Yamaha EMX5000 no power

[dosmun]

EMX5000 was working then shut down. Got it home and it started working again. A day or two later shut down again. This happened a couple more times before shutting down and won't turn back on. All fuses are fine.

I am assuming the problem is in SMPS 2/2. I do have the Service manual and PS diagrams. I am somewhat of a novice. I've googled this and read what I could find, it's sounds like it could be somewhat tricky without experience with SMPS.
Could someone possibly help me out troubleshooting this? Thanks in advance for any help.

[Enzo]

Don't assume. You could be right, or the SMPS could be doing its job by shutting down when a load problem exists. If we can disconect the power amp from the SMPS, that might help us look.

[dosmun]

No speakers plugged in.
3 wire harness to mixer ((B+,B-) disconnected.

Thank you Enzo.

[dosmun]

What is the next step in troubleshooting this? Thanks in advance.

[nickb]

I guess Enzo is busy. So I'll step into the breach for now. The 3 wire connector is the power to the main amp. The other voltage rails will still be connected via the 10 way cable so leave that in place for now. Power up and check the DCV on the pins of the B+/- connector to see if the power supply stays up. Take great care not to short any pins out and be aware these are something like 100V each. If the SMPS is still shutting down unplug the 10 way cable and retest. If it's still shutting down the SMPS is bad. If OK then I'd check that there is not a problem on on the rails carried on the 10 way cable.

[dosmun]

0volts on B+/- rails and 10 way cable

[Jazz P Bass]

Quote: "If the SMPS is still shutting down unplug the 10 way cable and retest.".

For those of you playing along from home: I have included the appropriate SMPS files.

emx-5000 SMPS Layout.pdf

emx-5000 SMPS.pdf

[dosmun]

I'm getting 120VAC on the primary side of T101.

[Enzo]

R101, 134, either one open? (upper right feeding main rectifier - they are soft start resistors.)

[dosmun]

Both are good (7 ohms)

[Jazz P Bass]

IC102 is the controller chip.

If you have voltage at pin 1 in reference to pin 4 and the supply will not start, I would replace that chip.

[dosmun]

Ovolts on Control chip

[dosmun]

To measure voltage at the Regulator IC 101, do I reference ground or common?
Can I measure the Diodes D103 & D105 in circuit?

[Enzo]

Common, nothing in this primary side circuit is referenced to ground. BEWARE, common is sitting about -170vDC ffrom ground.

This is a simple supply, you measures 120vAC at the primary of the little transformer T101, but is there AC on the secondary? 20vAC give or take 10. And with power off, is the primary intact? ie it is not open?

The diodes? They are just diodes. They are open, they are shorted, or they are working. Unusual to be anything else. besides, you can test them by their function. if there is no secondary AC, then there is nothing for the diode to rectify. Your regulator appears not to output 15v, so is there DC at its input pin?

[dosmun]

Ok update: was still getting sketchy measurements thought maybe I was doing some of them wrong (probably was at times). So I went back to SMPS 1/2 and poked around, not getting voltage. Pulled board and found AC input jack with bad solder joints. Solder would not even stick to posts. Pulled, cleaned, restored and happy to say it is now working.

I originally suspected this or the switch with it being intermittent before it completely quit. Somehow fooled myself into looking further down stream. Anyway lesson relearned. I did learn some stuff anyway so not a total waste of time.

Thanks again for everyone's help you guys are the best!