Yamaha EMX512SC

[lowell]

This came in with no power. Found that the pre-fuse resistors were getting quite hot with my limiter in place. Both switching MOSFETs are toast. Tested all surrounding, replaced FETs, and the Gate Driver to be sure.

Now R440, (startup resistor?) is getting real hot. Found that the IGBT was leaking, replaced it as well. Still, R440 getting hot. I'm suspecting the pre-biased transistor that turns the IGBT on, Q415, isn't conducting, therefore causing the IGBT to turn on too much and pull too much current through R440. Sound like I'm on the right Path? If so, since DTC114 transistors are obsolete, any suggestions on a sub?

Power amp is on pg. 140
http://bmamps.com/Schematics/Yamaha/...e%20manual.pdf

[lowell]

Here's the DTC114ESA data: http://www.mouser.com/ds/2/395/DTC11...C14-524805.pdf

Looks like this might work as a direct replacement? http://www.mouser.com/ds/2/149/FJN3302R-889141.pdf

[Jazz P Bass]

The startup resistors are there to 'startup'.

Then the relay kicks in.

If the relay is not closing you have other issues.

Aside: I have never used a limiter successfully on an SMPS. (to the point where I don't.)

[lowell]

Did you take a peek at the power supply? I put a "?" because I wasn't sure if I was right about that. Regardless, this resistor is getting real hot, with the limiter in circuit.

Shall I try it without the limiter? So do you just throw SMPS on after a repair? Or use a variac? What's your approach?

[J M Fahey]

Looks like your power supply is not doing the full startup cycle.
As JPB said, R418 and R424 are the surge limiters, a second or two after the supply reached reasonably close to intended voltages, RY401 shorts them; I guess it never gets activated.
And yes, it might be caused by the lamp limiter.

As of R440, same thing: it, together with Q414 , supply startup voltage/current to IC403.
As soon as voltage at Q403 IN rail reaches some 32 or 33V, Q415 turns on and clamps down Q414 gate, so it works like an "amplified Zener".
After main transformer T1 gets driven, low voltage secondary P2/P3 feeds the primary 15V supply and both R440 and Q414 turn off for good; you never reach that point.

Personally Iīd plug supply straight to mains with the proper fuse, and watch it closely, also watch R418 and 424 for overheating.

Everything only after having checked all transistors and diodes are not shorted and of course with no load attached .
24V coil RY401 gets triggered straight from +/-15V main rails, on the secondary side, do not confuse with primary +15V supply which is "hot".
So no +/-15V, no startup resistors shunting.

Everything points to lamp limiter doing its job "too well".

[nickb]

... soon as voltage at Q403...

Minor typo, but could be confusing - should be IC403.

The crucial thing is it has be be switching in order for the auxiliary power to be present and so turn off Q414.

A suggestion: When you've got it all working glue a piece of foam rubber between the switcher PCB and the metal chassis to prevent the board from touching the chassis and frying the PSU. I seen a few of these that have been moved hard with the power on with bad results.

[Jazz P Bass]

This may be of some help.

The EMX212S uses a similar power supply.

EMX212S_Pwr Supp.pdf

There is a Repair Guide in the service manual.

EMX212S_ PS Repair Guide.pdf

Take note that Yamaha recommends a 10K load on the + - 15Vdc supply when testing just the power supply.

[lowell]

Thanks guys. So I followed the repair guide and found that one reading, the 5.5k from pin3 to pin4 of IC402, was really low. So I replaced the 15v regulator. Still same symptoms, R440 glowing red hot. I have it going thru my variac. Turning it up slowly causes this and turning it on at full 120v causes it too.

The shunt relay before the rectifier works with my supply, but there is no +/-15v from the secondary reaching the relay. Not sure if this is because of a primary issue or secondary issue. The fuse has yet to blow so it doesn't seem like this issue is causing too much fault current. I have no load on any of the supplies except I do have 10k between +/-15v secondary supplies.

I am getting ~5v at the bottom of R438, the 120k resistor string. Which makes me think that Q415 is ok and is conducting.

so I'm a bit unclear where to look next. What are likely culprits at this point? Primary or secondary components? The 15v secondary supplies?

[Jazz P Bass]

"one reading, the 5.5k from pin3 to pin4 of IC402, was really low. So I replaced the 15v regulator"

I believe that the low reading on IC402, pin 3 to pin 4, indicates that the ic itself is at fault.

[lowell]

I had already replaced it. I guess it's possible it went bad again during testing.

[Jazz P Bass]

Measure the one that you took out.
Remove the one that is installed & check it.

If they test high resistance then that leaves the PMW ic 401.

As an aside: I don't know that a variac is helping any more than the lamp limiter.

[J M Fahey]

Iīd use an isolation transformer (primary supply side is DEADLY HOT) and scope the PWM IC, I guess there is no oscillation so no Mosfet/IGBT drive so no secondary voltages so no relay triggering-

Second option, is that the transformer itself is dead or has some winding open, but thatīs a very distant second possibility.

[lowell]

Ok will check those thanks

[lowell]

Pulled IC402, it is ok. The circuit measures short between pin 4 (ground) and pins 1/2 (outputs of controller IC). Ordered the controller IC. Hoping this does it.

[lowell]

Alright, well, got the PSU fixed after replacing the Controller IC. At least I think I do. With all the load resistors attached to the supply outputs per the repair guide, There is about a 1v difference between +/- supplies. Meaning I have about +48v and -47v. Is this of significance? The thing turns on and doesn't shutdown.

Now, when I connect the PA rail supplies, it still runs. But when I connect the PA CN101 ribbon cable, it's another story. It turns on for 1 second, then the Relay, before the rectifier on the primary side, shuts it down. The ribbon cable connects the AC input signals, SMPS shutdown modes, and bias voltages for the PA.

I've tested all the outputs, drivers, and the MOSFETS as these are all mounted to the heatsink. They all check as good with my meter semi-function test. All Re's checkout at .47ohms.

I'm thinking that there is DC offset, and that is feeding to the SMPS photo-coupler via the ribbon cable "DC" pin, which is then shutting it down. Does this seem right?

So at this point, how do I continue troubleshooting if the thing keeps shutting down on me? Without the ribbon cable connected, the PA doesn't have any bias voltages.

Thanks!