Yamaha PM700 console upgrade/mod

[spaceludwig]

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

Thanks, will do that now and post results. Might take a while as I have to release the hound first...

 

[spaceludwig]

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)

Pin 5 is not connected on the adapter.  If I should be disconnecting pin 1 can I simply remove the 47p cap going to ground and 10p cap gong to pin 6?

 

[spaceludwig]

Forgot to mention,

5 channels are not using the OPA604 but the MAX427. From the datasheet I cannot see what the current draw is but I will measure this shortly.

 

[keefaz]

Pin 5 is not connected on the adapter.  If I should be disconnecting pin 1 can I simply remove the 47p cap going to ground and 10p cap gong to pin 6?

Yes, I think it should be better to remove them when using the opa604 in the circuit, leaving pin1 of opa 604 not connected
Also, it is important to use decoupling capacitors at the IC pins, this opamp is fast and may oscillate

 

[spaceludwig]

Yes, I think it should be better to remove them when using the opa604 in the circuit, leaving pin1 of opa 604 not connected
Also, it is important to use decoupling capacitors at the IC pins, this opamp is fast and may oscillate

OK, thank you.

 

[spaceludwig]

Following is a table of the measurements I got from the individual input channels. I will measure the 5 output channels also and post.

Edit: table updated with output channels. I couldn't measure Monitor 2 as it is from this channel that all others are powered on the 15V rails - I wasn't sure how to go about it. Also, when I switched to the 22V rails I wired the positive/negative backwards and damaged something. Now the +22 gives something ridiculous like 6 volts. I'll have to fix the power supply tomorrow and continue. In the meanwhile, if these figures enlighten anyone, please post your thoughts.

My feeling is something is not quite right since the console is rated at 0.5A yet each channel is consuming half of that. I'm probably interpreting this incorrectly and am happy to be corrected by the knowledgeable members.

 

[spaceludwig]

NOTE*  Disconnecting pin 1 - as per Keefaz's suggestion above -  of the opamps did not result in a lower current draw (not that this is why it was recommended).

 

[s2udio]

My feeling is something is not quite right since the console is rated at 0.5A yet each channel is consuming half of that. I'm probably interpreting this incorrectly and am happy to be corrected by the knowledgeable members.

Thats most likely the max mains input current ,check with AC ammeter if in doubt(carefully !!!!!)
But looking at the mainly consistent draws......Hmmm Thats high per channel, would expect something  around 20- 30ma....

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

Thats what I always do, in fact I mod one then decide !
You can make sure the basics will work,and see if the PSU is up to it.

 

[spaceludwig]

But looking at the mainly consistent draws......Hmmm Thats high per channel, would expect something  around 20- 30ma....

The output channels - which measure around 30 mA - only have 1 opamp, and they are the stock IC's. The input channels have 3.

BTW, does anyone know what I can replace the following fusible resistor with?

It is burnt out and I cannot find anything rated the same way on the internet, only in Watts. Due to my ignorance regarding these matters, my calculations of how many watts would be equivalent makes no sense.

 

[spaceludwig]

OK, so found a temporary fix to the power supply, good enough to keep probing into what might be drawing so much current.

Answering to a post from another poster, it occured to me that since I was only going to use the console as a summing mixer, I could remove some of the opamps that were not gong to get used, namely; the 4 DOA`s in the Monitor 1 and 2 channels, and IC 3 in the input channels, since I have no intention of sending any of the signals to the Monitor channels.

Measuring current draw after removing IC 3 from channel 12 dropped the total current draw by around 6mA. I decided to remove IC 1 & 2 also just to measure the draw of the channel with no opamp in the circuit and made a curious discovery. Taking out IC 2 resulted in over a 100mA drop in current draw. IC 1 was around 6mA leaving the opamp-less channel drawing around 21mA. I stuck IC 2 back into the sockets and was pulling over 120mA immediately. Replacing it with the stock opamp, however, only results in a 10mA current draw.

For some reason that IC 2 is pulling way more current than the other opamps. It is not wired backwards, there are no shorts anywhere, it is consistent throughout the input channels. Perhaps looking at the schematics someone could explain why...

 

[MikeClev]

I don't know if its been suggested here before, but have you ruled out oscillation at high frequencies? I think that increases current draw...

Do you have 100nF capacitors for power rail HF bypassing on or near each of your little IC adaptor boards? If not, you need it!

 

[spaceludwig]

I don't know if its been suggested here before, but have you ruled out oscillation at high frequencies? I think that increases current draw...

Do you have 100nF capacitors for power rail HF bypassing on or near each of your little IC adaptor boards? If not, you need it!

Would it oscillate with no signal? And wouldn`t I hear the oscillation?

 

[MikeClev]

Yes it can occur with no signal, and the oscillation can occur above audible frequencies.. check to see if any of the opamps are hot to the touch; the unusually high current draw will make them warm or even too hot to hold your finger on!

 

[spaceludwig]

Yes it can occur with no signal, and the oscillation can occur above audible frequencies.. check to see if any of the opamps are hot to the touch; the unusually high current draw will make them warm or even too hot to hold your finger on!

I think you are right. I made a little adapter and attached only the power rails and it was taking little current. Then I plugged the output pin (6) and the current shot up to 120+mA but came back down around 40. When I touched the top of the opamp it immediately jumped back up to 120+

You think this can be solved by putting capacitors going from the pin of each power pin going to ground, correct?

 

[MikeClev]

That's the theory, yes! Make sure the caps connect to a nice power ground rather than audio ground if there is one available so audio ground doesn't get contaminated with power rail muck...

 

[spaceludwig]

I don't know why but the .1uF caps are not working, it is still pulling around 130mA. I have a hard time believing that the only opamps that will work are the stock ones.

Basically it is IC 2 that starts drawing serious current as soon as the inverting and non-inverting inputs are wired up to the circuit. This is getting seriously aggravating. I'm open to more suggestions on how to fix this problem.

 

[MikeClev]

IC2 is the one with two transistors following it designed (I guess) to provide a low impedance output to drive the faders and aux / monitor sends. I suspect that they are drawing the current, but I think somebody more knowledgable should take over from here....!

 

[spaceludwig]

...I suspect that they are drawing the current....

But when I put the original IC 2 opamp (TA7136P) back the channel only draws around 41mA. It's only when I swap it for a modern opamp that the current draw jumps over 120 mA.

 

[abechap024]

Yea....Seems like that much current draw would be hard pressed to come from an opamp alone, but include those transistors in the oscillation loop....

I'm no expert but...

Maybe try increasing the feedback loop capacitor from (27pf, 47pf?, 100pf??) to a higher value.

EDIT: I'm not sure what opamp your talking about, but those compensations do look pretty lean for some modern fast opamps.

 

[spaceludwig]

Maybe try increasing the feedback loop capacitor from (27pf, 47pf?, 100pf??) to a higher value.

EDIT: I'm not sure what opamp your talking about, but those compensations do look pretty lean for some modern fast opamps.

The only cap i am seeing in a feedback loop of ic 2 is the 22pF cap in parallel with the 33k. I don't know how changing that value to a higher cap would change anything. Could making a lowpass say around 25k help?

I'm using the OPA604. I thought they didn't need compensation caps. I stuck a 5534 in there with comp cap and it didn't lower the current draw.