Help needed troubleshootiung Logitech Z560 subwoofer amp - diyAudio
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Old 6th June 2004, 09:17 AM   #1
DcibeL is offline DcibeL  Canada
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Default Help needed troubleshootiung Logitech Z560 subwoofer amp

Hello,
The Z560 uses 2 ST TDA7293 chips to drive the subwoofer. These chips have blown and I have replaced them as well as several capacitors (all the 1000uF and 100nF supply caps). The amp works for a few seconds but then makes a pop and plays low volume with much distortion after this. I belive the problem is a surface mount capacitor between pins 1 and 3. This cap was fried but I tried to remove it to measure its value (maybe one of them was still good) but without the proper tools to work with surface mount components I destroyed both caps. If someone can help me with this it would be very helpful, as when I look at the spec sheet for this chip there is no capacitor between pins 1 (stand-by grnd) and 3 (non-inverting input). This is caps C214 and C250 for anyone who owns these speakers. They are on the backside of the circuitboard and are easily accessable with simple removing the amp from the sub box.

Thank-you in advance.
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Old 6th June 2004, 06:24 PM   #2
DcibeL is offline DcibeL  Canada
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I guess this should have been posted in chip amps. My bad.
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Old 6th June 2004, 07:26 PM   #3
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I repaired a set of these, however, I didn't have that problem.

I'd imagine that that cap is for preventing oscillation, but I'm not sure. If you have a scope, maybe check the output from the chips to see if there's anything.

Also, are the chips getting hot under no-input situations? Or do they stay cold when not amplifying.
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Old 6th June 2004, 08:19 PM   #4
DcibeL is offline DcibeL  Canada
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I left the amp turned on for several minutes and to my suprize one of the chips blew up (again). Back to the ol' drawing board I guess...

I think I will take the 4 working amplifier chips and make my own amp out of them. Sounds like a decent summer project, does it not? I guess the real question is should I salvage the logitech amp for parts (caps) or buy new ones. The board has 2 10,000 uF caps and a couple of voltage regulators for the power supply. All the caps are made by "Chang", so I don't really know how good they are going to be. I have seen a single film or poly cap being used in some chip amps to improve the sound quality. I wonder, is this the input coupling cap?

I am also wondering if I should use the XF from this unit. Since the 4 chips driving the satellite speakers were not being driven to their full potential (about 15 watts I would think), is this XF going to be large enough to drive 4 chips to their full potential. My output power would be 200 watts instead of the 160 watts the logitech speakers provide (100 watts subwoofer + 4*15 watts sattelites). It's too bad the spec sheet for the TDA7293 doesn't tell what the efficiency is when using the typical application circuit.
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Old 8th June 2004, 02:39 AM   #5
DcibeL is offline DcibeL  Canada
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If the case of the chip (pin 8, -Vs) was shorted to ground, could this have caused the chip to blow up? I have remove the amplifier from it's stupidly designed heatsink and I don't think that the mica strip was completely covering one of the chips, though it may have just been moved out of place in the struggle to remove the darned thing.
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Old 10th June 2004, 02:19 PM   #6
puggy is offline puggy  Canada
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I think building an amplifier from all the parts would be a great project. You have all the expensive parts already namely the PSU caps, transformer, ICs and heat sink.

I picked up a z560 at a garage sale but the unit was missing the control pod. I guess what usually happens when these things break is Logitech asks the customer to return the control pod and they send a new unit to the customer. I was able to temporarily hook the unit up and the only problem was a woofer that would buzz when played loudly. Turns out one of the flexible wires came loose so I soldered it back together and viola I had a working unit. Problem is I don't have a control pod so it is rather clunky to integrate into my computer.

As a result this unit has been sitting on the shelf simply because I don't have the technical ability to do what you propose, build a unit from scratch. Your post however has given me some hope that I may be able to at least copy the control pod. Would you be able to assist a fellow DIYer by posting some close-ups of the control pod inners and answering some questions for me? If you do decide to build a new unit what are the chances that I can get your old control pod complete with the DIN connector at the sub. I am not sure what it would be worth but I can pay you for it.

BTW are you in Alberta?
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Old 10th June 2004, 11:11 PM   #7
DcibeL is offline DcibeL  Canada
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The control unit is actually more complicated then you would think. It contains 4 op-amps, about 20 caps and 30 resistors. I am in Saskatoon, but I would be willing to sell you the unit for say $20? Do you have a paypal account? Email me privately at rtowsley@shaw.ca and we'll make a deal

I will get around to making some amps out of the logitech speakers one day, but I was offered a deal at my local hifi store a couple days ago for one big mother of a reciever that I just couldn't pass up. Have you ever seen "The Italian Job"? You know The Napster's stereo that will blow the clothes off of girls? The NAD T770? Yea, I bought it for the low low price of $500 CAD. WOW is it ever nice. It may be a couple years old but it doesn't have a scratch on it! The only thing it is missing is component inputs, but still it really is one lovely work of art
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Old 11th June 2004, 01:32 PM   #8
puggy is offline puggy  Canada
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Looks like a great deal. That is one nice amp. I doubt that you will miss the component inputs. I have always felt that it is best to go direct to the TV as there is less chance of signal degredation.

I don't have a paypal account but i am willing to send you cash. I will send you an e-mail shortly.

Thanks again for your offer. I am excited to know that I may be able to get the system working again.

BTW I need the control pod and the small PCB that supports the din connector to the control pod that is located on the amp. In my haste to get at the input wires I kind of destroyed this piece as well. Therefore without it I will not have a tidy interface to the amp. Without the contol pod it will not be of much use to you.

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Old 25th June 2004, 07:08 AM   #9
JBauer is offline JBauer  United States
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I need your guys help with my Z-560. Here's the story:

I come back to my room, and one of my rear speakers were on the ground. It had fallen after being hit by a light cover from my fan. I had no audio coming out of it, so I hooked it up to different wires. Works perfectly fine, so I changed the wires, and still no audio. I've rotated the same speaker and wires through each position on the subwoofer, and only the Right Rear outputs won't work. What gives? I took the subwoofer apart, but I'm really unfamiliar with taking apart this kind of equipment. Could it be something easy like a blown fuse? I'm handy with a soldering iron, so if you guys could help me out and fix this thing I would be extremely grateful, thanks.
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Old 25th June 2004, 03:37 PM   #10
DcibeL is offline DcibeL  Canada
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Default That's a thinker...

I would suspect that you have shorted the output of the amp if the speaker cable was yanked from the speaker when it fell. Each amp module on the z560 has it's own shrink wrapped fuse mounted on the side of the PCB that isn't accesible without completely removing the amp from the heatsink (except the subwoofer amp, it has nothing). Why couldn't logitech mount the fuses where they can actually be easily replaced? I dont know. I would also do a continuity check to make sure that the output on the amplifier chip makes it's way to the speaker terminal.
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