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Advice with Roland R-8 repair
Advice with Roland R-8 repair
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Old 21st February 2019, 10:50 PM   #1
cyborg16 is offline cyborg16
diyAudio Member
Join Date: Apr 2014
Default Advice with Roland R-8 repair

Hi everyone. This came to my shop because the client asked me to make a power supply, since isn't commercially avaible in my country, but when I opened it I saw a lot of damage. Apparetly it was fed with 220VAC instead of +/-10V, so I repared the power supply (diodes and regulators), alongside with a few more damaged parts (some zenners, a few blown tracks, burned resistors, etc.). After that, it powers on just fine, but it makes very ugly noises (check the video) . It sounds like awfull armonic distortion and some other weird things. Since right after the opamp (IC16 - LM6361) that's fed by the DAC (IC15 - PCM54) the noise was already present I replaced both IC's, but the noise is still the same. I also replaced all surrounding caps, but the power lines seems clean enough.
I will apreciate any ideas, since I have no idea what to check next.

Thanks in advance!
link to video: YouTube
link to service manual: http://www.synfo.nl/servicemanuals/R...VICE_NOTES.pdf
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Old 22nd February 2019, 04:24 AM   #2
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
I don't have sound on my computer, so...

Have you gone through all the diagnostic routines in the unit? Good description in the manual.

So coming out of the DAC it is distorted. Are all the data lines moving on the DAC? Are all the address lines moving? A stuck address or data line can certainly distort any audio.

With voltage abuse as you describe ANY CHIP IN IT can be damaged.

Powers on just fine, OK, does that mean all the computer functions work? I mean teh display is not garbled and all controls seem to do their jobs?
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Old 22nd February 2019, 01:18 PM   #3
cyborg16 is offline cyborg16
diyAudio Member
Join Date: Apr 2014
Hi! Thanks for answering! Let's go step by step.
Powers on perfectly, display has no errors, no stuck lines, no problems with contrast or anything else. All the buttons works fine too, they do change menus, but to make sure all the funtions work properly I should read the user manual because it's not very friendly. For now I can say that the sound banks change, the demo song works (but also sounds badly) and all the buttons and menus are responsive.
Yes, voltege abuse can burn from nothing to everything. When I saw the damage I was about to tell the client it was junk already, but then I fed the main board directly with +/-5V (PS rated output) and it powered on, so I decided to give it a try.
I didn't check all the lines thoroughly, but I most certainly will.
I went through the routines that might be relevant (actually the only relevant one seems to be the MSB adjustent), but I also ckecked the keypad (OK). I didn't hear any "pop" in the VR4 adjustment, but I hardly thing it'll make a difference with the current problem.

I'll update when I measure the data and adress lines. Thanks!!

(PS: sorry for bad english)
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Old 22nd February 2019, 02:12 PM   #4
cyborg16 is offline cyborg16
diyAudio Member
Join Date: Apr 2014
Updating. I can't edit the last message because it hasn't been approved yet.
Well, I don't quite understand what's going on. All the data lines seems to be inverted (normally 5V with no pad pressed, and the square signal goes to zero) except for Bit 1 (pin 2).
Also, added to the audio signal there's a pulse signal on pin 20 of the DAC that doesn's seems to change frequency nor amplitud with the pads pressing, but is only present while there's audio (seems reasonable, but I have no idea what is it). The weird thing is that connecting the osciloscope to that pin reduces significantly the noise, but doesn't seems to reduce the volume of the desired audio output. The pin is internally connected to a resistor on the chip and is used to close the loop of the internal opamp to get vout, but in the circuit the loop is closed after the external amplifier.
Another thing I noticed yesterday and I totally forgot is that some times the volume is completely random. It starts ok, but after a while it goes down to almos nothing and up again.
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Old 22nd February 2019, 02:43 PM   #5
cyborg16 is offline cyborg16
diyAudio Member
Join Date: Apr 2014
Update 2. Removing the opamp (IC15) and bypassing it doesn't make any diference with the noise (might even be worst). When in MSB calibration mode there is a constant noise (similar to the problematic one) that doesn't change with VR5 adjustment
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