Hi guys!
I have a Marantz Model 1530 that worked fine until I did some work on it. I installed new lamps in it the other day, and decided to replace some of the caps too. When starting it up next, I would only hear static on the right channel. This static was independent of volume settings. So I connected my source directly into the power amp, and apparently one channel is just totally silent (the static and "sort of sound" that came from the pre, seems to have come from a potentiometer). The power amp is what's at fault.
I've already checked, and the capacitors I replaced are not the culprit. They are fine, and were not installed wrong. Tried using others, too, no difference. I've also checked for bad solder joints (or solder bridges), and that doesn't seem to be the problem either.
Adjusted the idle current for the left (working) channel, which worked well. Tried to do it on the silent channel, but there is no idle current. I've checked all the fuses and all the output transistors, all are fine.
This amp uses a driver IC for each channel, LM391 N-80, and I fear that this may be the source of the problem. What I'm wondering is, how do I check this? If there's no easy way, I will swap them between channels and see if things change. If this is blown, is the amp done for? I cannot find this for sale anywhere, so I guess it is totally obsolete by now. Maybe there's a DIY solution in that case, which sounds fun actually. 🙂
Well, any tips on how to solve this would be highly appreciated. Thanks for reading. Oh, and here's the schematic: (GIF: http://i.imgur.com/YhsjK.gif) (PDF: Login | HiFi Engine)
I have a Marantz Model 1530 that worked fine until I did some work on it. I installed new lamps in it the other day, and decided to replace some of the caps too. When starting it up next, I would only hear static on the right channel. This static was independent of volume settings. So I connected my source directly into the power amp, and apparently one channel is just totally silent (the static and "sort of sound" that came from the pre, seems to have come from a potentiometer). The power amp is what's at fault.
I've already checked, and the capacitors I replaced are not the culprit. They are fine, and were not installed wrong. Tried using others, too, no difference. I've also checked for bad solder joints (or solder bridges), and that doesn't seem to be the problem either.
Adjusted the idle current for the left (working) channel, which worked well. Tried to do it on the silent channel, but there is no idle current. I've checked all the fuses and all the output transistors, all are fine.
This amp uses a driver IC for each channel, LM391 N-80, and I fear that this may be the source of the problem. What I'm wondering is, how do I check this? If there's no easy way, I will swap them between channels and see if things change. If this is blown, is the amp done for? I cannot find this for sale anywhere, so I guess it is totally obsolete by now. Maybe there's a DIY solution in that case, which sounds fun actually. 🙂
Well, any tips on how to solve this would be highly appreciated. Thanks for reading. Oh, and here's the schematic: (GIF: http://i.imgur.com/YhsjK.gif) (PDF: Login | HiFi Engine)
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I'm a bit puzzled about why the LM391 IC should die just because you are recaping the amp? I have a feeling that the problem may be elsewhere.
Can you tell us which caps you have replaced?
Can you tell us which caps you have replaced?
Start by checking EVERY voltage on all pins of the IC and compare with good channel.
It's something you have done, whether or not that has damaged the IC (or anything else) will have to be seen.
It's something you have done, whether or not that has damaged the IC (or anything else) will have to be seen.
I really don't know where the problem might be, I'm just guessing. I replaced C703, 704, 705 and 706. I guess it is possible that there was a spark from a charged cap or something like that, during the soldering job. Something like that happened to me once before, and that killed a small transistor.
Mooly: I'll check the voltages next. I was already planning on doing it, but was hoping there would be another way. I only have one mini grabber lead, so I'll have to do it one channel at a time. Risky business, those legs are really close together. 🙂
Quickest way for faultfinding is to have all the facts and info available such as voltages. Don't assume anything 🙂
I finally got a second set of mini grabber leads. I was going to compare sides. First thing I notice - before even starting up the amp - the faulty channel was totally shorted. The faulty channel's speaker out + had zero resistance to GND.
Turns out one wire was squeezed under a screw, which had destroyed its insulation. Moved that, and everything was fine. SORT OF.
New issue. There's no sound at all, until about 11 o clock on the pot (from there on it is normal). And, there's some scary crackle in the speakers when moving the volume control. Not dirty pot type crackle (it's squeaky clean), but something scarier. DC offset is fine. Idle current adjusted as per the service manual.
Also the balance pot (also squeaky clean) does not work right. It acts as if the right channel (the one that was shorted) does not exist, the sound disappears entirely when you turn the balance in its direction.
But that channel really does work. I get proper stereo sound when balance is in the middle. Also, bypassing the pre solves all issues - power amp is fine, despite having been shorted like that.
I've re-flowed most solder joints on the pre amp board. Not sure what else to do. All electrolytic caps are new and properly installed, but I do not know if they are working right, since I acidentally did that channel shorting during the recapping process (so I've never gotten a chance to properly listen to it after that). Could a bad cap cause something like this? Or chould the channel shorting have damaged the pre somehow?
Turns out one wire was squeezed under a screw, which had destroyed its insulation. Moved that, and everything was fine. SORT OF.
New issue. There's no sound at all, until about 11 o clock on the pot (from there on it is normal). And, there's some scary crackle in the speakers when moving the volume control. Not dirty pot type crackle (it's squeaky clean), but something scarier. DC offset is fine. Idle current adjusted as per the service manual.
Also the balance pot (also squeaky clean) does not work right. It acts as if the right channel (the one that was shorted) does not exist, the sound disappears entirely when you turn the balance in its direction.
But that channel really does work. I get proper stereo sound when balance is in the middle. Also, bypassing the pre solves all issues - power amp is fine, despite having been shorted like that.
I've re-flowed most solder joints on the pre amp board. Not sure what else to do. All electrolytic caps are new and properly installed, but I do not know if they are working right, since I acidentally did that channel shorting during the recapping process (so I've never gotten a chance to properly listen to it after that). Could a bad cap cause something like this? Or chould the channel shorting have damaged the pre somehow?
Little Diode have the -60 and the -100 in stock, a little research should tell if they are compatable or not. I suspect it is just the output power?
LittleDiode - Electronic Components Supplier :: Search results
I suspect if you weren't anti-static('d) up you have probably duffed the IC.
James.
LittleDiode - Electronic Components Supplier :: Search results
I suspect if you weren't anti-static('d) up you have probably duffed the IC.
James.
Hi, thanks for the reply, but the IC did not turn out to be the problem. It is working as it should. 🙂
This sounds like a DC fault. The operating point isn't right somewhere. Check for DC on the volume control as a starting point as that would cause the loud crackle when the pot is moved. The power amp can't have damaged the preamp. I would start by recheching all your work for any shorts/solder blobs etc.
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