Hey All,
Thanks in advance for any help you can offer.
I have a Marantz PM7200 which I’m struggling to get working. It powers on and lights up on the front, you hear the relay click in the power supply, but the relays on the amplifier board do not click and there is no sound. One can flip between input channels on the front of the device, but nothing happens internally.
This device has known problems with some of the capacitors on the power board and protect board going bad and falsely tripping the amp into protect mode. I tested them all with my atlas ESR and they seemed fine, but I’ve replaced anyway to be sure - no difference. I replaced the four caps on the protect board and caps 2304, 2302, 2305, 2210 on the power board.
I have tested the main voltages going from the power board to the amp board. My measurements are
VB+: 44.8v
B+: 44.8v
VB-: -44.8v
B-: -44.8v
These values are much too low, they should be +/- 56v according to the service manual. I suspect this is why the amp board isn’t switching on. Problem is - I cannot figure out why these values are low. The 12000uf filter caps are measuring within range, so it doesn’t seem to be that. Any ideas? I’m getting the same values even if I disconnect the board from the amplifier board.
Thanks!
Thanks in advance for any help you can offer.
I have a Marantz PM7200 which I’m struggling to get working. It powers on and lights up on the front, you hear the relay click in the power supply, but the relays on the amplifier board do not click and there is no sound. One can flip between input channels on the front of the device, but nothing happens internally.
This device has known problems with some of the capacitors on the power board and protect board going bad and falsely tripping the amp into protect mode. I tested them all with my atlas ESR and they seemed fine, but I’ve replaced anyway to be sure - no difference. I replaced the four caps on the protect board and caps 2304, 2302, 2305, 2210 on the power board.
I have tested the main voltages going from the power board to the amp board. My measurements are
VB+: 44.8v
B+: 44.8v
VB-: -44.8v
B-: -44.8v
These values are much too low, they should be +/- 56v according to the service manual. I suspect this is why the amp board isn’t switching on. Problem is - I cannot figure out why these values are low. The 12000uf filter caps are measuring within range, so it doesn’t seem to be that. Any ideas? I’m getting the same values even if I disconnect the board from the amplifier board.
Thanks!
Is the DC at the output (before the speaker relay) zero, or a high DC voltage?
An output device (and more) could be shorted.
0.025vdc measured at the amp side of speaker relays, specifically at t012 and t018.
The rail voltages depend upon the model suffix; N or U.
Don't get caught looking for a fault that is not there.
If you had shorted output transistors, you would have a buzzing mains transformer/lots of het or smoke.
Don't get bogged down, it is only an amplifier!
Check for DC on 5351 and 5352, if at zero, the amplifier is probably OK and you need to check for signal on those points.
All will become clear after those check as to which area your fault lies.
Don't get caught looking for a fault that is not there.
If you had shorted output transistors, you would have a buzzing mains transformer/lots of het or smoke.
Don't get bogged down, it is only an amplifier!
Check for DC on 5351 and 5352, if at zero, the amplifier is probably OK and you need to check for signal on those points.
All will become clear after those check as to which area your fault lies.
I'm really sorry - i'm probably being stupid, but I cannot find 5351 or 5352 anywhere, i've searched the schematic and boards. Can you advise?
Measuing 0.025vdc on the diodes to ground!
NOT getting 24v at the emitter of transistor - getting nothing!
Measuing 0.025vdc on the diodes to ground!
NOT getting 24v at the emitter of transistor - getting nothing!
Thats your problem. The protection circuits run from this voltage, so they won't be activating even though everything else is OK. Check the resistor at 3203, it's a fusible resistor and may have blown.
Personally I dont like the way Marantz implemented this - they would have done better to use a 7824 regulator.
I'm afraid r3203 seems to be fineany other suggestions?
Thanks so much for your help!
AC is coming in at 1503 to the tone circuit, but it goes no further because the fuses 1202 & 1201 are both blown. Diodes following these fuses don't seem to be blown, so i'm guessing there's a short somewhere after.
Sorry for the multiple posts! I can't seem to edit my old post to add more info.
I couldn't find any obvious shorts, so I replaced the fuses in 1202&1201. Annoyingly i don't have any T500ma fuses, so I used quick blow 500ma fuses. Interestingly 1201 blew straight away, 1202 did not. I swapped out 1201 again incase it was the quick-blow thing, but it popped straight away again. I'm pretty sure something is drawing too much current, but I haven't found any obvious shorts to ground or anything.
That explains why you're not getting 24V and why the unit is in protection!
Temporarily use 100 ohm 5W power resistors in place of the fuses. If something is still drawing excessive current, the voltage will be dropped across the resistors (which you can measure) and they will get hot (which you can also measure!). The rest of the circuit will be protected.
You may find the regulators 7201 and 7202 have gone bad - rare, but it happens. They are easy to get as they are just 7815 and 7915 regulators.
It may be helpful to remove the regulators, and then see if you can measure any short to ground (with a resistance test) both before and after the regulator.
Temporarily use 100 ohm 5W power resistors in place of the fuses. If something is still drawing excessive current, the voltage will be dropped across the resistors (which you can measure) and they will get hot (which you can also measure!). The rest of the circuit will be protected.
You may find the regulators 7201 and 7202 have gone bad - rare, but it happens. They are easy to get as they are just 7815 and 7915 regulators.
It may be helpful to remove the regulators, and then see if you can measure any short to ground (with a resistance test) both before and after the regulator.
I had the case recently, in fact, it came from the pre-amp.
I did not find the fault because this amp is worth nothing
and I had already spent a lot of time and as I have to charge my hours, I ended up him a small prampli inside so that the customer can still use the amp.
I think the failure came from the front panel.
good luck
I did not find the fault because this amp is worth nothing
and I had already spent a lot of time and as I have to charge my hours, I ended up him a small prampli inside so that the customer can still use the amp.
I think the failure came from the front panel.
good luck
in my case,this is not the NJM2068 in short cuts .
after, I do not know how much you charge for an hour of work, but here, considering the selling price of a pm7200, the mere fact of watching it already costs more than the amp and it is true that I do not do not like this kind of amp at all.
on the other hand, I did not charge half the time spent to give life back to a Nytech cpa602.
for me, this type of amp can only serve as a clipboard.
but again, this is only my opinion
after, I do not know how much you charge for an hour of work, but here, considering the selling price of a pm7200, the mere fact of watching it already costs more than the amp and it is true that I do not do not like this kind of amp at all.
on the other hand, I did not charge half the time spent to give life back to a Nytech cpa602.
for me, this type of amp can only serve as a clipboard.
but again, this is only my opinion
So - I tried the resistor trick. Nothing got hot at all! So i put a 1a fuse in, and the thing powers up without blowing, no heat, no smoke - even left on for ages. I think the 500ma one was probably only blowing due to not being a time-delay fuse to be honest? I have tested 7201 & 7202 and they seem fine - really not sure what the problem is here
You have a set time, 15 minutes? to edit after posting; after that you can't edit.
You can fix typos if you catch them quick. You can't go-back and change your story if you wait too long.
That does suggest gathering your thoughts before you post; but everybody is human (well, a few here I wonder, but most of us are).
So - I tried the resistor trick. Nothing got hot at all! So i put a 1a fuse in, and the thing powers up without blowing, no heat, no smoke - even left on for ages. I think the 500ma one was probably only blowing due to not being a time-delay fuse to be honest? I have tested 7201 & 7202 and they seem fine - really not sure what the problem is here
OK, so with those resistors in place, you're getting about +/-29V on the input pins of the regulators ? Youre getting +/-15V out of them ? What are you getting on the base and collector of 7203 ? (All measurements to ground)
Sorry for the delay here. It's been a bit of a journey!
So - replaced the fuses with T500ma ones. No more blowing, but the second set of relays still weren't clicking. I was not getting expected measurements around the regulators and 7203, but there was nothing obviously burnt. I got a bit stuck with it so left it for a while.
Came to it today and it powers up perfectly, relays and all voltages. Been playing it all day and it's working flawlessly. I think there must be a dry joint somewhere, so I'm going to go hunt for that now.
Thank you so much for your help - would never have found the problematic area was it not for the folks on here.
So - replaced the fuses with T500ma ones. No more blowing, but the second set of relays still weren't clicking. I was not getting expected measurements around the regulators and 7203, but there was nothing obviously burnt. I got a bit stuck with it so left it for a while.
Came to it today and it powers up perfectly, relays and all voltages. Been playing it all day and it's working flawlessly. I think there must be a dry joint somewhere, so I'm going to go hunt for that now.
Thank you so much for your help - would never have found the problematic area was it not for the folks on here.
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