Cold solder joints? Poor connectivity on the "jumper" cables between boards?

 

[kevzep]

I'll bet good old clinic-audio will know exactly what the problem is, he will no doubt respond within 24hrs....:thmbsp:

 

[damacman]

That dude is a cool cat for sure . . .

 

[dewickt]

Power supply board (one on right) has 2 ea 2200uF capacitors in a voltage doubler driven by the lamp supply 6.3V feed, they are going bad and shorting the 6.3V feed, may have taken out the 2 diodes between them.

 

[kevzep]

That dude is a cool cat for sure . . .

Looks like Terry beat him to it......totally sounds like the problem to me.....:yes:

 

[damacman]

'nuther cool dude for sure . . .

 

[c_dk]

I tread here lightly.....I believe Terry is referring to the MC2125/2205 not the MC2155/2255.

The lamps asked about by the op, in a MC2155, are all run on a partial tap off the transformer at 5.6 volts AC. This tap also supplies the 5 volt regulator.

 

[dewickt]

Thank you, hunted file and could not find 2155 manual so I went with memory, opps memory was close but no cigar...

 

[c_dk]

If it is a MC2155 then it is most likely just a local service disruption......and a failing bulb filament in the PG bulb.

When I depotted the MC2250 transformer I posted pictures showing the added windings (I believe it was 25) which provide the AC for the lamp circuits

 

[62caddy]

Correct- the problem was the MC 2155.

No issues last night or this morning.

I had recently replaced all the lower lamps when I installed a diffuser that was missing.

Interestingly there was a very brief power interruption the night before this all began but hadn't noticed any malfunction at the time; the problem began the following morning- after everything sat overnight turned off. Curious the PG issue also began at the same time...

PG bulbs (and "McIntosh" logo) bulbs are different- aren't they? Are they as easy to replace as the lower festoons? I remember there was something different about those upper lamps.

Thanks for the help.