MPS power supply transformer repair

marko · Post by **marko** » Fri Feb 12, 2010 12:10 pm

oldschoolfan wrote:No, definitely not imagining. My other amps have them but not this mystery machine.

just checked my mps2500 and that has no markings either!

Post by **Eric D** » Fri Feb 12, 2010 5:47 pm

What voltage are the big blue rail caps rated for?

See if you can find R110 on the board. R110 has the following values...

MPS2500 - 4.7k ohm
MS2125/MAC500 - 3.3k ohm
MS2250 - 1k ohm

oldschoolfan · Post by **oldschoolfan** » Fri Feb 12, 2010 10:26 pm

Well okey dokey. Eric per your info I guess this would be a 2125. R110 is 3.3k ohm. Rail caps are rated at 50 volts. So do you think when it was built they just wound two of the larger diameter cores? I guess that would explain why it looked a lot less busy than all the other MS transformers I have seen. Extra real estate for not so many windings. Here is the before I unwound it pic.

Post by **Eric D** » Sat Feb 13, 2010 7:21 am

What kind of power supply MOSFETs does it use? They should be IRF???

oldschoolfan · Post by **oldschoolfan** » Sat Feb 13, 2010 9:08 am

Yes, they were irfp044's.

marko · Post by **marko** » Sat Feb 13, 2010 10:45 am

i have seen irfp054's (ms2250 items) used in an ms2125, another example of pg using what ever parts they could get their hands on at the time!!

KUB3 · Post by **KUB3** » Sat Feb 13, 2010 10:56 am

Now that is hand made!

oldschoolfan · Post by **oldschoolfan** » Wed Feb 17, 2010 8:21 am

Eric D wrote:What kind of power supply MOSFETs does it use? They should be IRF???

So, um, Eric. Could I talk you into selling me that there 2250 core? I would gladly send you the uncoated one I have in addition to financial compensation.

Post by **Eric D** » Wed Feb 17, 2010 8:43 am

I only have two cores, and I use them when I change MS2250TAs into original MS2250s. I wind the pair of transformers as I unwind the originals.

If I had more I would gladly sell you one.

Aside from the lack of a coating, there is nothing wrong with your core. If you plan to re wind a core, just wrap the one you have with electrical tape. You really don't need a coating on the core at all. If you wind it, and then when finished coat the bottom of the core with epoxy, it will keep the wires from vibrating and shorting.

Also, are you sure the wires are shorted to the core, and not just to themselves? It is entirely possible they are shorted to the core, but they often short to themselves just as easily.

oldschoolfan · Post by **oldschoolfan** » Wed Feb 17, 2010 2:59 pm

I hear what you are saying about the tape. I actually really like electrical tape but it would not look as nice since we have decided this is a 2125 with a 2250 diameter core and it will be visible. I am trying to convince myself to live with the tape but I have not been able to do it yet.

Yes, it shorted to the core, poop. Here is a pic of the nude core.

Post by **Eric D** » Wed Feb 17, 2010 3:04 pm

Ok, it does look like that shorted to the core.

What wire are you going to wrap it with? The same gauge? I think there are two gauges in these amps.

If you do like I did and use smaller gauge wire, but more strands to make up for it, you have more control with hiding the core and you can make a tighter, neater looking transformer.

oldschoolfan · Post by **oldschoolfan** » Wed Feb 17, 2010 3:12 pm

Yes, two gauges.

Dang it! If I used more strands of a smaller gauge then I would have to rewind the other to match.

Sigh, I will just have to decide how to handle this. Decisions, decisions.

I never got through to Aamp. My email got bounced back for some reason. I will try them again before I make a final decision.

oldschoolfan · Post by **oldschoolfan** » Sat Mar 20, 2010 8:14 am

Ok, after futzing with this some more a good size chunk came loose from the core and I think it may be cracked all the way through. I have never received a response from AAMP. I have since contacted CWS Bytemark asking them to help me select a core as they have many alloys available. I don't know what the heck alloy was used originally. Anyhoo, this was their response.

"Use some hook-up wire, wind 10 turns and tell me what the inductance is. Then we will know the core to buy."

My friend that knows way more than I do said you need an LCR meter to get this measurement. Well, seeing as my core has a potential crack through it the measurement probably would not be accurate anyway.

Eric! Can you measure one of those unwound 2250 cores you have? Do you have an LCR meter?

Post by **Eric D** » Sat Mar 20, 2010 9:04 am

I just tried it and I can't get any useful reading out of my LCR meter.

Post by **ttocs** » Sat Mar 20, 2010 9:15 am

I had a large coil like that go bad on an amp one time. The shop I was working at had a great tech that could fix almost anything but I was suprised that my amp was the first thing he said he couldn't fix. This was years ago with an old memphis amp that they had quit making and he said he could not source a manf that made anything similar, nor find another amp that he could take one out of. He said that he coils are so specialized that they are often custom wound for each use and that substatuting a different one that was even a little bit off would cause major problems.

I always trusted tony's opinion but I also trust the opinion of those on here. Are the coils simple enough you can just get some transformer wire and magnet and bammo you made a coil that will work? Just curious.....

bogart · Post by **bogart** » Sat Mar 20, 2010 9:22 am

I have an os 2125 that had a rail cap take a shit and lite the board up...both of the torrids look to be solid to me.....Do you want em? I can pull em out as I am still harvesting parts of the board itself.....if ya need em I will sell em to ya already wound and all you got to do is plunk em in...

you wouldn't have the sexy 2250 cores...but she would be a runner

bogart · Post by **bogart** » Sat Mar 20, 2010 9:22 am

I will post pics in a sec.....

Post by **Eric D** » Sat Mar 20, 2010 9:23 am

The wire on the core and the number of winds is nothing special, but the chemical composition of the core and the way it is manufactured is pretty important. It needs to have a high iron content (you can't use a wood core for example), but from what I have learned it can't be a solid piece of iron. It needs to be made of iron powder that is pressed and baked together. I think this is because a solid piece would become permanently magnetized, and you don't want the core to become magnetized in a transformer.

bogart · Post by **bogart** » Sat Mar 20, 2010 9:30 am

pretty much the understanding I have....a great deal of pg's transformers were out sourced and built in bulk.....thus the tags on most...you wouldn't just want to wing it....but you are looking for a specific set of measurements....if you have in the end the correct figures then it shouldn't matter to much how you got em...

big wire...little wire....bigger core....smaller core.....as long as she lines up electrically you should be right on...

So my question here is what the fuck is an lcr meter.....something else I don't have.....

Post by **Eric D** » Sat Mar 20, 2010 9:37 am

LCR Meter...

L = Inductance
C = Capacitance
R = Resistance

bogart · Post by **bogart** » Sat Mar 20, 2010 9:38 am

pics of transforms

bogart · Post by **bogart** » Sat Mar 20, 2010 9:43 am

that is interesting with the meter...so it gives you a figure that is determined by all three variables? And you need one to measure what transformers are doing? I havn't even attempted to do anything with a transformer so I am not to sure....

looked over the chapter in the tutorial but had no real use for it......thanks Eric

bogart · Post by **bogart** » Sat Mar 20, 2010 9:46 am

Will I need one to tell if the transformer in an m100 that is purportedly bad, is actually bad beyond the visual once over? I think I want to try this on a smaller amp that only uses one.

Post by **Eric D** » Sat Mar 20, 2010 10:07 am

No, the LCR is not for measuring all three at the same time. It does it separately.

An LCR meter is just a DMM with different abilities. My Fluke DMM can measure resistance and capacitance. So it is sort of a RC meter. If I had a better Fluke DMM which had inductance as well it would be a LCR meter.

In my case I use the Fluke DMM for RC duties, but I have a separate meter which just does LCR. No voltage or frequency measurements are on my LCR meter. But, it is the only meter I own which will do inductance.

bogart · Post by **bogart** » Sat Mar 20, 2010 10:14 am

I see....I am reading my manual to see what this one will do but I am 99 percent sure the 87 5 will not give me anything on inductance..

looking for one on ebay to see what all they have....as of yet I've not needed more then the fluke, but I can see that I will eventually need something that will do so....still looking for my own esr meter