Realistic STA-2100D Weak Right Channel

[Live_Wire]

(Solved) Realistic STA-2100D Weak Right Channel

After a couple hours of listening and messing around, I noticed the right channel sounds a little weak compared to the left. At lower volumes, the right channel starts to distort a little too. When you turn the volume up a little (to about 0.5 watt) it goes back to normal. I thought it was just the attenuator switch, but I ruled that out. I turned the volume down to the point where it started to distort with the attenuator in, then I tried wiggling the button and it didn't change. As soon as I turned up the volume a little, it came back. I also did this with the loudness button and bass control.

Now, my question is, what can cause this? I have checked the DC offset, and I'm getting 4.5mV on the right, and 4.6mV on the left channel. I haven't checked Bias yet, but I just got the service manual. I will check that tomorrow. I'm wondering if the filter capacitors would cause this.

Any ideas to help point me in the right direction?

 

[Sir.Byrd]

Switch the speaker wires from left to right. Does the problem stay with the right SPEAKER or the right CHANNEL.

 

[ryuuoh]

It could be a relay, or any number of controls. The relay has come up in threads recently.
Issues like this are almost always contacts in controls, relays or failing solder joints. Have you cleaned the controls?

 

[Live_Wire]

Switch the speaker wires from left to right. Does the problem stay with the right SPEAKER or the right CHANNEL.

Ah, good idea. I will try this in the morning, too late to turn it up right now

It could be a relay, or any number of controls. The relay has come up in threads recently.
Issues like this are almost always contacts in controls, relays or failing solder joints. Have you cleaned the controls?

I have cleaned the controls out, took a long time to get em to the point where both speakers would be on at the same time. Maybe they still aren't entirely clean. I am going to take it back into the basement to work on for tomorrow.

 

[ryuuoh]

Sounds like there is hope!
I have cleaned controls on a few specimens, and some come clean right away, and some are really stubborn.

 

[Live_Wire]

Switch the speaker wires from left to right. Does the problem stay with the right SPEAKER or the right CHANNEL.

I did this, and it stayed on the left speaker. I also took the pre-amp out/in plugs out and changed them with a patch cord and tried reversing it there as well. It stayed on the right speaker.

I am going to take it into the basement and go over it once again. Through the night, I guess the controls got a little better, none of the buttons are making any noise anymore.

I hope I can get to the volume control this time, it's shielded by a piece of cardboard :sigh:


Edit 1:
I have it in the basement right now and I have re-adjusted the BIAS on both sides (I figured maybe the pot's needed to be moved a little bit, so I grabbed my meter and kept an eye on it afterwards).

I have it adjusted to 2mV on both sides. I figure that's ok.

Now the big problem, I don't think I can check the idling current on this thing without taking out the amplifier PCB and I'm not even sure that's the problem anyway. Does anyone here know how I can check the idling current without doing this?

I am in the process of going over the pots again right now too.


Edit 2:
I think I may have found something. I wondered if the protection relay might be doing this, so when the receiver was on, I started tapping at it with a rubber handled screwdriver. Sure enough, it started to cut in and out, and it actually got better at one point without me turning the volume up.

I now have the power board out of the receiver as far as I can with the wires still connected. Any ideas on how to get the cover off of the relay? I'd like to check the contacts, but I don't want to damage this part.

Edit 3:
I got the cover off, the contacts look fine actually. I still believe it is the relay though, when I have it at low volumes and tap on the relay, it will cut out, at high volumes it doesn't do this. I guess I might have to start looking for replacements?

I tried touching up the solder points on the board, but that didn't do anything. Still the same, at 0.1 - 0.5 watts it nearly drops out and at above 1.5 watts it comes back completely and sounds fine. When volume is too low to be measurable by the watt meters, it sounds OK too.

Thanks guys, I appreciate the help so far!

Regards,
Brian

 

[mchlwvr614]

I just ran into something that might be similar. I have a 2100D as well that I am currently cleaning up. I noticed the other day that at really low volume, 1-2 clicks the one channel will completely cut-out. Turn 1-2 clicks up and channel outputs again. I haven't checked the bias or dc offset yet. I have a set of t-200 speakers.

btw, I am a newbie to this forum and really like it so far.

also if you are looking for the 2100D service manual, not the 2100, you can get it here for $20 shipped. http://www.nbizz.com/soundsclassic/listings/907.html. It is even better than the scanned 2100 manual that is everywhere. Large, clear schematics. It is a copy, but VERY good copy.

 

[Live_Wire]

Hey mchlwvr614, thanks for the link. I'm seriously considering getting that manual.

I might have some good news for you. I got mine fixed up I believe. The contacts on the protector relay (The black box on the main power PCB right next to the transformer) needed to be cleaned severely. I pulled the spring off the relay and pulled it apart and the contacts were black. We used a contact burnishing tool and cleaned the contacts and put it all back together. Fixed it right up.

So, here's what I did, hopefully it helps you out. Determine if it is the relay.

Remember, do this at your own risk. No warranties!

1) With the amplifier on, and tuned to an FM station or playing something that is a relatively clean recording, press on the black relay box with something rubber (Don't use metal, in case you slip and short something out.)

2) listen to your sound output and if it starts to cut out and fade, then your on to something.

3) Turn the volume up and see if it doesn't do it anymore. It might still cut in and out, but if it's loud enough, it probably won't do it.

Now, I had to pull the PCB out (Just a few screws and it pops up) to get at the relay. It took some effort, but I got the cover off of the relay. There's one clip on each side.

When you get the cover off, remove the spring and take the contacts apart. Check and see if they are black, if they are, use a contact burnishing tool to clean it. Then use compressed air to blow the dust out and put it all back together.

Put it all back together and test it out.

As soon as we did that, it started working right away. I have had it playing now for about 2 hours and no problems. My dad helped me out with this, once he saw what I had found with the relay, he knew exactly how to get to it.

I know I might have not done it the way more experienced users here would have, but it worked. Can't argue with that

Best regards,
Brian

 

[ryuuoh]

The good thing is you can still get most of these relays. Coil voltage, footprint are what you need to know.

 

[Live_Wire]

Ah, good to know. I looked around a little, and found some. They are 24vdc, 4pdt. Not sure on amperage, think 5amps is what they are rated for.

 

[sd2649]

I know this is an old thread, so sorry to resurrect, but it is near my issue. My AMPs are both fine, but my right channel preamp is very weak and lacking bass. Is there a way to adjust the L/R fader? Is cleaning it out a typical fix? Is there a resistor/capacitor/whatever that goes out on the preamp side that would cause one channel to go quiet and lack some bass? Like I said, the amp is fine, if I switch the outputs to the main inputs, the problem is with the preamp output, not the amplifiers themselves... I appreciate any help!!!

 

[elnaldo]

Hello, Welcome to AK.

I suggest a deep cleaning with contact cleaner or "deoxit", following this thread, and starting a new thread with your amp model and the issue you describe here. There are hundreds of possibilities, but start a new thread and you'll fix it for sure.

 

[zebulon1]

I concur with "elnaldo".
The set is well built and designed. I restored one last spring and it was a fun project. It all started when the outputs shorted. It was caused by the temperature compensating transistor mounted between the heatsink and amplifier board. There are a few other components on the amp board that could be causing these symptoms but a good cleaning is the first step.

 

[sd2649]

Thanks! New thread coming soon.

 

[cmarti]

Resurrecting this old thread, I am having the same issues with my STA-2100. The right side volume sounds low when the volume dial is under dial #4.

The right wattmeter provides a lower reading that the left one, the audion on the right speaker also cuts out and or distorts at low volumes. Y adjusted the balance knob to 12 to compensate and listen at balanced volume around the 5 or 6 dial. I cleaned the clear relay but not the black one because it was very hard to pull even after I unscrewed the board entirely because of the cables which hold it in place from underneath the unit. I wonder if someone was able to find a replacement relay which is compatible to replace the protector relay (The black box on the main power PCB right next to the transformer).

Any help is appreciated, this will surely help other users since I even saw another STA-2100 listed for sale on eBay and it sufferers from the symptom

This is the one being sold right now: http://www.ebay.com/itm/Realistic-sta-2100-/182550342951?hash=item2a80d92d27:g:3TgAAOSw3gJZF0aV