Marantz 2245 in protection, advice for troubleshooting

tonefoto

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I have a 2245 that I received in non working condition, it had a broken power switch which I replaced. Its relay isn't allowing the receiver to come out of protection. I'm assuming the relay works, the power supply is adjustable to 35V, I recapped the 3 known problem caps on the PS board, 220uf, 47uf, 10uf. The right side amp had been worked on before it came to me. The outputs were replaced along with a resistor and a cylindrical transistor that attaches to the heat sync.

I initially powered it up with the dim bulb tester and noticed the right side outputs getting hot. I pulled the outputs which checked out good with diode test. After replacing 3 caps on the PS board, I powered it up again with outputs on right side removed to see if it would activate the relay, which it did not. Then it started getting real hot and smelled like it was cooking something on the rt driver board. The 100 ohm resistors R786 and R787 were getting real hot to touch and seemed to be what I was smelling.

Something of interest that I found; There is a large pair of 10 ohm resistors R784 and R785 that are have a wire jumper on the backside of the board. While checking resistors I found a lot of inconsistency in the values marked on the SM.

This is as far as I can go, if somebody could point me in the right direction it would be appreciated. I have limited experience here.
 
Hi Tony,
R784 and R785 can be any value from 0 (wire jumper) to several Ohms, the value can be adjusted to fine tune the bias current in the output transistors.
I would leave them as is until you find the short(s)
R786/787 heating up (especially with the output transistors removed) is indicative of too much current through the driver transistors, H758/759.
They may be bad, or the bias network consisting of H760/H761/R763 could be faulty. Perhaps someone installed H760 incorrectly, there should be markings on the component side of the power amp board with lead labeling.
If H760 (the part connected to the heat sink) is a cylindrical part (2SC984-B?), it should be replaced. See the 2270 service bulletin M-2270-1 (attached) for guidance. The SB calls for a 2SC496 transistor, I have been using the easier to source 2SC495 with good results. Be sure to insulate the transistor from the heat sink with a mica washer if required. You will have to modify the original transistor bracket to hold the new transistor and the bias diode (H761) against the heat sink.

A good place to start would be by testing the driver, bias transistors, R763 and H761 diode out of circuit with your DMM using Echowar's method.

Tom
 

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Hi Tony,
R784 and R785 can be any value from 0 (wire jumper) to several Ohms, the value can be adjusted to fine tune the bias current in the output transistors.
I would leave them as is until you find the short(s)
R786/787 heating up (especially with the output transistors removed) is indicative of too much current through the driver transistors, H758/759.
They may be bad, or the bias network consisting of H760/H761/R763 could be faulty. Perhaps someone installed H760 incorrectly, there should be markings on the component side of the power amp board with lead labeling.
If H760 (the part connected to the heat sink) is a cylindrical part (2SC984-B?), it should be replaced. See the 2270 service bulletin M-2270-1 (attached) for guidance. The SB calls for a 2SC496 transistor, I have been using the easier to source 2SC495 with good results. Be sure to insulate the transistor from the heat sink with a mica washer if required. You will have to modify the original transistor bracket to hold the new transistor and the bias diode (H761) against the heat sink.

A good place to start would be by testing the driver, bias transistors, R763 and H761 diode out of circuit with your DMM using Echowar's method.

Tom
Thanks Tom,
Someone installed a small NTE transistor where the original cylindrical one was and mounted it in rubberized putty. I'll start out by checking the bias circuit.
 
Thanks Tom,
Someone installed a small NTE transistor where the original cylindrical one was and mounted it in rubberized putty. I'll start out by checking the bias circuit.

Here are some pics of modified bracket courtesy of Tom. Used tin snips or diagonal cutter to snip of the rounded part.
H760 replacement.jpg H760 replacement-1.jpg
 
Hi Tony,
R784 and R785 can be any value from 0 (wire jumper) to several Ohms, the value can be adjusted to fine tune the bias current in the output transistors.
I would leave them as is until you find the short(s)
R786/787 heating up (especially with the output transistors removed) is indicative of too much current through the driver transistors, H758/759.
They may be bad, or the bias network consisting of H760/H761/R763 could be faulty. Perhaps someone installed H760 incorrectly, there should be markings on the component side of the power amp board with lead labeling.
If H760 (the part connected to the heat sink) is a cylindrical part (2SC984-B?), it should be replaced. See the 2270 service bulletin M-2270-1 (attached) for guidance. The SB calls for a 2SC496 transistor, I have been using the easier to source 2SC495 with good results. Be sure to insulate the transistor from the heat sink with a mica washer if required. You will have to modify the original transistor bracket to hold the new transistor and the bias diode (H761) against the heat sink.

A good place to start would be by testing the driver, bias transistors, R763 and H761 diode out of circuit with your DMM using Echowar's method.

Tom
I think this is a transistor (attachment) you provided awhile ago for replacing H760 cylindrical bias trans. on one of my 2270s. H760_trans.jpg I installed it in place of the NTE that was there. which side gets the insulation mica?
 
The back side with metal surface is conductive.
thanks for the photos of the bracket, I found that H761 diode was open, replaced with a 1N4007.

At this point I've checked R763 trimmer, replaced H760, H761. Outputs are not installed yet.

Is it safe to test circuit with DBT at this stage?
 
Drivers H758 H759 check OK, powered on with DBT with no outputs installed, R776 22Kohm heats up, R763 trimmer wouldn't adjust bias down from 85mV. DBT dimmed like it should. Everything Tom's pointed to was checked and replaced where needed. Where to now?
 
I can't find R776 on the schematic, I may be blind or the print might not match the real thing.
I am confused.;)
All measurements are with the Volume all the way down or no source selected.
With the outputs still removed and while still connected to the dim bulb tester.
Measure the DC voltage between H760 C (positive meter lead) and E (negative meter lead). You should see it vary from about 0 to +1.2V DC as you rotate R763.
Also, check from H760 C (positive meter lead) to chassis (negative meter lead). You should see it vary from about 0 to +0.6V DC as you rotate R763.
Check from H760 E (positive meter lead) to chassis (negative meter lead). You should see it vary from about 0 to -0.6V DC as you rotate R763.
Ecluser's excellent description about bias on the 2270 is relevant as the 2245 is just a lower powered version of the 2270.

Tom
 
I can't find R776 on the schematic, I may be blind or the print might not match the real thing.
I am confused.;)
All measurements are with the Volume all the way down or no source selected.
With the outputs still removed and while still connected to the dim bulb tester.
Measure the DC voltage between H760 C (positive meter lead) and E (negative meter lead). You should see it vary from about 0 to +1.2V DC as you rotate R763.
Also, check from H760 C (positive meter lead) to chassis (negative meter lead). You should see it vary from about 0 to +0.6V DC as you rotate R763.
Check from H760 E (positive meter lead) to chassis (negative meter lead). You should see it vary from about 0 to -0.6V DC as you rotate R763.
Ecluser's excellent description about bias on the 2270 is relevant as the 2245 is just a lower powered version of the 2270.

Tom
Tom,
I got no variation on R763, read 1.6V constantly while rotating R763, resistors R776 R786 was hot
 
I checked H758/H759 Driver Transistors in circuit and they tested good. I didn't get a good reading on H756/H757 (.300V) when testing in diode mode in circuit.

Should I pull H756/H757 and H758/H759 and test?
H756/H757 checked good out of circuit, emitter resistors were pulled and read .30 ohm and .45 ohms. Supposed to be .20 ohms? I am pretty sure the bias diode H761 is correct direction as shown in photo, at least the one that was open was in this direction. Still haven't figured out whats cooking R776/R777 and R786/R788
 

Attachments

  • biasdiode.jpg
    biasdiode.jpg
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I know it is more work, but transistors should be pulled out of circuit and tested, especially when you have a problem like this. I had an in circuit tester, but it was not always correct.
 
I know it is more work, but transistors should be pulled out of circuit and tested, especially when you have a problem like this. I had an in circuit tester, but it was not always correct.
Thanks again for your help here everybody, finally sorted out.
 
the board had incorrect driver transistors, suspect outputs, and I incorrectly installed bias diode. Thank you Catrafter for helping on this board.
 
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