[TenTec] 255 Power Supply
Dr. Gerald N. Johnson
geraldj at weather.net
Sat Mar 12 19:20:53 PST 2011
Check the paralleled transistor junctions with an ohmmeter. The should
be a difference in directions and not zero ohms. The symptoms are that
the junction in at least one of the transistors is melted and so shorted.
And it might be that the crowbar SCR has shorted.
73, Jerry, K0CQ
On 3/12/2011 9:11 PM, Jim Anderson wrote:
> Thanks, I have done a bit more digging since I posted.
> If I pull the wire that leads from the diode bridge to the board with the
> pass transistors no fuse blows. If I pull the internal 20 amp fuse and turn
> it on the AC fuse is OK. If I disconnect the three wire plug that leads from
> the transistor board to the regulator board it wants to blow the AC fuse.
> So, as Al said, it seems to be an issue with that board. Is there a way to
> check the transistors with them mounted or should I just assume it is one of
> them and order a couple of replacements.
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