• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Marantz 4300 no rear channels

goldswimmerb

goldswimmerb

Failed out of engineering, but look at me now!
Subscriber
Hey guys, so I recently got a Marantz 4300 to fix up. I havent worked on a quad unit before so any advice is appreciated.
6izjKS0.jpg

As you can see the front is very very clean, but the tuning needle is broken off as well. From the outside, you wouldn't think much was wrong but the inside is telling me a different story.
1. The filter Caps dont match for some reason
sw7wyHj.jpg

2. Theres a random PSU cap just chilling unsecured
BHOIGDI.jpg

It looks like someone tried to work on it in the past but didnt do a very good job. I spotted a few transistors that looked like they had been replaced and also noted that the amplifier board was missing its screws and looks coated in flux.

Qow8liQ.jpg
s34p02f.jpg

I know these have a few 2sc458s and a bunch of VD1212s, would one of those being bad in both channels cause null rear output? I tested bypassing the preamp as well.
Could it be a PSU issue? If so, why do the front channels work fine?
Both relays seem to engage normally and the front works on both main and remote.
Trying to think of why both rear channels could be out, seems unlikely that both would be blown.

So far all Ive done is clean all of the switches I could get to but that didnt change anything. I have a schematic but its fairly low resolution, so if anyone could weigh in that would be fantastic.

also, what is the layout for the channels on these boards? Im assuming one is FR and RR and the other is FL RL.

Thanks!
 
Register to hide this ad
Are all four jumpers inserted in the rear panel?


Left side board is LF and LR
Right side board is RF and RR

Both LF and LR circuits are strapped together (out of phase) for 100 watts when in 2 channel mode.
Same thing on right amp module.

As said before "Never change the back panel 2/4 knob when powered up'


Bob
 
Last edited:
wlhd1610 said:
Are all four jumpers inserted in the rear panel?

Bob
Click to expand...
Yes they are. Cleaned them too when I tested through the main in.
Both relays seem to operate normally too. Ill probably pull and test outputs just to be sure though.
 
It's odd,like you say ,that neither rear channel works.
Before you go pulling outputs,etc. I would dig into/check out both rear amp's signal in and out on the amp modules,2/4 channel selector switch.
Cross feed the front preamp outputs into the rear amp's in RCA jacks on the back .
That will show if it's the rear preamp or rear amp modules.
Make sure you're in 4 channel mode on front panel and rear panel.
 
wlhd1610 said:
It's odd,like you say ,that neither rear channel works.
Before you go pulling outputs,etc. I would dig into/check out both rear amp's signal in and out on the amp modules,2/4 channel selector switch.
Cross feed the front preamp outputs into the rear amp's in RCA jacks on the back .
That will show if it's the rear preamp or rear amp modules.
Make sure you're in 4 channel mode on front panel and rear panel.
Click to expand...

Thanks, will do when I get home later. To test I had the amp in 4 channel mode and ran my iPods line out right into the rear main amp inputs.
 
wlhd1610 said:
Are all four jumpers inserted in the rear panel?


Left side board is LF and LR
Right side board is RF and RR

Both LF and LR circuits are strapped together (out of phase) for 100 watts when in 2 channel mode.
Same thing on right amp module.

As said before "Never change the back panel 2/4 knob when powered up'


Bob
Click to expand...

Given the unknown history, it wouldn't surprise me if someone did that. Would that just destroy the rear amps or would it cause more issues down the line?
 
goldswimmerb said:
Given the unknown history, it wouldn't surprise me if someone did that. Would that just destroy the rear amps or would it cause more issues down the line?
Click to expand...

It's been preached and driven into our heads over the years to never switch the back panel switch while powered up saying it will destroy something internally.
I've never actually heard or read about the specific collateral damage that has occurred from doing so.

Bob
 
I was looking at the picture of the amp board. Are you sure you have continuity on all those tracings? it looks like there may be a break in one of the center traces??? Or a lift???

And it looks like someone was monkeying around with the red wire on the solder lug
 
airtime said:
I was looking at the picture of the amp board. Are you sure you have continuity on all those tracings? it looks like there may be a break in one of the center traces??? Or a lift???
Click to expand...

Will test tonight, thanks for the advice. My test leads broke last night (just old) and I have new ones arriving today :)
 
airtime said:
I was looking at the picture of the amp board. Are you sure you have continuity on all those tracings? it looks like there may be a break in one of the center traces??? Or a lift???

And it looks like someone was monkeying around with the red wire on the solder lug
Click to expand...

Tested continuity last night (didn't have too much time or I would have done more). The amps boards traces tested fine for continuity. Going to check power supply Vout next when I get a chance in a few days.
 
Richs_Trains said:
Just a novice here, but I have had trouble with quad units that have a remote/local switch on the back. Make sure that the switch is clean and operates correctly. Good luck, Rich
Click to expand...

I'm assuming that switch is for the remote plug in? Seems like if it bypassed the controls through that remote that could cause all kinds of weird stuff.
 
Alright, so, here's what I've narrowed it down to, I crossed the rear preouts to the front main in and those worked just fine. I then crossed the front pre outs to the rear main in and got no sound.

I tested the pins on the bottom of the amp board slots for voltages and they looked okay (although it's really hard to tell what's what on the low res schematic).

So what's between the main amps and the rear speaker connectors that could be dead?
 
goldswimmerb said:
Hey guys, so I recently got a Marantz 4300 to fix up. I havent worked on a quad unit before so any advice is appreciated.
6izjKS0.jpg

As you can see the front is very very clean, but the tuning needle is broken off as well. From the outside, you wouldn't think much was wrong but the inside is telling me a different story.
1. The filter Caps dont match for some reason
sw7wyHj.jpg

2. Theres a random PSU cap just chilling unsecured
BHOIGDI.jpg

It looks like someone tried to work on it in the past but didnt do a very good job. I spotted a few transistors that looked like they had been replaced and also noted that the amplifier board was missing its screws and looks coated in flux.

Qow8liQ.jpg
s34p02f.jpg

I know these have a few 2sc458s and a bunch of VD1212s, would one of those being bad in both channels cause null rear output? I tested bypassing the preamp as well.
Could it be a PSU issue? If so, why do the front channels work fine?
Both relays seem to engage normally and the front works on both main and remote.
Trying to think of why both rear channels could be out, seems unlikely that both would be blown.

So far all Ive done is clean all of the switches I could get to but that didnt change anything. I have a schematic but its fairly low resolution, so if anyone could weigh in that would be fantastic.

also, what is the layout for the channels on these boards? Im assuming one is FR and RR and the other is FL RL.

Thanks!
Click to expand...
is that the rear channels amp board ?
 
you could inject a signal at pins 1 and 43 amp board . or look for signal there whilst inputting a signal on rear panel .
 
You must log in or register to reply here.
Back
Top Bottom