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Marantz PM7200 - No Sound
Marantz PM7200 - No Sound
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Old 15th April 2019, 05:51 PM   #11
Passmore is offline Passmore
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Quote:
Originally Posted by Passmore View Post
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.
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Old 15th April 2019, 08:52 PM   #12
jaycee is offline jaycee  United Kingdom
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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.
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Old 16th April 2019, 04:39 PM   #13
huggygood is offline huggygood  France
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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
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Old 16th April 2019, 06:19 PM   #14
jaycee is offline jaycee  United Kingdom
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I wouldnt say theyre not worth anything, but its easy enough to isolate which board is causing the short... and then the only thing likely to be causing a short on the board is a bad opamp. NJM2068 is nothing special and easily subbed with a 5532
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Old 16th April 2019, 06:31 PM   #15
huggygood is offline huggygood  France
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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
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Old 17th April 2019, 08:38 PM   #16
Passmore is offline Passmore
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Quote:
Originally Posted by jaycee View Post
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.
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
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Old Yesterday, 04:06 AM   #17
PRR is offline PRR  United States
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Originally Posted by Passmore View Post
Sorry for the multiple posts! I can't seem to edit my old post to add more info.....
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).
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Old Yesterday, 02:15 PM   #18
jaycee is offline jaycee  United Kingdom
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Quote:
Originally Posted by Passmore View Post
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)
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