Marantz 18 receiver needs help

[bigdrums925]

The listen test is that both sides are distorted, and the right channel is weak.
Voltages to the power transistors are +/- 37V both channels.
Can anyone tell me how to upload & post the .pdf service manual to here already stored on my computer?
Or can I even do that in .pdf?
Here are the schematics:
hfe_marantz_model_18_schematics.pdf
The service manual is available at hifiengine as well as the service bulletin.


There was a post below this one that had a correct copy of the service manual but that post has since disappeared

[bob p]

Can anyone tell me how to upload & post the .pdf service manual to here already stored on my computer?
Or can I even do that in .pdf?

You can upload a PDF to the board as if you were positing a photograph. Click on the link above that looks like a framed photograph, follow the directions. You will probably need to have javascript running on your browser for things to work.

[olddawg]

Before you do anything clean the tape monitor switches.

[bigdrums925]

starting with the P/S I found a diode CR5 pn 35-1015 (Marantz number) bad
one end tied to C11 the 10uf 575v cap, the other end ties the red/grn secondary.
Can anyone hazard a guess at what the CR5 ratings need to be, better yet a common diode number as I have quite a few?
All the list says is its a rectifier diode. Would a 1N2070 work?
C11 & CR5 are only shown on pg 1 of the schematics posted in my opening post above

[Jazz P Bass]

It looks as if CR5 diode is for that goofy front panel meter (o scope).

That should have nothing to do with the amp sounding bad.

1N2070 is only a 400 volt part.
I would not use it.

[bigdrums925]

I found a parts request page on the Marantz pages so I see if they can enlighten me or provide the proper diode.
Funny that the o-scope seemed to be working properly though with the open diode.
Thanks for the response Jazz P Bass
I have now cleaned the tape switches and pots/switches, thanks olddawg

[Jazz P Bass]

1N4007 would work fine.

[bigdrums925]

I put in a 1N4005 which seems to be working ok
Tracing the distorted signals back to the point where they are no longer distorted, I find myself at the tone amp board
Shown on pg 8 of the schematics, I find -36 v is at -42 v. The 12 v supply is 14 v but past 15k resistor R804,
the +1 v on the schematic is really - 4.4 v
R804 does measure 15k so what else could make the +1v be negative?

[bigdrums925]

Anyone?

[nickb]

What's the voltage on the base of Q803?

[bigdrums925]

This project has been sitting for a few days but:

This time the -4.4 v past R804 measures +2.5

Base voltage on both Q803 & Q807 is about 1.1 v (where its supposed to be +.2)
Emitter on both is about 3.3 v (where it's supposed to be +.8)
Collector on both is about -30.5 v (where its supposed to be - 27)

Pic of the output on the tone board:


What does the scope pattern tell me?
I can see the negative swing is badly clipped but why?
The same pattern is shown on the other channel as well.

[nickb]

Don't worry about the off voltages in sheet 8. I see that the voltage depends critically of the gain of the two transistors as it relies on the bias current thru R810. What you have there is not unexpected.

We need to know the vertical scale in order to really interpret the scope shot - you might simply be giving t too big a signal. Since you have a scope probe the collector of Q802 and the base of Q801.

[bigdrums925]

The signal going into the aux inputs is 2v P-P and about 1.5v coming into the tone board
collector of Q802 shows an undistorted sine wave of 25v P-P
base of Q801 shows and undistorted sine wave of 1.5v P-P
I did roll off the gain just a bit and all tone controls are at center
But the vertical scale is 5v per division in sheet 11
Output negative swing distortion of the tone board is the same, just a little smaller gain on the scope now

[nickb]

The signal going into the aux inputs is 2v P-P and about 1.5v coming into the tone board
collector of Q802 shows an undistorted sine wave of 25v P-P
base of Q801 shows and undistorted sine wave of 1.5v P-P
I did roll off the gain just a bit and all tone controls are at center
But the vertical scale is 5v per division in sheet 11
Output negative swing distortion of the tone board is the same, just a little smaller gain on the scope now

You are driving it with about 10x the signal you should be. That is why it's clipped.

[bigdrums925]

OK you are right, but why would it not clip on the positive swing also?

This eliminated the distortion on the amp board but not at the speaker outputs.
I'll try for that tomorrow, Thank you