[TenTec] Titan 425 troubles, R1 and blown 20a fuses

Ken Brown ken.d.brown at hawaiiantel.net
Sat Jul 21 19:22:25 EDT 2007


Hi Carlin,

If one electrolytic capacitor in the bank is known to be bad, the rest 
of them should be expected to go bad soon. Faults in the capacitor bank 
could stress the diodes in the rectifier. You probably will save time, 
trouble and money by replacing all of the capacitors and all of the 
diodes, before powering it up again. My schematics for my 425 are 
apparently not similar enough for me to find the resistor you have 
smoked, so it is difficult to guess the cause of it's demise. (My AC 
BOARD SCHEMATIC has two different R2s and an R1 which is 20 ohm 25 watt, 
but you said the R1 you have trouble with is on a different board) 
Failures or arc overs inside the RF deck can also blow fuses and other 
components in the power supply. I suggest a thorough inspection of the 
RF deck and the interconnecting HV cable before energizing it again. Get 
the dust out of both the RF deck and the Power Supply.

I find it difficult to believe that a failed transformer would burn out 
parts in the secondary, HV rectifier and filter capacitor, parts of the 
circuit, although it certainly could blow fuses and other parts in the 
transformer primary circuitry. For the sake of your pocketbook, 
hopefully the transformer is still good.

Do not bypass any safety interlocks. Make sure it is not connected to 
the AC mains when working on it.

Good luck and work safely.

DE N6KB

Carlin Royal wrote:
> I have a Ten Tec Titan 425 that I have only had myself for about 6 months now. The amp when I received it had 1 bad HV capacitor in the power supply. Due to lack of funds at the time I replaced the one known bad capacitor. A few months later I was operating the amplifier during a cw pileup for about 30 minutes, I set everything on standby and went to lunch. When I returned to the shack I find the amp had blown one of the 20amp fuses in the supply.
> After checking in the PS, I found that R1 the 10ohm 25watt wire wound resistor on the rectifier board had went open. I replaced the blown resistor and powered the amp back up, this time again blowing a 20ampfuse and the same resistor. Ten Tec advised to replace the original rectifer board with a new one, (82112 rev E I beleive) since they thought some diodes were probably leaking and was the cause of all my troubles. Now after replacing the old rectifier board with the new one from Ten TEc, I power the amp on and it blows another 20amp fuse but did not appear to fry the resistor this time. Here is the main question to the list; Could I have another bad capacitor that is failing under high voltage since they do not read any shorts on the VOM when individually beng tested. I have on order 8 new 400uf 450v caps from Newark Electronics and will be replacing them this week, but I am looking for more input as to the trouble. It just seems odd to me that when sitting idle for just 3
>  0 minutes the thing went south and now I have had all this trouble. Hopefully I am on the right track and it will be one of the caps in the PS, but would be interested to hear any other areas that I might could check within reason here on the very limited bench. Thanks for any advise/comments.
> 73  
>
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