Smoked power transformer in my Hammond M3 organ?

[bram9206]

I just bought an old Hammond M3, European 230V/50Hz model (as I am in Belgium). Today I had it running for 2 hours and all of a sudden it started making a loud hissing sound, almost like a decompression of a steam engine. This was an acoustic sound, not coming from the speaker! And talking about steam, there was a lot of smoke too and a horrible smell (like burned WD-40 or something)! I immediately turned the M3 off and unplugged its power cord. When I took a closer look (I was lucky, because I had the back panel off) I could see the smoke and smell was probably coming from the power transformer or at least something located very close to it (filter caps maybe?).

Now, anyone knows what this could be? Is it indeed a fried power transformer? Then how comes there was this loud hissing sound? Suppose the PT is fried, any thoughts why it did? Failing filter caps? I was just about to replace them in a couple months...

I'm pretty good with a solder iron, mulitmeter, reading schematics, already built a few things, etc... So, with some help I should be able to repaire this M3!

Any advice is most welcome. Thanks!

 

[bruno2000]

Probably a filter cap.  You can get exact replacements ($$$) or roll your own ($).
My $0.02, but I may have over-charged you........

 

[bram9206]

Today I unmounted the Ao-29 amplifier so I could take a look underneath. Here is what I saw:
there is still this awfull smell and I can see a brown, greasy sludge that is clearly coming from the big filter cap can! Power transformer and all wires running from it look to be in fine condition.

So is this was happens when a filter cap runs bad? A loud hissing sound, smoke and some greasy sludge dripping from it?
Do you think I'm finished by simply replacing all electrolytics, including this big can-type cap? Or would anyone think there are other problems that caused the filter cap to run bad OR other problems that are now present caused by the failing filter cap?

 

[bruno2000]

Today I unmounted the Ao-29 amplifier so I could take a look underneath. Here is what I saw:
there is still this awfull smell and I can see a brown, greasy sludge that is clearly coming from the big filter cap can! Power transformer and all wires running from it look to be in fine condition.

So is this was happens when a filter cap runs bad? A loud hissing sound, smoke and some greasy sludge dripping from it?
Do you think I'm finished by simply replacing all electrolytics, including this big can-type cap? Or would anyone think there are other problems that caused the filter cap to run bad OR other problems that are now present caused by the failing filter cap?

Yep, the filter cap gets too hot, boils, and the hiss is pressure being released.
Change out ALL of the electrolytics.
My $0.01.  You get what you pay for......

 

[mjrippe]

Hiss isn't so bad, sometimes they POP!  Since you shut down right away there shouldn't be any further damage.  The cap just failed because it is really old and electrolytics don't last forever.

There are some great Hammond websites and forums out there where you can find all sort of info about servicing and caring for your M3.  Proper lubrication is important to keep the mechanical side of things working smoothly.

 

[musika]

Yep, THE ORGAN FORUM is the best, I think.  Members worldwide.  They have helped me many times.  Here is the link.

http://www.organforum.com/forums/

 

[rockinrob86]

This reminds me I need to get back into my M3. 

It had very low volume when the vibrato/chorus is turned on

 

[bram9206]

It took me a couple of weeks to get back to my M3, but I finally concluded that I wanted to get to the bottom of this and bought myself a Variac. This is what I did:
removed all tubes from the AO-29 amp and feeded the power transformer 1/3 of the wall voltage (230V in Europe) through my Variac. So I measured the PT at an input voltage of 75V (mainly because I was scared to do any harm to the PT).

At pin 4 and 6 of the rectifier socket I got 120V, which is more or less 1/3 of what it should be at 230V input
At pin 2 I got 1,7V, which again is more or less 1/3 of what it should be at 230V input
But at pin 8 I got nothing at all where I should have 1,7V like I have at pin 2. Does this mean I have a short here???

At the heaters I got only a little more than 1V, which is not 1/3 of the 6V it should have at 230V input. Does this also imply something, or is it just a weaker heaters voltage and maybe not bad at all?

Filters caps still bad of course (as one can clearly see brown sludge dripping out of it), but before replacing the caps (and maybe the rectifier) I'd like to be sure the PT is ok.

Anyone any thoughts?

Thanks!!

 

[bram9206]

In my previous post I was measuring voltages againt the ground instead of measuring between the pins, is that wrong? Today I also measured between the pins at 110V input (half of what it should be here in Belgium). This is what I get:

- between pin 4 and 6 of the rectifier socket: 380V
- between pin 2 and 8 of the rectifier socket: 2,5V
- between the heathers: 3V

When I bring the input voltage up to 220V the power transformer starts humming at around 205V, but I guess that's just what big transformers do (my old Variac also hums a little)? Voltages at the secondaries seems ok at 220V, but I'm a little afraid of running the PT at 220V because of the humming...

Would anyone here conclude after these measurements that the PT is good? So next step could be installing new filter caps, a new 5U4 tube and a 2amp fuse and do some new measurements?

 

[pucho812]

does your power transformer have 220 windings on the primary side?

 

[mjrippe]

Would anyone here conclude after these measurements that the PT is good? So next step could be installing new filter caps, a new 5U4 tube and a 2amp fuse and do some new measurements?

Ignoring the measurements, think about it logically:  The cap is an oozing mess - you have to replace it for sure so just do it.  The fuse did not blow, so the transformer is likely fine and so is the 5U4.  It is MUCH easier to blow a capacitor or fuse than a tube or power transformer.  Replace the cap and test it again on your Variac.

 

[bram9206]

@pucho812: yes, the power transformer is a 220V european type transformer.

@mjrippe: you're right about the cap, but before replacing the cap I also wanted to check the PT for a short. By the way, old Hammond organs don't have fuses... crazy, I know, but it's well know they don't have any fuse for protection, so number 1 on my list of restoring this Hammond is installing a fuse.

 

[bram9206]

just received the Tonewheel General recap kit for my M3 (field coil speaker). Got a few questions though, hoping that there were others before me who used this cap kit:

- the CE can cap misses the 30uF/25V cap. How would you cope with this?
- the black can cap has two 50uF taps. Only use one? Or would you use the second tap to replace that 30uF/25V cap?
- the kit also comes two 1M and two 560k resistors and two 100uF/35V caps? Any idea what these are for. Can't seem to find the 100uF caps on the schematic.

Thanks a lot!!

 

[musika]

Did you ask ToneWheel General about this?  I've installed kits from them in the past and they have been very supportive.  Their kits usually have installation instructions.  You may have received parts not specific to your M3.  Contact Rick at this email address:  <[email protected]> with your list of questions.

 

[bram9206]

This is what Tone Wheel General says, very supportive indeed!

"Late in the production of the B-3/C-3/A-100 AO-28 preamp, Hammond made a change in the
driver and output tube’s cathode bypass capacitor from 30 to 100 microfarads and installed it
directly on the tube socket. Presumably, if the AO-29 had been in production at that time it
would have also been upgraded with this change. Thus this kit provides 100 mfd capacitors for
that purpose."

And so I installed all capacitors without any problem. Resistors were included with the cap kit to replace the 6AU6 plate and screen grid resistors, as they tend to be the first to fail. I also replaced the 5U4 rectifier (just to be safe) and installed a 2 amp slow blow fuse.
After this overhaul I fired the Hammond up and all works well! I was very happy to find out the power transformer still is good and the secondaries measure out just fine. All works well, end of the story!

Now I have to get into that foldback mod...

 

[mjrippe]

Good work!  And thanks for sharing the solution and conclusion.