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Radio Shack Realistic STA-2100 channel unbalance

cmarti

cmarti

Well-Known Member
This seems to be a common thing among these receivers, I took a video show exactly how the output behaves.

I played a mono 440hz tone to ensure both channels were getting the same amount of input, anything under 4 leads to low output on the right channel, it evens once you reach 5 to 6.

 
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Need to clarify that the problem is that one channel does sound louder than the other. Or is it that the VU meters indicate
that one channel is louder. The VU meters are generally inaccurate. Trimmers VR603,4 are used to adjust the VU meters
refer to Chapter 7 of SM, Watt Meter Adjustment. Chapter 6 includes a flow chart for performing basic checks, maybe work
through the watt meter section.

If there is a sound level difference then prime candidates are switches, pots etc...
With the unit powered off/unpluged, input selector set to AUX, Vol=6, all other switches in normal position, measure
the resistance from the left AUX RCA(inside) to the wiper of the volume pot, left channel or R1001A, which ever is easiest.
Repeat for right AUX RCA(inside) and R1001B. Resistances should be about the same.
 
mbz said:
Need to clarify that the problem is that one channel does sound louder than the other. Or is it that the VU meters indicate
that one channel is louder. The VU meters are generally inaccurate. Trimmers VR603,4 are used to adjust the VU meters
refer to Chapter 7 of SM, Watt Meter Adjustment. Chapter 6 includes a flow chart for performing basic checks, maybe work
through the watt meter section.

If there is a sound level difference then prime candidates are switches, pots etc...
With the unit powered off/unpluged, input selector set to AUX, Vol=6, all other switches in normal position, measure
the resistance from the left AUX RCA(inside) to the wiper of the volume pot, left channel or R1001A, which ever is easiest.
Repeat for right AUX RCA(inside) and R1001B. Resistances should be about the same.
Click to expand...

Volume is lower on the right channel and at volumes 1 to 2 you can hear the right speaker crackling. Then sound output balances out around 5 to 6 and then the right channel becomes louder than the left channel after 7 -8

I'll do this test as soon as I get a chance, thanks so much for the clear explanation.
 
If your input level is adjustable put the volume control at full volume and check for channel imbalance. With the volume control at full volume it is essentially out of the circuit. If there is no channel imbalance now the volume control is at fault. I guessing bad volume control tracking.

Craig
 
The resistance test mentioned above should be performed at a point where there is significant difference between L&R channels, Vol=8 maybe.
Semi accurate pseudo log pots are difficult to make, some have +/-20% tolerances. You should give it a good spray but chances are a budget pot
was used so you might need to replace it with a "quality" item. Resistance measurements should indicate if needed.
 
Hello everyone, I have a new update.

Found the issue with the receiver, a dirty switch which I already cleaner with Deoxit but kept causing problems. The 'Low Filter' push button was the culprit, I cleaned it and now both channels play at the same volume and there is more bass on the right channel than before.

Thank you everyone for the help.

ONRTLBR.jpg
 
If you had been using an o'scope and a square wave it would have taken two seconds to see what was wrong.

Craig
 
cmarti said:
Hello everyone, I have a new update.

Found the issue with the receiver, a dirty switch which I already cleaner with Deoxit but kept causing problems. The 'Low Filter' push button was the culprit, I cleaned it and now both channels play at the same volume and there is more bass on the right channel than before.

Thank you everyone for the help.

ONRTLBR.jpg
Click to expand...

How did you clean those pushbutton switches with Deoxit? Aren't they enclosed in a plastic enclosure?
Did you have to remove the bottom cover on the receiver to get to that low filter switch to clean it?
 
Audiokingman said:
How did you clean those pushbutton switches with Deoxit? Aren't they enclosed in a plastic enclosure?
Did you have to remove the bottom cover on the receiver to get to that low filter switch to clean it?
Click to expand...
I did it from the top, also made an extra long straw for the Deoxit can. Forced the cleaner into the switch and kept pressing it working it out until it was cleaned.
 
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