Logitech Z506 power supply

[budm]

Re: Logitech Z506 power supply

"I'm beginning to guess that the transformer was the culprit (also found the primary coil measures almost nothing, about less than 0.3 ohm only" it has low resistance because you are measuring the DCR (DC resistance of the transformer winding), the transformer is made to be connected to high frequency switching DC by the SMPS, at those frequency, the impedance will be much higher than DC resistance. You have to use ringer tester and LCR to verify the transformer.

[lexwalker]

Re: Logitech Z506 power supply

Perhaps that 1N4007 diode really should be a FR107 or the like. AKA maybe the diode has too much switching losses.

The original diode was an 1N4007 (weird choice for the snubber), in fact. Just keeps blowing up whenever the power supply fails. So I put an 1N5408 diode there, and you can see its kinda big and cannot fit on the top of the PCB thus soldered it to the bottom...

But yeah, you replaced the PSU with that nice looking one, good job!

The first plan to make it sit but there were no secure places to hold down the new power supply board. Didn't like to use heat glue as I was afraid it may not hold nicely inside the very hot subwoofer enclosure environment. Thus I went for the screw on the heatsink, but that means it will be standing. Secured either side with double sided tape (pressed down firmly) to prevent it moving side to side. Two of the wires I kept short to make an anchor on either side.

Were the panasonic capacitors on the output of that PSU when you took it apart? If so, good job HP/whomever manufactured that PSU!

Nopes, the original capacitor was Ltec LXY series (ultra low impedance). Just did not trust them at all, so decided to replace them with Panasonic FR series. Both are very close, in terms of ripple current (1820mA vs 1790mA) and ESR (0.023R vs 0.028R). Perhaps I should go for Panasonic FM series (ripple current handling of 2180mA and ESR of 0.019R for 680uF 25VDC) but did not have those in hand/stock at that moment...

[ben7]

Re: Logitech Z506 power supply

Perhaps that 1N4007 diode really should be a FR107 or the like. AKA maybe the diode has too much switching losses.

But yeah, you replaced the PSU with that nice looking one, good job!
Were the panasonic capacitors on the output of that PSU when you took it apart? If so, good job HP/whomever manufactured that PSU!

[lexwalker]

Re: Logitech Z506 power supply

That snubber diode is the weak link. It must be replaced with a part rated 3A or more.

Unfortunately its not that FR207 diode that keeps blowing up, but the 1N4007S diode. It got to a point where I decided to replace it with power diode. In the next iteration, I've checked carefully, tested and replaced nearly all the discrete and SMD components as well (except for a few like the transformer). This time I could play it loud (volume almost full) in stereo. However as soon as I plug in all the speakers for the rear and center channels, the power supply went pop again! At this point, I'm beginning to guess that the transformer was the culprit (also found the primary coil measures almost nothing, about less than 0.3 ohm only)...

An interesting observation here, even though the audio source is stereo only however can hear the sounds not only at the front but also at the rear channels (no thanks to the heavy crosstalk). Add to that I've already replaced the power amplifier I.C also. In other words, all speakers are active even with only stereo music. That puts a much higher load on the underpowered (junk) power supply. My guess is that Logitech did not expect all speakers to be active together at the same time...

At this point i would just throw an EEEPC or Aspire One power adapter in there and call it a day.

Thanks for the advice, I went this path after giving up on the original power supply. Found a nice 90W HP adapter and did some modifications to the original board so that I could mount it inside rather than left hanging outside.

[Th3_uN1Qu3]

Re: Logitech Z506 power supply

That snubber diode is the weak link. It must be replaced with a part rated 3A or more.

At this point i would just throw an EEEPC or Aspire One power adapter in there and call it a day.

[lexwalker]

Re: Logitech Z506 power supply

Have not had much time to look thru the circuit yet, although the speaker is still with me (awaiting further repairs on that power amplifier I.C).

More update on that power supply. The power amplifier I.C finally arrived and put into place. At low volumes sounds fine. And then in just under a minute after cranking the volume at a little more than half (with a slow bass heavy song playing), the power supply blew again in same manner as it originally sent it! And that was just in stereo, only 2 channels used and have not used the 5.1 surround test yet...

The same diode at the turn off snubber this time cracked in half rather than becoming shorted. The same two rectifier diodes also went shorted. And the main TOP258MN I.C is cracked in half again (can see that from the side this time). Could there be a weak link/component somewhere?

[momaka]

Re: Logitech Z506 power supply

With the LM358 op-amp removed, check what voltages you are getting to its power and input pins. Since this is a dual op-amp IC, also check (without power) if its second output (pin 7) is shorted to ground or any of the supply rails. If everything appears to be normal, it could be that it just died. Why ? I don't know. But I have seen a few LM358 die/overheat like that for no reason, and upon being replaced, the circuit worked fine again. At least 358 op-amps are really cheap and abundant. I don't think I've ever needed to buy any. Many PC motherboards will have one. I have quite a few junk ones, and they all have one. So check your parts box .
Any 358 variant should do, no just ones with LM prefix.

[senz_90]

Re: Logitech Z506 power supply

aha. i was right. it is quite common today to see op amp ic on audio amplifier since transistor based audio amplifier is more complicated than one single ic op amp. unfortunately, i don't understand how to troubleshoot audio amplifier.

[budm]

Re: Logitech Z506 power supply

R700 may be isolation resistor which may be connected to another output of another circuit, you need to trace out where the other end of R700 is connected to.

[HWLemfoerder]

Re: Logitech Z506 power supply

OK, from the beginning ...

When I got these z506, no sound was comming out of the speakers.
Not even the background noise from the power supply (50Hz).
Possibly muted ?

First thought was the power supply. But that was ok. I replaced it
by a external power supply unit with current limitation.

I connected the right front speaker which has the power switch.
When the volume control was completly turned to the left, the power
consumption was 40mA. When turning it to the right, 230mA. Looking
at the standby input of both STA540. Switching from 0V to 5V when
turning volume control to the right.

After that I checked the main volume control IC PT2325. Also the standby
pin of that IC was changing from VCC to GND when turning right.

But no voltage at the supply pins. I followed the wires on the PCB and
got to the input of an 7812 TO-92 linear power regulator. Input voltage
2,3V. Not very much.

I supplied this pin external with 14V. Below that level, a +12V regulator
won't work correctly. So this must be the right input voltage for this
part of the system. Current consumption was 250mA (!)
But now the system was working. I checked all channels of the PT2325 with
a 1kHz signal and connected all speakers. Sound at every channel ...

I broke up the power connection to every IC connected to this supply.
All OP-AMP 4885 consume 2,5mA, the PTC325 30mA VCCA and 30mA VCCV.
Can't tell if theses values are to high, no typical value was inside
the datasheet.

When I got to the LM385, it was hot ...
I desoldered it and searched for an datasheet. I was confused about
the function of this IC. So I took a look with an microscope.

I was wrong, it is an LM358, as you can see with the attached images.
But why are pin 1&2 short cut ? OK, could be an voltage follower
with low impedance. But why a resistor (R700) 10k at the output ?
Where is the low impedance then ?

Regards ...

[senz_90]

Re: Logitech Z506 power supply

maybe LM 358 Op Amp IC?

[lexwalker]

Re: Logitech Z506 power supply

I just got a defective Z-506, the power supply is ok (hopefully
long). On the amplifier board two of the SO-8 IC get hot when
powering up the system.

In the picture I marked both Ic with a red box.

IC4 is a MC4558 (OpAmp).
IC 402 is a LM385 (Reference Voltage?)

Can someone make a scan or something similar from his
board for me? The pinout of an LM385 voltage reference does
not match the pads on the PCB. Some pins that are specified as
not connected inside the LM385 data sheet are connected to
resistors and capacitors on the board.

Sometimes current reference I.Cs can get hot. As for the opamp I.C, possible internal short which made it became hot. Anyway, what was the problem with the speaker system in the first place? What are the symptoms? You have not mentioned that to begin with...

Maybe LM385 is not right? Which IC is right?

Perhaps someone has also a schematic for this amplifier?

Thanks for the help ...

Have not had much time to look thru the circuit yet, although the speaker is still with me (awaiting further repairs on that power amplifier I.C).

[HWLemfoerder]

Re: Logitech Z506 power supply

Hello,

I am new to this forum and I'm not sure if I
should attach my problem to this threat.

I just got a defective Z-506, the power supply is ok (hopefully
long). On the amplifier board two of the SO-8 IC get hot when
powering up the system.

In the picture I marked both Ic with a red box.

IC4 is a MC4558 (OpAmp).
IC 402 is a LM385 (Reference Voltage?)

Can someone make a scan or something similar from his
board for me? The pinout of an LM385 voltage reference does
not match the pads on the PCB. Some pins that are specified as
not connected inside the LM385 data sheet are connected to
resistors and capacitors on the board.

Maybe LM385 is not right? Which IC is right?

Perhaps someone has also a schematic for this amplifier?

Thanks for the help ...

[lexwalker]

Re: Logitech Z506 power supply

Anyway one of the channels have a scratchy sound, possible badcap at audio input or the speaker output section. Will look into this further, though that will be another tale....

A little update on that problem. After some quick diagnostics, looks like its not badcap problem but the power amplifier I.C itself.

[dj_ricoh]

Re: Logitech Z506 power supply

Yes, 1206 size metric which is large enough to span 4mm to 5mm lead spacing. This one: element14: 1206GA680KAT1A - AVX - CAP, MLCC, C0G/NP0, 68PF, 2KV...

Exactly this...Anyway one of the channels have a scratchy sound, possible badcap at audio input or the speaker output section. Will look into this further, though that will be another tale....

pffff i envy you

when i started this thread i had 3 boxes (3x systems) i try to see what is inside.

yesterday i open the rest and install a TOSHIBA 15v adapter inside; i use silicon so it won`t vibrate or move .

40 min of work for both systems

[lexwalker]

Re: Logitech Z506 power supply

"68pF 2kV ceramic capacitor, used surface mount type instead" You are able to find SMD cap with 2KV rating? It must have quite large legs spacing for 2KV (>0.25"). btw,

Yes, 1206 size metric which is large enough to span 4mm to 5mm lead spacing. This one: element14: 1206GA680KAT1A - AVX - CAP, MLCC, C0G/NP0, 68PF, 2KV...

How is the sound quality of this unit?

Exactly this...

Sound quality is shit.

Anyway one of the channels have a scratchy sound, possible badcap at audio input or the speaker output section. Will look into this further, though that will be another tale....

[Th3_uN1Qu3]

Re: Logitech Z506 power supply

Sound quality is shit.

[budm]

Re: Logitech Z506 power supply

"68pF 2kV ceramic capacitor, used surface mount type instead" You are able to find SMD cap with 2KV rating? It must have quite large legs spacing for 2KV (>0.25"). btw, How is the sound quality of this unit?

[lexwalker]

Re: Logitech Z506 power supply

That TOP258MN I.C finally arrives, and soldered in place. Decided to use light bulb test this time as I do not want to break/damage that brand new I.C, and passed the test. Now the power supply is fully working...

Also replaced a number of other components. For that ceramic 68pF 1kV ceramic capacitor , used surface mount type instead (to avoid the heatsink, and higher 2kV rating instead of following the original 1kV). Replaced that 3.9nF 1.2kV film capacitor which had one of its lead corroded till broken (also it was already touching the heatsink when I first checked the board, thus not taking the risk keeping a possible unseen failed/problematic capacitor). Most of the electrolytics replaced (with Panasonic FR, Nichicon HE and Nippon Chemicon KZE), except for that big main filter/smoothing capacitor (120uF 400V) and a small one at the secondary side (220uf 25V) right after the choke, as there's already a big capacitor (6800uF 25V) on the power amplifier board (plus ran out of stock for 220uf 25VDC with 3.5mm lead pitch/spacing). Put an additional surface mount ceramic capacitor (100nF 100VDC) near the output connector...

[lexwalker]

Re: Logitech Z506 power supply

Yep, high voltage 'breakdown'. Measures as open-circuit, but the high voltage jumps the gap... and, well, yeah...

Being the "...MN" model (9 pin version), not an easy I.C to find. Ordered it from UTSource (and has yet to arrive)...

You could put some mylar tape (same stuff used in the smps transformers - usually it is yellow) around the new capacitor if you are worried about it being too close to the heatsink.

Actually the original capacitor is being pressed against the heatsink by that big main filter/smoothing capacitor (I guess the word "squeeze" isn't accurate enough, refer to the attached second image above). And that heatsink can get very toasty...