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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Roland HP-860 electronic piano has HUM
Hi.
I recently bought a 2nd-hand Roland HP-860 electronic piano (88-key, analogue). It has a louder hum than the piano notes. I'd like to fix it myself. I have been learning electronics most of my life & I'm in the 3rd year of Electronics Trades at TAFE NSW (Australia). I've removed the plug from the final stage PCB (Revo board), and the amplifier is quiet. This makes me think that somewhere before the amp, there is hum being made. I could poke around with my CRO, but I wouldn't know what to look for. This piano has heaps of boards, for which I've worked out most of the features. I could try replacing all the aluminum electrolytic caps, but that could just be a waste of time. It was made some where between the late 70's and early 80's. I looked for date codes, and only found 1, I think. This piano uses a wiring loom design, with some PCBs using plugs, but most are wired up (soldered). To see pics of it, search Google images for "roland hp-860" use quotes and thaisecondhand.com has the pictures. NOTE: I have the 240VAC version. Please help! TIA |
#2
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Roland HP-860 electronic piano has HUM
"Josh9.0" wrote in message ... Hi. I recently bought a 2nd-hand Roland HP-860 electronic piano (88-key, analogue). It has a louder hum than the piano notes. I'd like to fix it myself. I have been learning electronics most of my life & I'm in the 3rd year of Electronics Trades at TAFE NSW (Australia). I've removed the plug from the final stage PCB (Revo board), and the amplifier is quiet. This makes me think that somewhere before the amp, there is hum being made. I could poke around with my CRO, but I wouldn't know what to look for. This piano has heaps of boards, for which I've worked out most of the features. I could try replacing all the aluminum electrolytic caps, but that could just be a waste of time. It was made some where between the late 70's and early 80's. I looked for date codes, and only found 1, I think. This piano uses a wiring loom design, with some PCBs using plugs, but most are wired up (soldered). To see pics of it, search Google images for "roland hp-860" use quotes and thaisecondhand.com has the pictures. NOTE: I have the 240VAC version. Please help! TIA Have you looked at the power supplies with your scope? Here's your chance to put those 3 years of education to good use. Gareth. |
#3
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Roland HP-860 electronic piano has HUM
No I haven't!
Thanks for the tip, and thanks for the quick reply! I'll go and try it now. It has a bunch of different voltages out, and they're labelled on the PCB! I guess I should look for ripple on what should be DC, right?? Then trace it back to the offending cap(s). Then go buy some new ones of those only. BTW: It has a main voltage going to all the keys of 46V which measures 43V. |
#4
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Roland HP-860 electronic piano has HUM
"Josh9.0" wrote in message ... No I haven't! Thanks for the tip, and thanks for the quick reply! I'll go and try it now. It has a bunch of different voltages out, and they're labelled on the PCB! I guess I should look for ripple on what should be DC, right?? Then trace it back to the offending cap(s). Then go buy some new ones of those only. BTW: It has a main voltage going to all the keys of 46V which measures 43V. You seem to be jumping to lots of conclusions for no apparent reason. This is not going to help you. What's with this "offending caps" businsess? You seem to have decided there is a cap problem and replacing them will be the solution. Stop guessing, it will get you nowhere. You need to investigate and gather information. You start with the power supplies, If they are OK then you look elsewhere. Gareth. |
#5
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Roland HP-860 electronic piano has HUM
On Sat, 6 Sep 2008 14:36:12 -0700 (PDT), "Josh9.0"
wrote: No I haven't! Thanks for the tip, and thanks for the quick reply! I'll go and try it now. It has a bunch of different voltages out, and they're labelled on the PCB! I guess I should look for ripple on what should be DC, right?? Sounds good. Then trace it back to the offending cap(s). Then go buy some new ones of those only. BTW: It has a main voltage going to all the keys of 46V which measures 43V. Ba-ding... Now I wonder why that voltage is low? Could it be, oh, maybe... A bad filter cap? |
#6
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Roland HP-860 electronic piano has HUM
Gareth Magennis wrote:
"Josh9.0" wrote in message ... No I haven't! Thanks for the tip, and thanks for the quick reply! I'll go and try it now. It has a bunch of different voltages out, and they're labelled on the PCB! I guess I should look for ripple on what should be DC, right?? Then trace it back to the offending cap(s). Then go buy some new ones of those only. BTW: It has a main voltage going to all the keys of 46V which measures 43V. You seem to be jumping to lots of conclusions for no apparent reason. This is not going to help you. What's with this "offending caps" businsess? You seem to have decided there is a cap problem and replacing them will be the solution. Stop guessing, it will get you nowhere. You need to investigate and gather information. You start with the power supplies, If they are OK then you look elsewhere. Gareth. Thats because searching for any electronics problem on google comes up with "check all the electrolytics", ESR is the new religion. I get so many people bringing stuff to me saying, hey its probably a cap, you got an ESR meter?, can't be more than 10 bucks to fix. Yeah right. A little bit of knowledge can be dangerous. Good luck to the OP, with a scope should be an easy fix. |
#7
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Roland HP-860 electronic piano has HUM
"PeterD" wrote in message ... On Sat, 6 Sep 2008 14:36:12 -0700 (PDT), "Josh9.0" wrote: No I haven't! Thanks for the tip, and thanks for the quick reply! I'll go and try it now. It has a bunch of different voltages out, and they're labelled on the PCB! I guess I should look for ripple on what should be DC, right?? Sounds good. Then trace it back to the offending cap(s). Then go buy some new ones of those only. BTW: It has a main voltage going to all the keys of 46V which measures 43V. Ba-ding... Now I wonder why that voltage is low? Could it be, oh, maybe... A bad filter cap? Er, what exactly is this 46 volts supposed to be doing? I doubt there is anything like 46 volts anywhere near the keyboard. Please try again. Gareth. |
#8
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Roland HP-860 electronic piano has HUM
Er, what exactly is this 46 volts supposed to be doing? I doubt there is
anything like 46 volts anywhere near the keyboard. Please try again. Gareth. Yes... I checked it again. it's a common to all keys. No... there's little chance of electric shock, as there is a lot of plastic between the user and the switches. Sorry for jumping to conclusions. It's what I do, sometimes. And... as you will know, aluminum electrolytics are prone to going dry given a few decades (or less) ! |
#9
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Roland HP-860 electronic piano has HUM
"Josh9.0" wrote in message ... Er, what exactly is this 46 volts supposed to be doing? I doubt there is anything like 46 volts anywhere near the keyboard. Please try again. Gareth. Yes... I checked it again. it's a common to all keys. No... there's little chance of electric shock, as there is a lot of plastic between the user and the switches. Sorry for jumping to conclusions. It's what I do, sometimes. And... as you will know, aluminum electrolytics are prone to going dry given a few decades (or less) ! Your measurement is incorrect. No way is there 46 volts around the keyboard. Possibly 4.6 volts, a slight but possibly acceptable drop from the 5 volt supply. You are still wanting to find the answer in dry aluminium electrolytics or something else. Stop trying to make the symptoms fit your conjoured up answer. This is not the best way to fault find. You need to establish some facts. So far you have virtually none at all. Go get some and stop guessing. Really. Gareth. |
#10
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Roland HP-860 electronic piano has HUM
You need to establish some
facts. So far you have virtually none at all. Go get some and stop guessing. OK, How do I do that? Thanks. |
#11
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Roland HP-860 electronic piano has HUM
You need to establish some
facts. So far you have virtually none at all. Go get some and stop guessing. OK, How do I do that? Thanks. |
#12
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Roland HP-860 electronic piano has HUM
You need to establish some
facts. So far you have virtually none at all. Go get some and stop guessing. OK, How do I do that? Thanks. |
#13
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Roland HP-860 electronic piano has HUM
"Archon" wrote in message m... Gareth Magennis wrote: "Josh9.0" wrote in message ... No I haven't! Thanks for the tip, and thanks for the quick reply! I'll go and try it now. It has a bunch of different voltages out, and they're labelled on the PCB! I guess I should look for ripple on what should be DC, right?? Then trace it back to the offending cap(s). Then go buy some new ones of those only. BTW: It has a main voltage going to all the keys of 46V which measures 43V. You seem to be jumping to lots of conclusions for no apparent reason. This is not going to help you. What's with this "offending caps" businsess? You seem to have decided there is a cap problem and replacing them will be the solution. Stop guessing, it will get you nowhere. You need to investigate and gather information. You start with the power supplies, If they are OK then you look elsewhere. Gareth. Thats because searching for any electronics problem on google comes up with "check all the electrolytics", ESR is the new religion. I get so many people bringing stuff to me saying, hey its probably a cap, you got an ESR meter?, can't be more than 10 bucks to fix. Yeah right. A little bit of knowledge can be dangerous. Good luck to the OP, with a scope should be an easy fix. ESR is not a religion, it's a fact of life which, if you are a professional repair technician as your post suggests you might be, you must very well know ... Although of course not all, many faults these days are indeed due to electrolytic caps with a poor ESR. They are the single component which I, and everybody else I know in the business, change more of per week, than any other. That said, in this OP's case, the problem could easily be a leaky diode in the PSU, or something which may be a deal more difficult to pin down, such as a bad inter-board ground. The age of it would suggest a cap might be a firm first favourite though. Arfa |
#14
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Roland HP-860 electronic piano has HUM
"Josh9.0" wrote in message ... You need to establish some facts. So far you have virtually none at all. Go get some and stop guessing. OK, How do I do that? Thanks. Well, for a start, do as was suggested - and which you seemed to understand - and check each of the rails for ripple with your 'scope ... Arfa |
#15
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Roland HP-860 electronic piano has HUM
"Josh9.0" wrote in message
... You need to establish some facts. So far you have virtually none at all. Go get some and stop guessing. OK, How do I do that? Thanks. Make voltage measurements with your DMM. DC voltages first, then check for ripple on those DC voltage points. If, as you indicated, the voltage points are labeled, then start there... measure each voltage at its label. Check ripple by using the AC voltage function of your DMM. Beware that some DMMs are confused by a DC voltage, especially on the lowest voltage ranges. If so, temporarily connect a 1 uF capacitor (having a voltage rating above the voltages present in the organ) in series with one of the DMM leads to isolate the DC from the DMM. The DMM should now give you a reasonably correct AC voltage reading. The ripple voltage on a clean DC power supply point should be less than 0.100 VAC (ideally, less than 0.010 VAC). If one of the power supply points has much higher ripple voltage, then you can start looking at capacitor failure. Another cause of high ripple is rectifier failure, so you can't immediately blame the filter capacitors for high ripple. A bad regulator can cause high ripple, but you'll likely see a very wrong DC voltage as well. If all are reasonably correct (+/- 5% unless you have more specific documentation), then you have to look elsewhere. If all the power supply voltages seem to be OK, the next most likely cause of loud hum is the loss of a ground (shield) connection on an interconnecting wire. This will require that you visually inspect each wire connection where it goes off a board. If you find a broken wire, fix it and recheck to see if the hum is gone. Those suggestions should keep you busy for a bit. When you have found something that seems out of reason and don't understand or know what to do next, then come back with your questions. I'm sure we can get your organ back in service. -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes. |
#16
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Roland HP-860 electronic piano has HUM
On Sep 7, 11:33 am, "Arfa Daily" wrote:
"Josh9.0" wrote in message ... You need to establish some facts. So far you have virtually none at all. Go get some and stop guessing. OK, How do I do that? Thanks. Well, for a start, do as was suggested - and which you seemed to understand - and check each of the rails for ripple with your 'scope ... Arfa Thanks Afra. I checked the rails and they look clean. The hum has a certain "spike up, down, noise, spike up, down, silence" pattern. I'm off to Jaycar now, to buy some tantalums, as it can't hurt, and I don't like aluminium electros if tantalums are available. Where can I get a STK025 datasheet ? I find pages on Google saying such, but when I go there, it's just datasheets on STK0025 or STK0250. Even Sanyo's (mfg) site can't help me. |
#17
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Roland HP-860 electronic piano has HUM
On Sat, 6 Sep 2008 18:39:59 -0700 (PDT), "Josh9.0"
put finger to keyboard and composed: Where can I get a STK025 datasheet ? My vrt databook lists the following: STK025(G) = STK036: +/-30V, 20W (+22V/8 ohms) STK032 = STK036: +/-33V, 25W (+24V/8 ohms) STK036 audio amp +/-35V, 30W (+27V/8 ohms) http://pdf1.alldatasheet.co.kr/datas.../datasheet.pdf - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#18
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Roland HP-860 electronic piano has HUM
"Josh9.0" wrote in message ... On Sep 7, 11:33 am, "Arfa Daily" wrote: "Josh9.0" wrote in message ... You need to establish some facts. So far you have virtually none at all. Go get some and stop guessing. OK, How do I do that? Thanks. Well, for a start, do as was suggested - and which you seemed to understand - and check each of the rails for ripple with your 'scope ... Arfa Thanks Afra. I checked the rails and they look clean. The hum has a certain "spike up, down, noise, spike up, down, silence" pattern. I'm off to Jaycar now, to buy some tantalums, as it can't hurt, and I don't like aluminium electros if tantalums are available. Where can I get a STK025 datasheet ? I find pages on Google saying such, but when I go there, it's just datasheets on STK0025 or STK0250. Even Sanyo's (mfg) site can't help me. If the rails look clean, and the sound you are hearing has the described waveshape, then it is more likely that it is a buzz rather than a hum (subtle difference to the experienced ear) and not a power supply issue at all. It could be a grounding problem, but really, you need to know where the offending noise is actually getting in to the amplification chain. With items such as synths, where there are triangle and square wave generators running all the time, a simple bad ground can allow all sorts of nasty ground voltages to start appearing in amplification stages. Try here for your data sheet http://www.alldatasheet.com/view.jsp?sSearchword=STK025 Arfa |
#19
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Roland HP-860 electronic piano has HUM
If the rails look clean, and the sound you are hearing has the described
waveshape, then it is more likely that it is a buzz rather than a hum (subtle difference to the experienced ear) and not a power supply issue at all. It could be a grounding problem, but really, you need to know where the offending noise is actually getting in to the amplification chain. With items such as synths, where there are triangle and square wave generators running all the time, a simple bad ground can allow all sorts of nasty ground voltages to start appearing in amplification stages. OK, I could take a photo from the CRO, but how could I post it here ? I'm using Google. I could upload it to my site, and put a link, I suppose. Yes, a buzz it may be. All grounding wires look intact. If only I had another one of the same model, I could swap boards to determine where the problem is. Although, most are wired in place, it'd be a start, at least. BTW: I replaced the caps next to one of the STK025's and it didn't help, but I'm glad I did, because these caps should last another 30 years or so. Try here for your data sheet http://www.alldatasheet.com/view.jsp?sSearchword=STK025 Thanks, but I've been there b4 and all I find is other parts. EG: a 3 pin MOSFET. Is there a sci.electronics.organ.repair or similar group? |
#20
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Roland HP-860 electronic piano has HUM
"Josh9.0" wrote in
: Is there a sci.electronics.organ.repair or similar group? Might want to try persuing some of the vintage synth sites such as the following for information etc: http://www.vintagesynth.com/local/links.shtml |
#21
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Roland HP-860 electronic piano has HUM
On Sun, 7 Sep 2008 10:13:16 -0700 (PDT), "Josh9.0"
put finger to keyboard and composed: Try here for your data sheet http://www.alldatasheet.com/view.jsp?sSearchword=STK025 Thanks, but I've been there b4 and all I find is other parts. EG: a 3 pin MOSFET. Is there a sci.electronics.organ.repair or similar group? Did you see my other post? The datasheet for the STK032 should be appropriate. The STK032 appears to be a higher power pin compatible version of the STK025. http://pdf1.alldatasheet.co.kr/datas.../datasheet.pdf BTW, I would disconnect the input to the STK025, before the coupling capacitor (negative terminal), and ground it. That should confirm whether the noise is being generated in an earlier stage. If you need to purchase an STK025/STK032/STK036 (unlikely, IMHO), then they are available from "sales at starcomponents dot com dot au". Cost is AU$27.50 plus $3.30 postage (the STK036 is actually $1 cheaper). It may be an idea to buy a spare anyway, as Sanyo has obsoleted these devices long ago. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#22
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Roland HP-860 electronic piano has HUM
Arfa Daily wrote:
"Archon" wrote in message m... Gareth Magennis wrote: "Josh9.0" wrote in message ... No I haven't! Thanks for the tip, and thanks for the quick reply! I'll go and try it now. It has a bunch of different voltages out, and they're labelled on the PCB! I guess I should look for ripple on what should be DC, right?? Then trace it back to the offending cap(s). Then go buy some new ones of those only. BTW: It has a main voltage going to all the keys of 46V which measures 43V. You seem to be jumping to lots of conclusions for no apparent reason. This is not going to help you. What's with this "offending caps" businsess? You seem to have decided there is a cap problem and replacing them will be the solution. Stop guessing, it will get you nowhere. You need to investigate and gather information. You start with the power supplies, If they are OK then you look elsewhere. Gareth. Thats because searching for any electronics problem on google comes up with "check all the electrolytics", ESR is the new religion. I get so many people bringing stuff to me saying, hey its probably a cap, you got an ESR meter?, can't be more than 10 bucks to fix. Yeah right. A little bit of knowledge can be dangerous. Good luck to the OP, with a scope should be an easy fix. ESR is not a religion, it's a fact of life which, if you are a professional repair technician as your post suggests you might be, you must very well know ... Although of course not all, many faults these days are indeed due to electrolytic caps with a poor ESR. They are the single component which I, and everybody else I know in the business, change more of per week, than any other. you are in Australia then go down to Altronics and get yourself a Bob Parker ESR meter kit build it and then check the ESR in the power supply electro's That said, in this OP's case, the problem could easily be a leaky diode in the PSU, or something which may be a deal more difficult to pin down, such as a bad inter-board ground. The age of it would suggest a cap might be a firm first favourite though. Arfa |
#23
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Roland HP-860 electronic piano has HUM
Thanks Franc. I have tried that pdf link twice and each time I get a
pdf saying that the server is busy & to try again later! I'd like to try WES in Ashfield first. Only problem is, they're closed whenever I pass by. |
#24
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Roland HP-860 electronic piano has HUM
On Mon, 8 Sep 2008 08:15:11 -0700 (PDT), "Josh9.0"
put finger to keyboard and composed: Thanks Franc. I have tried that pdf link twice and each time I get a pdf saying that the server is busy & to try again later! I've uploaded it to my web space: http://www.users.on.net/~fzabkar/STK032.pdf I'd like to try WES in Ashfield first. Only problem is, they're closed whenever I pass by. I looked in the WES catalogue first but was unable to find it. This is the semiconductors section: http://www.wagner.net.au/catalogue/01.htm - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#25
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Roland HP-860 electronic piano has HUM
wrote in message ... On Sat, 6 Sep 2008 14:36:12 -0700 (PDT), "Josh9.0" wrote: No I haven't! Thanks for the tip, and thanks for the quick reply! I'll go and try it now. It has a bunch of different voltages out, and they're labelled on the PCB! I guess I should look for ripple on what should be DC, right?? Then trace it back to the offending cap(s). Then go buy some new ones of those only. BTW: It has a main voltage going to all the keys of 46V which measures 43V. Have you ever heard the hum when you pull the cord on a guitar amplifier, or some cable going to your home stereo? What do you get? A loud hum! This is momentarily because the ground is lost. Might you have a loose ground to one of the boards ahead of the audio amplifier (or in it)? There should be a potentiometer for volume control at the head (pre-amp) section of the amplifier. Remove the wire (or cut the PCB trace) where the input goes into the amp. Connect an auxilliary source, such as the output of a cd player or a radio tuner, to that point. Do you hear a hum? If yes, the problem is in the amp itself. If not, the problem is ahead of the amp. Of course, check the power supply first, and LOOK FOR LOOSE GROUNDS. Mister I've already said about the bad grounds twice so far in this thread, and once I think that he has replied that he hasn't found any, but I'm with you there. However, I don't think that he has the necessary professional background in service, to be able to run down a problem like this by disconnecting things, and running alternate grounds ... :-\ Arfa |
#26
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Roland HP-860 electronic piano has HUM
On Wed, 10 Sep 2008 09:58:27 +0100, "Arfa Daily"
wrote: However, I don't think that he has the necessary professional background in service, to be able to run down a problem like this by disconnecting things, and running alternate grounds ... :-\ Reminds me of an on-site repair job at a Scottish University (on a DVM). The Phd looking over my shoulder at the circuit points to the 1uF capacitor in the integrator section and says that will be the problem. I went for the 10M resistor rather than the polypropylene cap... Geo |
#27
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Roland HP-860 electronic piano has HUM
On Sep 11, 12:12 am, Geo wrote:
On Wed, 10 Sep 2008 09:58:27 +0100, "Arfa Daily" wrote: However, I don't think that he has the necessary professional background in service, to be able to run down a problem like this by disconnecting things, and running alternate grounds ... :-\ Reminds me of an on-site repair job at a Scottish University (on a DVM). The Phd looking over my shoulder at the circuit points to the 1uF capacitor in the integrator section and says that will be the problem. I went for the 10M resistor rather than the polypropylene cap... Geo Please tell me more, elaborate. This is interesting |
#28
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Roland HP-860 electronic piano has HUM
"Josh9.0" wrote in message ... On Sep 11, 12:12 am, Geo wrote: On Wed, 10 Sep 2008 09:58:27 +0100, "Arfa Daily" wrote: However, I don't think that he has the necessary professional background in service, to be able to run down a problem like this by disconnecting things, and running alternate grounds ... :-\ Reminds me of an on-site repair job at a Scottish University (on a DVM). The Phd looking over my shoulder at the circuit points to the 1uF capacitor in the integrator section and says that will be the problem. I went for the 10M resistor rather than the polypropylene cap... Geo Please tell me more, elaborate. This is interesting I would suggest that he is talking theory vs practical knowledge. Given the same situation, where an integrator was formed from a polyprop cap and a 10M resistor, I too would go for the resistor every time over the cap, because years of experience tells me that resistors over about 470k are far more likely to go high / open, even in non-stress situations, than that type of cap is to go faulty in any way ... It is this type of understanding of the fundamentals of servicing, that I was referring to when I made the comment about disconnecting and subbing grounds. The fact that the Phd picked the cap over the resistor shows that he understood the theory of the circuit involved, so was in the right area, but did not have the required practical experience to know that the cap, even though it's the more complex device, was probably a hundredth as likely as the high value resistor, to be at fault. Arfa |
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