MEP 002a Generator Diodes

[dangier]

Just acquired 2 MEP 002A's private sale. One is seized (Injector was left out-parts machine). The other has a couple of bad rotating diodes. Diodes are 1N1204A and 1N1204R as far as i can tell through research here and elsewhere. Been searching and have run into out of stock, long lead time, have to buy large quantities, or made in China.
I was wondering if anyone has been through this and bought the large quantities and now has them sitting on the shelf. I would be glad to take them off someone's hands and pay cost and postage. I am looking for 6 of each (or at least 3 of each).

Regards,
David

 

[Triple Jim]

Plugging the part numbers into octopart.com shows several suppliers of small quantities. You may not be able to get both from the same supplier at the moment, I didn't check that thoroughly.

Alternatively, you can probably find diodes with similar or higher ratings with the same packages. Stud mount diodes are pretty common items.

 

[dangier]

Triple Jim,

Had a feeling I would hear from you. Thanks for the info. How's life in NC?

David

 

[Triple Jim]

Not bad thanks David. Busy keeping up with work and trying to empty a house I sold (not where I live now). I trust things are OK at your end.

 

[dangier]

Jim,
Great! Have a question though. Isn't a diode with a positive anode and a diode with a negative cathode the same thing? Found diodes for my new to me 002A, with higher ratings than standard on the big auction site, but think I got tripped up and have "six of one and half dozen of the other....
Wouldn't be the first time.
Grr!

 

[Triple Jim]

Yes, but all diodes have positive anodes and negative cathodes by definition. The thing you want to be sure of is which three have the stud as the cathode and which have the stud as the anode, since there are three of each in the assembly.

 

[Guyfang]

Dangier,

When you get the right diodes, do not remove the old ones all at one time from the rotor. Remove one, compare it to the new one, and put it in. If you should by chance mix them up, and this does happen, you will want to jump from the nearest bridge. Do them one at a time. Don't overheat them when re soldering them in. Or use a heat sink. But don't overheat them.

 

[Triple Jim]

After doing a little research for David, I found that while the 1N1204A and 1N1204RA are in short supply, their 600v counterparts are not. The 1N1206A and 1N1206RA are in stock at several suppliers, Mouser being one, for about $6 each.

These days it's not surprising that they quit selling the 400 volt version, since if they move everyone to the 600v diodes, they can make just one type, and in higher quantity, and probably come out with a better price than manufacturing and stocking two different parts. There was a time when it was harder to make the higher voltage versions, but those days are over.

 

[dangier]

Triple Jim, Guyfang,
Many thanks for the support on this. Will post when installed and hopefully working.
David

 

[dougski]

Yes, but all diodes have positive anodes and negative cathodes by definition. The thing you want to be sure of is which three have the stud as the cathode and which have the stud as the anode, since there are three of each in the assembly.

Jim or anyone else that can help, There are 2 heat sinks on the rotor with 3 each diodes on each heat sink. Are the diodes on heat sink (48 per TM-34) of the same polarization and opposite on heat sink (49), or are they mixed? The reason I ask is I have a broken diode and there all rusted up. Everything looks like it was rode hard and put up wet. Thanks for any help

 

[dougski]

Sorry guys I answered my own question by accident, but I will post my findings so maybe it can help someone else. When I started cleaning heat sink (48 per TM-34) I found markings on it. Broke out my 2X3 foot schematic and answer was right there. sorry to bother yall.

 

[Guyfang]

Yeah, thats a ruff looking heatsink. It's been put up at least twice wet, I bet.

 

[Triple Jim]

I'm glad you found the answer. I've never had mine apart to see how they're arranged.

 

[dangier]

Didn't get a chance to respond sooner, but got the new diodes installed and the genny is producing power. Not full output though (18 amps max before it starts to smoke and bog down. Much blowby in the crankcase. Suspect stuck or broken/worn rings. Will do a compression check at some point. Since this is a secondary unit, not top priority.
Currently pulling down another unit with damaged flywheel ring gear when I can get time to work on it.
David

 

[Triple Jim]

By the way Dougski, I thought I recognized your avatar photo. Never say die.

 

[dougski]

By the way Dougski, I thought I recognized your avatar photo. Never say die.

You would be correct sir. Lol

 

[mtfleming]

I believe the 3 diodes on one heat sink are the same and the 3 on the opposing heat sink are reversed polarity.

 

[Guyfang]

Don't believe, check. It's been 25 years since I looked at it, so I won't even think about guessing. Just checked. You are correct. All three on each heatsink are the same.