I have a Roland CR -80 drum machine. It has a fault in that one of the output channels is lower in volume than the other and both of them are much lower than they should be on both the audio output and the phones output. I have already replaced the electrolytic capacitors on the final outputs before the jacks but this has not cured the fault.
Do you suspect it could be IC19 or 20 which I think are op amp chips or do I need to look somewhere else? (If it is these chips, then I presume I need to check the outputs on the correct pins with an oscilloscope?).
I really would appreciate some help.
Many thanks, Paul.
Hi, I can confirm at the volume pot is working smoothly. is it possible you could kindly give me advice on what I need to do to test the op amps I have got an oscilloscope but am only an amateur electronics enthusiast. If you could let me know what pin numbers and how to check for a signal etc that would be much appreciated. Many thanks Paul
I would first search the web for the service manual, which will have the schematics. Then start at the output jacks (usually on the right side of the schematics - signal generally goes left to right), and trace backwards until you see an op amp (typically drawn as a triangle). The schematic will probably show the pin number for each connection of the IC, so that should indicate the output pin(s), because they lead to the jacks. You can then locate that chip on the circuit board and probe the output pin with the scope. You can also Google to find the data sheet for that op amp, and that will show you the input and output pin numbers.
If you get nothing at the output, but you see signal at the input of that chip, then it’s a good bet you’ve found the culprit. If you see nothing at the input and output, then trace the schematic back to find the previous op amp in the path, and test that one in the same way.
Thank you Sam, I have found the schematic online and print it off and have found the op amp chips on the diagram and on the unit itself. I will report back my findings later this week. I will have to see if I can find an alternative if they need replacing as it looks like the particular one i.e M5218FP, is not available. (I must say it will be a tricky job to do solder them from the board as they appear to be surface mounted, I am fine with working on circuit boards with a fine soldering iron but these will test my abilities if they need replacing).
Hi Sam, I have managed to get a replacement chip which was a small 8-pin op amp chip I thought it was worth changing this as there was no amplification of the signal coming from the da converter when it was going through the first op amp chip which was a low pass filters and it was still the same signal coming out of the outputs of the second op amp chips which precede the line output circuit. Unfortunately whilst removing the old surface mounted chip I broke the contacts off the board so I can’t see any contacts and I’ve tried making new contacts to go to the associated surface mounted resistors and capacitors on the board next to these chip but nothing seems to be happening now even though before I took the old chip off there was a low output. I would appreciate it if you have any suggestions as at the moment the unit is completely dead when it comes to the audio output. Regards Paul Lee
If the board traces are broken, then it sounds like it might be time to go to a service center who can repair that (and find the original fault as well). There’s not much else I can suggest - if the board is damaged, it’s not going to work until those traces are fixed. And that’s some pretty delicate work that takes an experienced tech.
Thanks Sam, I contacted Roland UK and they suggested and experienced tech company who are indeed now going to be repairing the unit. Thank you very much for your help and advice. Best wishes, Paul.