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eHam Forums => Amplifiers => Topic started by: NE5C on August 15, 2010, 04:28:43 AM



Title: TenTec Centurion Amp main fuse
Post by: NE5C on August 15, 2010, 04:28:43 AM
I had my TenTec Centurion Amp turned on, not even keyed or used that morning, and the amp just went dark, shut down.
In checking I found it had one of the fuses on the rear (20amp) had Blown? I tried removing the 3-500Z tubes from the sockets -Fuse replaced- then Top placed back on and tried Re-Start- and it still, blew the main fuse again!
Now I wonder (sadly) if I am looking at a transformer gone bad problem?
Any advice is greatly appreciated folks? "God Bless Ya'll"
Jerry


Title: RE: TenTec Centurion Amp main fuse
Post by: KA5N on August 15, 2010, 04:42:08 AM
First thing is to check for shorts.  Most likely are shorted HV rectifiers and electrolytic capacitors.
Amp should be unplugged  and ectrolytics discharged.  Remember there can be lethal voltages present even with the power off and the fuse blown. 
A shorted transformer is possible but less likely than some other problem.  There might be a wire shorted to the chassis or a screw poking into something.  But the rectitiers and caps are most likely.
Allen


Title: RE: TenTec Centurion Amp main fuse
Post by: NE5C on August 15, 2010, 05:03:32 AM
Thank you very much Allen,
I appreciate the good advice,
last week I went ahead and ordered a new Power supply board from TenTec, figured I can't go wrong with that all new and fresh. These old eyes have searched with a flashlight, looking for anything that might be a short! No luck there. But to get the power supply board out I've had to remove the input lowpass filter board, along with the QSK board, and I have the 2ndary wires from the Hi Volt plate transformer lifted-Isolated. I was thinking maybe I can still place the top on back on and see if fuse still blows? But then, I have quite a bit disconnected, can't see or I don't know, that I can hurt anything by trying that experiment?   


Title: RE: TenTec Centurion Amp main fuse
Post by: KA5N on August 15, 2010, 10:42:59 AM
Jerry,
I was expecting that you would check for shorts using a DVM or VOM since often shorts in rectifiers or capacitors don't show any physical evidence.   Checking a transformer is near impossible using a DVM or VOM since it only takes one shorted turn in a winding for the transformer to be defective.  It is a bit dangerous to do, but you can check for transformer checks by disconnecting the secondary leads.  Heavily insulating them and then applying primary voltage.  If the fuse doesn't blow,
the the transformer is probably good.  With a DVM or VOM you can check each lead for shorts to ground.
Allen


Title: RE: TenTec Centurion Amp main fuse
Post by: AH6RR on August 15, 2010, 11:12:10 AM
Jerry,
As Allen said use a DVM/VOM and start on the HV/Rectifier board. Capacitors, diodes and Bleeder resistors will fail with age be sure to check them all you will probably need to remove the filter caps to test them properly. If any of the rectifier diodes show a short they all will need to be replaced to be safe.
Roland AH6RR


Title: RE: TenTec Centurion Amp main fuse
Post by: NE5C on August 15, 2010, 12:25:32 PM
Thanks Allen and Roland, and Allen I did give it a try with my VOM, even used the MegOhm scale to try and pick up any grounds I could possibly see. TenTec shipped me the entire new Board with Caps and whole smear ready to go, just thought before I put all that back together, maybe I better light it up to see without any Tubes and wires lifted if she still blows a fuse???

Hey Guys thank you so much, and God Bless you for your very valuable input.
73 Jerry N5JFJ