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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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11th Jan 2017, 4:10 pm | #21 |
Retired Dormant Member
Join Date: Jan 2017
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Re: Power Amp IC Replacement on Sharp VZ-3000
Very good point!
So the picture in my previous post was taken from the internet as my machine is still in with the Tech Guy. Once I have claimed it back I'll shoot up lots of fresh pics! Could the damage have been done by someone selecting the wrong voltage on the voltage selector? I ordered a DIY ESR Meter from ebay where you have to solder it together yourself... Probably a waste of time but it has the added value that I'll have gotten some soldering experience under my belt. I recon I'll buy that chip from amazon and tell the Tech that I'll pick it up tomorrow. I'll keep you guys posted, thanks again for all the help! |
11th Jan 2017, 10:04 pm | #22 | |
Heptode
Join Date: Dec 2016
Location: Sheffield, South Yorkshire, UK.
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Re: Power Amp IC Replacement on Sharp VZ-3000
Quote:
More likely in the case of capacitor failure is that they do go from time to time. The IC amp failure again, just general failure. Or someone having it at loud levels, so it generates heat, especially if the unit was housed in a tight space. Or possibly faulty speakers or wires to them. |
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11th Jan 2017, 11:18 pm | #23 |
Nonode
Join Date: Mar 2013
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Re: Power Amp IC Replacement on Sharp VZ-3000
I couldn't see anything obvious in the photos of OPs unit in post #6, but there was possibly something on the cap to the right of the top fuse in the picture in post #10. However, as stated by the OP, this is NOT his VZ3000 machine. Its a photo of a similar VZ3500 provided for illustrative purposes.
Still, the good advice in #20 remains applicable and it would be worthwhile to check for any bulging, gunged or otherwise suspect caps as part of that visual inspection. Last edited by WaveyDipole; 11th Jan 2017 at 11:37 pm. |
12th Jan 2017, 12:40 am | #24 |
Dekatron
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Re: Power Amp IC Replacement on Sharp VZ-3000
More than likely someone shorted out the speaker terminals, probably briefly, which harmed the IC. They do just go bad on their own, though.
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12th Jan 2017, 12:57 am | #25 |
Dekatron
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Re: Power Amp IC Replacement on Sharp VZ-3000
Those STK chips send some of the capacitors around them open circuit without them showing any visible signs.
I would be inclined to replace all the capacitors on the board the amplifier chip is soldered to since the audio is there under the hum. Only use capacitors from a big British based supplier like RS or CPC or it might kill the STK chip anyway. You may have been lucky this time. Those chips also blow up again if the capacitors are not done when they are changed. |
12th Jan 2017, 8:37 pm | #26 | |
Heptode
Join Date: Dec 2016
Location: Sheffield, South Yorkshire, UK.
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Re: Power Amp IC Replacement on Sharp VZ-3000
Quote:
I had an Awia amp in for service and it had an STK chip in it, but it didn't just send one capacitor open circuit, it blew it up! But I didn't know the chip had gone, just saw the blown 10 uf capacitor. So I replaced it and tried the amp. Bang With green smoke As there was little around the capacitor apart from the STK, which the circuit showed it went to, I quickly worked out the STK had gone. |
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12th Jan 2017, 9:20 pm | #27 |
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Re: Power Amp IC Replacement on Sharp VZ-3000
Hi Guys,
Got the machine back from the repair shop. I asked the guy if he could tell me what was wrong but he didn't know as it was another guy who worked on it. So basically £40 down the drain and no more knowledgeable than before I went in there. For £40 I was expecting a list of issues or something but he would only say "Some capacitors and transistors are damaged, no working as it's old", lessoned learned there for me. Anyway, I've broken down the machine. It seems like they didn't go past taking off the rear panel(now missing a screw..) as there was no evidence anyone have taken off the front panel in a long time. I'm going to chuck a few detailed pics below. My first impression is that there are major issues with the circuit board that the Power AMP IC is connected to. Looks like someone has been at it with a lot of solder to re bridge burnt out connections on the board. I'll get out my DMM and see if the connections are broken. Please let me know what you guys think? The Capacitors on the power board look OK. Maybe a little residue at the bottom of it or maybe that's some liquid used to hold it down... High Resolution images can be found here: https://********/s/aHskSoCTRS |
12th Jan 2017, 9:56 pm | #28 |
Octode
Join Date: Aug 2008
Location: Rotherham, South Yorkshire, UK.
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Re: Power Amp IC Replacement on Sharp VZ-3000
Frankly after paying £40 I would demand a written list of faults. If they are unable to provide one I would demand a refund and the missing screw!
I have one of these that spent several years outside, arbeit roughly covered, and it still works so good luck with yours. Peter |
12th Jan 2017, 9:59 pm | #29 |
Octode
Join Date: Feb 2009
Location: Cornwall, UK.
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Re: Power Amp IC Replacement on Sharp VZ-3000
These are basically reliable units, I have worked on a few in the past, I have done one with a blown power amp IC, I also remember some of the Fusable Resistors on the power supply board blow (as they should if there is a problem) worth checking those aswell.
Yes the caps on the power amp board look ok, no obviously blown ones there. Carry on you will get it working. Gary |
12th Jan 2017, 10:02 pm | #30 |
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Re: Power Amp IC Replacement on Sharp VZ-3000
If there is an undiagnosed amp fault and you have limited expertise, it may be easier to replace the power amps with modern chips. These are available for little money from Chinese eBay sellers, either as the bare chips or as preassembled modules. Search eBay for 'audio amplifier module' and you will see lots of options.
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12th Jan 2017, 10:05 pm | #31 |
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Re: Power Amp IC Replacement on Sharp VZ-3000
The extra solder on the tracks was sometimes a cheapskate method of allowing them to carry more current, and may well be original. There does seem to be rather a lot of flux around the module connections, though. I wonder if someone has already tried replacing it?
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12th Jan 2017, 10:23 pm | #32 |
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Re: Power Amp IC Replacement on Sharp VZ-3000
Thanks Guys,
On closer inspection of the board I can see it has a large enough crack up the top left corner. Could be the issue? Last edited by BillyTheKid; 12th Jan 2017 at 10:38 pm. |
12th Jan 2017, 10:37 pm | #33 |
Dekatron
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Re: Power Amp IC Replacement on Sharp VZ-3000
That is what the solder bridges appear to have been applied to fix, but it looks - in your photos at least - as though the bridges are intact. It may be worth metering end to end on all of them (the horseshoe shaped one and the two parallel ones down the side of the PCB) to make sure those track repairs are still working.
Personally, I would always jump a broken track like that with insulated wire soldered to the first available pads on each side of the track break, rather than using a solder blob. Solder is too soft and will fracture easily if the PCB is ever flexed. I can remember (in the dim and distant past) hastily replacing an STK module which was producing a loud buzz only to find that the real culprit was just an open circuit low value resistor nearby. Always eliminate the cheap stuff first. |
12th Jan 2017, 11:22 pm | #34 |
Nonode
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Re: Power Amp IC Replacement on Sharp VZ-3000
It looks to me like there is the posibility of that big blob of solder touching one end of the connection to R419. Personally I'd clean off all the excess solder with de-soldering braid, clean up the break with IPA, super glue the pcb back together, then remake the connections across the breaks with wire. Once that's done it's time to start checking voltages against the service data.
Regards, Lloyd. |
13th Jan 2017, 12:05 am | #35 |
Hexode
Join Date: Mar 2012
Location: Liverpool, Merseyside, UK.
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Re: Power Amp IC Replacement on Sharp VZ-3000
I did have an amplifier using STK modules that had an open circuit fuse on one of the supply rails, which caused the speaker outputs to have a large DC voltage on them and as a consequence burnt out whatever speakers were connected. I had dived in hastily when I first got it and replaced the STK, which may not have been necessary. The fuse didn't look blown either.
I don't recall having a unit using one of these modules that gave any output with the module faulty, but a lot of amplifiers have relays that keep the speakers disconnected until the correct operating conditions are satisfied. Your photo showing the module doesn't show the full number, but from what I can see there doesn't appear to be a suffix on the end, so I expect the one you found online will do the job. If you do decide to have a go replacing it get some desoldering wick or a solder sucker so you don't damage any of the printed tracks, and you'll need some heatsink compound for the replacement. |
13th Jan 2017, 2:26 am | #36 |
Heptode
Join Date: Dec 2016
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Re: Power Amp IC Replacement on Sharp VZ-3000
I would say that maybe the STK has been replaced before and whoever did damaged the board. Hence the soldering to the board. Sometimes you get a part that just will not come out. And you destroy the printed board tracks in the process. That's happened here. Also what is that blob under pins 2-4 (right) of the STK it looks like a lump of solder under the pins
What I also noticed that ALL transistors mounted on heatsinks have been replaced. Hence all the white heat sink cream all over the edges. You might want to test and check them with the circuit diagram just in case somebody has fitted a wrong type. Also replace the 4700UF capacitor with a modern 105c type, just to be on the safe side. Just noticed there are fusible resistors in it. Are the two with insulated covering fusible type? Whhich is why they were replaced making a mess on the board? Last edited by Grubhead; 13th Jan 2017 at 2:33 am. Reason: Extra infromation |
13th Jan 2017, 6:47 am | #37 |
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Re: Power Amp IC Replacement on Sharp VZ-3000
Can't add anything much but what lloyd says is bang on. And as other's have said, it's been repaired before. Noticed a brown stain on the big 4700u cap, may be the gunk they use to secure caps. I've found the big electrolytic cap's are usually ok and it's little cap's that fail. Still a new cap as above wouldn't hurt.
One thing though, they have to be in the right way. IE there should be a + or - on the board or schematic. Caps have a big stripe with - on to denote the negative end. It might be an idea to get a sharpie and put a dot on each electrolytic all facing one way, to the front for instance. This helps to orientate them. Take loads of pics too, close up of wires and from different angles. It's a good idea to break up things like this into separate section's. So start with the power supply once you have fixed the amp board or replaced it as per Paul's advice. Make sure all voltages are present and correct. Then check each board in turn. An audio probe might be useful, it emits a tone which you stick in one end and trace it though the circuit's. Good luck, Andy..
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13th Jan 2017, 11:13 am | #38 | |
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Re: Power Amp IC Replacement on Sharp VZ-3000
Quote:
I mean how could he tell that transistors or caps were "damaged". I hate this kind of thing. And not even a worksheet for the £40 spent. The OP can trust the Members here though.
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13th Jan 2017, 1:38 pm | #39 |
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Re: Power Amp IC Replacement on Sharp VZ-3000
Like many of us here, I never need to get estimates for this sort of repair, but as far as I know it's normal to have to pay if you don't accept it. Also, I can understand the lack of detail, find out what's wrong and then get your mate to do the repair cheaper. The shop probably gets a lot of that, especially in a City.
That crack is just as likely to be the result of a previous drop. The repairs could be neater, and would be if we were repairing our own kit, but you have to be realistic in a commercial world. Whether you accept the prices or not, someone has actually examined this machine in the flesh, not just photographs and well meaning descriptions. The diagnosis is probably reasonable, but a working one can be had for about the same. |
13th Jan 2017, 4:49 pm | #40 | |||
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Re: Power Amp IC Replacement on Sharp VZ-3000
Thanks, I'm very very happy I came here for help! I'd have given up days ago otherwise!
I'm not too bothered by the £40... It would have been nice if they could have given me a general list of things but it seems to me that they didn't do much investigation at all. I'm sure if they had that they would have mentioned the bespoke soldering and cracked board. Anyway! I'm going to drive on and get cracking on the advice. Quote:
Good shout re the transistors, if you zoom in on the pic you can actually see the guy's fingerprints: I will test these bad boys out and see if they are good. Quote:
Quote:
TODO: Power: Check transistors against Spec Swap out 4700UF Capacitor with new 105 degree modern cap AMP: Check the soldered tracks for continuity. Re Solder if short circuit Check the AMP IC for correct voltages(Continuity through each pin to the ground pin??) Shopping List: Soldering Iron De Solder Solder ESR Meter Capacitor(s) Transistors(maybe) I'll update once I've made any progress. Thanks! |
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