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

[Jason Cooper]

If one capacitor went south, there is a very good possibility that some others were also very close to failure.  You are doing the right thing by ordering some new ones.  There is a possibility of a transformer failure, however, a Peter Dahl replacement is very expensive and you would have to replace the caps if you cannot test them at high voltage.  I restored a 425 about 6 months ago and tested each capacitor with a variable HV power supply and an ammeter.  After re-forming them, all my caps were well under 200uA at 500V so I did not replace them.  If you can get to a HV supply or a HV curve tracer, you could test the caps and that would give you some reasonable input if the failure was caused by the caps.  Also an ESR test is useful if you can find someone with an ESR meter.  If I remember correctly, R1 (It's R2 on my schematic) is in the soft-start circuit and would certainly blow if one of the caps was drawing excess current.  

By the way, I just bought a whole lot of 2nF 10KV ceramic capacitors to replace the plate blocking caps (C6 and C7)  These caps have the X5R dialectric and will drift very little with heat unlike the OEM caps that Ten-Tec used.  This will fix the tuning drift problem on 80M and 160M.  I would be willing to sell off the excess if there is any interest

Good luck fixing your 425.  Jason KN7AZ


----- Original Message ----- 
  From: Carlin Royal<mailto:n5oe at nctwb.net> 
  To: tentec at contesting.com<mailto:tentec at contesting.com> 
  Sent: Friday, July 20, 2007 2:45 PM
  Subject: [TenTec] Titan 425 troubles, R1 and blown 20a fuses



  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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