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Marantz 2235B popping

Traverso

Traverso

Active Member
Hello,

I acquired a superb 2235B popping from time to time, it can be silent for hours.
In between everything is normal and it is singing nicely.
Although this popping is not continuous this should not be and I would like to correct this but how?

The following has be done so far: output transistors checking, cleaning the pots and switches, bias and offset adjustments (the bias trimmers changed) after electrolytics changed on P800 Power supply board as well as the ones on PE01 preamp and P700 amplifier boards.

What should be next to correct this issue , any idea kindly advise.

Thanks a lot


Alain
 
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Is the popping in both channels? If so, it might be a power supply issue. Otherwise, if you have another amp you can separate the amp/preamp sections by connecting the 2235B preamp output to the spare amp and see if the popping stops or continues. If it stops then the issue is in the main amps. If not can be power supply or preamp. It might be a transistor somewhere starting to break down.
 
The popping very loud is on the right channel only and is coming whatever the selected input.
Power supply checked ok, I changed the two big filtering capacitors C001 and C002.

I will open the link preamp/amp and connect to an other amp. but I suspect the right channel P700 amp section.
In between, how to identify a break down transistor this is the main issue. Is there some value I could measure Vbe or else or do I have to replace all of them one after one?
 
There was a thread with a list of transistors to replace that fixed my problem (which was also popping in the right channel, just on a 2270). I'll see if I can find a link to it!
 
I can't for the life of me find the original thread, BUT. What did the trick for me was replacing the transistors on board P400 (tone amplifier). I'm sure that some Marantz solid state experts will chime in, but there are a number of threads on here that list the best replacement component choices.
 
My 2245 had pops and noise until I replaced the transistors on the tone board. I'm going to back to my 2226B and 2230 and do the same on them. My 2285B was done so it's fine :) What I can't tell you is if the noise if from the "creeping black death" that crawls up the legs of the transistors over time or just junk transistors. But they are noisy.

Here is the tone board with two replaced and two left to do ( these are the metal caps) for that channel.

IMG_7472.jpg
 
After some time, the pop is coming again very loud on right channel only and the volume control was done to zero
Is it enough to conclude this is coming from the P 700 amp section?
 
There was a notorious transistor thread (read that as noisy)
I'd look carefully at your unit.
You can split amp preamp and narrow it to which section.
Unless it's a real PITA change them all (the usual suspects).
Do it a board at a time and recheck. Let it warm up (it seems thermally related
What pinouts carefully. Some modern subs have different lead orientation .
 
OK , cannot find this thread
I am ready to change all the possible noisy transistors if I know which ones, there are not so many
Which ones are usually "noisy" or should I suspect all?

Thanks

20181126_190034.jpg
 
It almost sounds like it's coming from the main amp (but confrim). While looking at the transistors, check the diodes they are also prone to failure.
 
This is correct, it looks like coming from right channel P700 amp section
Change all transistors there?
I would like to know the one's prone to be noisy, I am missing this info
 
My first 'guess' would be bad differential pair transistors in the offending channel, either H701 and H703 or H702 and H704.
An Hfe matched pair of KSA992F should work fine, they are the ones in the picture bound together with white heat shrink tubing. A smear of thermal compound on the 'flats' is a good idea.

Tom
KG2235B 019.jpg
 
Some feedback

When I was on the way to make the recommended change H702 and 704 I discovered a R731: 33 Ohms a bit burned and suddenly no sound at all, the protection relay stopped the link to the loudspeakers
After checking one after one the transistors of this right channel, I found H 706 dead the rest including diodes were ok
This H706 was strangely a 2N1711, I replaced with BC130

I finally replaced the differential pair H702 and 704 (Hfe being 400 and 402) as suggested by Tom
The already in place were not apparently bad but with a gap of 100 between Hfe

Now the 2235B is singing again for a while, hopefully no poping sound will come again

Thank you Tom and all of you for your support

Alain
 
Some more
The offset on the right channel is quite high 200mV and fluctuating
I believe I should change the H706 I put there a BC140-16 not BC130 as already stated by a more suitable replacement such as SC2316Y

Also, I hava a question,if the output transistors are not Hfe paired will it have a big influence on the offset?
 
OK noted

Now that the popping issue is solved by changing the differential input pair and the 2N1711 H706 on right channel of P700, I have two new issues on the same P700 right channel:

- the offset is 80mV cannot be adjusted lower
- the bias remains at some fraction of mV
this was not before so what should I do and or where to look at?

I believed H721 could have suffered and I changed it, the diodes as well changed to 1N4148 except H005 I do not know what to replace with if necessary

Please advise

Alain
 
What transistors did you use to replace the differential pair with? I usually use KSA992 for those.
I have not seen a '2N' transistor in a 2235B before. They are usually '2S' Japanese types. (most TO-92 Japanese transistors have the collector in the middle).
I have no experience with BC transistors.

According to my crappy, error ridden service documentation, H721 is a 2SC735 type, H715 should be a 17.7 V zener diode. H716, H117,729 and 730 are usually failure prone MV-13 types and each one should be replaced by TWO 1N4148 diodes in series.
H005 is an SV-02 bias diode, Vf is about 1.2V, so it probably contains two silicon diodes in series, these rarely fail unless you break a lead or damage them somehow.

YMMV
Tom
 
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