Yamaha PM700 console upgrade/mod

[spaceludwig]

Yes, the resistance between the white and yellow leads are under triple the value of the blue and green, i.e. 90 to 250.

 

[spaceludwig]

OK, so I changed the xfmr's on 10 of the 12 input channels. Below are some pictures of how I mounted them on the boards. Nothing particularly exciting, simply a visual reference in the event someone would need one in the future.

First, I removed the stock (GA8027) transformer which leaves three holes on the PCB 

I wrapped each transformer I was putting in with duct tape to make sure it didn't short anything or pick up random noise through contact with other components. I also twisted the leads

I also put a small piece of tape on the casing of the input gain switch that the xfmr's end up resting on

Next, I pass the leads through the small holes closest to their respective pads. I left the bigger middle hole for the tie-wrap.

The bolt coming out the center of the bottom of the xfmr should rest on top of the input gain switch housing. This prevents from having to move components around to accommodate the rather larger  GA80071 transformer.

I secure the transformer using a tie-wrap. Component side:

PCB side:

And I solder the leads of the GA80071 as follows:

GA80071 = GA8027
Green  =  Brown
Blue    =    Red
Yellow  =  Black/Blue
White  =  Green

This worked for me, all units work 

 

[3nity]

you gotta keep at least 1 channel stock for later comparisons!!!
Thanks

 

[spaceludwig]

I started a thread a few weeks ago asking if anyone had the PM-700 service manual, to no avail. I ended up calling Yamaha today and was emailed the info I was looking for. Here are the links in the event someone needs them.

Schematics (tiff file):
http://dl.dropbox.com/u/18935229/PM700/PM700_CD_C.tif

Parts list (PDF):
http://dl.dropbox.com/u/18935229/PM700/PM700_PL_C.pdf

PCB Layout:
http://dl.dropbox.com/u/18935229/PM700/PM700_PCB_C.pdf

Service Manual:
http://dl.dropbox.com/u/18935229/PM700/PM700_SM_C.pdf

 

[spaceludwig]

you gotta keep at least 1 channel stock for later comparisons!!!
Thanks

I kept 2 though I would have to put the original opamps back in.

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

 

[spaceludwig]

After putting the channel strips back into the console, the knobs back in their appropriate place (having washed each with a toothbrush and soap) I fired up the console to make sure everything was in working order. For now, each channel seems to work. However, I seem to be having a power supply issue, which I`ll describe below.

Around 10 minutes after turning the unit on, the headphones started to hum. I unplugged them and stuck them into each (left and right) +4 unbalanced 1/4 inch output since the program out is separate from the headphone out. Same results, sound was distorted and crapping out. I measured the outputs of the power supply and discovered that the negative half of the 15 and 22 Volt rails were operating at half the voltage it's supposed to, i.e. -7.5 and -10.something volts. I turned the unit off, let it cool off, then powered it back on. Since everything was playing properly without distortion I immediately measured the PSU output and the negative and positive rails were operating at their rated voltages. As soon as the distortion came back, the negative rails again measured at about half of what they were supposed to be putting out. I noticed that I could reduce the distortion by unplugging individual channel strips from the main ribbon cable. The volume from the headphone amp got progressively louder as I unplugged  more units. Eventually, the distortion was eliminated. Both heatsinks on the power supply (see picture on other page) were very hot.

So my question is, what causes the power supply to get weaker. Is it as the power transistors heat up? The console ran fine at some point, could run the whole night. Are the opamps I substituted demanding more current? If this is the case, how can I upgrade the PSU, with transistors that have a higher power dissipation or current rating?  Is it possible that the stock power transistors (2SD526 & 2SB596) are burnt or kaput?

In the datasheet of the 2SB596 there is a power derating graph

Does this mean that as the transistor temperature rises - i.e. the less efficient the heat sink -  the less power it has?

I can't figure out how to proceed from here.

 

[abechap024]

I would offer the suggestion that maybe the opamps you upgraded to are pulling more current than the original opamps, therefore maxing out your power supply...

If I were you I would just perfboard a new power supply. Thats what I did with my board...and the difference was quite profound...I was maxing out the power supply before, it had a small transformer....zener regulated. So I got a new nice and big transformer from antek for 40$ and then some 5A regulators - let me dig up the schematic...

I found this on the board...i forget were, but it works great!!


Or you could just try bigger heatsinks...

 

[spaceludwig]

Thanks, Abe. That is definitely an option though I would like to see if I can resolve the problem with the PSU I have now.

Let me ask you, am I reading that power derating graph (I posted above) correctly? The hotter the transistor gets, the less power it can put out?

 

[abechap024]

Yes that seems to be what it says....seems to make sense I guess.

Maybe larger heatsinks?

 

[spaceludwig]

Also can't figure out why only the negative rails would be affected. This doesn't make sense to me.

 

[abechap024]

The negative rails of the opamps?

 

[spaceludwig]

The negative rails of the opamps?

The negative rails of the power supply. The supply is putting out +/- 15 and 22 volts, 15 for the IC opamps and 22 for the DOA's. When the sound starts to get distorted and crapping out the negative rails are measuring about half of what they are supposed to, i.e. 7.5 and 10.5 volts. When I disconnect the jumper cable from the power supply (supplying the various channels), the voltages go back to what they are supposed to, i.e. 15 and 22 volts.

What I find hard to believe is that an extra 100 mA is going to make the power supply fizzle out like that, especially seeing that I am only running 2 channels of audio. The supply must be designed to handle all 12 channels amplifying plus the program out and monitor DOA's working  hard. This is what leads me to believe that it can't only be the extra current draw. Something is amiss. 

 

[abechap024]

Oh so even with 2 channels it still craps out?? Hmmm maybe measure current draw?

Seems strange for sure.

 

[spaceludwig]

With 2 channels playing audio, i.e. a stereo signal split Left and Right. The other channels are still plugged in but they are not amplifying anything. However, when I unplug the other channels from the ribbon cable that connects the individual strips together (outlined in red)

the distortion is reduced and after unplugging maybe 3 channels it is eliminated completely.  Unplugging channels from the ribbon cable also makes the volume of the headphone output get progressively louder. This seems to suggest that the power supply is operating at the peak of it's threshold.  One would think that the power supply would be designed to handle all those channels without the output dipping.

 

[spaceludwig]

I dont know if this helps but below is a table of the measurements I get from the PSU when it is plugged to all channels and when it is unplugged and has no load.

It is the positive, not the negative, rails that are losing power, so my apologies for the sloppiness. Also, the power transistors on the PSU cool down after I un-plug the power supply from the rest of the console. So I must have made a mistake somewhere.  I will remove each channel and see if I can find where I went wrong.

In the event it is the new opamps I put in that are the problem, given the schematic above can I change the output transistors from 4.0 amps to 5.0 amps?

 

[spaceludwig]

Oops, didn't include the schematics in this post. Here it is:

 

[keefaz]

Why do you think pin 2 & pin 3 should be swaped  ?

To me, it looks like pin 2 of TA 7136AP is IN- and pin 3 is IN+ in the datasheet (so same as opa604)
Also what do you mean with "make some jumpers between pins 6 & 7" ?

 

[3nity]

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

 

[abechap024]

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?

 

[spaceludwig]

Why do you think pin 2 & pin 3 should be swaped  ?

To me, it looks like pin 2 of TA 7136AP is IN- and pin 3 is IN+ in the datasheet (so same as opa604)
Also what do you mean with "make some jumpers between pins 6 & 7" ?

Pins 2 & 3 of the TA7031P are not the same as on modern DIP opamps, they are reversed. I just made jumpers so pins 6 & 7 of the opamps could reach pins six and seven on the adapters I made.