Yamaha PM700 console upgrade/mod

[spaceludwig]

No reversed capacitors??
Did you measure how hot the regs got when all channels are plugged?
Thanks

Reversed capacitors on the power supply, no. On the rest of the boards, none that I saw when I double checked the individual channels. I am now pulling out the channels one by one to see if I can find a problem.

 

[spaceludwig]

Your going to get some sonic benefits from upgrading that old power supply.

Not that its horrible....but a new chip based power supply is going to do a lot better job of regulation...just sayin

You could just try to upgrade that transistors, but what about the transformer? what is it rated at..?
does it get warm? It could be the transformers fault that the power is decreasing....it heats up too much starts crapping out.

Does it get hot too I imagine?

The power transformer is BIG. I don't remember feeling any heat coming off it but will check when I put all the channels back and turn the unit on again. I don't think it is the problem. I'm not opposed to an upgrade but would just like to get this thing working for now. I just can't believe that the power supply would go bonkers for 100 mA increase in load. However, I am not well versed in electronics so I don't make that claim with certainty, just a gut feeling.

 

[spaceludwig]

Removed every channel and checked each one thoroughly for any problems. I didn't find anything.  However, when I plugged the units back in and turned the console on I managed to play some stuff on the same 2 channel for almost 30 minutes without the power supply fizzling out. So I guess that's good but I have no idea what happened. I just hope the problem doesn't come back as i won't know how it occurred in the first place.

I would like to upgrade the power supply, however, as it seems to dip somewhat (a little over 10% on the 22V rails and the 12V headphone supply) when all the channels are hooked up. The power transformer doesn't get hot at all so I would probably use the same one.

 

[3nity]

BTW, whereabouts the 514 are you located? I'm near Guy.

Im in North Montreal, near the Pie-Ix bridge.
Good luck with your project man!

Thansk

 

[spaceludwig]

Abe,

Are the 10K pots on the Amek schematic trim pots for fine adjustment of the output voltage?

 

[spaceludwig]

BTW, whereabouts the 514 are you located? I'm near Guy.

Im in North Montreal, near the Pie-Ix bridge.
Good luck with your project man!

Thansk

Tres cool!

 

[abechap024]

Abe,

Are the 10K pots on the Amek schematic trim pots for fine adjustment of the output voltage?

yea its fully adjustable. I was able to ride the voltages a little higher on my console to squeeze a little more headroom out of it. Seemed to clean things up a bit.

Anyway good luck! Might help with noise floor too, but if its working now, and noise floor is good, no reason to really upgrade!

Cheers,
Abe

 

[spaceludwig]

Problem not solved, re-occurred again. At the risk of being redundant the problems are as follows: sound will play fine when suddenly it starts getting distorted; if I stop the music the headphone amp has a low hum which is not there when I power the unit on and everything is working fine; only the positive rails are being affected, i.e. they are the only ones whose output is halved - see chart on page 2 - the negative rails stay consistent; when I pan the signal the VU meters do not react accordingly, i.e. if I pan hard left both VU's are still moving in sync (headphones adjust accordingly, VU meters did work normally); heat sinks from power transistors on PSU are extremely hot and now the power transformer heats up too.

I've tried unplugging the channels individually to see if any one channel was the cause of the problem. This is apparently not the case. When I unplug the Monitor 1 channel, Monitor 2 -which has the headphone amp - stops working.

I'm stumped (not that I ever felt like I gained some understanding of the problem) and still find it very strange that only one part of the power supply is being affected. Having said that, the 12 volts powering the headphone IC remains constant.

Any thoughts???

 

[spaceludwig]

Important: At one point while I was trying to figure out where the problem might originate from the sound came back and the measurement I got from the PSU output was back to normal. I believe I was fiddling with a pan control or the input gain selector. I doubt those controls have anything to do with the problem but thought it was worth mentioning since it suggests that perhaps the problem is with the power supply itself. I mean, why wold the power supply switch back and forth like that?

 

[3nity]

Its that with all the strips plugged in??
If so tried only half the strips and see...that way you've cutted down in half the amps needed.
this way you can verify the psu might be at trouble.

Hope it helps.

 

[spaceludwig]

Its that with all the strips plugged in??
If so tried only half the strips and see...that way you've cutted down in half the amps needed.
this way you can verify the psu might be at trouble.

Yes, as stated in an earlier post when I unplug the strips the distortion will eventually go away and the output will get louder. When half the strips are unplugged everything works fine.

So you think I should just change the power supply? Can I change the output power transistors  (2SD526 & 2SB596) which are rated at 4 amps 80 Volts 30 watts for similar transistors rated at 5 amps?

 

[abechap024]

Hmmm so it went back to nomal for a moment you say? Maybe there is a short somewhere in the master channel maybe? or maybe in the wires themselves?

Are there any lights? Those suck a lot of juice....if they run of the same rails...

Edit the lamps run on thier own rail....did you replace all the caps on the power supply? Maybe the zeners are failing? or other components? See if the zeners get hot, maybe experiment with heat sinks...

You'll get it! Good luck!

 

[spaceludwig]

My thinking is if there was a short it would just go and blow a fuse, no?

The lights are powered by a 10Vac rail that is separate from the 15 and 22 volt rails. They are also fed by different leads from the power transformer.

 

[spaceludwig]

Edit the lamps run on thier own rail....did you replace all the caps on the power supply? Maybe the zeners are failing? or other components? See if the zeners get hot, maybe experiment with heat sinks...

You'll get it! Good luck!

Caps were replaced on the PSU a few years ago and I didn't use the console after that.

If the zeners get hot that is a bad sign?

 

[abechap024]

welll i'm not exactly sure....but if the zeners get too hot I could imagine they "go soft" possibly...maybe worth checking out...

since they are what regulates the voltage it seems like a good place to start.

 

[s2udio]

Have you actually tested each module seperately and confirmed they work as they should ?,
Ahh i see you say you have But..... have you noted the +/- rail current draw of each module ?.
This test would verify induvidual current consumption and potential faults causing excess
draw and psu stability.
Once you know total  current requirements ,load the psu with some large wattage resistors to simulate total desk consumption.........otherwise i fear your in for a long haul....and fried bits !
Also check the ground rail integrity through the whole desk,missing grounds cause the strangest of head scratchers ! And a logical approach to testing is far more sensible than assumption.
PS

That +22 rail looks a good place to start,and rated at 500ma ...something pulling it down there !
Also the +15 is very low ,ouch,thats why its getting hot, again how much current is the fault
Drawing on those rails ?

 

[MikeClev]

I would second replacing the caps in the power supply... if they have never been replaced they are a couple of decades old and if they haven't gone bad already, they eventually will do!

If I remember right, don't caps gradually lose capacitance? So a cap labelled 2200uf might only measure say half or a quarter that after decades of use in a hot enclosure...

 

[s2udio]

Yup good point replace all psu electros..
Standard procedure as the whole desk has been recapped imho.
A  SCOPE  on the output would give a good indication of AC ripple under load
Which could be high ? but ?..........

 

[3nity]

look some replys behind he said psu recapped some years ago!
Thanks.

 

[keefaz]

Looking at the circuit in page 1, I would disconnect the 604's offset trim pins (pin 1 and pin 5) from the circuit (at the adaptor board for example), the original opamp pin 5 is used to bias the opamp (resistor between psu + pin7 and bias pin 5), also I would solder 0.1uF psu decoupling  caps close to the opa 604 psu pins (so at the adaptor board)