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Rock-Ola power supply zap

Posted: Tue Jun 23, 2015 4:05 pm
by ebuturla
I hav a Rock-Ola 490-2. I keep loosing the LED that indicates 26V DC on my power supply box. I replace it as well as the Zener diode and transistor that are used to create 28V DC. The 28 V goes to the LED and then gets reduced to 26V DC. The 26 V DC line goes to the main cpu board. I put a 100 m amp fuse in that line and it does not get blow when I try to run the unit. However, something is causing the LED to fail.
When the LED blows, I measure the output of the rectifier board and get 0 V DC rather than 28 V DC. Any idea on what is causing the LED and the transistor to get zapped?
Thanks, Ed

Re: Rock-Ola power supply zap

Posted: Tue Jun 23, 2015 4:19 pm
by MattTech
From the way you describe things, you're making it sound like 20+ volts illuminate an LED.
A resistor of the proper value needs to be put in series with the LED of course, to limit current/voltage - to about 1.8 volts "across" the LED.
Are you technically educated as to the theory of electronics and the trobleshooting procedures involved?
Do you have the proper service manual and schematics?

Asides from that, it's impossible to diagnose such problems across a screen with any accuracy.