The schematic I got from HF is showing a different board layout and the schematic is drastically different at the input stage. The amp on my bench, s/n 7687, has a darlington input configuration.
Where can I find the schematic for this version of the 240? All of the copies I found online are for a different version of the 240.
Where can I find the schematic for this version of the 240? All of the copies I found online are for a different version of the 240.
The serial number you quote is way above the manual/schematic on hi-fi engine which says -quote its applicable for the Marantz 240 above sn-2500.
I think your problem is that Philips sold off Marantz in 2001 to Marantz Japan Inc and in 2002 MJ & Denon merged to form D & M Holdings +others and in 2014 Marantz Professional was acquired by inMusic Brands .
In 2017 Sound United LLC acquires D&M Holdings .
Your website looks quite impressive --to me- no flashy color photos just photos of you test equipment and prices etc honestly put .
What you have might be termed "badge labeling " if its under a later company --keeping the original label but made by others.
That would tie in with hi-fi engine,s version just mentioning "applicable to versions above sn-2500 "
I think your problem is that Philips sold off Marantz in 2001 to Marantz Japan Inc and in 2002 MJ & Denon merged to form D & M Holdings +others and in 2014 Marantz Professional was acquired by inMusic Brands .
In 2017 Sound United LLC acquires D&M Holdings .
Your website looks quite impressive --to me- no flashy color photos just photos of you test equipment and prices etc honestly put .
What you have might be termed "badge labeling " if its under a later company --keeping the original label but made by others.
That would tie in with hi-fi engine,s version just mentioning "applicable to versions above sn-2500 "
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The unit in question appears to have been manufactured in the early 1970s. Apparently there has been a revision to the design.
This was brought to us by a customer who'd sent it to a shop in Chicago to be recapped. Customer said it worked for 30 minutes then the right channel made some fizzing/popping sounds and it quit working. Customer sent it back to the shop. The shop claimed they tried but could not fix it.
When we got it, the right channel was pegged the pos rail. A check of all transistors revealed none shorted. I started looking for parts installed wrong and found one transistor that was backwards. Corrected that but still didn't solve problem.
Eventually I started pulling transistors and testing them on curve tracer. That's when I found the current limit transistor on the positive rail was open. I replaced that and brought the amp up slowly on variac. The DC output balanced, so I was optimistic that I'd found the problem. Ramped it up to the full line and then smoke. The output transistors had shorted. Upon investigation, it turned out that someone had replaced all the outputs and swapped P and N junctions! So rebuilt output stage with proper devices and was able to get the amp working.
During testing, I increased the input signal to measure the power, and at about 120 wpc, I heard the relay open. The right channel is pegged to the pos rail again. No shorted transistors. No burned or open resistors. But tracking this is turning into a real hassle because the documentation differs from the board layout and circuit.
This was brought to us by a customer who'd sent it to a shop in Chicago to be recapped. Customer said it worked for 30 minutes then the right channel made some fizzing/popping sounds and it quit working. Customer sent it back to the shop. The shop claimed they tried but could not fix it.
When we got it, the right channel was pegged the pos rail. A check of all transistors revealed none shorted. I started looking for parts installed wrong and found one transistor that was backwards. Corrected that but still didn't solve problem.
Eventually I started pulling transistors and testing them on curve tracer. That's when I found the current limit transistor on the positive rail was open. I replaced that and brought the amp up slowly on variac. The DC output balanced, so I was optimistic that I'd found the problem. Ramped it up to the full line and then smoke. The output transistors had shorted. Upon investigation, it turned out that someone had replaced all the outputs and swapped P and N junctions! So rebuilt output stage with proper devices and was able to get the amp working.
During testing, I increased the input signal to measure the power, and at about 120 wpc, I heard the relay open. The right channel is pegged to the pos rail again. No shorted transistors. No burned or open resistors. But tracking this is turning into a real hassle because the documentation differs from the board layout and circuit.
Marantz 240/250
This is why we replace the amplifier drive boards. The Marantz circuit is totally unstable and tough to get stable under all conditions.
The CFP design has only one advantage over emitter followers and that is that the B-E junctions of the output devices are not in the thermal loop.
Zed Audio
This is why we replace the amplifier drive boards. The Marantz circuit is totally unstable and tough to get stable under all conditions.
The CFP design has only one advantage over emitter followers and that is that the B-E junctions of the output devices are not in the thermal loop.
Zed Audio
As you say "early 1970,s " there appears to be a separate "Black " FACTORY model first sold -1974--last year -1977 .
It has two versions -special option #1 - RA1 Rack Adapter ,
special option #2-LT70 Line Transformer .
It quotes a wooden case =WC-2
Blue Face =yes .
matching preamp -3300.
matching integrated amplifier 4100.
RMS power/channel =125 @8 ohms .
THD 0.1 %
Input impedance =100 Kohms .
Sensitivity for full output =1.5 Volts .
FR+0/-1.5dB to 100KHz
Sound like it ?
It has two versions -special option #1 - RA1 Rack Adapter ,
special option #2-LT70 Line Transformer .
It quotes a wooden case =WC-2
Blue Face =yes .
matching preamp -3300.
matching integrated amplifier 4100.
RMS power/channel =125 @8 ohms .
THD 0.1 %
Input impedance =100 Kohms .
Sensitivity for full output =1.5 Volts .
FR+0/-1.5dB to 100KHz
Sound like it ?
This particular unit just has an inset front panel without the meters but with the Marantz logo instead. The service manual for the earlier serial numbers quotes 120 wpc.
But the difference in this unit starts at the input stage--two transistors in a darlington configuration. From that point forward, there are several differences from the service manual version, even the PCB layout is different.
I'd prefer to solve it and make it work normally again rather than take the easy way out and find a new driver PCB. I just need a proper schematic and layout so I can find my way around without having to spend a dozen hours tracing everything by hand and drawing my own schematic.
But the difference in this unit starts at the input stage--two transistors in a darlington configuration. From that point forward, there are several differences from the service manual version, even the PCB layout is different.
I'd prefer to solve it and make it work normally again rather than take the easy way out and find a new driver PCB. I just need a proper schematic and layout so I can find my way around without having to spend a dozen hours tracing everything by hand and drawing my own schematic.