Yamaha EMX5000/20 SMPS parts Identification

[jbmdisco]

Hi,
I took a trade in of a Yamaha EMX5000 mixer amp a couple of months ago. Having dragged it out from the corner is was carefully placed i decided to carry out the repairs needed - a few broken pots, a general tidy and now I am left with the no power problem. Usually I sub out SMPS work as I am very wary of tackling such work (after my first experience chasing faults around the board and back again).
Starting at the beginning quickly found that the start-up resistors (6.8K 5W R101 + R134) were dead - Replaced and powered up but they fried almost instantly - Replaced again and using short circuit lamp powered up again. Showing a faint glow indicating a short. The resistors get warm reasonably quickly but don't blow.
Powered down and removed board again, making safe the caps, I have metered a few diodes and resistors - all showing correct. However having also metered the power transformer T101 on the input side there is no resistance. Yamaha Identify this as part number XY594A00 but no values. Have tried contacting yamaha with a couple of Emails (UK) to which they are reluctant to reply to with info - supplying me with details of my 'Local' service center (500 miles away) who also won't supply info (Box it up and send it to us, we'll fix it and give you a mighty bill).
Anyway - can anyone identify this tranny and give me a reference for CPC Farnell, RS components, Mouser or in the extreme DIGI-key. also been trying to get an IR2153 control chip for another SMPS - Anyone got a compatible part number as my suppliers cannot source because of ROhS regs.

Regards

Joe

[jbmdisco]

Should add, No fuses blow when amp is powered up.

[diydidi]

Definitely a controller IC by the sound of things.

[vintagekiki]

http://www.owner-manuals.com/EMX500020-owners-manual-YAMAHA.html

http://www.owner-manuals.com/EMX500020-service-manual-YAMAHA.html

[Enzo]

The transformer is going to be some Yamaha part, not an off the shelf common part. But it is very unlikely the transformer is bad anyway. It is made of wire with relatively low turn count, it will measure low.

Disconnect any load from the SMPS, like the power amps. Check all the diodes on the SMPS, in particular the rectifiers on the secondary side. Check the main switching transistors on the primary side. And VIntage could be right with the controller IC call.


But to me the suspect list is always:
load problem like a blown channel
shorted rectifier
blown switchers.

[jbmdisco]

Initial switching on, after replacing resistors, was done with smps disconnected from amp+mixer which eliminated a fault with amp. When switched on with 100w lamp load the lamp glowed reasonably dim but the resistors (start up) warmed up reasonably quickly indicating the short. I changed the rectifier with no change. I will remove and check the igbt's tomorrow and the diodes. As it is my own unit I am not in a rush to repair as I am on a learning curve with SMPS's.
Is there any decent publications regarding smps repair/diagnosis that are known of ? Internet searches come up with many including 1 from a Malaysian Gentleman who guarantees within 1 week you will be an SMPS pro
As for the IGBT's they are 1MBK50D's - are there any alternatives available as these are rather on the expensive side ?
Regards All
J.

[g1]

There is an article about SMPS here:
http://music-electronics-forum.com/t23974/#post339605

[Enzo]

I changed the rectifier with no change.

There isn;t a THE rectifier, each secondary side supply has a rectifier or two. I find one or two of those shorted somewhat more often than I do failed switchers.


Make sure you need the switchers first. I'd leave them in circuit initially and check for S_D shorts.

[jbmdisco]

Thanks for advice so far guys. I am just about there with this smps. Found 2 diodes to be blown and replaces the control chip. Only problem I am having now is locating 1mbk50 in UK. RS components is the only supplier that could get me this from their US stock but a minimum order applies and upto 90 day wait !!! Is there any reputable component specialists that I could contact in the US direct who would be able to ship this to the UK without the constraints of minimum orders etc ?

[g1]

Search with full part number, 1MBK50D-060S
Allied has them available for export, minimum quantity of 1 Fuji Semiconductor - 1MBK50D-060S - Semiconductors - IGBT - Insulated Gate Bipolar Transistor - Allied Electronics

[jbmdisco]

After finding the faulty diodes I removed 1MBK50 from the board. I performed a quick continuity check on this and found that no matter where or by which polarity the leads of the meter where attached there was full continuity between all legs transistor tester also showed to be completely shorted. I hope when these are replaced that I will be able to chalk up a success in my 1st adventure into SMPS.

Thanks folks for all advice.

[jbmdisco]

Having now replaced the 1MBK50's, I have had a 'slight' success - no longer blows the start up resistors but when I meter the transformer T104 there is no input voltage. I replaced the control IC 2153 at the same time as the switchers (could this be a faulty new part). I also metered across C118 while the unit was switched on this read 97 v which drops over about a minute to 1-2 volts. After reading a few other posts on smps I also swapped out the optocoupler with no difference. Also noticed that the relay rly101 does not switch on.
I am sure that I am really close to sorting this but there is a little diode or transistor which is sitting on the board laughing at me. Again I am in no hurry to repair this as it is for myself when repaired but it would be nice to hear something out of it !
Having nearly given in to this smps I then contacted a service center in UK who suggested I sent them the ps for repair. I did so after taking various pictures to compare and see what I had missed. 2 days later I recieved the ps back with a note that they didn't have a test rig for this ps but could supply me with a new ps !!!!!

[paleeman]

Hi jbmdisco!

1.If the transformer T101 measures no resistance on the primary side, it is definitely faulty. This transformer supplies the IR 2153 with the operating voltage. The secondary winding of T101 must deliver around 15V AC. Any transformer with 220V AC input on primary, and 13-15V AC on secondary, with 300mA, would do the trick.

2. You cannot measure any voltage on the T104 primary, because that is the SMPS transformer. Without the circuit oscillating, you have zero voltage referenced to ground. But if the circuit is oscillating, don't even try to measure on those points, with a regular voltmeter, 'cause you would end up, frying the poor thing. (100kHz oscillating frequency, with high voltage peaks, when running )

3. The relay RY101 will not click, until there is voltage present on the PSU's secondary side. Once the PSU kicks in, the relay will short the two 6K8 resistors. It acts as an in-rush current limiter.

4. The first thing that I would check, after you've replaced the IGBT's, IR2153, 6K8 resistors, removed the shorted components, does the IR 2153 has 15V DC, on its VCC pin 1., referenced to GND pin 4. Also you might want to check the if the emitter resistors, 0R1/5W R119 and R120, are blown.

This PSU is fairly simple, but quite tricky to repair without some basic knowledge of SMPS (read what g-one suggested). I will gladly walk you through the repair process.

[Enzo]

DANGER:

Remember that pin 4 of the IC is its common not ground. All those control circuits are referenced to V-, NOT ground. DO NOT ground any point in the primary side circuit of the SMPS


T101: what do you mean no resistance? To me that means zero ohms - a dead short circuit. Is that what you mean? In that case, it would instantly blow the main fuse.

Or do you mean it is open?

[paleeman]

To quote what jbmdisco wrote: " However having also metered the power transformer T101 on the input side there is no resistance."

By this, and I am pretty sure, he means that the transformer primary shows no resistance, as in not zero by measure, but as in the ohm meter shows nothing. Of course, I agree with you, Enzo, the correct term here would be infinite resistance or open circuit. But thanks to the power of deduction, we can conclude, that in this case we do not have zero ohms on the primary, but a broken winding, because the main fuse is not blown. Ha!

I, also, emphasized, to measure the IR 2153 VCC (pin 1) supply, only, to its GND (pin 4), or primary side negative.

The most important advice here is, do not engage in SMPS reapir, unless you are familiar with the concept.

cheers