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Get the Accuphase P300 running again

I

ixobert

New Member
Hello
Im a young guy from germany and i have Accuphase P300 amplifier thats not working. The main fuse did blew everytime i switched it on. I did find some destroyed output transistors on one side and replaced them, but i dont know why they were destroyed.

Then the amp seemed to run fine but when i put an input signal to the chinch inputs like this one. (sorry for the bad picture) :rolleyes:

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I got a very unhealthy and not amplified signal like this one at the speaker terminal.
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I found a blown Transistor on the powersupply board i replaced it as well but nothing changed.

I found a list Voltages in a post ofTransconductor in this thread:
http://audiokarma.org/forums/index.php?threads/accuphase-p300-restoration-help.481933/

here are his voltages at the connector to the PS-Board mine are the one written bold, there is clearly something wrong in my unit

Pin
1 / 68v/70v
2 / 80v/-82v (i think he forgot the "-" )
3 / -68/-70v
4 / -26/-9V
5 / 0/0
6 / 26/10,9v
7 / 0/0
8 / 0/0
9 / 80/82v
10 / 0/0
11 / 21 ac/21,8ac
12 / 21 ac/21,8ac
13 / 28/29v
14 / 17/10.9V
15 / 16/10,4v
16 / 16.2/10,4v
17 / -16/-9,6v
18 / -27/-27v


Please can someone help me?
Thank you
Stefan
 
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Have you found and downloaded a copy of the service manual?

Does the protect circuit work? Is the output relay engaing - or are your VU meter lightbulbs fashing as the protect circuit is not taking the unit out of protection?
 
Hello
I couldnt find a free download of the service manual.

How can I test the the protection circuit ?
Yes the relay seems to work right and the light bulbs are not flashing at any time
 
Are both channels distorted, or is it just the one you replaced the destroyed output transistors? If both channels are distorted, then you definitely have a power supply problem. Your 68v and 80v rails (1,2,3,9) look good, but the low voltage 25v rails for the input buffers look low (4,6).
 
Yes it's basically the same on both channels. But why can the low voltages be that bad?

Does anyone know where to download the service manual for free or can send it to me?:bowdown:
 
HiFi Engine has a schematic for the P300.
It has a voltage selector on the back. Make sure its set correctly.
And yes, PS needs attention.
Never listened to a Accuphase, the amp looks handsome.
 
The schematic is the only thing I found to. A bit more information about the circuits maybe described in the service manual.
The selector is set to 220v this should be just fine.

Yes it looks absolutely astonishing and the build quality and the removable circuitboards are a nice feature for service works.:banana:
But the soldering on all the boards really looks terrible :biggrin:
 
Update !

i got the PS-Board working right as far as i Think

Pin
1 / 68v/70v/65V
2 / 80v/-82v/-75V
3 / -68/-70v/-65V
4 / -26/-9V/-25V
5 / 0/0/0
6 / 26/10,9v/25V
7 / 0/0/55V ac
8 / 0/0/55V ac
9 / 80/82v/75V
10 / 0/0/0
11 / 21 ac/21,8ac/20V ac
12 / 21 ac/21,8ac/20V ac
13 / 28/29v/27V
14 / 17/10.9V/16V
15 / 16/10,4v/16V
16 / 16.2/10,4v/16V
17 / -16/-9,6v/-16V
18 / -27/-27v/-25V

When i put in all Boards the amp plays just fine:bigok:

But
  • The 16v Rail sinks down to around 11V when i put in the protection board. It plays nice but the lights are not that bright and get only 11v instead of 16V. I dont know if the Problem is still on the PS-Board or the Protection board.

  • And the Meters are barely moving even on -20dB but the Music is quiet loud, with headphones Plugged in it works as it should i think. With Speakers hooked up i cant turn the volume up more than 1/8 of the knob because it gets to loud with some little JBL control one
P.S. Can someone please send me the Service manual ?:bowdown:, slimecity unfortunately didnt response to my conversation.
 
Check R16 (.24 ohms) on the power supply board. Also, where are you measuring the +16V at?
 
Last edited:
Thanks for your replie EchoWars
R16 seems to be fine 0.3ohm

I measured at pin 15 on the backside of the connectors and on the lamp sockets

Thank you very much seems to be working
 
Sorry I havent forgotten to get you a scan of the manual - just have been busy. If EW's link works OK then you shoudl be fine.

I find I need to have the music cranking to get those meters working at all on the lowest setting. Hi sensitivity speakers dont help!
 
ixobert said:
R16 seems to be fine 0.3ohm

I measured at pin 15 on the backside of the connectors and on the lamp sockets
Click to expand...
OK...measure the voltage on the positive terminal of the 2200uf 35V C5 capacitor. If it is dropping in a big way, then it may need to be replaced.
 
So I'm back from holiday.:beatnik:

Things changed a bit the lamps now get 14.6v don't ask me why ;)

Without the protection board the capacitor get 26v with the protection board it's at 24v doesn't sound like it's to bad or?
 
No Problem ;)

The Voltage Problem seemd to be a transistor that was bad. I Changed it now it's fine.

The next Problem I noticed was that the output Signal on one channel was cut at the negative wave. Took me a few days till I found out that the Failure was in the Powerlimiter circuit.
20160911_134556.jpg
A audioshop in Germany replaced one of the two transistors with a npn instead of a pnp i ordered the right one and know it's working fine.

Then I noticed problems with the bias setting drifting and jumping on one channel I replaced the poti that solved the drift . The jumping of the bias voltage reacts to small movements of the driver board I think maybe the connectors don't make a good contact anymore?

And the last thing I noticed when I switch on the amp after it didn't run a day or two. There is a slight crackling on one channel for 10-20 seconds after the start but then it goes away.
Maybe the Relais or some bad voltages?

It would be nice if I can solve the two little problems with your help. I really enjoy the amp at the moment it's a wonderful piece of equipment. Sounds great with my other gear
20160927_152932.jpg
 
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