PS Audio P600 Power Plant repair & mod.

[Reid Malenfant]

Do not try & do any of this unless you absolutely know what you are doing! Electricity can kill, & if it doesn't kill you it can damn well hurt!


Having gotten that out of the way I can get to business :)


As some of you may or may not know my P600 decided to pop it's clogs a week or two ago, luckily I had already bought MartinTs' previously used Power Plant Premier & it was actually going to replace the P600. It just ended up doing it a little sooner than planned :lol:

The P600 runs hot, it's like a rather big class A amp in that respect & this was a bit of a problem in the summer months (though rather nice in Winter :eyebrows:).

Well it expired while in use, things went pitch black all of a sudden as I happened to be watching a film on the projector at the time. A second or so later there was a rather ominous sound of things going bang in the night inside the unit so I moved as quickly as I could & isolated the whole rack.


Things didn't look too bad at all on first inspection, I was actually expecting more physical damage. The only things that appear to be damaged are a couple of Metal Oxide Varistors, though it's the particular MOVs that have blown that tell a bit of a story. There are five MOVs protecting the input to the 1.4KW mains transformer, one goes directly accross from Live to Neutral, two more go from both Live to Earth & Neutral to Earth. These were all 100% fine.

The MOVs that both blew were accross the two series primaries of the transformer, remember this unit can also operate on 110 - 120V. So something put these way out of balance all of a sudden & that something can only be some kind of short inside the unit.


Having had a good look at the unit itself & then having fully tested the mains transformer I decided it could be economically repaired by myself. As a few of the main PSU capacitors were doing a Mr Blobby impression (they are kind of bulging) I decided that a complete re-cap wouldn't be a bad idea while I was at it.

The main PSU capacitors are mounted onto the amplifier PCBs, yes this thing is a pair of big amplifiers that output 120V RMS. Each amplifier actually outputs 60V RMS, but they are in a bridge so accross the two you get 120V RMS. Another advantage of this is that the output is actually balanced about Earth. As we are in the UK there is a step up transformer on the output of the amps that converts the output to 240V.


I bought all the capacitors off of our favourite auction site, though some I couldn't find which is where the modification comes in (more of that later). Then I proceded to strip the whole thing down as thanks to PS Audio the only way of getting to the amp PCBs is to gut the thing :rolleyes:

That's where I'm at right now...


Now depending on what I find it may well take about a month to get her up & running again. You see if I find any dead output transistors I'll renew the whole lot, any that aren't replaced will only go the same way as any dead ones & probably very quickly. It's the thermal stress of heating up & cooling down over so many cycles that kills them due to the differing expansion of the silicon die (that is the transistor) mounted on the copper substrate (that hopefully takes the heat away. After so many cycles of this they start fracturing & heat can't get away fast enough so thermal runaway occurs...


6741


Enough yacking...

The P600 whole sans top case cover.. If you spotted the sockets missing top left & wondered why, it's because Mark is lazy & used them to connect to the American plugs that he couldn't be bothered to replace right then. It's sitting near the output of the PPP now :eyebrows:

http://i939.photobucket.com/albums/ad240/speakermark/guess%20the%20pic/Picture010-1.jpg

P600 minus the "hub" PCB.

http://i939.photobucket.com/albums/ad240/speakermark/guess%20the%20pic/Picture011-1.jpg

The "hub" PCB minus a couple of MOVs, you might see Z1 & Z2 missing on the right hand side about half way down.

http://i939.photobucket.com/albums/ad240/speakermark/guess%20the%20pic/Image5-1.jpg

Main & output transformer removed... Fat heavy b'stards :rolleyes:

http://i939.photobucket.com/albums/ad240/speakermark/guess%20the%20pic/Picture013-1.jpg

One of the power amps in situ..

http://i939.photobucket.com/albums/ad240/speakermark/guess%20the%20pic/Picture014-1.jpg

Amps out, not a lot left..

http://i939.photobucket.com/albums/ad240/speakermark/guess%20the%20pic/Picture017-1.jpg

Now the interesting bit.... I have seen this done before but frankly it certainly isn't the way I'd do things :doh: There is only a thin layer of what amounts to tape or plastic between the power transistors & the heatsinks (which are at Earth potential). So damn near 100V DC being insulated by stuff that doesn't exactly conduct heat too well. That's going to change.

http://i939.photobucket.com/albums/ad240/speakermark/guess%20the%20pic/Image1-1.jpg

Capacitors that need replacing & the very dead MOVs

http://i939.photobucket.com/albums/ad240/speakermark/guess%20the%20pic/Image3-1.jpghttp://i939.photobucket.com/albums/ad240/speakermark/guess%20the%20pic/Image6-1.jpg

Finally one of the 24 output transistors. It won't be cheap to replace this lot unfortunately :rolleyes: 12 x MJL21193 & 12 x MJL21194

http://i939.photobucket.com/albums/ad240/speakermark/guess%20the%20pic/Image2-1.jpg


Thankfully that's it for today :D More soon enough...


Hope you all have a superb weekend!

[MartinT]

I can't see very clearly, Mark, but is the heatsink insulator one strip of plastic rather than individual mica or silicon insulators for each transistor? If so, then I agree that you can do a lot better.

Do I also spot an opportunity to add more reservoir caps into unused positions on the PCB?

[Reid Malenfant]

I can't see very clearly, Mark, but is the heatsink insulator one strip of plastic rather than individual mica or silicon insulators for each transistor? If so, then I agree that you can do a lot better.

Do I also spot an opportunity to add more reservoir caps into unused positions on the PCB?
Yes, if you look at the rather hefty anodised aluminium bars that clamp the transistors to the heatsinks you'll see that the main output transistors are broken up into triples. They use a strip of plastic between them & the heatsink :rolleyes: Each three have there own little bit of plastic insulator...

I have a big roll of thermally conductive silicone stuff that can be cut to length, something tells me that might be a better option. Also no thermal paste needed :)

As for the slots on the PCB, are you looking at the "hub" PCB, if so then there are two slots for extra capacitors & I reckon they'd be used on the P1000. These are Bipolar caps though & while I could find the correct ones from a supplier in USA they never got back to me.

This is where the modification will come into effect :) Frankly the whole thing isn't outstanding & could be improved with a lower output impedance.

I'm not 100% sure yet, but time will tell, the amps look at first glance to be inverting as looking at the hub I see a novel way of current control used to drive the output amps. We'll see though in the end.

One thing I can say is there is no variable for quiescent current on the output amps :scratch: This appears to be preset via resistors, though I'll trace out the circuit & see what is actually going on...


I have said this before, but it's not the way I'd do things :eyebrows:

[MartinT]

I have said this before, but it's not the way I'd do things :eyebrows:

No, but I'll bet the PPP circuit is an almighty bit more complex again. Floating amps riding the waveform, neat.

I don't think you ever told me if you can hear the difference with the PPP driving things over the P600?

[Reid Malenfant]

No, but I'll bet the PPP circuit is an almighty bit more complex again. Floating amps riding the waveform, neat.

I don't think you ever told me if you can hear the difference with the PPP driving things over the P600?
Do you want me to take a look :D Yeah, it would be interesting, though I reckon I can see how they did it :)


The difference between the PPP & P600... I have said this before, but I don't know where :lol:

The PPP is effectively as good as the P600 everywhere that I can hear, though it's better in the bass end with an even more solid presentation which also happens to be more deft on it's feet at the same time.

Everything else is very similar, though there is a tad more hum in my system with the PPP, than the P600.

That'll be to do with the balanced mains.

If the P600 had the low output impedance of the PPP it might win... If you don't mind paying for a big electricity bill :eyebrows:

[MartinT]

Do you want me to take a look :D

Yes, go on!

Does the fan ever kick in for you? It never did for me, running the entire system.

[Reid Malenfant]

No, the fan hasn't kicked in. But it gets quite warm :D

You need to remember it's an odd system where the output of the amp can be a heavy current but with the same output voltage as the mains input. The amp could have lots of voltage & current accross it at the same time.

It'd actually be more efficient when it has to boost or cut voltage compared to the input, the more the merrier up to say 5 - 7V :)

Not good for distortion on the output though.

[MartinT]

Have you sorted your main earthing yet? I worry that it had something to do with blowing your P600 in the first place.

[Reid Malenfant]

Yep, that's sorted at least for the main spur to this room.

Looks like the house needs rewiring though :eyebrows:

Finally managed to get the amplifier circuit traced, this is bloody odd as only the output stage, biasing transistor & a constant current load are on the amp PCB.

The VAS (voltage amplifier stage) is on the hub module :rolleyes: :scratch:

I'm guessing that the rest of the amp is also on the hub PCB, though I'm going to go hunting for it & you never know, I might find it on the bloody oscillator PCB :rfl:

Someone needs a good kicking & I'd like to be the person that gives it :eyebrows:


I know these circuit diagrams simply aren't available as I have heard that PS Audio don't like anyone else to fix their kit. Well it's tough because they'll be going up on here when I transfer it/them from paper to a circuit diagram done via LTSpice.


Both amps appear to be ok, but I can test them with a low voltage split rail supply & a function generator. The quiescent current appears to be fixed, there is no way of adjusting it - yet. I'm not convinced that the bias current is going to stay stable, due to the circuit layout, so I'll be testing this into a low impedance load but with a low voltage split supply as I already mentioned.

I'm quite likely to fit a trimmer so it can be adjusted in situ :)

[Reid Malenfant]

I'm guessing that the rest of the amp is also on the hub PCB, though I'm going to go hunting for it & you never know, I might find it on the bloody oscillator PCB :rfl:

Someone needs a good kicking & I'd like to be the person that gives it :eyebrows:
I honestly don't believe it, but the front end of the amp is actually on the oscillator PCB :steam: :steam: :steam: :steam:

These people are taking the piss bigstyle :mental:


Ok, so here is the oscillator PCB with the amplifier front end near the bottom. All the transistors are part of the amplifier & they get fed the 50Hz or whatever signal from the 318 op amps.

http://i939.photobucket.com/albums/ad240/speakermark/guess%20the%20pic/Picture-1.jpg


You have heard the one about the leg bone connecting to the knee bone :lol:

Well this PCB connects to the "hub" PCB, which also has part of the amplifiers on it & that connects to the output stages etc, etc...

No wonder they don't dish out circuit diagrams :mental:

[MartinT]

I'm fairly sure the P300 was similar, with the oscillator/1st stage amp on a daughter board which also contained the waveform curves on a ROM. The Multiwave upgrade consisted of swapping out a couple of chips on that board.

[Reid Malenfant]

It's a daft system as a connector could become a bit dodgy over time & then you have an amp that may not have any feedback so becomes saturated & clips left right & centre :rolleyes:

However I can see why they recommend only themselves to fix their kit as to test any individual board involves setting up other components to use as part of a testbed.

Quite annoying, but I'll get round it all :eyebrows:

[Reid Malenfant]

I haven't forgotten this thread or fixing the P600, I'm just considering my options at the moment :)

While I can't appear to find a fault with any of the output transistors (which is obviously good news), the opportunity has sort of come about to increase the longevity of the whole unit.

I managed to pick up ten brand new MJL21193 power transistors very cheaply indeed, this unit uses twelve each of MJL21193 & MJL21194. The thing that got me thinking was the dissipation of each device, which must be fairly substantial as it puts out a good bit of heat. Well having looked at it there is more than enough space inside the unit on the heatsinks each side to mount another five output transistors for each voltage rail.

If I happen to pick up ten MJL21194 then I can swap out the emitter resistors (0.22 Ohm) & replace them with 0.39 Ohm giving me the same current limit. The thing is though that each power transistor would be dissipating just over half of what it was having to previously, each junction would run quite a bit cooler :scratch:

Another bonus would be that each transitor would be further away from the edge of the safe operating area...


So this is on hold until I get the remaining power transistors :eyebrows:

[MartinT]

Good idea Mark, although obviously the heat output of the whole P600 would be pretty much unchanged.

[Reid Malenfant]

Good idea Mark, although obviously the heat output of the whole P600 would be pretty much unchanged.
Exactly, but each transistor junction will be running cooler, so it'll last longer than it would if it was standard.

The heat output is going to be investigated though. The quiescent current is preset, there is no way of altering it :rolleyes: While there is a transistor used to keep the bias stable I have my doubts that it will all that accurately when things start warming up.

As a minimum I'll be making sure I can adjust the quiescent current without having to strip the unit & I'll be altering the circuit slightly so it stays stable with current variations through that Vbe multiplier, which there will be due to the units design. It just a question of adding a resistor & wiring it in a certain way to keep the voltages on the bases of the driver transistors stable even if the current through the voltage amplifier is changing :)

[goraman]

You guys amaze me.
I enjoy reading and looking at threads like this.
I learn a lot from you guys.

I have a APC H110,no where near as good as PS Audio but it dose reduce line noise and gives me some piece of mind.

I have 8 PS Audio 10 awg. Prelude SC power cords and I love them.
When I have money again I will get the power plant premier (very expensive)
I hope you are able to get it going again Mark, I haven't seen one totally die before but if all else fails you could send it to PS Audio for repair, I'm told they stand behind their stuff.
My APC is I believe around 7 years old and still working well,I've been told 10 years is the average life but I don't leave mine on unless the stereo is in use so it may last longer.

[Reid Malenfant]

I guess I should add that I now have the required number of MJL21194 winging there way to me from USA, in two packages to avoid Gus Thoms & Heck Size ;)

Saves me £11.50 or so from purchasing them in the UK.


I'll have to strip the unit down further so I can add extra bolts & an extended clamp to accomodate the new power transistors. I'll be needing that bench drill press that I have been looking at as well, it was only a question of time :)

[goraman]

You may as well do 2 of them at once.
http://www.ebay.com/itm/PS-Audio-P600-Power-Conditioner-or-Plant-/160822518285?pt=LH_DefaultDomain_0&hash=item2571c4e20d#ht_542wt_1135

[Reid Malenfant]

:lol: Not much good to me unfortunately Jeff, it's an American model, & as such it won't have the 120 - 240V step up transformer..

I bet shipping wouldn't be cheap either, not to mention import duties & VAT :eek:

Nice thought though.

[lensi]

Hi Mark
I read your findings with great interest as I have the same exact unit .. which has now gone down on one side. The Current UK PS Agent has been totally useless and I wonder if it's worth Moding the unit myself . .was evening thinking if it could become a 240 to 115v 60 hz PS as I have some US equipment that would love that. What do you think ?

Best
Lensi

[Reid Malenfant]

Hi Laurence, I should be getting back on with this fairly shortly. At one point I was waiting on a set of six output transistors (I bought ten in two lots to avoid import duties), unfortunately they got lost in the post, probably fell out of the aircraft as it was mid Atlantic :lol:

Anyway, the seller sent me another load which arrived safely.

I now just need a pillar drill so I can accurately drill the heatsinks, as I'm increasing the number of them for longevity reasons. I also need to find a big real of silicone thermal compound, I just don't like the idea of using tape as PS did :eek:

As in the VM I sent you, you'll need to use both amplifiers unless you do some serious modification of the circuitry. Take it from me, that it would be easier to fix the dead amp than modify it to run on one!

If you intend to power US equipment, simply bypass the step up transformer on the output, you'd then have the same P600 as the US version ;)