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C-4 went south

H

H.Huester

Active Member
All worked yesterday - the last time I ran the C-4. I had a power button light burnt out - it's happened before and I planned to swap bulbs for LEDs. I pulled the case and front panel, and removed the bad bulb at the power switch. Plugged the unit back in to figure out which LED lead goes to the red & white wires, and I now have no power at any of the bulbs. I used to hear a relay click 3-5 seconds after I push the power switch - now I hear nothing. I cycled the power switch a number of times and checked for power at the switched outlets - all good. Checked the four fuses by the power transformer - all good. Checked primary side of transformer - good. What should I be looking for next?
 
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Have you tried replacing the power button light with a good bulb to see if that supplies continuity to the LED's?
 
What voltage LED did you use? Which leg went where? Based on the schematic, the power lamp is running off of a -11.5V line. So you’d need a 12V LED and the negative leg goes to ‘pl’ and positive to ‘E’. Or else, you’d need a resistor to match the -11.5V to whatever voltage your LED is, but that would generate some heat, I wouldn’t do it.
 
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Mark: The bulb for the power switch was burnt out, and the unit still worked until I unplugged it and started work.
Sparkplug: I have not yet installed any LED, because I have no voltage at any of the leads for the three illuminated switches. In the past, I've had these bulbs out, and the relay still kicked in and the unit played just fine.
 
H.Huester said:
Sparkplug: I have not yet installed any LED, because I have no voltage at any of the leads for the three illuminated switches. In the past, I've had these bulbs out, and the relay still kicked in and the unit played just fine.
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Check the transistor voltages in the section below, especially Tr623e and Tr621c, if you’re comfortable doing so. Something might have burned, or you’ve done other things we don’t know about. :biggrin:

54F1F5E6-9639-44F2-A7D4-2CC1924AFCBE.jpeg
 
H.Huester said:
I used to hear a relay click 3-5 seconds after I push the power switch - now I hear nothing.
Click to expand...
your timer circuit no longer works, TR622 is shorted or for other reasons no longer turned on.

Check what the two gentlemen above suggested. We need to first know if you have power on the PCB on the 11.4V rail.
 
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