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Old 04-30-2019, 06:52 AM   #1
dicky96
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Default Powersoft D4002 no power

Hi guys, anyone here familiar with these amps?

The one I have has no output from the PSU board, when switched on it draws a very small amount of power from the mains (I can see my current limiter bulbs glow very very dimly) but that is all.

I have the schematics but for the life of me can't figure out how this amp is supposed to power up

I have about 250V DC on VRECT and CTRSWITCH (when the front power switch is on) but I have no VAUX so I can't see how it could ever power up in this condition.

As much as I have looked over the schematics I can not understand where VAUX is derived. I would have expected to find a small switch mode or even a regular mains transformer providing VAUX, but no. All I can see is VAUX comes from A on SCH.QD-ALSU but it isn't obvious to me how that should work.

Or maybe I am totally misunderstanding how this amp should start up?


Also, to improve my own knowledge, while examining the schematics I did notice that Q3/Q4 form part of a PFC circuit to give VBOOST but what is the purpose of M1 in the same circuit?

Schematic attached. The version PSU I have is the SCH.QD-ALIN-14EN.01 version
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File Type: zip powersoft_series_q_d.zip (2.76 MB, 12 views)

Last edited by dicky96; 04-30-2019 at 06:53 AM..
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Old 04-30-2019, 01:44 PM   #2
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Default Re: Powersoft D4002 no power

It took a while, but i think i figured it out - VAUX is most likely created by U1 (on ALSU__13EN), driving Q6 on the main PSU board (on ALIN__14EN). L1/2 and L3/4 form the primary and the secondary of an "improvised" flyback converter.

Not quite sure where "OV OUT" comes from, or what J5 connects to, though.



Looking at ALSU__13EN, looks like Q3/Q4 and M1 are driven in parallel at the same time, but M1 is having its turn-off delayed. I wouldn't be surprised if it had to do with the different body-diode recovery speeds between the IGBTs and the MOSFET.
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Old 05-01-2019, 03:30 AM   #3
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Default Re: Powersoft D4002 no power

Hi Khron, thanks for your time and effort.

Looking at that circuit it seems zeners D1, D2, D3, D25 form a high voltage divider circuit that drops 373V and produces OV OUT which would be 4.7V across zener D4. From that it seems reasonable that OV OUT is possibly an Overvoltage signal (also clue in the name).

That would mean there is a high voltage input on D and if this is really an Overvoltage detect circuit then D must be derived from VBOOST somewhere to have such a high potential.

Of course at startup VBOOST isn't there yet but should still be about 250V on D until the PFC kicks in. U1 Vcc would then derive from R3+R4 in series.

Regards J5, the schematic says 'X Collaudo' and I know this is an Italian amplifier. A quick Google Translate says that means 'X Test'

I'll have a look to see if U1 has Vcc and see what is happening around that IC (datasheet says its a PWM controller which would make sense)

Having said that it's a public holiday today here is Gran Canaria and I think it's only right to observe the Spanish public holidays here in my adopted country of residence. Even though they have at least 15 of them a year compared to the measly 7 we got in England! It's a matter of respect lol.

So I'll look tomorrow and report back.

Rich.
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Old 05-01-2019, 04:08 AM   #4
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Default Re: Powersoft D4002 no power

The source of the voltage for that small flyback kinda baffled me (too), but it can't be coming from "D" (the switching MOSFET's drain pin), because that would defeat the whole flyback converter.

I'd much rather expect the input voltage to that to be where the pin 2 of J5 is.

http://uzzors2k.4hv.org/projectfiles...0Converter.GIF

The (high) input voltage should come in at the other end of the "primary" than where the switching MOSFET's drain is connected.

Hmmmmm... There might be some inconsistency in the schematic labeling, though. See that "CTRL S", that is only connected to pin 1 of J3, both on ALIN and ALSU? What're the odds that is actually the same signal as the "CTRSWITCH" on ALIN?

That's the only possible way, that i can see, that the small flyback converter CAN get its input voltage. So you'll wanna look at J6, that's at the "front" end of the group of 8 capacitors on the front-right side of the power supply board.

[later edit] Or is that where the front panel "power switch" connects to?


On a side-note, I don't really get how the feedback for that small flyback works, though, with D5 pointing the way it is.

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Old 05-01-2019, 05:29 AM   #5
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Default Re: Powersoft D4002 no power

J6 is where the front panel on/off switch connects and the switch is working OK

It is rather an odd circuit I agree, but checking for Vcc on U1 seems a very good place to start diagnosis. Will try that tomorrow and see if I can work out where the supply actually comes from.

Of course if U1 does have Vcc but isn't oscillating for some reason I don't really have to care exactly how the Vcc supply got there

best regards

Rich.
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Old 05-01-2019, 06:04 AM   #6
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Default Re: Powersoft D4002 no power

Fair point. Might also be worth double-checking the associated MOSFET (Q6 on the main board). If that happened to kick the bucket, it's not unheard of for it to have taken out the UC3842 as well.

A potentially more telling test would be to see if the UC3842 puts out 5V on its "Vref" pin 8. If it doesn't, despite having Vcc (which should be higher than its UVLO threshold of 16V), then you know for sure that's a dud.

Either way, on the bright side, no "esoteric" components used there, so even if you had to fully rebuild that section, the (easy-to-find) parts shouldn't be more than a handful of euros.

Out of sheer curiosity, whenever you pop the hood again, do a continuity-check between pin 1 of J3, and pin 2 of J5 - i'd expect those to be in fact directly connected.
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Old 05-16-2019, 06:30 AM   #7
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Default Re: Powersoft D4002 no power

I've no got my new workshop set up and I'm back to looking at this amplifier

To clarify one thing - J5 on ALSU is a 2 pin header, it does not connect to anything.

There is definitely a problem in this area as U1 does not have any Vcc and I still can't figure out where it should come from.

The cathode of D1 slowly increases up to 4.5V over a number of seconds, like a capacitor is charginf through a high value resistor.

J5 Pin 2 does the same thing and stabilises at 4.25V

I removed and tested the FET Q6 on QALIN and it test OK

I tested U1 [UC3842] in circuit using my bench PSU, with the amplifier unpowered. At 16.5V Vcc applied to pin 7 I get 5.0V on Vref and it is oscillating nicely on Pin 6

So U1 appears to work fine and so does Q6 - just I have no Vcc when the amp is powered on

Any thoughts?

Rich
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Old 05-16-2019, 10:48 AM   #8
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Default Re: Powersoft D4002 no power

any idea where CTRSWITCH and CTRL S connect? I see it on the diagram D5 connects to R42, to J6 to CTRSWITCH. CTRL S has a capacitor on it and thats it.
Is ctrswitch and ctrl s connected? That looks like it might be a source for a small standby voltage, maybe?
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Old 05-16-2019, 11:48 AM   #9
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Default Re: Powersoft D4002 no power

HI R_J

CTRSWITCH is the SPST front panel on/off switch which connects to J6. There was some discussion it could also be same as as CTRL S (or maybe CTRL S is just the other side of the switch pole)

I didn't get to look today, but I will tomorrow. The front panel switch does work by the way and there is high voltage on both pins of J6 when the switch is turned on.

It seems obvious to me that this PSU can not start unless U1 has Vcc. It would make sense that this has to come from VRECT somewhere (or VBOOST as the PCF circuit isn't able to run yet so that would be the same thing really)

Hmm it does seem very odd that CTRL S shows connected to J3 pin 1 but does not show anywhere else on schematic ALSU. But it must go somewhere otherwise why connect it to J3 Pin 1 in the first place.....

Rich

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Old 05-16-2019, 02:46 PM   #10
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Default Re: Powersoft D4002 no power

I'd expect pin 2 of J5 to connect to either VRECT or VBOOST. That's the only way the U1 / UC3842-operated flyback can work.

Although, in many other such supplies, its Vcc capacitor is far larger (10-47uF).

When that ages and loses capacitance, the thing goes into a hiccup mode, where the cap gets trickle-charged through those large value resistors, but when the chip powers up and takes a big gulp of current, there's not enough to keep it on until the next cycle (where it would then power itself from a winding on the flyback transformer).

I'd try to trace out all the places that node is connected to. "That node" = the common point of R1, R3, J5 (pin 2) and L1. That has to connect to the high-voltage DC bus - otherwise there's no point for D1-4 being the values they are. Speaking of which, it might be interesting to check those, as well.
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Old 05-17-2019, 05:37 AM   #11
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Default Re: Powersoft D4002 no power

Ahaa I got it

The Junction L1, R1, J5 pin 2 does indeed connect directly to J3 Pin 1 (CTRL S) on ALSU. It just doesn't show the connection on the schematic because whoever created the schematic obviously didn't do their job properly!

CTRL S is one side of the front panel power switch. CTRSWITCH is the othe side.

I previously thought I had a high voltage on CTRL S and CTRSWITCH but I don't, just about 11V slowly charging up.

The fault was a simple one - I'm surprised I didn't find it before but think somewhere down the line I've confused myself

R42 on QALIN14 is reading very high resistance (should be 22 ohm)

I'm not sure what wattage that is, can I tell by the size? I think it may be 2W... in which case would this physically smaller resistor be OK as a replacement? I'm sure that is 2W, just a different type. See pics
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File Type: jpg 20190517_121752.jpg (739.3 KB, 5 views)
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Old 05-17-2019, 06:38 AM   #12
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Default Re: Powersoft D4002 no power

At least for testing, i'm sure it'll do the job. It's there just to act as a "soft fuse", as it were, to limit the current drawn by the control board circuitry.

If they're rated the same (and especially if the new one's not some random Chinese "ebay special), then the new one should be fine, despite the smaller physical size.

Glad we finally manage to nail the main(?) issue Looking forward to hearing back post-resistor-swap...
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Old 05-17-2019, 07:27 AM   #13
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Default Re: Powersoft D4002 no power

Hi Khron
Yes it's fixed and I have to say mostly due to your help

What's even better this amp came to me via a new customer i picked up who has become a regular. He has a previous repair shop and they couldn't fix this one.

And it's funny how it turned out so simple in the end, isn't that just the way it goes sometime..

I got a whole box full of those type of resistors, I picked them up with a load of new old stock at an Amateur Radio rally some years ago.

I fitted and ran the amp for about 30 mins. The resistor isn't even warm to the touch afterwards. I guess it is gonna be just fine

Thanks for the help, if you ever find yourself down here in the sunny south of Gran Canaria you are welcome to join me for a beer or three

Rich
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Old 05-17-2019, 08:59 AM   #14
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Default Re: Powersoft D4002 no power

I'll have to keep that in mind, then But yeah, glad to hear that's all sorted out.

I've got a bit of a monster on my "operating table" myself (Ram Audio S6000 / LD Systems SP6k). One of the four IGBT's in the power supply was shorted, along with one of the two IR2110S drivers, but after fixing that, turns out that at least one channel's toast as well...
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