carver TFM-25 amp

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negbias
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carver TFM-25 amp

Post by negbias » Sat May 13, 2017 8:54 pm

can the output relays on the carver TFM-25 be cleaned?

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radioeng2
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Re: carver TFM-25 amp

Post by radioeng2 » Sun May 14, 2017 7:17 pm

Hello,

Since no one with direct experience has answered yet, let me throw in a little about cleaning relays.

I'm used to big open frame relays used for higher voltages. And some of the what I think of as medium sized ones that are about an inch square or so. On these types, I carry and use a special file made just for contact cleaning, a burnishing tool. On a relay that opens and closes with enough potential on it, the action of the contact movement will have a small spark across it. This over time builds up carbon and some pitting maybe if the potential is enough. The file action will clean off the carbon, smooth the pitting a little. But even then it's regarded as bettering it for now. It probably won't last. It's best to replace if much problem follows.

In lower current applications, I think of contacts in relays much like in switches. The make up of the materials varies depending on the application. For instance, low current, like for line level audio, has next to no current. So silvered contacts are necessary. I'd worry that in the case of contacts like that, you'd strip away the necessary plating and essentially ruin the contacts.

In the case of the output relays, they aren't that low of current. Lower voltage and some current I'd think. They probably are built in what they consider a sealed environment. In bigger relays, they are built with tabs that you can carefully use to pry off the top cap, clean the contact and snap back down the top. In the mini ones in consumer electronics, I'd not expect them built to open. Now can you? I have no experience in them. That's why I'd prefer someone that fooled with them to answer. I'd wonder if a tiny hole could be drilled and spray in a contact cleaner and then resealed in some way. I'm not suggesting this and I don't have any experience. But I'm wondering.

You should be able to look up the part number right off the top of the relays and order them from somewhere like Digi-Key or Mouser. Primarily they are rated for the contact voltage being used, the contact number and styles, and the type of footprint. Unless you're sure of what you're doing, then I'd assume it's best to pass it to a service person. Not complicated, not expensive for just the relay. Likely about 8 points per to unsolder and resolder. Should be close to a bench minimum + parts if that's all that's wrong.

Hopefully someone with direct experience will be along. Otherwise, I hope my rambling will help with some understanding in someway of what's involved.

Mark
I was there "At the Fest!" Hope you were too!

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xavionics
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Re: carver TFM-25 amp

Post by xavionics » Sun Dec 31, 2017 11:23 am

Hi all, thought I would weigh in here.

Just replace them.

I recently overhauled a pair of TFM-25's. Relays, caps, binding posts, IEC Socket
Here are some of the parts used. The relays are available through E-Bay from seller Circuits and Concepts
IEC, Posts, Relays.JPG
Replacing the relays only requires removing the top and bottom covers, unsoldering the 8 (I think) contacts and soldering the new relays.
This is where they are:
1312 Rear Panel Mods Output.JPG
Hope this helps.
Sorry but I didn't take a pic of the underside. ](*,)

kve777
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Re: carver TFM-25 amp

Post by kve777 » Fri Jan 12, 2018 6:22 pm

Cleaning, sanding or burnishing the contacts is only a temporary fix at best. Good for diagnostics and temporary use until correct replacements can be obtained. Not a long-term repair. Aged contacts are lacking the factory finish and plating. Nothing you can do at home will duplicate originals. So, go ahead and clean them up, make sure the rest of the amp is in good order, then get some new ones. BTW- I have a limited quantity of relays for the hard to get TFM-6/TFM- 15 amps. Blue "ice cubes". The originals are 24V, mine are 120V. all you need to do is swap out the coils. Not a difficult job.
Kevin

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