Marantz 2325 Dolby Troubleshooting

[MBuras]

Not really sure where to go next on this one and hoping the experts can help point me in the right direction.

This is my 2325 receiver that was completely rebuilt last year HERE. I've had it out of rotation for a while and decided to get it back on the bench to check a few things. I found that in normal modes everything works fine and it sound great, but feeding AUX signal and flipping to Dolby PLAY almost all the volume goes to the right speaker. This is also true of Dolby FM while in FM mode. I don't recall this being broken when I restored it but I also don't recall specifically checking it either. Sorry.

I've already done the easy to think of things. Completely disassembled and cleaned every push button switch on the unit. They were shiny when i took the plunger out but what the heck. Pots all got a bath again including the small Dolby (play and record) pots under the meters. Also pulled the Dolby board and rechecked previous recap for bad solder joints, etc. Nothing found and no difference on putting it all back together.

I have the schematic, DMM and O scope and anxious to learn. It's the Dolby function so I'm not overly concerned about it not working but I would like to have the unit in 100% working shape in case I try to sell it.

Thanks!!
Mike

 

[blhagstrom]

Didn't have time to read the whole thread but I didn't see a DOLBY rebuild post.
Did you rebuild it and what did you do?

 

[catrafter]

I'm sure you've checked all the push on connectors on the Dolby processor board, do the play level controls seem to work?

Tom

 

[MBuras]

Actually I haven't looked at that thread in a while either. I might not have pictured or described that part. Oops!

The dolby board received new caps all around. C601/C602 got films. C607-C614, C623/C624, C627/C628, C631/C632, C635/C636 and C641 got exact value electrolytic replacements. All solder joints looked good but have been touched up just to make sure.

 

[MBuras]

checked all the push on connectors on the Dolby processor board, do the play level controls seem to work?

I was sure one of those connectors was not fitted right (not a great connection system) but redid them very carefully and no change. Will do it again for peace of mind.
As far as the play level controls, only the right play pot affects volume (on the right side). Moving the left play pot doesn't do anything (left or right).

 

[MBuras]

Confirmed power at J806 is 20.2vdc (schematic hard to read but maybe says 18v) and continues through to J615 at same voltage. Not that I thought it was an overall board voltage problem.

I'm also trying to understand the schematic, specifically which side is left and right. It seems the board has a central ground plane with mirrored circuits on each side but how to tell which one serves the left and right? Thanks!

 

[Steven Tate]

I wonder if right channel-odd number and left channel-even numbers is a standard with Marantz. I know on that P700 board that just drove me crazy, the odd numbers were definitely right channel.

 

[MBuras]

That makes sense @Steven Tate . Thanks!

BTW...using mode switch to go Mono L+R during Dolby play equalizes both sides. Hmmm....

My biggest fear is a broken wire somewhere in that rats nest of a Dolby mode switch. I sure hope not.

 

[MBuras]

Also, does anyone have a 2325 (or 4270?) open or maybe previously documented the wire placements? I'm pretty sure I carefully documented each wire the first time I removed this board but would like to verify.

Here's what I have:

J601 = solid brown
J602 = white/red
J603 = white/orange
J604 = white/yellow
J605 = white/green
J606 = white/blue
J607 = white/purple
J608 = white/gray
J611 = solid white
J612 = white/black
J615 = solid red
J617 = solid black

Thanks!

 

[dr*audio]

There are internal adjustment pots on the Dolby board. Possibly one is dirty. Mark the position with a sharpie before you mess with them.

 

[MBuras]

There are internal adjustment pots on the Dolby board. Possibly one is dirty. Mark the position with a sharpie before you mess with them.

Good idea. I had thought about it and then talked myself out of it because the original white paint (is it paint or glue?) was still on the pots so I assumed they would be set properly. Never thought one could have developed corrosion or otherwise become dirty. Thanks!

 

[petehall347]

does L+R mix happen before or after Dolby board ?

 

[catrafter]

Also, does anyone have a 2325 (or 4270?) open or maybe previously documented the wire placements? I'm pretty sure I carefully documented each wire the first time I removed this board but would like to verify.

Here's what I have:

J601 = solid brown
J602 = white/red
J603 = white/orange
J604 = white/yellow
J605 = white/green
J606 = white/blue
J607 = white/purple
J608 = white/gray
J611 = solid white
J612 = white/black
J615 = solid red
J617 = solid black

Thanks!

Your wire colors/Jacks match my notes on the 2325.

IIRC, the quads use a different color scheme.

Tom

 

[MBuras]

does L+R mix happen before or after Dolby board ?

Great question and honest answer is I don't know. My knowledge of schematics is weak at best and these multi-position switches are very difficult to look at.
http://akdatabase.org/AKview/displayimage.php?album=1&pos=101

Looks like there are 3 positions of the S003 (Stereo Mode Switch) depicted on the schematic.

Label S003-1F shows 14vdc (actual 12.7vdc) from J807 to position 2 and jumpered to position 11. This then goes to S001 (Dolby Mode Switch) labeled S001-4R position 9. Also shows (inbound maybe?) from J307 on the MPX board to position 10 on the switch.

Label S003-2F appears to only have one connection depicted from the hi blend switch and beyond that from the balance slider going to position 7 on the switch.

Label S003-2R has few connections. Seems to tap off the S002 function switch going to position 9 and 11 on S003. Then it also repeats the connection listed above from the hi blend and balance slider to position 1 on S003 this time.

Of note is the hi blend switch is the only one that makes any sound difference when in Dolby mode. Only slightly but it is noticeable. No amount of manipulating any other switches makes any difference.

 

[rBuckner]

I have seen the Dolby board connections plugged in nearly backwards except the power connections of course. I have a sketch of both some 900 miles away but I saw that Tom confirmed your list. One time when I had a channel out on one it was one of the standup resistors bent over during the recap touching something. The leads have a coating or sleeve but somehow some portion was exposed. Hope you find it!

 

[Autobahn]

Weird.........
I have a 2325 on my bench right now waiting for parts to fix one of the amp boards. I just pulled the Dolby board up to check for you, and this is how the wires are plugged to the board:
J601 = white/red
J602 = solid brown
J603 = white/yellow
J604 = white/orange
J605 = white/blue
J606 = white/green
J607 = white/gray
J608 = white/purple
J611 = white/black
J612 = solid white
J615 = solid red
J617 = solid black

My board looks all original, wire ties and all. The 2325 I have is from 1975.

Mike
View attachment 779724
View attachment 779724

 

[MBuras]

Interesting your board has all the connection pairs reversed. I'll be interested to see those pictures. Thanks!!!

I have checked the whole board for touching components (top & bottom), bad solders, bad traces, etc. Just had the connector of J607 fall off (brittle stranded wire connection). I fixed that but no change. Also found the orange J304 wire was partially crushed under the MPX board (eventually travels to muting switch) but it's fine and made no difference. Inspected and touched up blending board but also not helpful.

 

[catrafter]

I have seen the Dolby board connections plugged in nearly backwards except the power connections of course. I have a sketch of both some 900 miles away but I saw that Tom confirmed your list. One time when I had a channel out on one it was one of the standup resistors bent over during the recap touching something. The leads have a coating or sleeve but somehow some portion was exposed. Hope you find it!

What Randy said...
Since the top half and bottom half of the P600 board are mirror images of each other, the wires on the odd and even J numbers, with the exception of J615 (power), and J617 (ground) can be swapped.

Tom

 

[MBuras]

Ok. Received a donor board in the mail today. Plugged it in according to my original wiring notations. No change in Dolby mode. Right channel still normal and left still whisper quiet. I then swapped wires as talked about above and and both sides are whisper quiet, or at least one. Hard to tell.

So can someone chime in if the following logic is sound?

It appears the signal is likely making it through the dolby board which means the issue is occurring after dolby output. YES/NO?

I'm pretty sure C641 is the inbound local DC filter. Does that then make J601 and J602 the left and right output for this circuit? YES/NO?

If so J601 goes to S002-4F (pin 7) and J602 goes to S002-2F (pin 7). S002 is the Dolby Mode switch. How do I read those multiple S002 versions and how to tell where it goes from there?

BTW...no matter how much I jiggle or manipulate the Dolby switch it does not change the result at all so I assume it's as clean as it will get but will clean again just to make sure.

 

[catrafter]

The moving parts of the switches are hard to figure out.
This is what I think I know: There is a legend on the left side of the schematic indicating the position of the switch as it is drawn on the schematic.
S0002 is the Dolby switch and this legend says it's drawn in the Dolby FM position. S002-2F (pin 7) should be the (F)ront side of the (2) second wafer back, 7th pin. Note that the five position switch has two wipers and 10 other contacts. I am not sure where pin 1 is.
If I had a 2325 in here, we could compare switch wiring. Unfortunately I finished the one I had here and sent it back to the owner last Monday. It may be months before I see another one.

Now my head hurts.
Tom