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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 9th Jan 2017, 7:06 pm   #1
BillyTheKid
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Default Power Amp IC Replacement on Sharp VZ-3000

Hi All,

I'm new here. Please go easy on me.

I have a question regarding my Sharp VZ-3000. I know, I know it a heap of junk and it'll give me nothing but trouble etc... But I just love how it looks and how it functions and think it looks damn awesome on my shelf.

The power transformer seems to be shot(according to the tech that has it now) and that's what's causing the loud hum. He wants £200 to fix it which is way outside of what I was expecting. He's going to see if he can get the part cheaper and get back to me with another price if he can tomorrow. He says that the thing is in amazing shape for it's age and seems like it was never used.

I can find a replacement mains transformer online for £96. Do you think it's possible for a newbie like myself to swap this thing out?

I've replaced a few capacitors and sprayed some contact cleaner around things in the past but maybe this job requires more than just pulling out and plugging in. It may also require specific tools to test etc..

Other than telling me to chuck it out what do you guys think? save a £100 and do it myself or hemorrhage another £200 into this thing?

Thanks,

Billy
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Old 10th Jan 2017, 12:48 am   #2
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Default Re: Power Transformer DIY Replacement on Sharp VZ-3000

Regarding the loud hum. Is this coming from the loudspeakers or is it mechanical vibration? If the hum disappears when you disconnect the loudspeakers then the problem is unlikely to be the transformer.

With regard to replacing the transformer yourself, I don't know this unit and assume it might be a bit fiddly to work on, but if you can replace capacitors you should have no problems, assuming you get an identical replacement at worst the connections will need soldering to the relevant points.
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Old 10th Jan 2017, 1:12 am   #3
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Default Re: Power Transformer DIY Replacement on Sharp VZ-3000

Recent sold prices online suggest that apart from serviced units offered by dealers, you should be able to pick up a VZ3000 for<£50, perhaps a lot less. Transformers are pretty reliable........
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Old 10th Jan 2017, 1:13 am   #4
Lloyd 1985
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Default Re: Power Transformer DIY Replacement on Sharp VZ-3000

Hi,
Just been having a look at the service manual available from this link, it shows the transformer on the circuit diagram as having a primary with 240, 220 and 110V tappings, it also has a thermal fuse on the primary. the secondary consists of 2 centre tapped windings, it says AC20V on the circuit, so I'm stabbing a guess that they are 20V windings. I wonder if anyone on here has such a transformer hidden in a junk box? Might be worth posting in the sets and parts wanted section for one? You might get lucky!

If you can get one then you can replace it yourself easily enough, just make notes on how the old one is fitted, remove it, and put the new one in the same way. Definitely worth a shot before shelling out 200 quid, which doesn't sound worth it at all to me.

A question about the loud hum, did the unit power up ok even with the hum? Do any functions work? Is the hum coming out of the speakers, or is it coming from the unit itself?

Personally, I quite like these stereo's! I had fun with a VZ3500 when I was back at school, me and a mate found one dumped, so we took it home and tried it out, the belt was shot on the record deck, so we replaced it with an elastic band... The results had us rolling around on the floor! I'd love to get hold of another one day (when I've got more room!!)

Regards,
Lloyd.
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Old 10th Jan 2017, 7:45 am   #5
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Default Re: Power Transformer DIY Replacement on Sharp VZ-3000

£200 seems fair to me, though it should be an easy fix for yourself if you have some experience with fixing stuff. Have you got a multimeter?

If it powers up, then the transformer is more than likely ok and the hum could be caused be smoothing capacitors. Where it could get tricky is if you replace the caps and still have the hum then tracing the source of the hum needs experience and some test gear.

As Lloyd says if it is the transformer chances are someone has one here in their junkbox. If not you should be able to get one cheaper than £96.

Andy.
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Old 10th Jan 2017, 4:14 pm   #6
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Default Re: Power Transformer DIY Replacement on Sharp VZ-3000

Wow thanks for all the replies guys! This forum rocks!

Regarding the troubleshooting of the Hum. IT comes from the speakers, it kicks in after about 2 seconds from being powered on. The hum is constant, stays the same regardless of volume or input selection. It's on both channels and also appears on the headphone out(My headphones went hot after about a minute). I've tried it on a few power sockets and there are no other inputs connected to the system.

Here is the machine in question:
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The insides look clean:
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Here's the back of the power parts:
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I have a multi-meter and a soldering iron so maybe could get this done... I'm still waiting for the tech to call me back today with hopefully a lower estimate. If he can pin point everything that's wrong, at least I have a solid list of things I need to fix. I'll still need to give him £40 but at least I'll know with confidence what's wrong.

If I could do this myself I'd get a kick out of learning how to do it and would feel good about it. However, if I mess it right up I'll be pretty deflated.

I'll have a look in parts forum to see if anyone has anything that will do the job.

Thanks All!
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Old 10th Jan 2017, 4:49 pm   #7
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Default Re: Power Transformer DIY Replacement on Sharp VZ-3000

If the hum is coming from the speakers, then it's not down to a faulty power (mains) transformer. It's more likely to be faulty smoothing capacitors, or spurious hum being picked up somewhere.

EDIT. I see that Dr Wobble has already said this.
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Old 10th Jan 2017, 5:02 pm   #8
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Default Re: Power Transformer DIY Replacement on Sharp VZ-3000

I've had (and have) several of these and never found a bad transformer. I would be very wary of that diagnosis. As suggested, first thing to check is the rectifier which is downstream of it. You can also disconnect all loads and measure its output, comparing this with it loaded.
Also leave it on, without a load, for 10 mins and check if it is hot to the touch.
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Old 10th Jan 2017, 5:05 pm   #9
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Default Re: Power Transformer DIY Replacement on Sharp VZ-3000

If your headphones "went hot" then it suggests to me that you probably have a faulty power amplifier that is putting a DC voltage through them. It could also be caused the capacitors mentioned above.
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Old 10th Jan 2017, 6:51 pm   #10
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Default Re: Power Transformer DIY Replacement on Sharp VZ-3000

Thanks Guys,

I went back to my notes from the call I had with the Tech and see that I actually wrote down Power Amp IC(Not Transformer) I'm a bit new to all this... In my defense his English is pretty poor.

Is swapping out the Power AMP IC a big deal? L

Thanks for the testing advice Ben

Is the Power Amp the black chip backing up against the large heat sink?
Similar to this pic of a VZ 3500:
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If it is then it seems like Screw out/in type of job.

I'm now thinking I might try this myself
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Old 10th Jan 2017, 7:32 pm   #11
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Default Re: Power Transformer DIY Replacement on Sharp VZ-3000

I found the Power Amp(STK 461SL) in the manual and can find similar ones on line. The one on line don't have the SL part of the part number. Is this a problem?

Click image for larger version

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How do I find the rectifier?
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Old 10th Jan 2017, 7:34 pm   #12
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Thread title edited.
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Old 10th Jan 2017, 8:27 pm   #13
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Yes, the power amplifier is the STK461SL. One 'chip' (actually, it's more like a module) handles both channels. Page 22 of the .pdf manual mentioned above shows the circuit of the 'Audio Power PWB' (PWB = Printed Wiring Board, just another name for PCB). The power amplifier module will be screwed to the heatsink and has a row of pins that are soldered to the PCB.

The rectifier and smoothing capacitors are shown on the same page. The rectifier is a 4-diode bridge rectifier unit labelled 'D701'. The smoothing capacitors are C701 and C702. The layout diagrams (not too clear in this .pdf) show where they are on the board.

But before you replace anything, you should do some tests (and don't trust what anyone might have told you is wrong). Around the power amplifier IC, some of the pins have voltages given. In particular +25V and -25V from the power supply, 0V on each of the inputs (the pin on the left end of the 'triangle') and 0V on the outputs (the pin on the right point of the 'triangle'). They are all measured with respect to the earth rail of the unit, for example the 'sleeve' of the headphone socket, or the -ve side of the speaker sockets. Connect the black probe of your DMM (set to DC volts) there and check the other points with the red probe.

Do you have, or have access to, an oscilloscope?
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Old 10th Jan 2017, 9:34 pm   #14
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Is there any sound output at all, or just the hum? My guess is that STK module is cooked, and will probably cook your speakers and headphones if you leave it on too long! They are usually very easy to replace, just remember to put new thermal heatsink compound on and then solder into place.

The hardest thing is actually finding a replacement module from a reputable source. Be careful with the likes of eBay!
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Old 10th Jan 2017, 10:46 pm   #15
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Quote:
Originally Posted by Station X View Post
Thread title edited.
Good call Station X

Thanks for the detailed help Tony! Once I get it back I'll get started on testing these components. I don't have an oscilloscope and don't think the OH will let me get one but will ask around and see if I can borrow one.

@John yeah, plenty sound, radio, turn table and tape all working well. Just a loud hum in the background..

I'll ring the tech dude tomorrow and reclaim the VZ

Cheers!
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Old 10th Jan 2017, 11:04 pm   #16
Lloyd 1985
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

This sounds familiar! I have an amp that had a faulty STK module, the guy I bought it off said he blew up 2 pairs of speakers with it before deciding to give up! Whatever you do, don't connect any speakers or headphones to this again until it's sorted. With my amp, you could connect a multimeter to the speaker sockets and measure 45 Volts DC, no wonder it toasted speakers.

I also had a small Sony stereo which made a loud hum from the speakers, again, DC voltage present on the speaker terminals (about 30V on that unit), but I got lucky with that one, it turned out to be bad solder joints on the STK module, which were easily fixed.

There was someone offering STK modules on here not long ago, might be worth looking for that thread in sets and parts offered?

Regards,
Lloyd.
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Old 10th Jan 2017, 11:48 pm   #17
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Was it Boater Sam, yes here it is.
https://www.vintage-radio.net/forum/...d.php?t=132188

Mike
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Old 11th Jan 2017, 12:10 am   #18
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

I'm completely open to being told I'm wrong, but I'd be pretty sure that the STK461 is identical to theSTK461SL except that Sharp had the suffix added to make out their ICs were somehow improved. I can find only one varient of the STK461.
It seems to me that your 'tech' may be a little over the odds with his estimate (does he drive a Porsche), perhaps you should seek out a reputable Sharp dealer.....
That said, given the value of the unit, I'd buy the IC for the tenner it's available for online and have a bash at fitting it. Watch a couple of youtube videos on soldering and I'm sure you could do it....
You could buy yourself some serious vynl for £190
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Old 11th Jan 2017, 1:34 am   #19
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Found the chip on Amazon new for £7.40
https://www.amazon.co.uk/Hybrid-IC-S.../dp/B00N7IBJ70

I was looking at the picture and noticed the Capacitor near the top fuse had gung on top. It could be just sealant, but since the thing is humming I would replace it and the chip!
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Old 11th Jan 2017, 6:59 am   #20
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

A word of caution before you get too excited, it may not be as simple as replacing the amp IC. Something caused the IC to fail. Grubhead noticed a cap with gunge on ( not sure how, all I can see is blurred caps) well done BTW, which could be part of the cause.

To diagnose faulty caps an ESR meter is useful, but they ain't cheap. If you can get yourself a digital multi meter - DMM, that would be a start. A good visual inspection of the PCB is a good place to start and the same for the underside of the PCB. Some nice pic's posted here would help too.

Another word of caution about buying IC's, there are a lot fakes out there. Sorry to be Dr Doom. Sam might still be away in the sun, but I might have one.

Still, if your lucky a new IC might fix it and all will be well. Worth a try.

Andy.
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