Pair of Roland MA-8s troubleshooting
RandyWilliamson
Posts: 178
So I have a pair of Roland MA-8's that I have to say I have been in love with for a few years now...well i dont know exactly WHO or why but the mid/bass driver is dead and I'm trying to find a replacement its basically 4 inches and is 4 ohms 10 watts looks shielded and of ample size magnet not wimpy type but i guess all shielded look this way, anyway I havent had much luck finding a perfect replacement but I have found some variations of higher wattage. It is labeled P4DUC-4 and then the ratings. If you know of a good source let me know..I was trying to place an order for one via madisound but their cheapest is much higher spec than this i am sure and is at 50x dollars and I cant go for that....a shame because I have an order ready to go with them on other items.
What is more difficult though is that on this channel which is the right channel as I raise the volume it has dead spots and is scratchy as I raise. Certain levels have volume and others dont. So as I go up it will make scratching noises almost like poor reception then suddenly ill get signal and volume..then if I nudge it a little more I might get nothing again..then another nudge and volume again. I can't seem to figure out what to replace as stuff on the board looks good and there is nothing burnt out or visually wrong. I know it's not the pot/volume knob because the other channel goes up in volume just fine and no scratches. And I know it is working because like I said there are areas of volume that do work fine and since the tweeter is working I can hear it all still.
I'll attach some pics of this sweet sounding pair. I know its not polk but you guys know your stuff and well I don't rap about speakers elsewhere. Wish you could hear them in their prime they are a true size marvel and ample self powered as well.
Im thinking the rear corner big cap since its in series before the positive lead that goes to the positive side of mid driver. But it doesnt look bad. I dont know how to measure these, although I do have a multimeter. sorry no oscilloscope. Do you guys think it's the mosfet for the right channel? im damned if so because Id probably not be able to source that at all. I wanted to fix it since I have it open for the day I find the driver.
the big cap im talking about is in the 4th pic from the top.
What is more difficult though is that on this channel which is the right channel as I raise the volume it has dead spots and is scratchy as I raise. Certain levels have volume and others dont. So as I go up it will make scratching noises almost like poor reception then suddenly ill get signal and volume..then if I nudge it a little more I might get nothing again..then another nudge and volume again. I can't seem to figure out what to replace as stuff on the board looks good and there is nothing burnt out or visually wrong. I know it's not the pot/volume knob because the other channel goes up in volume just fine and no scratches. And I know it is working because like I said there are areas of volume that do work fine and since the tweeter is working I can hear it all still.
I'll attach some pics of this sweet sounding pair. I know its not polk but you guys know your stuff and well I don't rap about speakers elsewhere. Wish you could hear them in their prime they are a true size marvel and ample self powered as well.
Im thinking the rear corner big cap since its in series before the positive lead that goes to the positive side of mid driver. But it doesnt look bad. I dont know how to measure these, although I do have a multimeter. sorry no oscilloscope. Do you guys think it's the mosfet for the right channel? im damned if so because Id probably not be able to source that at all. I wanted to fix it since I have it open for the day I find the driver.
the big cap im talking about is in the 4th pic from the top.
Cool stuff: Adcom GFA-555, GFP-710, Oppo BDP-83, Monitor 10's w/RDO198s, rebuilt and modded XO: Sonicap/Mundorf topside, Daytons Low.
Benq W5000
"Leaning back like a maxwell tape commercial listening to pure polk bliss"
Benq W5000
"Leaning back like a maxwell tape commercial listening to pure polk bliss"
Comments
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Is there one volume control for both channels? Can you remove the driver in question and test it on its own, or even swap it with the other channel speaker?2 Channel - Polk SDA-2BTL, Carver TFM-35, Peachtree iDAC, Qobuz streamed via Episode Lynk using bubble UPnP server
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Am,
Yes the pot most to the right controls volume for both channels...what i was able to do after removing the broken right channel driver was place its wires over the left channel driver setup and it did the same screechy noises w the volume. But when i leave the left channel alone on its own wiring it works perfectly and always has no screeching as i raise the volume. I also using the right channel wiring and low volume applied right mid driver signal to the right side tweeter and it works fine but still screechy as i raise volume. Then right after same right side wiring applied the signal using the tweeters wiring which has a tiny cap...and it still worked but screechy volume....so there is signal on right channel to both drivers for sure.
It seems the right mid driver is dead....and that same right channel has messed up volume control...but only that channel. I guess I could live w it...but im wondering if maybe that lead to the driver fail.....the drive itself looks perfect and is not seized and has flexibility. So its just maybe fried. I forgot to bring it back home for more testing but its safe to say its dead i think.
Looks like the pot is not in question too right. Which means diode, cap, or mosfet ? The paths are tricky w no diagram, im sure theres more complex ones but theres plenty going on here for its size.
oh also jumpered from left channel to right mid driver and nothing...but i forgot to do it to the tweeter. Ill do it today.Cool stuff: Adcom GFA-555, GFP-710, Oppo BDP-83, Monitor 10's w/RDO198s, rebuilt and modded XO: Sonicap/Mundorf topside, Daytons Low.
Benq W5000
"Leaning back like a maxwell tape commercial listening to pure polk bliss" -
I'm having a hard time following your troubleshooting. You can check signal at the headphone jack as that feeds from the same line as the main output for the speakers (just through a couple 100ohm resistors). See if signal is clean there and if you still have issues with the volume control (if it crackles when adjusted it may just need to be cleaned). If all checks well at that point the woofer has most likely failed. This could be confirmed by hooking the suspect woofer up to another amp at low volume and seeing what it sounds like. Roland appears to have 4 of those drivers available - part # SJ021013. They cost around $25.2 Channel - Polk SDA-2BTL, Carver TFM-35, Peachtree iDAC, Qobuz streamed via Episode Lynk using bubble UPnP server
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Thanks for the Roland find. What should I clean? The right channel is crackling even with the left channel mid and tweet. It crackles for sure with its own right channel tweeter. So basically the right channel is crackling during volume being raised....the troubleshooting done seems to show this happens to the right channel specific and the left seems fine.
Ill check with headphones now too to see if it crackles right side there. Thanks.
Maybe our phrasing is different I dont know but music plays fine both channels except not thru right side mid driver because its bad but the tweeter does play but with crackling when volume is raised or down. I applied the right channel to the left speaker and it showed crackling then too....but the left channel has no crackling and raises up and down just fine. Right channel is the only one crackling.
Post edited by RandyWilliamson onCool stuff: Adcom GFA-555, GFP-710, Oppo BDP-83, Monitor 10's w/RDO198s, rebuilt and modded XO: Sonicap/Mundorf topside, Daytons Low.
Benq W5000
"Leaning back like a maxwell tape commercial listening to pure polk bliss" -
Let's see if there are any issues with headphones. I would suggest a spray contact cleaner for the volume pot - something safe on plastics like deoxit d5.2 Channel - Polk SDA-2BTL, Carver TFM-35, Peachtree iDAC, Qobuz streamed via Episode Lynk using bubble UPnP server
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So i was thinking if the pot really was the culprit it would have to have more than 2 leads on it....and sure enough it has 6! Each. To my demise i didnt have headphones...ill bring some in tomorrow or maybe just swap the last pot w the first since that does volume for input mic which i never use. Lets see tomorrow.Cool stuff: Adcom GFA-555, GFP-710, Oppo BDP-83, Monitor 10's w/RDO198s, rebuilt and modded XO: Sonicap/Mundorf topside, Daytons Low.
Benq W5000
"Leaning back like a maxwell tape commercial listening to pure polk bliss" -
Ok Ambi...it does it through the headphones too. Spray clean spray clean spray?Cool stuff: Adcom GFA-555, GFP-710, Oppo BDP-83, Monitor 10's w/RDO198s, rebuilt and modded XO: Sonicap/Mundorf topside, Daytons Low.
Benq W5000
"Leaning back like a maxwell tape commercial listening to pure polk bliss" -
So it crackles a little when you adjust the volume even through headphones, but otherwise sounds fine? If that's the case I'd try the contact cleaner on that pot and see if it helps.2 Channel - Polk SDA-2BTL, Carver TFM-35, Peachtree iDAC, Qobuz streamed via Episode Lynk using bubble UPnP server
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It did my friend it did tremendously..well i used an air can and hand sanitizer, but its working almost like perfect. I think im going to change it over to the more unused pot though. Where did you find the roland driver...international site or US?...i was trying the US just now and doesnt seem to pull anything using model # or part # you said. I think this is going to end up like new once all said and done.Cool stuff: Adcom GFA-555, GFP-710, Oppo BDP-83, Monitor 10's w/RDO198s, rebuilt and modded XO: Sonicap/Mundorf topside, Daytons Low.
Benq W5000
"Leaning back like a maxwell tape commercial listening to pure polk bliss" -
Hand sanitizer and air?
Call Roland US with the part number I gave you. It's not on their site. You could probably order a new pot from them as well for around $5, not sure I'd trust one after putting hand sanitizer in it...2 Channel - Polk SDA-2BTL, Carver TFM-35, Peachtree iDAC, Qobuz streamed via Episode Lynk using bubble UPnP server -
ok ...hah yes alcohol based plus air...dries quick and cleans...i got impatient about making some progess on it day3 and radio shack is a big let down past recent years. though they probably have another variation of deoxit. bear with me im unorthodox. it is working much better much smaller crackling now. thank you.Cool stuff: Adcom GFA-555, GFP-710, Oppo BDP-83, Monitor 10's w/RDO198s, rebuilt and modded XO: Sonicap/Mundorf topside, Daytons Low.
Benq W5000
"Leaning back like a maxwell tape commercial listening to pure polk bliss" -
Well I swapped pots...and it's pretty much cleared slight crackling in upper volumes now but hey. Im guessing they're all worn or degrading. Strange thing is when I raise treble more than half way it starts to depower the right channel and send more to left channel. Overall it seems like the left has a bit more power than the right for some reason but it's more noticeable at upper volumes and when treble is all the way up.
And for more strange oct 31st happenings...I took your advice and took the broken driver home, lowered the volume unhooked a polkie and tried the bad driver. Got nothing...moved the tips to other areas. tried the edges...the small holes on the metal prongs..more nothing...then as I was about to hook wires back to polkies I figured id give it 1 more shot but this time Id bypassed the metal connectors and hooked up straight to the wires behind the cone....and bingo came to life. A little thrown back, I went back to the metal connector and sure enough nothing again. Then tried its edges and central holes nothing....went back to wires to wires again and was greeted with some U2. Then went back to edges of metal connector and now low and behold it was working...then back to central holes of metal and still more music...disconnected and went back.......now it was working anywhere on the metal connector!!?!?!
I inspected the wires behind the cone and they're not lose on the cone or behind the metal connector...strange phenomena. Ever seen this !?!? What do u think about the treble and power distribution issue? (this was happening from way before but they been broke for like 2yrs and I had forgotten)
Cool stuff: Adcom GFA-555, GFP-710, Oppo BDP-83, Monitor 10's w/RDO198s, rebuilt and modded XO: Sonicap/Mundorf topside, Daytons Low.
Benq W5000
"Leaning back like a maxwell tape commercial listening to pure polk bliss" -
I'd recommend replacing all three pots, it's not surprising the one that was acting up in the volume location would cause issues elsewhere. I've seen woofers before have a bad connection between the + and - terminals and the wire that goes to the voicecoil, perhaps a cold solder joint or something. The new driver is pretty cheap though. Anyway, glad you got things sorted out.2 Channel - Polk SDA-2BTL, Carver TFM-35, Peachtree iDAC, Qobuz streamed via Episode Lynk using bubble UPnP server
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Hello. I realise this is an old thread but maybe someone is still listening.
I want to resurrect my old Roland MA-8's to give to my mother who is having a hard time hearing her tv. I need to fix them first. One side cutting out, seems like it could be just a dirty pot. I probably will fail because I know diddly about repairing but sometimes get i get lucky. First is getting it open. Do I just need a very long Phillips screwdriver to get down the long holes?
Any glue after that?
Thanks.
