IC PS125 No output

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Joined: Sat Dec 15, 2018 8:37 pm

IC PS125 No output

Post by fsi894 » Sun Dec 30, 2018 11:46 pm

My PS-125 has no output. Zener diode ZNR1 is burned up. I can find no info. on this zener diode on the internet and it is not listed in the parts list in the service manual. Has anyone had to replace this part and if so do you have any specs. on this part. Thanks

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Re: IC PS125 No output

Post by k9yli » Mon Dec 31, 2018 4:43 pm

the zener is likely part of the crow bar circuit.. so just replaceing it wont fix the problem, but would likely just burn up again.
I dont have a schematic of the 125 but it must be similar to the 28 volt supply in the HANDBOOK.
The zener , I think is to trigger the crow bar circuit causing the DC input fuse to blow, protecting the radio from over voltage.
Possibility you have shorted pass transistors, as I think the supply should work with the zener removed.
With the schematic you can figure out the value of the zener,, It circuit is likely set to conduct at something around 15 volts to trigger the overvoltage protection..
Get you meter out and start following the voltages through the supply..

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