Accuphase P300 intermittent Fuzz in right channel

[Big_T]

Hello All,

I have been lurking this forum for a couple weeks devouring all info on the P300 and reading many excellent posts. I have learnt a lot but am still a novice. It is time for my question:

I have an Accuphase P300 that has been pulled out of 20 year retirement. I've been playing it for about 4 months. It does sound great, better than any amp I have every owned, but there is an intermittent static/fuzz in the right channel that has been getting worse lately.

I did the EchoWars DC offset Test and with the amp settled for 1hr

Left Channel: -26 mv
Right Channel: 24 mv

When using headphones to reference and no speakers hooked up and leads still on the speaker posts, once the static/fuzz presents the right channel drops about 5 mv to about 19 mv for about a second or two then comes back up to around 26 and the channel is clear. Then does this every minute or so.

• it is definitely the amp. I have changed interconnects, changed sound sources and changed from rear to front inputs. The problem persists.

• Problem is also present when using headphones also although I suspect it takes longer to present when using headphones with less resistance.

• The Static comes in after about 5 min of play and comes in for couple seconds every minute or so.

• Starting and stopping the music signal a few times will cure the problem and halt the static fuzz (lifting the needle a couple times or start stoping the dac). Before I would only have to do this once per listening session but it is getting more persistent now.

• It sounds almost like inner groove distortion but more pronounced and fuzzes / softly distorts the sound.

• it only fuzzes/static when music is being played, it is silent without any signal



Preexisting issues :

The other speaker outputs produce no sound. It could be because of faulty output selector. Changing from main to anything else does cut the main speaker output. I tried to deoxit the contacts to no effect.

The power output amount selector (%25,%50,%100) produces no effect.

When I first turned it on the first 6 times or so there was a heavy crackle from the left channel regardless of a signal and regardless of volume level that lasted about 10 seconds. It has not done that again in over 50 hours of playtime.



I know the right thing to do would be to take it to a professional and have a full cap and transistor overhaul (If I could find someone qualified in my city). This Amp certainly deserves it.

Yet..... with the current financial uncertainty, a lot of time on my hands recently I would like to take some careful measured steps if possible.

Would setting the DC offset and bias be a good place to start or does it sound more like dead transistors?


many thanks for any insight.

 

[reddish75]

Later versions of this amp has the 2SC1451 and 2SA809 transistors in it, which could cause your problems. Search the forum for p300 restorations and find the most commonly use subs.

 

[blhagstrom]

Later versions of this amp has the 2SC1451 and 2SA809 transistors in it, which could cause your problems. Search the forum for p300 restorations and find the most commonly use subs.

Agreed.

 

[Big_T]

Thank you guys I will order them and update this post once the new transistors are installed. I came across quite a few variations and suggestions for substitutes but I will probably settle on the 2sc2911 & 2sa1209 from sanyo (circa EW 2014 recommendation) as unless anyone has any last suggestions.

 

[blhagstrom]

I think it was the 2SC1451 gone noisy in my amp here and I dropped in KSC3503.
Working fine.

 

[reddish75]

KSC3503 and its complementary mate check the datasheet as the part number escapes me at the moment. Order from Mouser/Digikey. The parts you mentioned are NLA.

 

[Big_T]

Thanks Guys. It looks like A1381/C3503 for the transistor replacements. I have them sourced from mouser and ready to go but.... when I double checked to see if i did indeed have the later model of amp with offending transistors I noticed the main capacitors have left rusty like residue which assume is a leak. This seems like a mandatory replacement so I'm going down this path also. It will be a while but I will update with progress.

 

[reddish75]

Thanks Guys. It looks like A1381/C3503 for the transistor replacements. I have them sourced from mouser and ready to go but.... when I double checked to see if i did indeed have the later model of amp with offending transistors I noticed the main capacitors have left rusty like residue which assume is a leak. This seems like a mandatory replacement so I'm going down this path also. It will be a while but I will update with progress.

Sounds like a plan, look up the big Nichicon gold tune cap, check diameter before ordering any.

 

[Big_T]

Update:

It took a little longer than expected as I needed a real clear break in my schedule to go about the repairs in a very slow and careful way. Again thank you for the advise!!

I have replace the 6 transistors (A1381/C3503) on each board. It has cleared the problem but more adjustments are needed. After switching the right channel transistors I was delighted to see the DC offset go down from a fluctuating 24mv to a surprisingly steady 1.1mv..Wow! After changing the left channel board transistors I was expecting another nice low reading but actually now the DC offset reading is higher on the left side: -50.0mv hmmm. I'm hoping a DC offset adjustment can bring this number down to a reasonable level.

I'm in the process of switching the main Capacitors I bought the 47000uf 80v Nippon Chemi-con caps and they are ready to install. I do have one slightly embarrassing and novice question before I proceed though: Can someone please confirm the negative and positive terminals on the main Caps. I'm %98 sure I have it right but thought I might as well ask before making a very serious mistake.

In the Diagram I have:

#1 : Positive
#2: Negative

Then

#3: Positive
#4: Negative


Is this correct?

I sort of got muddled because at first I thought for some reason the both negative terminals would terminate negative on the copper plate in the middle but I think they are hooking up in parallel.

 

[blhagstrom]

main filter caps supply positive and negative rail voltage.
so one filter has negative to ground and the other has positive to ground.
negative to ground supplies the positive rail and positive to ground supplies negative rail.

I recently discovered that the flat Grey metalized poly caps on these go bad.
They should be replaced, especially if they are on the audio path.

 

[slimecity]

I recently discovered that the flat Grey metalized poly caps on these go bad

Whoa - these things - and the C200 preamp - are full of those caps.

Im glad I sold my P300 and C200 in that case - it couldve been expensive replacing all of those....

 

[blhagstrom]

Whoa - these things - and the C200 preamp - are full of those caps.

Im glad I sold my P300 and C200 in that case - it couldve been expensive replacing all of those....

they are not expensive and since the boards are modular, very easy to replace. It’s not widely known that they fail, so I’m spreading the word to replace them.

had an E-202 here, one coupling cap in one amp was open and the other was is sad condition.

after discovering that, I went to my E-202 that echowars has recapped and never seemed great. I changed all the metal poly caps and Bam! Excellent as it should be.

I have some recapped old Marantz that act funny, I need to peek inside those. It may or may not be the mystery.

 

[Big_T]

main filter caps supply positive and negative rail voltage.
so one filter has negative to ground and the other has positive to ground.
negative to ground supplies the positive rail and positive to ground supplies negative rail.

Thank you for that! It gives piece of mind.

I recently discovered that the flat Grey metalized poly caps on these go bad.
They should be replaced, especially if they are on the audio path.

So on both sound boards all these caps outlined here?

 

[blhagstrom]

All but the top middle are metal poly. They are the flat ones. But while you’re changing them, you may as well change the e-cap on the top also.

The metal poly caps are non-polarized and the e-cap is a bi-polar, non-polarized. I haven’t found any non-polar e-caps in axial form so you’ll need to use a radial cap and just spread the legs.

 

[reddish75]

I recently discovered that the flat Grey metalized poly caps on these go bad.
They should be replaced, especially if they are on the audio path.

What was the failure mode?

 

[blhagstrom]

What was the failure mode?

open

 

[Big_T]

Update:

After replacing the above mentioned transistors and main large filter caps (47Kuf 80V) I adjusted the DC offset and achieved a DC offset to about 1mv on each side. (Wow those pots are sensitive).

Ok sounds good but....a static /fuzz/dropouts still presents after about 10 min of play with (8ohm) speakers hooked up and after about 40min of play with only headphones hooked up and no speakers. Same right channel. The left channel seems unaffected.

The difference this time is it takes longer to present when only using headphones. Also changing the source or start stopping the music has no effect on the static whereas last time it would clear it. As well the static seems somehow softer than before and more prone to drop out completely for a second or two.

Any idea where to look? Could it be those metal poly caps on the sound board or does it still seem like a transistor issue? I am meaning to change out those metal poly caps.

 

[Cesari0]

Update:

After replacing the above mentioned transistors and main large filter caps (47Kuf 80V) I adjusted the DC offset and achieved a DC offset to about 1mv on each side. (Wow those pots are sensitive).

Ok sounds good but....a static /fuzz/dropouts still presents after about 10 min of play with (8ohm) speakers hooked up and after about 40min of play with only headphones hooked up and no speakers. Same right channel. The left channel seems unaffected.

The difference this time is it takes longer to present when only using headphones. Also changing the source or start stopping the music has no effect on the static whereas last time it would clear it. As well the static seems somehow softer than before and more prone to drop out completely for a second or two.

Any idea where to look? Could it be those metal poly caps on the sound board or does it still seem like a transistor issue? I am meaning to change out those metal poly caps.

Is it both channels, or one?
What preamp are you using, could it be the source of the noise?
You clean the pots?
Have you tried hooking up the tuner directly to the P300, to see if the noise persists.
I would check all resistors. Make sure that there aren't any showing signs of wear.
One resistor that heats up, and might be suffering from wear is R30 on the Protection circuit board.
The Output Power pot is pretty much 100% useless.

My advice is to read up EWs C200 and P300 recap.
I did the recap... it went wrong, sent it to a tech, came back with issues, but the issues were solved when I re-installed components that the tech had removed that he shouldn't have.
I honestly think the tech did more work on it to charge more I looked at what he did, and he replaced part that I had replaced with new parts. and removed parts he shouldn't have. Afterwards the tech mentioned that the meter lights were not working, the P300 doesn't power up if the meter lights don't work, I never checked the lights before I sent the unit to the tech.


My C-200/P300 sound way better than my fully recapped AU20000 with the nichicon Super Through caps.

 

[slimecity]

I'd be looking at transistors if this issue presents after about 10 mins.

I'd also be looking at the "semi random freeze spray" approach to try to diagnose.

So to confirm - the DC offset fluctuates when the noise kicks in - or stays stable?

 

[Big_T]

Is it both channels, or one?
What preamp are you using, could it be the source of the noise?
You clean the pots?
Have you tried hooking up the tuner directly to the P300, to see if the noise persists.
I would check all resistors. Make sure that there aren't any showing signs of wear.
One resistor that heats up, and might be suffering from wear is R30 on the Protection circuit board.
The Output Power pot is pretty much 100% useless.

Cesari0: It is only the right channel and certainly the amp, I have gone through all tests to eliminate sources, cables and inputs. I will check R30 on the protection circuit.

I'd be looking at transistors if this issue presents after about 10 mins.
I'd also be looking at the "semi random freeze spray" approach to try to diagnose.
So to confirm - the DC offset fluctuates when the noise kicks in - or stays stable?

slimecity: Yes the DC offset drops temporarily when the static comes. about 3mv to 4mv less DC, could this still be a connection issue though? If a bad switch or cold solder point, would it not also drop the DC since the connection is dropping?


Since my last post I have tried:

• Switching the Left/Right sound boards (the problem persists in the right channel so I would assume it is not in the sound board)

• Extra cleaning to the output selection rotary switch and volume pots

• Cleaning the right side large relay switch

• Double checking the speaker connector terminals (same result through all outputs)

• Using freeze spray on all the components on the power board and the protection board (no change although it is hard to tell as the static comes and goes but after double freezing suspected areas it seems there is no change)

• Checking for for cold solder spots and touching up suspect solder points on the power board and protection board

• Visual inspection of all components on the power and protection boards, I'm not really a pro here but everything seems to appear ok.




My next Steps forward will be to try to clean or bypass the power selector switch, same for the output selector rotary switch and the front/back rca input selector switch.


Reading through other threads it seem like it might be a connection issue somewhere and it is not really a classic transistor crackling but more like a sputtering static like the signal cannot get through. There are complete dropouts also now.

I am confused as to why the static starts happening when the amp is warmed up and why after changing the main caps and transistors on both sound boards that the problem does not clear after changing the output selector or start/stopping the source like it used to. That has me puzzled, it seems like the problem is more permanent now where it would clear before the transistor and main caps upgrades.