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Author Topic: Yaesu FT-902DM Power Transformer Specs.  (Read 4099 times)
WA4EHO
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« on: April 21, 2013, 02:00:24 PM »

I picked up a Yaesu FT-902DM cheap and found the power transformer (PT1) is fried. I like my 901DM so much that I'm looking to try and get a replacement transformer manufactured since I can't find a used PT anywhere. What I need are the specs. for the  12.6 / 250 / 190 / 120 / 320 voltage/current output capabilities of the transformer. It will never be run mobile so I'm not interested in anything associated with the DC/DC converter portion of the transformer. Any help will be greatly appreciated. Sam
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AC5UP
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« Reply #1 on: April 21, 2013, 02:05:57 PM »

http://members.tripod.com/tubes_tubes_tubes/transformerrewindingservice/id63.html

(?)
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Never change a password on a Friday                
KE3WD
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« Reply #2 on: April 21, 2013, 03:31:34 PM »

Use your ohmmeter to check the Primary winding carefully.  

If the primary is open, it may just be an internal thermal fuse that is in need of replacement.  

This can be done by disassembling the can if the transformer has covers, then slitting into the fish paper carefully adjacent to the two leads to the primary until you locate the little bullet fuse inline with one of the leads.  NTE has replacement temp fuses graded by temperature at opening.  

A rewinder would also know about this and replece.


73
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WA4EHO
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« Reply #3 on: April 21, 2013, 07:13:27 PM »

Use your ohmmeter to check the Primary winding carefully.  

If the primary is open, it may just be an internal thermal fuse that is in need of replacement.  

This can be done by disassembling the can if the transformer has covers, then slitting into the fish paper carefully adjacent to the two leads to the primary until you locate the little bullet fuse inline with one of the leads.  NTE has replacement temp fuses graded by temperature at opening.  

A rewinder would also know about this and replece.


73

Unfortunately, I don't think it's the fuse as when I said fried, I meant fried. This bugger has stuff that has run out both sides of the transformer and both primaries are open. It's anybody's guess why the main fuse didn't blow before the primaries opened. The secondaries read continuity but without any specs on the transformer, I don't know if they have been damaged. I checked out the rewinding service and may have to go that route but $195+ shipping is tough to spend without knowing the condition of the rest of the radio.

I'm working on building an external PS from some transformers I have in the shop. That is one of the reasons I mainly needed the current specs. I'm going to apply a 12.5 vdc and see if I can get the RX to come up first and then go from there with the TX.

Will probably have to do some calculations on the screen and plate current values for the other voltages for the dual 6146 output tubes. It would have been nice if Yaesu had published the current requirements for these radios.

Thanks for the replies,
Sam
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KE3WD
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« Reply #4 on: April 22, 2013, 05:57:28 AM »

Don't have to go with "anybody's guess" for the forensic evaluation. 

Early transformers that did not have the Thermal bullet fuse inside them that would suffer from internal insulation breakdown and start to short windings would get HOT. 

At first, likely not noticeable or a problem when perhaps only one winding becomes shorted, but that one winding creates more internal heat, which only serves to continue breaking down the insulation on the wires, creating more shorts. 

More shorts = even more heat and at some point the situation can get very hot in there indeed.  But it does not draw enough current to blow the fuse. 

The fuse is not a smart device, it cannot tell if the amount of current is being used to operate the device or is, in fact, just going into heating up the transformer, and in many cases the winding of the transformer is heating all that mass of the transformer iron. 

Which is one of the key reasons that the Thremal fuses came into use.  Placing them inside the xformer is a necessary thing because that's where the heat would be. 

Sounds like you need to find another 902 power xformer at this point, don't overlook the $ savings of searching for someone parting out a radio. 


73
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WA4EHO
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« Reply #5 on: April 22, 2013, 07:15:05 AM »

Thanks for the help. I've been searching for over two months now for a transformer with no luck. Lots of other parts and boards available but no transformers, so it appears the parts came from radios with bad transformers. This must have been a major problem with Yaesu FT-901/902DM radios. What a shame.

73,
Sam
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M1BCM
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« Reply #6 on: April 22, 2013, 08:26:46 AM »

Try this Sam, he almost always has transformers ...

http://www.hifissb.com/yaesu-bft901902-c-108_81_91.html?page=2&sort=2a

Jeff
M1BCM

http://www.m1bcm-ham-radio.co.uk/
« Last Edit: April 22, 2013, 08:29:52 AM by M1BCM » Logged

WA4EHO
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« Reply #7 on: April 22, 2013, 12:18:14 PM »

Sent off an email. Thanks for the link.
73
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KG6YV
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« Reply #8 on: April 24, 2013, 11:20:08 AM »

The FT902 is a 80's vintage hybrid much like the Kenwood 820,530,830.  You might hunt around for a transformer out of a Kenwood.  there are a couple of guys on the Kenwood 820, 830, 520,530 Yahoo Groups who sell parts.  Lots of parts for these still around.

Gud Luck,

Greg
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W9GB
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« Reply #9 on: April 24, 2013, 01:37:55 PM »

Quote
Thanks for the help. I've been searching for over two months now for a transformer with no luck.
BE PATIENT, unless you want to spend $150 to have own custom wound by Heyboer Transformers in Michigan.

PLACE WANT ADs on the QTH, QRZ, and eHam.net reflectors.

There are radio chop shops, parts strippers, and estate flippers in UK and US (found on eBay, sometimes QTH)
They often toss the transformer or mainframe chassis, due to lack of buyers.
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M1BCM
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« Reply #10 on: April 24, 2013, 01:48:37 PM »

I KNOW THAT THE GUY AT THE LINK I PSTED SELLS 'EM FOR £50 .. APPROX $75
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ZS5WC
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« Reply #11 on: April 29, 2013, 06:38:14 AM »

 :)A good bet would be to find another Donor FT-901 / 902 or even FT-101ZD.
They all had around the same transformer windings.
I have just rebuilt the HV supplies on an FT-901 and 902, used new 1w MOF 470k resistors and 1N5408 diodes.

Just a word of caution: There should be NO reason for the Transformer to burn out--the supply fuse could be overrated-(Someone had 'uprated' my FT-901's to 15A!!)

Things that could cause problems and transformer failure IF the fuse was overrated:
*Leaky DC blocking cap from 12BY7 to 6146B grids. (Download the "FT901/2 survival guide" for more detail.)
*Shorted HV caps--the 100uF , 500v caps are prone to shorts --they are old after all!.)
Replace with new caps--BE SURE TO REPLACE ALL 470K equalizing resistors with new 470K, 1W MOF resistors.(ON THE HV PSU BOARD>)
(Access to this board is quite difficult--I also had to make 'tags' to attach the HV board to the capacitor board as the new modern caps have short tags.)
Set primary tap to 117V not 110V if you install 220uF 500V caps.
*Regulator board failures.
*Tube shorts.


I feel it is better to check all these things before replacing the transformer, as it probably will fail again,and cause financial loss to you.

73 de William
ZS4L




 


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KE3WD
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« Reply #12 on: April 29, 2013, 12:42:27 PM »

Sometimes transformers fail due to simple insulation breakdown...
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G3RZP
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« Reply #13 on: April 30, 2013, 12:47:12 AM »

I have heard that the coupling cap to the PA grids going leaky is a common problem in many Yaesu rigs.
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ZS5WC
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« Reply #14 on: April 30, 2013, 04:13:29 AM »

yes the coupling cap from the driver to finals have have caused MANY rig / transformer failures , because the final tubes turn on hard, being supplied potential from the driver anode via the coupling cap, and the transformer goes up in smoke IF the fuse has been oversized.
I have seen this failure on 101's , 501's , 901's and have lost HT supplies on severAL DUE TO THE EQUALISING RESISTORS CHANGING VALUE WITH TIME.
They are ALL now ticking time bombs-so rather be safe than sorry.
Hence my suggestion--I would rather ensure the rig is good for another 30+ years , instead of it running for a week and suffering the same fate as before.

73!.
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