Hi, there I recently picked up a working Marantz 4400 with a non-working oscilloscope. I checked the power supply board which had seemingly had a recap at some point in the past (rubycon, nichicon caps). I checked the connector too which some people have said has arching from the plastic and found nothing. I also desoldered the connector (J813) to see if there was any burnt/carbonized plastic but there is again nothing there. I also checked FP02 as I have heard some people say that this specific fuse blows but on mine it is fine and does not glow. I checked it with a multimeter just to be sure and its still nominal. What are my other options here? Is the scope itself dead or is there something I am missing?
Help with Marantz 4400 scope
- Thread starter Mecrookie
- Start date
Register to hide this ad
Hi thanks for the comment. I don't see any soft glowing light from the tube in the receiver when I power it on. Should there be?
By filament supply do you mean the fuses near the power supply or the actual tube itself? Also where exactly are the brightness and focus controls on the board?
Oh ok I turned out the lights in the room and yes I see a faint flowing filament at the back of the tube. How should I test this?
As you said, I also checked pins 3 and 4, and I am getting 25-150V to them instead of the 50-250v as you said was regular, does this mean there is a fault either on the power supply or the oscilloscope circuit itself?
That's likely a good test - the visual glow. But you'd want to measure the two filament terminals directly, keeping in mind it's an AC voltage that rides on many dc volts with respect to the chassis.
How do I go about testing the filaments directly?
If you don't have the service manual, here is a link to one:
http://akdatabase.com/AKview/albums/userpics/10004/Marantz 4400 Service.pdf
The schematic is separate:
http://akdatabase.com/AKview/displayimage.php?album=1&pos=161
The heater pins on the tube are 1 and 14 but are inaccessible. Measure them at J910 and at J917, with one probe on each pin. The polarity of the probes doesn't matter for this measurement. I highly suggest making the connections with the power off and then hit the juice. I bet it's fine.
http://akdatabase.com/AKview/albums/userpics/10004/Marantz 4400 Service.pdf
The schematic is separate:
http://akdatabase.com/AKview/displayimage.php?album=1&pos=161
The heater pins on the tube are 1 and 14 but are inaccessible. Measure them at J910 and at J917, with one probe on each pin. The polarity of the probes doesn't matter for this measurement. I highly suggest making the connections with the power off and then hit the juice. I bet it's fine.
Hey thanks for the reply. I just tested those two pins as stated and am getting 6.5V AC through it.
dr*audio
Fish fingers and custard!
It's low, half what it should be. Is the unit set for your AC mains voltage? If it's a 220V unit and you have 120V mains, that could be the problem.
I believe it is set for 120V mains. I am located in Canada and the unit runs fine on the outlet.
dr*audio
Fish fingers and custard!
Ok, just checking. This indicates a problem with the 215V supply. Check FP-03 and FP-04, H802, H803. Verify the voltages on the cathodes of H802, H803, output side of R801, Anode of H801.
Last edited:
hmm ok thank you for letting me know. Do you know where to look by chance on the psu? Or should I go ahead for a psu cap kit?
Ah ok I will do these and get back to you
dr*audio
Fish fingers and custard!
I edited my post above with instructions.
Ah ok do you by chance have a cap kit list I can follow?
Sorry, I sure don't. Give me a list of the values of the caps - what's printed on them. I'll cobble up a list. BTW, great kits can be gotten on eBay from seller peacelovemusic. Great support too and an AK member @EastPoint.