Acoustic 470 Lamp Driver Issue

[gbono]

http://i284.photobucket.com/albums/l...rf/470Lamp.jpg

I'm having problems with the indicator drive for the B channel only. I checked the bulb(s), replaced Q210/211 and resoldered everything that looked like it was in the path. All resistors check out as well as the switches.

Both transistors appear to receive the correct base bias in the A/B mode though the collector voltage on Q210 is 26V instead of 33V in the B mode. Simple circuit and I'm stumped!!

[Amp Kat]

26 is enough to light the bulb. Are you sure the socket isn't bad. Where does your voltage stop. Check it at the socket and then move back from there.

[gbono]

470

The bulbs are hard wired so there is no socket to speak of. I have tested the bulbs on the bench and though 26V will turn them on they are dim at this voltage. There must be some additional current limiting but I can't find it.

[Amp Kat]

Is there a number on the bulb ?

[gbono]

470

No mark on the bulbs - these are Grain of Wheat style Incandescent Pilot Lamp Lights with 6" of purple wire attached - no socket.

I swapped out the bulbs and the problem tracked the swap. I tested the "bad" bulb on the bench with a seperate supply and it works?? Go figure. Hopefully, I'll find a replacement. THX