Marantz 2265 P700 Amp Board issue

mpr2000

Active Member
I'm working on a 2265 that's a little rough - internally. Looks like several people have been inside over the years. I've gone through it and swapped out all the caps on the P800 PS board and the P700 Amp boards. The PS board had a bad 2SC945 (HB03) and an open resistor.

The amp board outputs were bad on one side along with a few resistors. All transistors were pulled and tested - and tested okay. Emitter resistors were replaced, multi-turn pots installed, etc. Outputs on both sides have been replaced with MJ21193/MJ21194's.

Here's my issue. On one channel, I am getting 28vdc at J713 below (output). Not good. The other channel is fine, and if I pull the wire at J713 on the bad channel the protection relay works, etc. J706 is 35vdc in to the board. All wiring has been triple checked, I pulled the outputs and retested, then reinstalled and checked for mounting shorts. All diodes were tested (in place) on the board. Replacement cap polarities verified, etc. I'm just starting to work my way back from J706, but wanted to see if anyone had any thoughts.

marantz-P700-P800.jpg


One board "rebuilt" and as it went back in the 2265:
IMG_0668.jpeg
 
I had a 2265 with this same exact problem.
I had to look through my notes as this was back in July of 2011!
It was a bad Q705 transistor that was leaky.
It was a 2sc1885 ,I replaced it with a ksc2310ybu and all was fine.

Btw- you should have replaced the differential input pairs with HFE matched and thermally bonded new transistors.
The old ones can wreak havoc with adjusting dc offset.
On my board the printing for Q701/702 was reversed.

Bob
 
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Bob - thank you. I did a quick test of the transistors, but not leakage... lesson learned if that is the issue.

I will check in to you suggestions right away.

Thanks again - Mark
 
Progress. Q705 was very leaky. I had an ECG399 in my parts bin and dropped that in. Fired it up and almost there...

Now I am good for about 1 min, then DC Offset climbs and finally triggers the protection relay. During that 1 minute, offset seems unadjustable. So now on to the differential input pairs as mentioned...

For Q701 and Q702, these are 2SA722's. Any recommendation for current replacements?

I do have these neat transistor sinks - think that is appropriate to thermally couple the input pair (Q701 & 702)?

thermal.jpeg
 
That's what I'll do. I did find another pair - don't remember the PN, but matched them and got things working. I have -200mv dc offset that I can't make more positive, but I'm getting closer. It plays very well on test speakers and the idle current is stable.

The originals in this channel test at 206 and 362 beta...
 
For future reference just push the two input pair together face to face with a little heatsink grease/compound between them and then put a piece of 3/8" heatshrink to bond them together.
Your setup is cute but kinda defeats the purpose of immediate heat transfer between them.:yes:
 
It's not too late, and I will do that. As found, they were close but not touching. Was this as designed, or were they meant to be thermally coupled physically?
 
Most if not all of the 2265/2270/2275/2285/2325/2330 and 2330b units I have worked on came with heatshrink bonded diff pairs as oem.

It is usually a tan colored heatshrink.

Can't say for certain on the smaller Marantz 22xx units.
 
Question : Did you break it or was it broke ? I cannot stress enough that you have to have the thing working before starting a restore. Otherwise you add too many variables. I need to know this.

Next : Disconnect the collectors of the output transistors and see what happens to the voltages.

Question : Is it getting hot ?
 
Most if not all of the 2265/2270/2275/2285/2325/2330 and 2330b units I have worked on came with heatshrink bonded diff pairs as oem.

It is usually a tan colored heatshrink.

Can't say for certain on the smaller Marantz 22xx units.

This one did have a lot of previous work done by someone in the past. And as handed to me, they were not bonded - but I definitely will bond them. The build date on this 2265 is Jan-1977 in case that makes a difference with regards to updates.
 
Success. Closely matching the differential pair and bonding them did the trick. I replaced both sides and all is rock solid. Thanks for the help!
 
Quick summary notes on my 'restoration' to date. This 2265 was a bit of a mess with lots of work done in the past and missing regulated 35v and a bad left channel. I got through the troubleshooting thanks to the folks above. Along the way I also upgraded various components as part of maintenance (caps, oot parts, etc).

I removed the power amp boards completely (P700) for ease of work.

Note: I used a rubberized glue to stabilize the leads on the thermal sensors (SU-3A) on each heat-sink. These are old with brittle wiring and hard to find, so stabilizing the wires helps prevent an inevitable break right at the sensor.
thermal2.jpg


Another note - having a good solder removal tool is important. I invested in an Aoyue 474A++ desoldering station and it makes short, safe work of removing components - and not lifting traces, etc.

- I replaced all caps on the main amp (P700), Power supply (P800) and the tone board (PE01) with Nichicon FG electrolytics.

- Main caps were replaced with 10,000uf 100v (had on hand), low ESR caps.

- Bias and idle current pots were replaced with multi-turn pots.

- On the P800 board, I replaced R807 with a 7 watt WW resistor, replaced the relay with an Omron MY2-02 and added a heatsink to H801.


Replacement semiconductor list for P700 board (valid as of Feb 2015):

Q701, Q702 - 2SA722 - Replaced with KSA992 (beta matched and thermally bonded)

Q705 - 2SC1885 - Replaced with 2SC2705

Q706 - 2SC1568 - Replaced with 2SC568 (BDENT)

Q707 - 2SD415 - Replaced with MJR243GOS-ND

Q708 - 2SB549 - Replaced with 2SB549 (BDENT)

Q709 - 2SC945 - Replaced with 2SB945 (BDENT)

Q710 - 2SA733 - Replaced with 2SA733 (BDENT)

Q703, Q704 - Replaced with 1N4148 (two in series each)

Q717, Q718 - Replaced with 1N4005

Q711 through Q716 - Replaced with 1N4148

H001-H004 (outputs) - were replaced with MJ21193G/MJ21194G

- Emitter resistors were replaced


That's roughly it currently. Next are the lamps, then cosmetics.
 
Thanks. They are the stv-3h's and I forgot to mention I myself broke one of the leads at the body. After some scraping I was able to solder a single strand of wire to the nub and saved the diode. That's when I decided to anchor the leads. The original wire is actually only covered by a sleeve, so even after gluing down the leads you still have to be careful not to pull on the wire at the other end.
 
This one did have a lot of previous work done by someone in the past. And as handed to me, they were not bonded - but I definitely will bond them. The build date on this 2265 is Jan-1977 in case that makes a difference with regards to updates.
How do you find the build date?
 
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