Logitech Z506 power supply

[Th3_uN1Qu3]

Re: Logitech Z506 power supply

Curious question... what amp ICs does it use?
I sure hope it's something capable of BTL configuration. Otherwise with 12V, you won't get much more than a watt or two at output with 8 Ohm speakers.

Two STA540.

Satellite speakers are in single ended configuration, and most likely 4 ohms each, while the center uses two of the same drivers in series on a bridged amp. The subwoofer is 6 ohms, again run from a bridged section. I only have the sub and the sat with the controls, so i can't say for sure, but this is the usual configuration for these 5.1 systems.

20W RMS isn't that little if you have some nice proper big speakers positioned at the right spots .

It is little, when the speakers are shit like these...

I fixed up the power supply to the degree that i trust it now, so it'll be going back in. I replaced the 10 ohm resistor with a 3W one (original was 1W), and the snubber diode with a HER307 (3A, 1kV fast recovery). Finally, i replaced the 13v zener on the output with a 15v one, this now gives about 17.5V idle, and will help the amps have more dynamic range.

With a 12v, 40W lightbulb as load, output voltage is 14.55v. Previously it used to fall to around 13.8v with this load. Anyway, at this level the PSU has entered current limiting already. The hottest part is still the snubber diode, currently reading 86C after ~15 minutes of continuous load. A bit warm, but better than 106C that the 800 volt diode reached! The resistor does not go past 60C whereas it used to go to 90 previously.

In the subwoofer, the PSU will run a bit cooler than that due to air movement thru the port, and will not be asked to deliver full power all the time, so it should be good. I'll post some pics too.

[dj_ricoh]

Re: Logitech Z506 power supply

I hope this also resolves my Z506's issue too. How any amps does your 12v source supply to the unit?

3 or 4a

[lexwalker]

Re: Logitech Z506 power supply

Well, speaking of this speaker just recently one came in for repair.

Initial impressions was that the degraded glue cause most of the problems (secondary failures). Found at least one burned resistor, blown fuse and one failed diode. There could be more failed components. Not sure if the main I.C is toast though the likelihood is high...

[Khron]

Re: Logitech Z506 power supply

By the looks of it, trouble seems to be in the RCD snubber are in this case, as well...

[lexwalker]

Re: Logitech Z506 power supply

A little update: That "burned resistor" was not burned, rather the blackish spot was (stubborn) degraded glue stain. The resistor measured fine (removed off the board to check and measure). Everything around that TOP258M I.C looks good (although the state/condition of the I.C is still unknown), except that failed diode at the turn-off snubber section. Then found 2 more failed diodes (RL205) at the primary rectifier section.

Thus decided to replace all the failed components I've found so far...

- 1x T3.15A 250VAC with 1x Wickman TR5/372 T3.15A 250VAC
- 2x RL205 (2A 1kV) with 2x RL257 (2.5A 1kV)
- 1x 1N4007S with 1x 1N4007

Then connect to the mains power and see what would happen. Aye, I'm expecting some components to get blown up again. Putting a light bulb in series would not be much fun...

Sure enough the same components replaced got toasted.

Looking back at the "path of destruction", one conclusion is that ceramic disc capacitor with the markings "68 1kV" (possibly 68pF). Could be breakdown at high voltage (encounter such problems before). And this capacitor is literally touching and/or pressed against the heatsink (not hard to see why this capacitor can fail). Also hardly any space to manouvere the capacitor away from the heatsink (plus squeezed in on the other side by the big main filter/smoothing capacitor), and the through hole is literally almost on the edge of one of the the heatsink sides...

Replacing that capacitor decision time. My options are...

#1. Use back a leaded through hole capacitor, which means the new capacitor will be literally touching the heatsink again! Besides ceramics, another option would be silver mica capacitor (rated for 150C).

Or...

#2. Use SMT ceramic capacitor (125C ones) which can be placed away from the heatsink, on the bottom of the PCB.

At the moment, option #2 looks interesting. What do you guys think?

[budm]

Re: Logitech Z506 power supply

"2x RL205 (2A 1kV) with 2x RL257 (2.5A 1kV)" What is the RL?
the 68PF is the one on thesecoandry side for the RC snubber for the secondary rectifier?
Never mind, that is the Diode P/N.

[lexwalker]

Re: Logitech Z506 power supply

"2x RL205 (2A 1kV) with 2x RL257 (2.5A 1kV)" What is the RL?
the 68PF is the one on thesecoandry side for the RC snubber for the secondary rectifier?
Never mind, that is the Diode P/N.

All of those are on the primary side. That 68pF capacitor is right between the heatsink and the large main filter/smoothing capacitor. The original diode was RL207, and that "RL205" was a typo...

[budm]

Re: Logitech Z506 power supply

OK, that cap is the RC snubber which hooked up between the Drain pin of the SMPS IC (another snubber is RCD which connected in parallel with the primary winding) and the Primary circuit Ground, that cap should have been rated at 2KV (I have seen this setup in the other power supply that has this cap failed as well). I think the SMPS IC is more likely to be bad now.

[lexwalker]

Re: Logitech Z506 power supply

OK, that cap is the RC snubber which hooked up between the Drain pin of the SMPS IC (another snubber is RCD which connected in parallel with the primary winding) and the Primary circuit Ground, that cap should have been rated at 2KV (I have seen this setup in the other power supply that has this cap failed as well). I think the SMPS IC is more likely to be bad now.

Well, you were right about the SMPS I.C being bad. In fact it blew spectacularly and broke into 2 pieces (found this out after removing it from the board, with much difficulty due to that heatsink). May replace another capacitor there, that 3.9nF 1.2kV one, just in case. Some pictures below (in the attachments). The first one are the failed components pulled out (one fuse, four diodes, one ceramic capacitor and the main SMPS I.C). The top of the SMPS I.C literally cracked/split from the blow out. The second picture shows the results after some degraded glue removal (earlier snapshot before trying out again). One of the leads on that green colored film capacitor (3.9nF 1.2kV) corroded badly by the chemicals from the degraded glue until broken. Also on the right there, notice the blue ceramic capacitor getting squeezed and between the heatsink and the big main filter/smoothing capacitor...

[budm]

Re: Logitech Z506 power supply

Glad you found the bad parts, when fuse is blackened like that, it definitely indicated something shorted out badly.

[lexwalker]

Re: Logitech Z506 power supply

Glad you found the bad parts, when fuse is blackened like that, it definitely indicated something shorted out badly.

That failed I.C does not measure as a short, but I do suspect the short only happens when there is voltage coming in. All parts ordered (gonna replace most of the parts anyway) have arrived except that I.C unfortunately (still waiting)...

[ben7]

Re: Logitech Z506 power supply

That failed I.C does not measure as a short, but I do suspect the short only happens when there is voltage coming in.

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

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.

[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...

[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...

[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?

[Th3_uN1Qu3]

Re: Logitech Z506 power supply

Sound quality is shit.

[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....

[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

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.

[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 ...