Repair ZP120


The amp has no power. Is there an internal fuse for this unit?

Has anyone taken one apart?

285 replies

Userlevel 2
I too am keen to work out where the fuse is. I tried here and here but not much joy. Anyone got better info? B.
Userlevel 2
This guide might help although it is for the ZP100.

http://www.mediafire.com/download/0duavcuf1zyuc8u/sonos_dismantle.pdf
Userlevel 2
I bought a used Z120 with an unidentified power issue. It was dead.

The 5A fuse is open. No other components show visible damage. When I shorted out the fuse to see if the amp would power up there was a momentary flash of light near the centre of the power board. I say momentary because I quickly opened up the fuse again.

It appears to me as if something arced or there is a short somewhere downstream of the fuse. Everything I measure with an ohm meter seems to react ok. The varistors near the large filtering caps are not shorted. Before I try to replicate the action of shorting the fuse again to see what is arcing I thought I'd see if anyone had any ideas as to the fault.

Also, has anyone created a schematic of the power supply?
piperdog,

A flash of light usually indicates something has died -- in a hurry -- usually letting out its smoke. Of course, everyone knows that smoke is required for proper operation and after the smoke leaks out, operation ceases. Further, the flash of light (former) device is usually the victim of another issue.

Some units will blow fuses for no good reason other than the fuse was probably poorly specified and fatigues over time, eventually failing. I don't have enough data to know if ZP120 is one of these units or not.

I can't recommend the strategy of inserting a fuse eliminator as an expedient. Unless I know that a given (dead) unit is subject to nuisance fuse failures, I'll track down the root cause of the failure before applying power to a unit. Powering a (dead) unit prior to repairing the root cause typically expands the failure, fuse or not. Also, even if they appear to be OK, replace any components in the current path of the root failure because these components were probably stressed during the original failure and you will likely be faced with another similar failure as these stressed components fail in the future.

Inspect the board using a magnifying glass. There is almost always some sort of visual physical clue indicating which component gave out its smoke. Of course, with our modern, ever shrinking components, these physical clues can be small too. Sometimes the only clue is a small black dot on the non visible side of a surface mount component.
Userlevel 2
Lacking a schematic to do proper trouble shooting I slowly applied power to force evidence of a fault without hopefully doing damage. One of the varisters eventually exploded. I desoldered its remains. Although I had measured it as open it was evidently damaged and shorted out under power. I reassembled the unit but still don't have power so I'll look for another faulty component on the power board. At least now I can apply full power without any shorting occurring.
Userlevel 2
Upon closer examination I see that a current limiting in-rush thermistor has over heated and cracked. Its a SCk054 (schematic TH16001) which I'll have to replace to progress further.
piperdog,

Be sure to purchase at least two of these thermistors because the first will likely blow again as soon a you apply power. I suggest that you track down the root cause before applying power again. This is not a hard as it seems, just follow the current that blew up the original thermistor. This will lead you to a really sick component. Be sure to replace everything in that current path.

Also, I am leery about running up the power voltage as a strategy to troubleshoot switch mode power supplies. When the voltage is much lower than expected, the switch mode stuff will really try hard to maintain the specified output. This could imply much more current than average use cases.

If you have lab power supplies available, separate the ZP120 into modules, power them up and test them separately. The lab supply will have current limit capabilities to protect itself and the device under test from unreasonable current levels.
Userlevel 3
Badge +2
You could have sent it in for replacement for a modest cost. I sent back a ZP100 for around $150. SONOS sent me back a brand new ZP120.
Userlevel 2
I didn't realize that it would be that inexpensive for Sonos to repair an out of warranty unit. Thanks for the info. Unfortunately they may not touch my unit now that I've opened it up. At any rate, I received replacement fuses, varistors and thermistors today from Digikey. If things work out I'll post the Digikey part numbers. Now I have to find time to install them. Hopefully they are all that is required but of course there is a reasonable chance that something else is wrong with the power supply causing these parts to fail. I'll know soon.
Google Dim Bulb Tester for a simple, low cost way to protect devices that may still have issues...
Userlevel 2
I decided to skip the dim bulb tester although I'll keep it in mind for the future. I replaced the 2 thermistors, 2 varistors and 5A fuse in the power supply section and applied power. The good news is nothing shorted out. The bad news is that some component must be open downstream because I'm not getting voltages where I should. I wish I had a schematic. It would be so easy now to trouble shoot with it. Or another good unit to compare voltages.
Userlevel 2
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Piperdog, Any chance you've got any updates? I'm in the same situation.
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I don't have any updates. I put my repair on hold until I can find someone who has had more time than me and who has created a schematic of at least the power supply section. Alternatively I'm keeping my eyes open for an inexpensive used ZP120 so that I can use it as a reference for the correct voltages and therefore to trouble shoot my nonworking unit..
Any new updates? I just bought a dead ZP120 on eBay and will be diving into it next week.
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No updates. Keep us posted on your repair efforts.
Userlevel 1
Badge +2
I repaired the one I am using. It was a no power failure as well. It appeared to have some sort of liquid damage on the logic board that shorted an output of the power supply. I fixed that damage on the logic board, then started looking through the power supply. What I found was a TO-220 (or similar) package dual schottky rectifier was now shorted, also the main bridge rectifier on the front end of the power supply was also a short. Once replacing those 2, the dim-bulb went bright then dim and the indicator started flashing. And I friends was in business!
I liked the ZP120 described above so much that I just bought another ZP120 with the same fail description. I crack it open tonight. Will update this forum when I get it working.
The amp has no power. Is there an internal fuse for this unit?

Has anyone taken one apart?
Dose any one know where is the fuse ?
Userlevel 1
Badge +2
The fuse is a small orange cylindrical part by the input connector. Through hole, axial lead. I wouldn't just swap it out, it will blow again. If you comfortable around high voltage, I would try the dim bulb.
Userlevel 1
Badge +2
So as promised above I have repaired my new ZP120, and another 120.
The first one:
Just the input bridge rectifier has a shorted diode that blew the fuse. Once the bridge was replaced it has worked fine.

Second one:
SOmetimes it came up no led, totally dead, other times it came up and would get 1/2 way through setup before crashing my network.
Noticed a primary side 350V 33uF electrolytic cap was toast. Replaced It and nothing really changed.
This one was a real head scratcher. The blown cap belonged to what appeared to be power converter circuit that provides biases around the board. Noticed that the GND test point had no continuity to the outputs of the tapped winding. I probed a good working ZP120 and found that all of the outputs of the bias converter were grounded together. So I shorted the return of the tapped winding(8.5V and 15V outputs) to the return of the single winding (3.3V output). Was nervious to power it back up, so just in case i used the dim bulb and it worked great. Replaced the dimbulb with the fuse and I am in business.
I did a chart so my crappy memory will have some help next time i tange with a ZP100. See below.

Is there any YouTube video that shows how to replace the fuse ? Pls add the link - Tnx
Is there any YouTube video that shows how to replace the fuse ? Pls add the link - Tnx
For your Information:

Hi everyone, interesting discussion but I want to make sure that anyone who gets to this thread knows not to open your Sonos products if you're looking to do any sort of replacement or repair with us.

Sonos products are not designed to be opened and repaired out in the world, and we do not provide any resources or replacement components for doing this. The warranty services for Sonos components also does not cover units that have been opened in any way.

Even if your player is outside the standard warranty time, we can probably still assist with a replacement as long as it hasn't been opened. There will likely be a fee for the replacement if it's out of warranty.

Anytime a unit fails, we want them to come back to us when possible so that we can review what happened and make adjustments if there's need.
Userlevel 2
Badge +2
@gruv2ths - Outstanding job. I have a SONOS ZP120 that unfortunately got wet and the power blew a 10ohm 2W resistor (R16017). I replaced it. I plugged it in and that resistor blew again... and it looks like it took out one of the SCK054 thermistors (TH16001). The thermistor was a wee bit charred however it tested 5ohms which is the normal rating. I have ordered new ones since I don't trust anything that got charred, but they will take 10-4 days to get from China... nobody sells em here in the US.

I tested the rectifier on the input side (the one clamped to the chassis) and it looks good. I tested the diodes and those look fine. All caps are looking good too. The fuse is fine... it never blew.

I am guessing the problem lies downstream from the components listed above. A couple of questions...

1 - That TO-220 you mentioned... is that the one that has a heatsink screwed into it and standing up? Do you know the code on it or type as I cannot tell.

2 - What is the secondary rectifier your are referring to? I would like to test mine to see if its checking out (or not).

If you have any recommendations, I would love to know how to any techniques are parts I should be checking on the PS board... I am thinking this is simple... but I am having a tough time narrowing it down.

Thanks!
Userlevel 2
Badge +2
Slight update... as I am waiting for the SCK054s from China... I decided to check everything in the path. All looked good except for the 115/220 red switch. It showed 0L on the meter at 115. I switched it to 220 and it was 0L. Switched back to 115 and had continuity. My guess is when the unit got wet, something happened to that switch and hence it made the unit look like it was supposed to be connected to 220v. I followed the trace and with 220v, it all leads to the blown resistor and thermistor. But with 115 active (continuity) it throws in a drop through the varistors and the other path meets it. Just a guess, but it appears that the 220v setting may have caused the current consumption along the resistor/thermistor path to exceed what it was normally supposed to see. That may be a red herring and I will find out when my thermistors arrive... but I thought the 220v setting running on 115v wouldn't hurt the PS...worst case it just wouldn't fire up. I'm just guessing that perhaps it does indeed have an impact on a PS.
Userlevel 2
Badge +2
Ok... I tested the thermistor and under heat etc and it seems to test out ok. Due to the excellent posts in this thread, I decided to put together a dim bulb tester so I would stop blowing components. Great idea...

So I decided to fire it up under the dim bulb tester after replacing the 10 ohm resistor and putting back the thermistor... and the light bulb shined brightly so I still have a short somewhere....

I cut the power and decided to test for heat. Again, that resistor was getting hot (and was saved due to the dim bulb tester).

Here is the resistor and it is hot (notice the circle labeled hot):



Anyone have ideas on how to hunt down the short?

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