Logitech Z680 toroidal power problem? - diyAudio
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Old 8th August 2010, 11:28 AM   #1
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Question Logitech Z680 toroidal power problem?

Hi All,

This is my coat check and 1st post rolled into one. I have been reading up on a few post on this forum for help with a problem I am faced with regards to my Logitech Z680 speaker/amp unit.

The unit was working fine one day and just all of a sudden stopped powering on. I initially thought it was the fuse but have confirmed with a spare one and a multimeter continuance test that it's not the problem.

There were no signs of failure prior to the unit actually not powering up at all. I have opened it up and confirmed that there is no burnt capacitors, resistors, IC's e.t.c and it appears that all the LM chip amps are still in fine working order.

I have tried to do some troubleshooting with my limited knowledge and I have come down to what I think is the problem causing part.........The TOROIDAL TRANSFORMER. Although, I am not 100% sure as I'm not very certain on how to test it properly to see if there is a short in the windings.

Before I go any further the specs of the toroid are as follows:

The transformer is a Tenpao Model # TOU543005F0

The diagram on the side shows the Primary as 240v brown 0v black and Secondarys with a 26.2v orange, 0v black, 26.2v yellow, and then a 14.5v blue and 0v blue.

I have tried using the multimeter to test the secondary rails with red probe on orange and black probe on the 0v black but don't seem to get a very clear reading.

What i would really like your much appreciated help with is either how to 100% confirm if it is the transformer that needs replacing or method to test the unit so I get a clear more definitive answer.

If possible I would also like some advice on whether the Toroidal's I found at these sites below will be a suitable replacement for my unit. If so then which one would you recommend.

https://secure.vividcluster.crox.net...T&SUBCATID=539

OR

160VA Toroid Transformer

Sorry to make it such a long post but if you still feel like it is not enough details then please let me know and I will try to answer them to the best of my ability.

Thank you kindly in advance for you help and any sort of assistance/advice will be greatly appreciated.
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Old 8th August 2010, 04:09 PM   #2
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It's not likely to be a shorted winding if the fuse didn't blow, it might be an open winding. With your meter on AC and a range of greater than 60V, measure across the orange and yellow wires. Then measure from the blue to the blue.
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Old 10th August 2010, 01:14 AM   #3
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Quote:
Originally Posted by Redshift187 View Post
It's not likely to be a shorted winding if the fuse didn't blow, it might be an open winding. With your meter on AC and a range of greater than 60V, measure across the orange and yellow wires. Then measure from the blue to the blue.

Thanks for your reply and advice.

I have tried testing the unit with the power in the following ways.
probes red--->orange--->yellow but don't get any reading | multimeter set at 200/500 Volts ~
probes red--->orange + black--->black but don't get any reading | multimeter set at 200/500 Volts ~
probes red--->blue + black-->blue but don't get any reading | multimeter set at set at 200/500 Volts ~
I have also tried with the power off but get similar results. I have only been able to test the secondary rails so far as the primaries are still solder in. I didn't want to unsolder or remove anything just yet in case it wasn't the power transformer. I have also tried setting the multimeter to resistance and I do get continuance. But I have a feeling I am doing something wrong or have set the meter at the incorrect mode.
Am I setting the multimeter correctly and should be I setting it to 20 Volts AC or DC?

One more bit of detail I would like to provide is I gone out to buy a non touch AC voltage tester (the one's that beep when a current is detected). The really weird thing is when I use it to test the unit it seems to detect a current from the mains cable all the way to the fuse but then it seems to stop close to the power switch??? Could this possibly mean that the power switch is faulty or dead? But it looks perfectly fine and I have checked the soldered connections that connect it to the fuse then to the mains as well and they all appear to be fine.

Any help is greatly appreciated and thank you kindly in advanced.
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Old 10th August 2010, 03:01 PM   #4
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You should be testing with the meter set to AC. A range of 20V is not high enough for the red-black-yellow secondaries, but would be fine for the blue-blue secondary.

It sounds like your primaries are not getting power. The switch could very well be the fault.
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Old 11th August 2010, 04:15 AM   #5
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Thank you for your help once again.

I have retested again with the multimeter set to 200V~ and to make sure I have used another multimeter to perform the same test as well but that also shows the same result.

If it is the switch that is faulty then would it be advisable to unsolder the primaries from the switch/fuse and connect another one? I'm just scared that if I do unsolder it and it doesn't end up being the switch which is faulty then I've screwed things up.

Or can I somehow test the switch itself with the multimeter to find out if it is actually faulty or not?
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Old 11th August 2010, 04:51 AM   #6
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If it's a removable plug, you can remove the plug, turn the switch on, and check for continuity between the outside of the plug and the inside (assuming you can get to bare points on either side to probe).
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Old 11th August 2010, 01:56 PM   #7
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Unfortunately, the plug is not removable as it is soldered on so I guess the only way to get it off to check is to unsolder it.

I have taken it to a repair tech for a professional quote and he will let me know how much it would cost to fix it. If the quote is too expensive then I will just try to unsolder a few things and try my luck.

Redshift187, thank you kindly for all of your advice and assistance so far. I will surely post an update after a couple of days with how things went.

If I'm not able to fix the unit then I might just use the TDA's and other parts I can salvage off it to build my very first custom amp project.
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Old 13th August 2010, 02:40 AM   #8
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Just got the unit back from the so called professional electronic repair man and he reckons that there is more than one problem with it. Apparently, there is a problem with the input and output of the unit??? (I'm not sure how he was able to test that without being able to get any power to it.)

Also, he thinks that there may also be a problem with the power supply which is sort of confirming my concerns. I had to leave the unit with him overnight so could not see what was happening hence not able to say exactly how he troubleshooted it. He apparently tested the power switch as well and that was fine according to him. However, due to his lack of or should I say incoherent english skills I was not able to get a clear and concise answers or diagnosis out of him. He said that it is unrepairable and even if it was he wouldn't be able to locate the required parts for it. I somehow find that hard to accept as in this day and age you can pretty much find any part with help of the internet. Also, I don't believe that this unit is damaged beyond repair as there are no burnt parts or signs of damage anywhere.

May I ask if there is anybody from around Australia reading this post may be able to recommend a local repair shop/man close to the Lidcombe/Bankstown/Fairfield area of Sydney NSW so I can take it to for a 2nd opinion?

Or alternatively, if there are any Pro's or experienced McGuyvers reading this post and are local then please PM me. I am a Professional IT Technical Analyst with 10years+ experience so can offer help and assistance with any IT (Hardware or software) assistance in return for your help or maybe even offer a gift of a cartoon of beer, mobile phone or cash to anybody who is able to fix this for me.
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Old 13th August 2010, 04:10 AM   #9
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Can you probe the connections at the back of the switch? You could test between the plug end of the power cable and the back of the switch for continuity.
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Old 13th August 2010, 04:46 AM   #10
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The connections to the switch, power cable and fuse are all hidden under sheaths so I guess I can cut the sheaths open to reveal the actual solder connections.
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