Hi everybody!
Been restoring a mixing desk (Roland RM-1600) without any problem since I was plugged to the unbalanced Out (TRS). Both channels working, nor mayor problems but a buzzing noise coming and going. I connected then the balanced output and Left chanel was dead. Testing with multimeter arrived to a smoked carbonized Resistor (R60/ 47Ohm). I have been looking for a short, soldering mistakes since I changed all caps of this board, Monitor Board and Channels Boards. Since couldn't find any short, my suspicions are between C87/C88 (470uf. 16V) and C47/C48 (47uf, 16V) since I have not way to test them I'm stuck.
Any thoughts, ideas or tips would be highly appreciated.
Been restoring a mixing desk (Roland RM-1600) without any problem since I was plugged to the unbalanced Out (TRS). Both channels working, nor mayor problems but a buzzing noise coming and going. I connected then the balanced output and Left chanel was dead. Testing with multimeter arrived to a smoked carbonized Resistor (R60/ 47Ohm). I have been looking for a short, soldering mistakes since I changed all caps of this board, Monitor Board and Channels Boards. Since couldn't find any short, my suspicions are between C87/C88 (470uf. 16V) and C47/C48 (47uf, 16V) since I have not way to test them I'm stuck.
Any thoughts, ideas or tips would be highly appreciated.
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Check the voltage at the op amp of the resistor, to ground. Either the op amp or the capacitor must have a short to ground. You may have installed an electrolytic capacitor backwards. Just replace the suspected parts, there are only a few.
Just hook up the meter, and turn on the power briefly. Probably you won't get much voltage,
if any, which means a short. The resistor's already shot and needs to be replaced.
My bet is on a backwards capacitor.
if any, which means a short. The resistor's already shot and needs to be replaced.
My bet is on a backwards capacitor.
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Thank you Rayma but I know that the resistor should be replaced. However there is any capacitor backward and voltages are ok.
Any thoughts anyone else?
Since the operational amplifier cannot provide enough current to burn that resistor the fault must reside elsewhere.
Disconnect C48, replace R60 and power up.
Look for a short in C48, short in your solder
points or C48 inserted with wrong polarity.
It has been said before.
Look for a short in C48, short in your solder
points or C48 inserted with wrong polarity.
It has been said before.
Replace the IC, (LM4558 etc) and the resistor. Check the capacitors across the rails, C47/8, easier just to fit two new 47u 16V caps and all should be well.
TRS is balanced! TS is unbalanced.
TRS is balanced! TS is unbalanced.
Not essentially. Try it, they only cost pennies.
Forget the theory if you are not sure how the IC works under stressed conditions. Repair the stage and then figure out what happened to destroy the supply feed.
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The op changed caps so the error is where he changed caps.
May be more harm will happen when soldering at the IC pins.
"Stressed conditions" ..
May be more harm will happen when soldering at the IC pins.
"Stressed conditions" ..
What do you mean by that?
"OK" is not a voltage value.
What do you measure at both ends of R60 to ground?
Please measure and post values.
I expect two "numbers" , not "they are OK".
Thanks.
Ok guys, after hours and hours of measurements and debugging possible failures this is what I found: somehow the plastic that wraps C48 it opened at the edge and the positive leg was in short with the aluminium can. It was microscopic. In circuit C48 didn't present a short cut, however I desoldered this guy to replace it but didn't found any other of its specifications. Having no option to get a new one till tomorrow I just start to looking at it and thinking and suddenly had the idea to replicate its legs position in the circuit with the fingers while testing it in diode mode, and voilá!!!! The beep brought back the light.
Finally wrapped all legs of all caps in all parallel circuits in the same board with shrinking spaguetti insultation to prevent any future burn because I have no idea how this problem happened since the console was working fine.
Now the console is on in test mode and till now all good.
Thank you everybody for time and attention to helping me find out.
Finally wrapped all legs of all caps in all parallel circuits in the same board with shrinking spaguetti insultation to prevent any future burn because I have no idea how this problem happened since the console was working fine.
Now the console is on in test mode and till now all good.
Thank you everybody for time and attention to helping me find out.
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