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Author Topic: Ten Tec Titan 425 Fuses Blew  (Read 2961 times)
N1UK
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« on: February 16, 2013, 07:52:47 PM »

Both the 20 amp fast blow 240v fuses just blew in my Ten Titan 425 this evening while I was keying about 1200 watts on 160m. I am told that I can get Microwave 20 amp fuses from Home Depot.

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?productId=100161118&storeId=10051&langId=-1&catalogId=10053&cm_sp=BazVoice-_-RLP-_-100161118-_-x#product_description

 
If these new fuses blow and I need to do some fault finding,  can I power up the TenTec psu via the rf deck with the HV cable disconnected at the psu end as I would want to be able to take the rf deck out of the circuit
 
Any other fault finding tips would be appreciated.
 
 
73 Mark N1UK.
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W1QJ
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« Reply #1 on: February 17, 2013, 06:45:28 AM »

The PS has a 9 pin MPlex female on it.  If you use a short piece of stranded #16 wire you can ball up the end or tin it to fit into the female pins to complete  the start up relay circuit however I troubleshoot using a variac so I pulled the mains on the power contactor and fed them direct to the Variac, use a fuse in line.  I never troubleshoot unless I use a variac.  it avoids big bangs and further damage until the problem is found. 
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K2DC
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« Reply #2 on: February 17, 2013, 08:11:36 AM »

Mark,

   If the fuses blow with the PS disconnected from the RF deck, it's most likely a shorted filter cap.  If they don't blow, it's likely a tube.  Pull the tubes, reconnect the PS and try again.  If they blow again, you have a short somewhere in the RF deck other than the tubes.  If they don't blow, it's absolutely a tube and you'll have to try them one at a time to find out which one.  I had the same symptoms with my Alpha 86 (same tubes) and it was a shorted tube.

73,

Don, K2DC
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N4RSS
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« Reply #3 on: February 17, 2013, 02:39:23 PM »

The fuses blow on my QRO 2500 only on 10 meters and only when the fan switch is on low. Fan switch on high, the fuses don't blow.

Very strange
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N1UK
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« Reply #4 on: February 17, 2013, 02:41:40 PM »

OK thank you for the tips.

I had a major virus problem on my main pc today and that has wasted most of the day. I am typing this on a second pc in my shack.

I will run down to Home Depot and get some fuses tomorrow morning and get back to the amp. I found a good deal for the fuses on Amazon.com but I can get the Home Depot ones quickly for now. If the first set blows then I will get the cheaper Amazon ones to help with the fault finding. It would be nice to use resettable breakers but I am not sure if they are fast enough to prevent further damage.

I hope it isn't one of those expensive tubes. I was in the middle of sending my call sign on 160m last night when the fuses blew.

Can I replace one tube or are they matched pairs?  If it is a filter cap, I suppose they can be check with an ohmmeter after a thorough discharge.




Quote
The fuses blow on my QRO 2500 only on 10 meters and only when the fan switch is on low. Fan switch on high, the fuses don't blow.

Very strange

Yes strange...I run my fans on high and I have 2 clip on fans blowing air across the cabinet as well


73 Mark
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W8JX
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« Reply #5 on: February 17, 2013, 03:08:33 PM »

The fuses blow on my QRO 2500 only on 10 meters and only when the fan switch is on low. Fan switch on high, the fuses don't blow.

Very strange

Actually not that strange. A tube or tubes is/are a bit gassy and hotter they get the more prone they are to arc over.
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W8JX
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« Reply #6 on: February 17, 2013, 03:40:09 PM »

The fuses blow on my QRO 2500 only on 10 meters and only when the fan switch is on low. Fan switch on high, the fuses don't blow.

Very strange

Actually not that strange. A tube or tubes is/are a bit gassy and hotter they get the more prone they are to arc over.

Can't be heat related. Fuses blow on a mere toggling of the fan switch and attempting to drive again in 10

Try it with one tube at a time.
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N4RSS
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« Reply #7 on: February 17, 2013, 03:44:28 PM »

But why is this doing this with a cold amp and just by toggling the fan switch ?  Maybe it's a tube but I can't fathom why it it only happens with the switch on low and a cold amp
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KE3WD
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« Reply #8 on: February 17, 2013, 05:12:38 PM »

But why is this doing this with a cold amp and just by toggling the fan switch ?  Maybe it's a tube but I can't fathom why it it only happens with the switch on low and a cold amp

Could be due to a bad fan motor. 

If the Low switch setting puts another motor coil in series with a High coil and the HIGH coil has shorted windings, then that could blow the fuse. 


Ammeter in series with the fan should answer any questions rather quickly. 


73
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W8JX
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« Reply #9 on: February 17, 2013, 09:01:21 PM »


Could be due to a bad fan motor. 

If the Low switch setting puts another motor coil in series with a High coil and the HIGH coil has shorted windings, then that could blow the fuse. 


Not likely, there would be some very serious burn/smoke for fan motor to blow main fuse.
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KE3WD
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« Reply #10 on: February 18, 2013, 09:15:03 AM »

I've encountered AC motors that apparently only had enough of one of the coils shorted to draw high amperage.  Very little smoke or burn smell with those.  I imagine if left in operation long enough, there would be, of course.  But such could come to light more readily if there was a fuse involved that was not overspec'd as to current rating. 

There may be other issues with this guy's fan circuit, or even the amp, anything posted here without having the amp to bench is going to be in the SWAG column anyway. 

But, given the only data we were given, that the fuses blow only when fan is switched to High, don't blow when fan is switched to Low, something is likely up with the High wiring, coil, etc. as what else could there be to blow the fuse if you consider just those two datapoints given? 

Something drawing Current in the High circuit.  Somewhere. 


73
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N1UK
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« Reply #11 on: February 18, 2013, 09:40:24 AM »

Returning to my hijacked thread..hi hi

I replaced the two 20A fast blow fuses in the power supply and the amp seems to be running OK so far.


Mark N1UK
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K2DC
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« Reply #12 on: February 18, 2013, 11:11:04 AM »

Mark,

   The first time the fuses blew in my Alpha 86, I replaced them and the amp ran just fine for several months.  Then the fuses went again, and I went through several sets before checking the tubes.  So, this fuse blow for you may have been just a single arcing incident, but don't be surprised if it happens again.  And then again and again and again.

   The tubes are 3CX800A7's. and yes - new ones are expensive.  New Eimacs are $880 each at RF Parts.  But if you watch eBay and the swap boards, good used pulls show up regularly for a few hundred.  And yes, you can change them one at a time.

73,

Don, K2DC
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W8JX
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« Reply #13 on: February 18, 2013, 11:53:32 AM »

I've encountered AC motors that apparently only had enough of one of the coils shorted to draw high amperage.  Very little smoke or burn smell with those.  I imagine if left in operation long enough, there would be, of course.  But such could come to light more readily if there was a fuse involved that was not overspec'd as to current rating. 

I understand you point but we are talking about 75 watt motor (give or take) taking out a 230 volt 20 amp fuse. Its going to burn some.
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N4RSS
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« Reply #14 on: February 18, 2013, 12:52:28 PM »

There were no hostages taken in this thread hijacking, although the OP might feel otherwise.

The fan continues to operate just fine, whether in hi or low.  The amp just doesn't like being driven by more than 15 watts on 10 meters when the fan is on low, from a cold start-up.  It responds with the power supply shuddering and if allowed to continue for more than a few seconds, both 25 amp fuses blowing.

Flip the fan switch to hi and I can drive to 2400 + watts if I wanted on 10.  No other bands have issues in any way.

Here's the schematic, first page shows the fan to the upper right with a capacitor in each power lead which I assume is to filter out hum ? and then two resistors plus switch to drop voltage on low    http://qrotec.com/Documents/HF2500circuits.PDF
« Last Edit: February 18, 2013, 01:01:44 PM by N4RSS » Logged
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