Don't know if I'm posting in the proper forum but here I go... I have 2 msr250 rca dimensia amps. They use a stk4192 II chip,so I'm posting in chip amp. The problems I'm having is with the speaker selection. One amp the A speakers have a problem,the other the b speakers have the same problem. When I first tested the A problem when I moved the receiver to just check I was on the correct input the speakers started to work. Jiggling slightly would cause them to be sporadic. Same with the other receiver except on B speakers. I'm thinking the mechanical switches for the speakers are mounted to the pc board and then have "extensions" going to the front panel so there is some stress on the switches and I'm thinking maybe the solder joints are bad/cracked/broken. I don't do much amp repair but have a couple times seen situations where switches soldered to the board like that eventually get the solder joints bad.
I don't have any schematics but I got wondering, are those switches the only thing that send the signal directly to the speaker output terminals or does it just send a signal somewhere and from there it goes where ever and eventually to the terminals?
I haven't looked at the back of the pc board yet to examine the solder joints but I've been curious about how the speaker selection works.
At first I thought maybe the switch was broken or faulty but with the cover removed the switch looks fine and appears to be working properly. I also tried getting some de-oxit into the switch. I then bought the second receiver just trying to get a receiver with both speaker sets working,but the second receiver pretty much has the same problem but on speaker B.
I don't have any schematics but I got wondering, are those switches the only thing that send the signal directly to the speaker output terminals or does it just send a signal somewhere and from there it goes where ever and eventually to the terminals?
I haven't looked at the back of the pc board yet to examine the solder joints but I've been curious about how the speaker selection works.
At first I thought maybe the switch was broken or faulty but with the cover removed the switch looks fine and appears to be working properly. I also tried getting some de-oxit into the switch. I then bought the second receiver just trying to get a receiver with both speaker sets working,but the second receiver pretty much has the same problem but on speaker B.
The switch is is series with the speaker lead. Either the switch could be dirty and/or worn,
or the solder joints holding it on the board could be bad. If you don't really need the switch,
you can jumper it with a piece of wire. It's not unusual for old audio equipment to have such problems.
If you need the switching, jumper the internal switch and use an external one instead.
or the solder joints holding it on the board could be bad. If you don't really need the switch,
you can jumper it with a piece of wire. It's not unusual for old audio equipment to have such problems.
If you need the switching, jumper the internal switch and use an external one instead.
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Thanks. I just also thought once I see the back of the board I'd see the traces leading either to the terminals or somewhere else. I did a repair of a power switch in my friends amp and it was a pretty hefty switch on it's own little pc board and the board would flex a little bit. My buddy said he needed to turn it of and on "like 50 times" to get it to turn on or off. There was almost nothing left of the solder joints from all the arcing. The main voltake went right to the switch.
If those are mechanical latching switches, they could be dirty or have broken solder pads. If they are touch switches there should be relays for switching the speakers. Follow the circuit on the PCB and check continuity on the switches and relays with a DMM powered off and also check if relays click when powered. There could be also DC on the outputs triggering the protection circuit. Check also the STK solder pads.
Thanks,I did check the dc and it's fine. I'm going with the solder pads are going to be cracked. I've also seen other components on boards that have larger wire/terminals coming thru the board (as opposed to a small resistor lead/transistor lead etc) and it almost seems as though there wasn't enough heat buildup in the larger terminal to make a good solder joint. I've often seen failed or ready to fail solder joints when dealing with larger terminals/wires.
The switches are the mechanical latching type. I just need to get the back cover /chassis off. The board is screwed to the back cover and pretty much keeps the back cover in place.
The switches are the mechanical latching type. I just need to get the back cover /chassis off. The board is screwed to the back cover and pretty much keeps the back cover in place.
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