Faulty ICEpower 50ASX2

[almamater]

Hello everyone.

I have an audio amplifier (which doesn't work) and I'd like to get it working because it's good stuff (Fender Rumble 150 Bass Amplifier Head) 

It just doesn't turn on. From what I can see the power supply (ICEpower 50ASX2) doesn't have any active output... but it's something more complex than the ones I've been trying to repair and learn, this one has more components 

If anyone can give me some help.

I found some information available for this power supply:

Esquema do Amplificador
Manual da Fonte
Datasheet da Fonte

But I can't find the schematic of the entire circuit\components







I've been doing some measurements and unfortunately the fuses (which are about 3) are all fine, the 2 giant capacitors (primary side) have a voltage of ~150V each

On the secondary side, I don't have any voltage, even on the Enable Pin that should be +5V (according to the manual) has 0V.

There is one component that is an NTC 5.0 and has a resistance of ~5R, which makes me believe that it's fine too.

I don't know however if this is normal:

There are 2 components at the bottom, and next to the larger transformer (on the primary side), which on one side have voltage but not on the other, it's a capacitor and a black component (looks like a diode, it says "EB 11"), the voltages in this part are like this:



is supposed to have on one side of the capacitor, and that diode, voltage but not on the other side?

Testing the "diode EB 11" in the normal way (with the multimeter in the diode mode) has 0.445 and in the reverse it has 2.950 (but it could be because it is in the circuit, I haven't tested it outside).

All the elect. capacitors from the board, i measured them (with the multimeter in the capacitor mode) and the values, even being in the circuit (I didn't remove them), seems to be ok, and they seem to be of good brand and quality..


There are 2 large transistors next to the larger transformer (primary side), are they responsible for activating the voltages?

[Manul]

So the controller seems to be SG2525 SG3525. Does it have power? What about voltage on this capacitor?

[almamater]

Thanks for the reply.

The Pin Vi (15) of the SG3525 is connected to the capacitor C300 the voltage oscillates between 0 and 1.3v..

(The Vc (13) pin have the same voltage.. 0 and 1.3v..)

[Manul]

I guess I misread part number from picture, it is SG3525. But these ICs are very similar, so it does not matter. As far as I understand, it should get power on pin 15, without it nothing can start. So that supply might have problem or it could be that IC tries to start and shorts the supply. I would try to remove all power, wait until capacitors discharge and try to reverse engineer how pin 15 is powered.

[almamater]

From what I see pin 15 is connected to a circuit that has a PNP Transistor (BCP53):

I'll try to check if this PNP is working ..



P.S.:
The PNP has continuity between The Collector and the Emitter.
Base and Emitter has ~15v input. But Collector Output is only ~1.3V

Should i remove this transistor ant test it out of circuit?

[Manul]

The PNP has continuity between The Collector and the Emitter.
Base and Emitter has ~15v input. But Collector Output is only ~1.3V

If both base and emitter is at 15V, so it means there is 0V between them? Is this what you mean? Then it should be off. What exactly you mean by saying that there is continuity?

It can be hard to follow such PSU without schematic. Scope with differential probe is very useful. For example, here in this case we don't know if this PNP is off all the time or pulsed on with short pulses.

[almamater]

Sorry, by "continuity" i mean that i test it with the multimeter (postitive meter lead to the COLLECTOR (C) and the negative meter lead to the EMITTER (E)) supposedly there shouldn't be conductivity..

And yes, he has ~15v at Base and Emissor Pins...

[Manul]

According to datasheet there are three protection circuits which may stop the PSU from running. Overcurrent protection would keep PSU trying to restart (cycling). It is good to keep in mind, because it might be related. It also has low mains voltage detection. If it thinks voltage is too low, it might not start.

I wonder if you short PNP base and emitter (to guarantee it is off) does it still have 1.3V on collector? If no, then probably it means that it is actually trying to start in quick cycles and 1.3V is what your multimeter sees as average. Then the suspicion would move to overcurrent protection turning it off very rapidly after it starts. Do you by any chance hear something? Like clicking, buzzing, something like that? Or is it perfectly silent?

[Audiorepair]

Check C300 isn't faulty.


Unless you have at least a constant 8v on pin15 the IC will not run.

Usually on power up this is supplied by a string of resistors connected to the rectified mains HT.
Once the IC starts, the supply via the mains HT through the high value resistors is not enough to keep up with the extra current draw, and the IC is then supplied via the now working power supply.
Is the PNP transistor actually acting as a diode, which takes over from the resistor string from HT once the power supply is running?


It doesn't make sense that you are measuring very low voltages (1.3v) on pin 15 yet the IC is still attempting to start.

[almamater]

Hello and thanks.

The power supply is perfectly silent, no clicking or buzzing noises..

I made a little video:
http://youtu.be/VXpCVsWPq4M

[Manul]

As a further test I suggest to solder a small wire to short base and emitter of BCP53. Does it still have 1.3V on collector?

[almamater]

Hello.

I connected the Emitter with the Base directly and the collector now has 0v, do it means that this PNP transistor is ok?

[Manul]

I would guess that it is good. This PNP seems to control power to the SG3525. The voltage 1.3V was strange, but after this test we can probably say that it was just cycling on-off, and 1.3V is average (multimeter is not fast enough to show short pulses). When you forced PNP to be off - there is 0V to SG3525. So it can be cycling, which means that PSU senses something worng and goes shutdown - restart (more likely). Or it could be something wrong with the circuit which is driving the base of that PNP (less likely).

[Manul]

For such repair it would be very useful to have isolation transformer, then you could use scope to look the signals. Or differential probe, but these are quite expensive.

[Audiorepair]

Isolation transformers can be cheap, and invaluable with SMPS.

https://www.screwfix.com/p/carroll-meynell-1-5kva-intermittent-isolation-transformer-230v-230v/752HV?tc=NA7&ds_kid=92700055281954493&ds_rl=1249401&gclid=Cj0KCQjw_dWGBhDAARIsAMcYuJxrvBJdl7Q7A0sLYAhGohyYVMQ-l7Pf1wDbsLA-oBjr9VH5PDzTPPEaAnqTEALw_wcB&gclsrc=aw.ds

[Chris56000]

Hi!

It's very likely there's a short–circuit across one or more of the power supply rails, most likely due to switching MOSFET failures in the output stages – you'll need to test between the drain (middle or tab) and the source (right–hand leg of TO–220 or surface mount type) – if you do find a MOSFET has gone you also need to examine the inductors in the Output Stage that filter the audio–modulated PWM back into audio – failure of these inductors is usually self–evident as obvious overheating damage!

If there is signs of such damage, then you may have to bin the complete module as ICE Power/B & O will NOT support component level repairs on their ICEPower modules if anything like a choke, transformer or specialist IC has been damaged – I think these use a custom A–D pwm driver device if my memory serves me correctly!

If you're certain there's no obvious physical damage to flter inductors, feed chokes, etc., that would potentially write the module off, then you might be able to persue it further – begin with the Output MOSFETs, checking them for shorts drain/source, then look at the output rectifier diodes from the power supply transformer in the switch–mode PSU – my experience with this type of unit is that the rectifier diodes are usually OK and the fault is down to short–circuits across the power amplifier supply rails, again down to faulty MOSFETs as mentioned above!

Chris Williams

[almamater]

Hello.

So the MOSFETS you mentioned are the TR301 and TR300 (two 9N50C NPN Mosfets)?



They has:

TR301
G -> 0v
D -> 295v
S -> 0v


TR300
G -> 290v
D -> 311v
S -> 290v

The secondary side doesn't has any voltage..

[Chris56000]

Hi!

TR300 and TR301 are the primary side switching MOSFETs and from the readings you provided they are not short circuited – they are simply not being driven!

The MOSFETs I was referring to in my previous note are NOT TR300 and TR301 – I was referring to the output stage PWM class D switching MOSFETs on the right-hand side of the board above the output coils!

Chris Williams

[Manul]

The mosfets Chris56000 mentioned are these. You should test them with PSU off, maybe best to use diode mode. Look if they are shorted. Could try to test other things on the output side too. Also output power rails. There are 4 electrolytic capacitors on the output side, check if they are not shorted. 5V rail too.

What seems puzzling to me is that the PSU seems to not make any output at all. With the shorted output I would expect at least some 10's of millivolts apearing on the output until overcurrent kicks in. Usually together with some ticking sound from transformer.

TR301
G -> 0v
D -> 295v
S -> 0v


TR300
G -> 290v
D -> 311v
S -> 290v

Generally, it is a bit dangerous to probe primary side mosfet gate (G) with multimeter. If the gate driver is in high impedance (for example, not powered), multimeter and lead capacitance could potentially cause false turn on.

[almamater]

Oh ok!

With multimeter in Diode Mode i´m not sure. The readings are strange.. for all of them.

D->S   2.68
S-> D  0.52
G-> S  1.62
S-> G  0.57
G->D  1.62
D->G  2.82

Probably it's better to take them out of the circuit and make the test..

[Manul]

Oh ok!

With multimeter in Diode Mode i´m not sure. The readings are strange.. for all of them.

D->S   2.68
S-> D  0.52
G-> S  1.62
S-> G  0.57
G->D  1.62
D->G  2.82

Probably it's better to take them out of the circuit and make the test..

All 4 of them measure like this? I would say it looks really good. What about output rails? Nothing shorted? Did you measure on the capacitors? What about +5 rail?

[RayRay]

I'd suggest you replace the 35V 470UF capacitors. Visually, I can tell that at least 3 of em are faulty (the top of a healthy capacitor is suppose to be flat, and those look like they're gonna burst!). Since your'e from Finland, I think you'd be best getting em from TME
https://www.tme.eu/en/details/uhw1v471mpd/105degc-tht-electrolytic-capacitors/nichicon/

Edit: Sorry, didn't notice that that particular one is out of stock (not to mention the minimum quantity!). Get these instead:
https://www.tme.eu/en/details/eeufr1h471/tht-low-imped-electrolytic-capacitors/panasonic/

[Manul]

I'd suggest you replace the 35V 470UF capacitors. Visually, I can tell that at least 3 of em are faulty (the top of a healthy capacitor is suppose to be flat, and those look like they're gonna burst!).

Really?

[RayRay]

Really?

From a side profile (2nd pic, first post) their top doesn't look good.

[Manul]

From a side profile (2nd pic, first post) their top doesn't look good.

Must be lens distortion.