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Author Topic: Tentec Titan 425 Blowing 20 Amp Fuses  (Read 15847 times)
N1UK
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Posts: 1457




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« on: May 08, 2013, 07:48:33 PM »

My Tentec Titan 425 was idling on in the shack and it just blew the main 20 amp fuses. I tried disconnecting the HV line at the psu and tried it again. The fuses blew again, so I am thinking that I might have a shorted capacitor. Is this a good place to start looking?

Any tips would be grateful. I will start working on it tomorrow. I think Mouser stock the capacitors?

73 Mark N1UK
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W9GB
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Posts: 2623




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« Reply #1 on: May 08, 2013, 08:13:46 PM »

Mark -

There were early and later versions of this amplifier, check board numbers.
Correct manual is available from Ten-Tec Service. 865-428-0364.
http://www.tentec.com/downloads/manuals/Model%20425%20Titan%20Manual.pdf

Another Tentec Titan 425 owner, restoration process.
http://www.pj2t.org/ccc/notes.on.titanI.htm

Bob Hutchinson, N5CNN
http://www.hamradiomarket.com/articles/Titan%20P%20Hybrid.htm
Comments on the Titan 425, rectifier board, and the replacement
HV power supply board (HV-2) by WD7S - which is no longer sold as a kit (only assembled).

http://home.earthlink.net/~wd7s/hv-2.htm

TenTec used CDE Electrolytic Capacitors with Screw terminals.
Specifically, they used the CGS series, 400 mfd, 450 VDC.
http://www.cde.com/products/aluminum-electrolytic/

CGS401T450xxx .. The last 3 alpha-numeric characters (xxx) are mfg week and year.
PHOTO in a TecTec Titan 425 HV supply
http://www.pj2t.org/ccc/titan.I.power.supply.caps.nomenclature.jpg

CDE Catalog - CGS series
http://www.cde.com/catalogs/CGS.pdf

MOUSER has Eight IN Stock (The CGS series were also used by Alpha amplifiers).
Typically these capacitors cost $25 to $30 each (last time I bought them in 2005).

SHOP around with CDE distributirs for best price, Contact TenTec and
Harbach Electronics (Ohio) for price quotes -- for best price.

Mouser Part #: 539-CGS450V400
CDE Part #: CGS401T450R5L
Page 738, Mouser Enhanced Catalog
    
« Last Edit: May 08, 2013, 08:59:46 PM by W9GB » Logged
N1UK
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Posts: 1457




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« Reply #2 on: May 08, 2013, 08:33:06 PM »

Thank you for all the great information. That saved me a lot of searching. I will open the psu tomorrow and get working on it. I will call Tentec in the morning. Are the rectifier diodes likely to have been damaged? I presume that I can just ohm them out without lifting them off the circuit board.


73 Mark N1UK
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W9GB
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Posts: 2623




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« Reply #3 on: May 08, 2013, 09:10:31 PM »

Mark -

It's all in TenTec 425 manual (link in first response),
just look through parts list and X-Ray view of PC Boards.

BE SAFE, with HV.  Disconnect from AC mains and have a HV kill stick.
WHY?  In case bleeder resistors failed, capacitors could be charged (and kill you),

DEAD MEN are not around to tell stories or discuss their mistakes.
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N1UK
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Posts: 1457




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« Reply #4 on: May 08, 2013, 09:20:30 PM »

I will certainly measure them and then gnd them all.....I have a nice high voltage probe.

Do these caps normally fail short circuit...does that cause excessive current which blows the fuse. I am not sure of the mechanism that leads to mains fuse blowing.

I thought I saw a flash inside the last time that the fuse blew and certainly a chemical smell but I have noticed that a few times over the last few weeks.


Mark N1UK


« Last Edit: May 08, 2013, 09:23:01 PM by N1UK » Logged
W1QJ
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Posts: 1447




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« Reply #5 on: May 09, 2013, 04:03:23 AM »

Mark, please see the thread on this very subject about a 425 PS blowing fuses.  Scroll back through about 2 months ago.  There are several pages on Rocco's PS problem.  The PS ended up with me and was found to have a bad transformer.  I retrofitted an Ameritron AL-800H transformer in it for Rocco at a total cost cheaper than TenTec quoted him on a new transformer.  To save you some time let me tell you the procedure for testing your problem.  First, check out the diodes using you ohm meter on the diode check function.  The diodes should read between 450 and 650.  A shorted diode will show up immediately.  Replace any bad diodes.  If no didoes turn up bad then disconnect the + side of the diode take off to the cap board and safe off the wire, then try the supply again to see if a fuse blows.  If not then you most likely have a bad capacitor and you should change them all.  I sell replacement caps if you need them.  If the fuse still blows after you have disconnected the capacitor stack then you might have a shorted transformer like Rocco did.  Seems like they do go over time.  Not the first one I heard go.  If that is the case I can do a similar overhaul of your supply as I did for Rocco cheaper than you can get a replacement transformer from TT.  I believe the thread is worth reading.  Lou
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N1UK
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Posts: 1457




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« Reply #6 on: May 09, 2013, 05:29:21 AM »

Thank you for your help and the information about the useful thread with the Tentec Titan PSU with the failed transformer.

If a diode fails short circuit s/c does this take out the rest of the series stack or do they survive?



73 Mark N1UK
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KA5N
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Posts: 4380




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« Reply #7 on: May 09, 2013, 08:17:35 AM »

Rectifier diodes are so cheap that one can replace the whole string for a couple of bucks
(or less) and diodes from the same manufacturing batch tend to have very similar characteristics and  that lessens the chance of a stray shorting.  Also if one diode in a
string shorts, that may stress the other diodes in the string.

Allen KA5N
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N1UK
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« Reply #8 on: May 09, 2013, 08:40:51 AM »

I wasn't quite expecting this..what is this board? It has 330uF 450V caps. Not sure what the caps are?

http://imageshack.us/a/img16/1148/dscn8743p.jpg

http://imageshack.us/a/img845/3874/dscn8744v.jpg


73 Mark N1UK
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K8AXW
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Posts: 3860




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« Reply #9 on: May 09, 2013, 08:42:34 AM »

Quote
I will certainly measure them and then gnd them all.....I have a nice high voltage probe.

Mark:  I hate to be nit-picky but this is WRONG!

The procedure is to GROUND THEM ALL and then check them!  

Quote
BE SAFE, with HV.  Disconnect from AC mains and have a HV kill stick.

This "kill stick" is another name for a "chicken stick."  It is a two foot stick of dry wood with a wire fastened to one end.  The wire has a hook in the end to hook around a HV lead.  The other end of the wire has an alligator clip that connects to ground.  The procedure is to clip the alligator clip to ground and then hook the other end of the wire to the HV circuit.

I have a 1M 1W resistor connected between my "hook" and the wire because sparks make me very nervous.  I just make sure I hold the hook on the HV lead for a long period of time.

There isn't too much any of us can say about being careful here Mark.  As an apparent "newbie" with HV power supplies, you must learn what every one here has learned.... that is to THINK before you make a move.  Keep one hand in your pocket while working with the other hand.

You get only ONE chance to get it right.

Al - K8AXW
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K8AXW
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« Reply #10 on: May 09, 2013, 08:47:00 AM »

Mark:

You posted about the same time I did. 

After looking at your photos and reading your question a few times, I strongly suggest you get QJ or someone familiar with HV power supplies to check out your amp.

Al - K8AXW

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AH6RR
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Posts: 803




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« Reply #11 on: May 09, 2013, 09:30:06 AM »

I wasn't quite expecting this..what is this board? It has 330uF 450V caps. Not sure what the caps are?

http://imageshack.us/a/img16/1148/dscn8743p.jpg

http://imageshack.us/a/img845/3874/dscn8744v.jpg


73 Mark N1UK

It looks like someone used 3 different filter caps. Having never worked on a TT425 but a HV Supply is a HV supply and that board looks good BUT the caps need to be the same not just in value but dimensions and manufacturer and the ones in the pictures do not.  It looks like 4 of them are the same then you have 2 pairs of completely different ones. That is where I would start I would remove all of them and the bleeder resistors and replace them with 8 of the same value and manufacturer.
Of course I would also check the Rectifier Diodes and if any of them are bad I would change them all.

Roland AH6RR
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N1UK
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Posts: 1457




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« Reply #12 on: May 09, 2013, 10:05:36 AM »

Quote
Mark:  I hate to be nit-picky but this is WRONG!

The procedure is to GROUND THEM ALL and then check them!  

I understand..what I meant was I will measure the voltage on the caps with my 6kV high voltage probe to see if there is any voltage there and then ground them as a double safety.

I have had my chance with electricity as a young apprentice when I strung myself with 240VAC in one hand and a factory ground in the other and got stuck on it....I shouldn't be alive so I am very very careful now.


I talked to a Tentec tech this morning and he suspects the transformer and gave me some ohming instructions for the transformer. I am going to start there,


Mark N1UK
« Last Edit: May 09, 2013, 10:10:58 AM by N1UK » Logged
W9GB
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Posts: 2623




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« Reply #13 on: May 09, 2013, 12:52:03 PM »

Mark,

TenTec had production changes to the Titan 425 power supply and RF assembly.
IF you read the PC Board ID numbers, this can be passed on to TenTec tech support for specific schematic/PC board layout details.

The HV Board in your TT Titan 425 power supply is a LATE version OR third party replacement unit.
The capacitors are SNAP-IN variety with the HV diode string and bleeder resistors all on 1 board.

Follow TenTec technical advise on the resistance (ohm) measurements.
« Last Edit: May 09, 2013, 12:56:25 PM by W9GB » Logged
N1UK
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Posts: 1457




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« Reply #14 on: May 09, 2013, 01:18:55 PM »

Yes it looks like it is a Tentec late version power supply board. This amp is one of the Golden Series, so very late.

The good news is that the transformer seems OK. I was able to run the rf deck with the 4 pin HV connector disconnected in the power supply and no fuses blew.

So now I am going to remove the combined diode cap board and start checking the diodes out.

This board uses 330uF 450V electrolytic caps. They have an M on them. Does anyone have a part number for these caps? It is the Tentec 81627 power supply board

What seems strange is that measuring across the two paralleled 150K 2w electrolytic capacitor bleeder resistors my DVM reads in the meg ohm range. I would have expected to see 75K or less.


73 Mark N1UK
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