Logitech Z506 power supply

[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

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)...

[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

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

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

"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

"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

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?

[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

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...

[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

[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.

[momaka]

Re: Logitech Z506 power supply

I'll be on the hunt for a second-hand (cheap but does the job) laptop power brick capable of 19V 2A.

Doesn't have to be exactly 19V and 2A. I'd say anywhere between 15V and 20V and capable of at least 2A should be fine. Many laptops use 19.5V power bricks.

In my experience, not all of them work, though. In particular, some just tend to have a very noisy output. Also, avoid anything that has a groud pin. Otherwise you may get some "interesting" noises at the output of your speakers.

I first tested with an UPS battery and the speakers distorted pretty early. It's much better with 19v. The amplifier chips inside this thing can take up to 24v supply so 19v is no problem.

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.

All speakers driven, this thing will output 20W max.

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

[Th3_uN1Qu3]

Re: Logitech Z506 power supply

Just in case you stumble upon an identical one, the exact model of my Asus power brick is EXA0901XH. It's white and it originally had a tiny jack at the output. I got it for free because it was dead. Reason: Output jack was bent and shorted. Nothing wrong with the adapter itself.

I also found the blown part in the original PSU. Along with the visibly burnt resistor R2, the snubber diode D5 was also shorted, read 0.003v both ways. It was a FR207 (2A, 1kV, 500ns), and i decided to replace it with a BY399 (3A, 800V, 250ns). It should work now... Still pondering whether i'll put the original PSU back in or just leave this Asus brick. It depends on how lazy will i feel tomorrow.

Anyway, the reason why it dies is they picked the completely wrong type of PSU for the application. The power supply is a flyback type, which subjects the switching transistor to high voltage stress, that's why a snubber circuit must absolutely be used. To compound this problem, this PSU was most likely designed for a mostly continuous load such as a small laptop or DVD/Blu-Ray player, while an audio amplifier is a pulsed load, which at high volume varies from near zero to maximum power many times a second. If the feedback loop of the PSU isn't fast enough (and with just a zener on the secondary driving the optocoupler, it certainly isn't), this will cause voltage pumping at the output of the PSU, which will then reflect thru the transformer as high voltage spikes in the primary. This is likely what caused the snubber to blow.

[a.bug]

Re: Logitech Z506 power supply

Thanks for the reply Th3_uN1Qu3!
I'll be on the hunt for a second-hand (cheap but does the job) laptop power brick capable of 19V 2A.

Cheers!

[Th3_uN1Qu3]

Re: Logitech Z506 power supply

Had the same system in for repair today, looks like that power supply they put into it is absolute crap. Also looks like i won't have to post pictures since someone already did.

I did something different: Pulled the PSU (decided it isn't worth fixing), pulled the original AC power cord out and patched an Asus Eee PC power brick (19v, 2.1A) into the DC input of the board. Power brick stays outside. Works great. One advantage of this particular power brick is that it's got "soft" current limiting - when it is overloaded, it does not shut down, it just limits the output.

The original power supply puts out 13-15v, so 12v would be a bit on the low side. I first tested with an UPS battery and the speakers distorted pretty early. It's much better with 19v. The amplifier chips inside this thing can take up to 24v supply so 19v is no problem.

You could use a 3A or bigger power brick for more oomph, but with this pile of trash, i don't think it'll make too much of a difference. Looks like Logitech quality has gone way downhill.

Apparently the Z-506 replaces the X-530, which is a superior system in every way. 75W RMS... yeah right, when the power supply is 35W. All speakers driven, this thing will output 20W max. It's just barely adequate for a small room, but there are better choices for the price. The woofer is a joke, the sattelite speakers have those caps on the top to make you believe they've got tweeters... nope, they aren't tweets. Just for show.

[a.bug]

Re: Logitech Z506 power supply

Try for replying.
Forgot I have bench PSU, just bought few weeks ago.
This morning when I was meditating after the coffee I realized that I could try to power without the internal PSU.
The PSU was faulty and install another one.
I tested to see if it runs on 12v and it does work.
I'm so happy that I manage to finish this stupid project.
I put new thermal compound and I close the box.
Thank you again.

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

[momaka]

Re: Logitech Z506 power supply

Good to hear you got it working .

By the way, the original power supply looks quite simple, so the problem will likely be easy to fix... if you want to troubleshoot it, that is.

[dj_ricoh]

Re: Logitech Z506 power supply

Try for replying.
Forgot I have bench PSU, just bought few weeks ago.
This morning when I was meditating after the coffee I realized that I could try to power without the internal PSU.
The PSU was faulty and install another one.
I tested to see if it runs on 12v and it does work.
I'm so happy that I manage to finish this stupid project.
I put new thermal compound and I close the box.
Thank you again.

[momaka]

Re: Logitech Z506 power supply

This is a simple single output rail power supply. Since the power supply isn't working when connected to the audio board but otherwise appears to work fine when the audio board is disconnected, you need to check first if this is a fault within the power supply or the audio board. To do that, disconnect the audio board from the power supply and measure the resistance on the connector of the audio board where the power comes in. - If you do get a short circuit or very low resistance reading (under 10 Ohms), then there's a short on the audio board and that's where the problem is.
- If you do NOT get a short circuit or low resistance on the audio board power connector, then the problem is likely within the power supply. In that case, I would suggest recapping the entire power supply with good quality capacitors (except maybe for the main input 400V/450V capacitor - that one rarely fails).

Also, what is the voltage output of the power supply when it is not connected to the audio board?