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Author Topic: Titan 425 Help (Blowing Fuses)  (Read 13830 times)
WU2M
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Posts: 29




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« on: January 21, 2013, 04:52:32 PM »

Hello All,

I just purchased a Ten Tec Titan 425 amp used. I hooked it up and ran it to test everything. All seemed to be working well but as it sat running it blew one of the 20 amp fuses. I replaced the fuse and tried to power it up again and it would not power up. I pulled the tubes out and tried again and still nothing so I pulled the cover off the power supply and found that the 1.5 amp fuse had blown. I replaced the fuse and as soon as I turned it on, it blew the 1.5 amp fuse again.
 The previous owner told me when I purchased it that he had replaced the filter caps in the power supply.
Any suggestions? I would like to get this thing running as my backup amp.

Thanks,

Rocco WU2M
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KC4MOP
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Posts: 729




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« Reply #1 on: January 21, 2013, 05:23:57 PM »

Sounds like the amp didn't make the trip shipping too well.
Were the tubes removed during shipping? Shouldn't have been a problem. But something not happy now!
My personal opinion about the 425 is that I would never own another one. Extremely difficult to get into and service. Mine had a defective band switch and Ten Tec charged me $750.00 to repair. I dealt with that repair and got rid of it immediately and bought an Ameritron AL1500.
Fred
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KA5N
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Posts: 4380




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« Reply #2 on: January 21, 2013, 05:30:05 PM »

Fuses blow because there is too much current flowing through them.  This is usually because
of a short somewhere.  If you have a DVM or multimeter, with the power off and the amp
unplugged check for shorts.  Most often shorts will be in the power supply section.  
Did you see the amp operating before you bought it?  Just because the previous owner says
that he replaced the filter caps doesn't mean that he did, or if he did replace them that the
new ones were good, or that he put them in with the correct polarity connections. ETC.
If you don't know how to troubleshoot an amplifier then get local help from some knowledgeble
ham. Tube type Amplifiers have lethal voltages present when powered up which can produce
deadly shocks.  BE CAREFUL!!
Allen   KA5N
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WU2M
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Posts: 29




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« Reply #3 on: January 21, 2013, 05:36:06 PM »

The tubes were not removed for shipping and I did not see it run. The shipping was excellent with everything double boxed, transformer removed and bolted to a board. Everything was wrapped in bubble wrap and then surrounded with peanuts.
 The amp I had the amp running for about 4 hours and I made several contacts with it. It was just sitting there running in the stand by position when the fuse blew. I was thinking abut sending it to Tan-Tec but $750.00 to change a band switch sounds a bit high to me. I hate to eat the thing and pull the tubes for spares for my Alpha89 thats for sure.
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KE3WD
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« Reply #4 on: January 21, 2013, 06:34:40 PM »

On the other hand, one single report of a large repair bill does not a trend make. 

This could be something as simple as a shorted rectifier or a tube that shorted. 

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W1QJ
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« Reply #5 on: January 21, 2013, 06:39:08 PM »

Do you have a manual for the amp?  Do you have the schematic for the amp?  I looked on line for the schematic and from what I can tell there is a low current fuse in the power supply.  The fuse SHOULD BE A 4 AMP SLOW BLOW FUSE.  If you have a 1.5 amp fast acting fuse that could be why it is blowing.  I did not have a complete schematic but if there is only one low current glass fuse in the power supply other thasn the 20A mains then it should be a 4 Amp slow blow not a 1.5 fast acting.  SO that could be your problem.  Check the schematic and see because that is what I see in there. Lou
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KO4NX
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« Reply #6 on: January 21, 2013, 06:45:29 PM »

Rocco:

I have had the unpleasant experience of servicing the 425 on numerous occasions.  I really do not like working on the power supply as it is very tight, and you have to unsolder wire harnesses to pull the printed circuit boards out.

If I recall correctly, the 1.5A fuse is for the 28V supply.   There should be a smaller set of rectifiers and an Electrolytic associated with this part of the supply. Check those for a short. The diodes in question should be found on the AC board which also contains two relays.

Rich
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KO4NX
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« Reply #7 on: January 21, 2013, 06:52:13 PM »

I just pulled the schematic I have from the basement.  You did not specify which 1.5A Fuse. It appears as though there is another 1.5A associated with K7. This is your softstart relay.  Check there too!

Rich
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WU2M
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« Reply #8 on: January 21, 2013, 07:02:12 PM »

First of all, I want to thank everyone for their help and replies. The fuse I am talking about is F3 which the schematic shows to be a 1.5A slow blow. I will check around for a short. To be honest, this thing scares me a bit due to the high voltage.
 Another question that I have is should I pull the tubes out and try to power up the amp after I find the problem with the power supply? I'm not sure how I would test them other than to put them in my primary amp and fire it up.
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KO4NX
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« Reply #9 on: January 21, 2013, 07:08:20 PM »

Hi Rocco:

In this case, I would not worry about pulling the tube. Seperate the Power Supply from the RF Deck. If the amplfier has been in operation recently, make sure the crowbar falls down on the HV connector, and I would wait until tomorrow to start looking.

The failure I have seen here most often is a open R1 which does not sound like your issue, but take a look at it anyway to see if it looks as though its been "cooking".

Next I would check the values of R3 - R5, and C6 as this sets up the RC time constant for RL K7A. If something has gone amiss here, it may explain why you are seeing F3 Blow.
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KC4MOP
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« Reply #10 on: January 22, 2013, 04:42:32 AM »

Please remember the High voltage rules working in this amplifier!!.
I was not trying to scare the OP, but Ten Tec did a good repair. The bandswitch is buried deep deep inside the amp. They wanted a very compact design to sit on your desk.
The power supply filters are easy to replace. I got mine from Mouser and they were exact replacements.
I hope your fuse is just needing to go to slow blow and you might be ok.
Let us know how you get this resolved.
Fred
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W1QJ
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« Reply #11 on: January 22, 2013, 05:44:00 AM »

What fuse did I see labled 4A slow blow?  I can't seem to find a schematic in full.  The PDF on the Ten Tec website seems to be cut off.  But from what I am hearing my approach to the problem would be to pull the tubes out.  Doing so eliminates them as probable cause.  If all is OK with them out then put them back in.  if something goes wrong then it is a safe bet one or both tubes have an issue.  When doing any type of repair work it is good to do one thing at a time and see if the one thing solves the problem this way one learns what the problem was instead of guessing what was wrong if you shot gun it.  I have 2 of these amps stored away but when I used to use them I really liked them very much.  I did not have to work on them however, but I did look inside the power supply and it sure is busy in there and could imagine it is hard to service.  I do remember that.  I would think that if the problem was with the step start the fuse would blow right away and not 10 minutes down the road.  SInce I can't seem to get the schematic off the net I would think that the problem is with whatever circuit that fuse protects.  I don;t have my manual handy to look at.  it is stored away someplace.
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WU2M
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« Reply #12 on: January 22, 2013, 09:45:31 AM »

I'm not sure where the 4A fuse would be located. I looked at the schematic and I don't see one in my amp. F3 is the 1.5A fuse that I have the issue with at the moment. When the problem first happened, it blew that and one of the 20A fuses as well. I am going to try to see what I can come up with this weekend otherwise I'm afraid I'm going to have the box the whole thing up and send it to Ten-Tec unless someone has a power supply for a Titan that they want to sell which is unlikely.
 While the amp was running, everything seemed normal with it. I checked it over and made sure it was clean inside bothe the power supply and the RF deck. I did notice that the HV seemed to be on the lower end of what the manual said it should be but it was still withing
it's operating perameters so I didn't think anything of it. It loaded up normally and the power output was as it should be. It was just sitting there in the stand by mode when I heard the fuse pop and the power went out.
 I checked the outlet and it is at 243VAC so that should not be an issue. I will update everyone on what I find. Again, I want to thank everyone for the help and advice I am getting, it is greaty appreciated!

Rocco
WU2M
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KO4NX
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« Reply #13 on: January 22, 2013, 10:11:39 AM »

I'm not sure where the 4A fuse would be located. I looked at the schematic and I don't see one in my amp. F3 is the 1.5A fuse that I have the issue with at the moment. When the problem first happened, it blew that and one of the 20A fuses as well.
 
I did notice that the HV seemed to be on the lower end of what the manual said it should be but it was still withing it's operating perameters so I didn't think anything of it. WU2M

Rocco - What you describe could certianly happen if the problem were in the Soft Start Circuit as I described in an earlier post. Have you been able to open the power supply today and take a look at the components I called out?

Rich, AJ3G
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KE3WD
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« Reply #14 on: January 22, 2013, 12:45:22 PM »

...It was just sitting there in the stand by mode when I heard the fuse pop and the power went out.
 

All the more reason to suspect a powerline transient that popped a rectifier.

Rather common problem if the stuff that passes over my testbench is any indication. 

I LIKE it when I find such, for it is easy to find, "walk" every rectifier you see using the ohmmeter on diode scale function, the failure mode of the rectifier is nearly always a dead short. 

And, the rectifier will fail as a short, faster than a fuse can react, thus protecting other more epensive components that are wired in after that rectifier. 


Good Troubleshooting,


73
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