Hi All
I have a Marantz PM40SE repair as a project.
Tested with a DBT. The relay does not click on obviously!.
Right channel bias reads 5mv but left channel reads 35volts (approx).
Q763 - 2SA1265N and Q751- 2SD1508 have blown on the left.
Q761- 2SC3182N on the left is ok
General resistors look ok.
Q759 on left was getting hot even with DBT but tested OK.
Please can you give me modern equivalents for Q763 and Q761 (change in pairs if needed) and Q751. Any other advice would be appreciated.
Thanks
I have a Marantz PM40SE repair as a project.
Tested with a DBT. The relay does not click on obviously!.
Right channel bias reads 5mv but left channel reads 35volts (approx).
Q763 - 2SA1265N and Q751- 2SD1508 have blown on the left.
Q761- 2SC3182N on the left is ok
General resistors look ok.
Q759 on left was getting hot even with DBT but tested OK.
Please can you give me modern equivalents for Q763 and Q761 (change in pairs if needed) and Q751. Any other advice would be appreciated.
Thanks
A BD679 would probably work in place of the 2SD1508.
The output transistors could be replaced with NJW3281G/NJW1302G pairs.
Q759 should not get hot at idle. This would indicate another problem. It's possible the AN7062 has failed.
The output transistors could be replaced with NJW3281G/NJW1302G pairs.
Q759 should not get hot at idle. This would indicate another problem. It's possible the AN7062 has failed.
Thanks Jaycee - you have helped me before when I was fixing a rotel RB970BX
I have a spare AN7062. How should I proceed?
Put the replacement transistors in > test with DBT > if relay does not click on> swap AN7062?
Thanks
I have a spare AN7062. How should I proceed?
Put the replacement transistors in > test with DBT > if relay does not click on> swap AN7062?
Thanks
I would do some voltage tests first against the values shown on the schematic (available on Hifi Engine), for both channels.
If you have a failed output transistor and the bias device also failed, I would be suspecting the driver and predriver transistors in that channel too
If you have a failed output transistor and the bias device also failed, I would be suspecting the driver and predriver transistors in that channel too
"Q759 on left was getting hot even with DBT but tested OK."
Can driver / pre drivers get hot if amp run with power transistors removed?
Removed and tested transistors on blown channel. All power / driver / pre driver transistors OK except for previously blown ones. All fusible resistors OK.
Amp relay powers on with blown transistors removed. Right channel good with speaker DC at 16mv.
Marantz PM-66SE KI - bin or repair?
Using above thread as well as pm66se is similar to pm40se.
Can driver / pre drivers get hot if amp run with power transistors removed?
Removed and tested transistors on blown channel. All power / driver / pre driver transistors OK except for previously blown ones. All fusible resistors OK.
Amp relay powers on with blown transistors removed. Right channel good with speaker DC at 16mv.
Marantz PM-66SE KI - bin or repair?
Using above thread as well as pm66se is similar to pm40se.
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R763 getting hot and smoking after re fitting transistors minus power transistors and driver transistor. Any ideas?
Help! This looks harder than I thought!
Right channel on its own is fine. R763 gets smokey after I refitted transistors Q757/9 but the transistors tested OK.
Right channel on its own is fine. R763 gets smokey after I refitted transistors Q757/9 but the transistors tested OK.
Almost Fixed
Following the PM66 thread above. I changed the main output transistors and the single driver transistor on the heat sink for the blown left channel. Used new backing pads.
Powers up using DBT and relay clicks on. DC on both channels at speaker terminals is around 15mv.
BUT
Bias on repaired channel is 0.5v and cannot get it down by much using the bias adjust. The large white bias resistor is open although it was OK when I tested it before. I swapped it with the good one on the other side and I could adjust bias within normal parameters.
Ordered replacement resistors as per PM66 thread and transistors for the other channel. Did not want to waste cash buying transistors if I could not get it working.
R763 no longer smoking and still around 305 ohms but ordered replacements (330ohms)
Tested with headphones briefly and sound on both channels.
Hopefully this should work. We shall see!
Following the PM66 thread above. I changed the main output transistors and the single driver transistor on the heat sink for the blown left channel. Used new backing pads.
Powers up using DBT and relay clicks on. DC on both channels at speaker terminals is around 15mv.
BUT
Bias on repaired channel is 0.5v and cannot get it down by much using the bias adjust. The large white bias resistor is open although it was OK when I tested it before. I swapped it with the good one on the other side and I could adjust bias within normal parameters.
Ordered replacement resistors as per PM66 thread and transistors for the other channel. Did not want to waste cash buying transistors if I could not get it working.
R763 no longer smoking and still around 305 ohms but ordered replacements (330ohms)
Tested with headphones briefly and sound on both channels.
Hopefully this should work. We shall see!
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OK fitted replacement resistors (linked 2 resistors together for bias adjust) and all working. DC around 15mv at speaker terminals.
There was a slight drop in sound for a few seconds on the repaired channel but seems ok now - could have been a loose phono plug.
Will repalce main transistors and drivers on other channel as well when I have time. Will also recheck soldering and look for cold joints.
There was a slight drop in sound for a few seconds on the repaired channel but seems ok now - could have been a loose phono plug.
Will repalce main transistors and drivers on other channel as well when I have time. Will also recheck soldering and look for cold joints.
Do I have to replace power transistors on "good" Channel?
Repaired blown channel but..... do I have to replace power transistors on "good" Channel? I have the replacements but can't be bothered to change them right now. Am I ok running it for now?
The amp sounds fine and no difference between the channels but the repaired channel gets slightly warmer probably because it has larger replacement transistors. Each pair of transistors has its own heat sink. The amp seems to run pretty cool anyway.
Just curious.
Repaired blown channel but..... do I have to replace power transistors on "good" Channel? I have the replacements but can't be bothered to change them right now. Am I ok running it for now?
The amp sounds fine and no difference between the channels but the repaired channel gets slightly warmer probably because it has larger replacement transistors. Each pair of transistors has its own heat sink. The amp seems to run pretty cool anyway.
Just curious.
You don't need replace the other transistors, also any difference in temperature is most likely caused by slight differences in bias current. Check, set and forget.
Thanks Mooly - used your step by step on the PM66 thread to do this repair. Will leave it as it is for now and perhpas put the new transistors in on a wet weekend.
Hi ssi,
from technical aspect, i wouldn't change the working channel.
From the sonic aspect i would do the same changes in the working channel, there are sonic differences, if you not use the same semiconductors from the same supplier. Actual examples, the original Hitachi/Renesas PowerMosfet 2SK1058/2SJ162 and the equivalent Parts from Exicon. Another example from past was the NE5534 from Philips compared with the same from Signetics.
But keep in mind "Never change a running system"
BR
Günni
from technical aspect, i wouldn't change the working channel.
From the sonic aspect i would do the same changes in the working channel, there are sonic differences, if you not use the same semiconductors from the same supplier. Actual examples, the original Hitachi/Renesas PowerMosfet 2SK1058/2SJ162 and the equivalent Parts from Exicon. Another example from past was the NE5534 from Philips compared with the same from Signetics.
But keep in mind "Never change a running system"
BR
Günni
Thanks
Would that also apply for swapped resistors and driver transistors to ensure that both sides are properly matched from a sonic perspective? I have all the required components.
Would that also apply for swapped resistors and driver transistors to ensure that both sides are properly matched from a sonic perspective? I have all the required components.
Volume pots and loudness - curious?
Driving a pair of not very sensitive "test" Wharfedale Diamond II's from 1987with volume control running at 1/3 vol in the garage:
Marantz P40SE- 50wpc : not very loud
Technics SUV4x- 65wpc: very loud
Rotel 921 / 931- 25 & 30wpc: quite loud
Sony TA2650- 43wpc: very loud.
Why the differences? Is it the way the volume gain is set up?
Driving a pair of not very sensitive "test" Wharfedale Diamond II's from 1987with volume control running at 1/3 vol in the garage:
Marantz P40SE- 50wpc : not very loud
Technics SUV4x- 65wpc: very loud
Rotel 921 / 931- 25 & 30wpc: quite loud
Sony TA2650- 43wpc: very loud.
Why the differences? Is it the way the volume gain is set up?
Matching replaced parts in left vs right has little scientific validity, only the satisfaction of knowing they are the same.
For the volume control question you could try setting each amp at a third volume, disconnect the speakers and then measure the output voltage of the amp. Use a 400Hz to 1kHz test tone. I'm sure you will find a big difference in apparent output levels.
For the volume control question you could try setting each amp at a third volume, disconnect the speakers and then measure the output voltage of the amp. Use a 400Hz to 1kHz test tone. I'm sure you will find a big difference in apparent output levels.
I bought a PM40SE in supposedly working condition, however, after a full recap I discovered it had an intermittent fault. The right channel sometimes failed to come on from a cold start up. After a few seconds it would wake up and be fine thereafter.
Having done a general check around for obvious failed components to no avail, I replaced the four main power transistors. When this proved to be fruitless I moved on the the two Darlington D1508 transistors. Following advice on the thread I tried a pair of BD679, however, the dim bulb test showed an issue immediately.
I put the originals back in and lo and behold, the problem now appeared on the left. I could claim I'd put them back the other way around on purpose, but it was just a fluke, but either way it was proof I was on the right track! I bought two original replacement 2SD1508 from a UK supplier, at something of a premium.
To complete the job I followed the procedure in the service manual and set the bias voltage to 14mV each side and checked the DC offset at the speaker posts was okay. It came in at 10mV and 11mV for the two channels, so very happy.
On testing, it's clear that neither transistor was working to its full spec. The sound is much better. More authority, better bass definition, very sweet and open midrange. Overall an excellent result. With its new DNM and Elna Silmic II caps it's better than when it came from the factory. I think it's new owner is going to be delighted.
Having done a general check around for obvious failed components to no avail, I replaced the four main power transistors. When this proved to be fruitless I moved on the the two Darlington D1508 transistors. Following advice on the thread I tried a pair of BD679, however, the dim bulb test showed an issue immediately.
I put the originals back in and lo and behold, the problem now appeared on the left. I could claim I'd put them back the other way around on purpose, but it was just a fluke, but either way it was proof I was on the right track! I bought two original replacement 2SD1508 from a UK supplier, at something of a premium.
To complete the job I followed the procedure in the service manual and set the bias voltage to 14mV each side and checked the DC offset at the speaker posts was okay. It came in at 10mV and 11mV for the two channels, so very happy.
On testing, it's clear that neither transistor was working to its full spec. The sound is much better. More authority, better bass definition, very sweet and open midrange. Overall an excellent result. With its new DNM and Elna Silmic II caps it's better than when it came from the factory. I think it's new owner is going to be delighted.
Well done fixing your amp 
Some of the old 2SD and 2SB type devices (generally) can suffer weird failure modes.
Excellent 🙂
Some of the old 2SD and 2SB type devices (generally) can suffer weird failure modes.Excellent 🙂