Yamaha PM2000 troubles

[Aaron W]

Hi,

I'm having a strange problem with my Yamaha PM2000.

The console was working fine...then it started not powering on some of the time randomly. When it did power on it would operate fine.

I checked and recapped the power supply. I ended up having troubles with the + 24.5 voltage. I replaced the Toshiba IC. However the power was still intermittently not working on first start up.

I decided to bypass the +/- 24 v and get some Acopian power supplies (5 amps). I had a knowledgeable tech rack me two supplies (one is inverted for the  - 24.5 volt rail). Console still would not operate.

I thought it might even be bad caps so I recapped 16 channels and 4 busses (these all operate fine and sound great).

I had the tech come over (I'm an hour out of the city so it's expensive). Basically now the -24 volt rail is oscillating. If I pull channels down to 14 - 16 channels everything operates fine. Sometimes when it has been sitting idle (cold) I can get 20 channels going on first start up. But after its been on only 14-16 channels can be on or it fails to start. On the techs scope it looked like it was a loading issue. I double checked that the new power supplies were rated for 5 amps. The back of the old Yamaha power supply says 2.5 amps.

Basically the console can run any combination of 14-16 channels. I tried pulling them all in many ways and can't find anything wrong. Tech didn't find any obvious short...no burning. I don't know where to look. I've traced just about everything I can find and it all checks out on my meter.

The power supply has been triple checked and seems to be in perfect working order...it only seems to crap out under load. What could pull the -24 v rail down? I only see one card in the console (besides meters and the headphone amp card) that has resistors on it. It is for the Program and echo inputs. Could a bad resistor cause something like this without burning?

Anyone seen anything like this? (Go slow - I'm pretty new to all of this!) Cheers,

Aaron

 

[jwhmca]

Are you swapping the channels around in the same locations or just pulling channels out? i.e. are you troubleshooting for bad channels or bad channel locations?

You could have channel strip connections that are dirty, causing excessive current in that location(s) and/or bent pins etc...

 

[pucho812]

Assuming all the channels are o.k. which is a huge assumption your back at a fault in the power supply... But lets work it from another direction, the power supply is o.k.  and you have a fault in a channel causing it to pull down the -24V rail.  I would suspect an opamp is faulty

 

[mjrippe]

Hi Aaron, I noticed you also posted this on another group that starts with "G".  You might want to check the advice there from Ike Zimbel, who is also in Toronto and is a highly qualified tech...

 

[pucho812]

link it over, would love to read it.

 

[Aaron W]

Hi Guys thanks for the replies. I am away on vacation without much wifi.

It turns out that I ordered the Acopian supplies with "V"suffix designating over-voltage protection. Apparently this was what was causing the hiccuping on start up and then that supply would automatically shut down. I called Todd at Acopian and he walked me through de-soldering component C7 on the board which is a 2.2 uf cap at 100v. Once I did this on the supply I thought was problematic - I tested the output with my multi-meter and then under load and then the opposite rail immediately failed. I removed the same cap from the twin supply and everything works perfectly. Without the over-voltage however if there was a short on the DC side from the console and it was left unchecked it would cause damage to the Acopians. I had it up and running multiple times for over an hour all seems good.

When I get back from vacation I will see about adding a couple of in-line fuses to protect the Acopian supplies.

Cheers,

Aaron

 

[Aaron W]

Yes, that is a rather good point about testing channels and also channel locations...I didn't immediately consider that. Yes I did post on another Forum "G"...but I was desperate to get any feedback....then of course slow to let you guys know what happened (but posted a reply there first) - apologies. I hope to use this forum more frequently since there are some very interesting build threads...especially on DIY microphones.

Also thanks for the tip on Ike. It turns out that he had previously done work on this console - and remembers it.

Thanks everyone for your replies.

Aaron