Realistic STA 2100 Issues

[Husmasher]

I have two 2100's and 1 2100D. All three are not working due to output issues. What I would like to have done is to rebuild all of the main amps. I am assuming that there are bad caps and transistors galore. What would be a suitable replacement for the output transistors? I am an electrician, but I have very limited knowledge of electronics. Where do I even start? Is there a safe way to test the left and right amps? Any help is appreciated and I will try to make this as painless as possible.

 

[6taafondo]

You should start by knowing what's wrong with each unit, otherwise you won't know what needs to be repair. It's not a matter of just replacing output transistors or caps; you need to know if they are bad i the first place.

First thing I'd do is download both 2100 and 2100D service manuals from hifi engine; those are free. Then choose one unit and begin the troubleshooting process, starting from checking out thoroughly what the reciever is doing and what not. Check all source inputs.

We can guide you afterwards.

 

[Husmasher]

Groovy. That's kind of what I figured. Rebuilding the amps and then having something before them that was causing the problem will just blow them up again. All I have is a volt meter. Will that be enough?

 

[6taafondo]

No, that won't be enough. You need on hand at least a good multimeter to attempt digging into an electronic device. A good one in my book is also able to read capacitor values.
It doesn't need to be a Fluke; as e.g Uni-T or Sanwa have nice units available at a lower price range than Fluke.

 

[Husmasher]

Ok cool. I have a Fluke 289 and that will check everything. So no oscilloscope required? The scope is what I was worried about.

 

[6taafondo]

The Fluke 289 is a great meter. An oscilloscope is not mandatory in the first instance, but could turn out to be at a certain point.

 

[KingBubba]

A set of meter leads with minigrabbers is a must as far as I am concerned. I would also tape you regular leads so only the points at the end are the only thing showing. You blow up less things this way.

 

[Copa1934]

Let me start by saying I own 2 STA-2000, predecessor to your 2100. Both function perfectly (and obviously are older units). But they didn't prior to a very complete cleaning, what people commonly refer to as "deoxit". I use CRC electronics cleaner and bath the pots and switches, one at a time and work them like crazy. I'll repeat this process a couple times. First thing you should notice is a change in "resistance", i.e. less when turning knobs. With switches they go from a dull click (or no click) to a very noticeable and solid click. When they don't click solidly, it means they are gummed up and possibly have contaminated contacts. I just finished restoring a Pioneer SA-8800. Had no left channel to speak of. After a very good cleaning she's operating like new and she sounds awesome. OH, follow up with tuner/electronics "lubricant". You don't want dry contacts.

 

[OMGCat!]

For starting off I'd grab a decent meter lead kit like the Extech ones you can find on Amazon. They aren't the type of things I'd bring to the jobsite every day but they have a set of pointed leads that have removable insulators on them and a pair of really nice mini grabbers. They will save you some smoke and/or flashes of blown up stuff from a slip once you get going into the diagnostic procedure. Plus they will be used rarely so the relatively lower build quality shouldn't become an issue.

 

[Husmasher]

Copa1934, I had one of the 2100's connected to my Mach 1's and had been using it for about a year. Two weeks ago I came home for work and was going to listen to some music and play pinball. I pushed in the power button and all was good, went from red to green just the way it always had. I turned my back and heard a strange sound coming out of the left speaker, nothing loud, no pop, just a couple of quiet hums. I heard the relay drop out and saw the green light had turned to red again and a small puff of smoke came out of the top vent just above the protection relay board. I opened it up and one of the contacts on the relay was welded together. I bought a new realy and stuck it in thinking that would fix the problem but I have no output on the left side. That story makes mad sad every time I tell it.

OMGCat, I am going to try to find some mini grabbers tomorrow, and maybe heat shrink a set of meter leads down to the points. I have seen enough smoke.....

Thanks for all the advice. I can use all the help I can get.

 

[Husmasher]

 

[Husmasher]

Those are both 2100's. Protection relay welded in both.

 

[zebulon1]

Check this thread from one I did a few years ago:

http://audiokarma.org/forums/index....recap-list-grrrrrrrrrrrr.576781/#post-7638134

There is some but not all the driver transistors equivalents listed in the posts.
I could help out further if needed. PM?
Work only one set at first or you will have three sets in a big heap! Once you you get the hang of it the other sets will be easy and fun to fix. Take my advice!!!!
The compensating transistor, attached to the heatsink can be a stinker on those sets. They can be had. (B&D)?
The STA-2100(D)'s are a fantastic set and easy to repair - well worth the money!

 

[Husmasher]

zebulon1, my plan is to get one working and then deal with the other two. I am going to replace the protection relay tonight. I found an Omron 2 pole 24vdc rated for 10 amps. ( I am not sure why they used four poles. ) Once I get that installed and working I can continue the going through the service manual. The thing that sucks is that it is the left channel on both that failed so I cant even swap outputs for the time being. I wonder if left channel failure is common for these units?

 

[zebulon1]

You can use the MJ21193's and MJ21194's ($6.00 - Mouser) for the outputs.
Do you know how to test transistors?
If the outputs are truly shorted then:
Take images of the bottom of the set for reassembly. The amp boards and heatsink are removed as an assembly. Do not remove the over temp sensor from the heatsink. Cut the wires where they meet at the crimp terminations. This makes working on the amps a joy. Check every component on the boards (Caps diodes, transistors and resistors). It wont take long. Use the boards and manual for reference. Note the values before you start ripping and tearing. The compensating transistor I spoke of in the last post, replace them as GP (General Practice). Test'em. If their bad, it probably was the catalyst to the output blow-outs. Don't forget to check the emitter resistors.

Note:
The over temp sensor circuit is a set of temp sensors (RTV'ed to the amp heatsink's and transformer) Their in series, so after the set is up and running, you can then reconnect the circuit. In the meantime, short the the two wires from the protection board together so the set will operate. Look at the schematic and you can follow the circuit from there (You'll see what I mean).

 

[Husmasher]

I may have a positive result. I replaced the protection relay in one of the units and I have sound in both channels through the headphone jack, and movement on both left and right watt meters. I am getting FM mono, and stereo if I work the mono button like mad. The FM signal meter is not working, but that is minor right now. I am going to give this one a bath in deoxit tomorrow and then try it with speakers. Any advice as far as the deoxit goes? Any place to stay away from? When I can get this one running, I am going to rebuild the others. Thanks for all the help so far!

 

[paymenow]

I always put a bit of wadded paper towel under the switch or pot that I am using Deoxit on. That can reduce or eliminate the mess on the PCBs.

 

[jblmar]

A DMM is a very important and reliable tool for troubleshooting. However, a good oscilloscope (at least 20MHz) will allow you to see the test waveform after you complete your repair. You can go to Distortion Analyzers for testing WPC & distortion (THD), Component testers and a whole slue of test gear if you wish to.
Husmasher, You have a PM.

 

[Husmasher]

So I have cleaned all the pots and switches. I have strong clear signal through the headphones and am assuming through the speaker outputs ( I am a little scared to try connecting speakers ) but I want to make sure everything else is working before I actually connect my Mach 1s. The next issue is I have drilled 1/8" holes into the switches to get deoxit in to them. All the switches cleaned up except the loudness, the bass cut and the treble cut. These are causing balance issues. Does anyone have any experience disassembling these or cleaning them better that I have? I don't want to put this back together until it is 100% working.