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

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Old 13th Jan 2017, 6:23 pm   #41
Grubhead
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Since you need a soldering iron don't get one greater than 15 watts. And look out for extra small tips for it, get a stand to go with it. I like the vacuum bulbs rather than a de-soldering pumps. They are easier to handle and the tips can be poked out with a large safety pin. I actually use a bent large sized paper clip to get the tip free.
If you intend to do more electrical repair work invest in a anti-static strap. If the new chip has a yellow triangle on the bag it will come with get one anyway.
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Old 13th Jan 2017, 7:35 pm   #42
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

This is very much a personal choice, but I much prefer the spring-operated desoldering pump to tbe rubber bulb type. And I found a 15W iron to be far too small for most work. The Antex X25 (25W) is reasonable, but having used a temperature-controller iron I would not want to go back. The problem is that temperature controlled irons (at least good ones) are not cheap. That's fine if you spend half your time soldering or desoldering something. Not so fine if you just want to fix one unit.

I've just noticed where the OP is. Not too far from me. If you want somebody to have a quick look, give you a few hints, etc, I would be happy to do so sometime (but not for a couple of weeks). And no, I don't charge £40 to say that some transistors are faulty. I don't charge at all.
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Old 13th Jan 2017, 8:32 pm   #43
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

The problem with most de-soldering things is clogging, the rubber bulb and the springy pump type both suffer it. I prefer the springy one to the rubber bulb type, but the springy ones when they get clogged it usually waits until you have just got the solder joint molten then you press the release button and nothing happens, or it happens very slowly! I normally use both a de-solder pump to get the worst of the solder off, then use de-soldering braid (also known as de-soldering wick) to mop up what's left.

Antex soldering irons are excellent value for money, I had one for years as my first proper iron, don't get one of those cheap £3.99 things from a DIY shed that looks like a screwdriver with a plug on it, they are rubbish! They get way too hot, and burn the cheap nasty tip away very quickly. I can also say that the temperature controlled soldering stations from Maplin are pretty good, I have one that has served me well for a few years, I think they were about £30 when I got mine.

Get some decent solder too, I got a roll of it from Farnell, cost me about £30 but it lasted me nearly 7 years!

For checking the voltages, have a good study of the service manual I linked to earlier, on the circuit diagram there are what voltages should be expected in certain places, you will need your multimeter set to read voltage (select the correct range on DC Volts, if it isn't an auto-ranging meter), black probe goes to ground, red to where the voltage your trying to measure is supposed to be according to the diagram.

Regards,
Lloyd.
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Old 13th Jan 2017, 8:51 pm   #44
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

If you won't be doing too many repairs then Lidl have a temperature controlled soldering iron kit for about £10 - think it's next week (check their online brochure) but they only have them while stock lasts. A more expensive iron would be better but only if you are going to make full use of it, otherwise it's an unnecessary cost.
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Old 15th Jan 2017, 4:50 pm   #45
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Hi guys quick update,
I bought a soldering iron off of Amazon that had great reviews and also came with a number of different heads together with a de soldering Spring pump thingamajig. I also grabbed one of those soldering for beginners kits from Maplin and put together a quick audio circuit board thingy. Unfortunately this didn't work but I think my soldering skills have improved and I don't think the issue was with my sordering more something to do with my putting the components in with the incorrect polarity. When it comes to desoldering I find that adding a bit of solder to it makes it come off cleaner however sometimes it looks like some is left and I worry that the remaining solder that is left bridge The pads when it is covering both. I have some disordering coil so will use that to mop up the remainder .

I also picked up a cheap esr meter, using that I tested all the caps on the power pwb and they all read as healthy against the spec. Maybe I should apply some heat to them and retest ? I did find one cap that was reading 1000mfd but the manual says it's a 2200. However the cap itself says on it 1000mfd. Maybe the manual I have is for slightly different model.
Anyway, I believe the power supply is clean how can I test just the power unit if I turn it on and it is not connected to anything can I just test the outputs with my DMM??

Regarding the power amp I have taken this out and had a look at it in more detail. I don't know if I will be able to fix this one as I am unsure how to test it. I will do my best with it and try to bridge the track as best as I can. however if it doesn't work out I'll go down the route of replacing the amp with a modern one as per Paul's suggestion. I've found sure electronics jab 2 as something I'd like to go with as it's compact and good quality. I can also have Bluetooth, line in and USB to it( sacrilege ). This one looks good:
http://store3.sure-electronics.com/aa-ja32171-1751
Do I need 2 x 50 watts? I'm a bit confused as to where the current set up adds the power to the speakers...
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Old 16th Jan 2017, 2:08 pm   #46
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Hi All,

So I removed the audio power PWB. De Soldered the lump and put in a wire. I mopped up as much of the lump as I could.I also ran over the two track on the side with a bit more sloder to see it it helps. However, it seems to me like those tracks go to points not connected to anything...?

Here some rough pics:
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I turned on the radio and still getting the same Hum. So the good news is I've not made it any worse and the bad news is I didn't fix it.

I have attached a PDF(not sure if that will work) which shows my testing for the Caps on the power board against what's in the manual. I feel like it's in good enough shape. Capacitor Testing.pdf <- Hopefully this might help someone else.

I'm now thinking that the issue is definitely in the Power AMP IC... I'm going to swap this out next and see what happens. If that fails I'll swap the AMP out with a modern amp.
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Old 16th Jan 2017, 2:10 pm   #47
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Also adding in a graphic I made to help others with cabinet removal:
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Old 16th Jan 2017, 8:33 pm   #48
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Those points you've indicated are 'print-thrrough'connections. The circuit board is double sided, and these join tracks on the upper(component) side of the board to those on the lower side. Such joints can give rise to various problems, and it is sometimes possible to run a short length of tinned copper wire through the board at the junction points, bend over a short length of wire onto both the upper and lower tracks, soldering both sides. In some cases if the exsisting solder is cleared away, a small hole will be present, through which the wire can be inserted, otherwise a hole can be drilled, using asmall diameter bit, and small drill. Obviously there are points on the PCB, where drilling is not possible due to closely spaced components leaving no room for a drill, but where this is possible, it's a good way to rectify a bad connection on a double-sided PCB.
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Old 16th Jan 2017, 9:29 pm   #49
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

I don't think that it's a double sided PCB, most double sided PCB's I've encountered are green both sides, this is just standard single sided PCB. Those points look to me like alternative connection points for PTH401, which is a thermistor, possibly mounted on the heatsink along with the STK IC. It is shown in the manual on the page with the PCB layouts connected here, I can only assume that it was a later revision to move where it's connected.

Next thing to try would be voltage measurements to see what is going into and coming out of the STK, try and rule out everything else before fitting another STK, especially if it's another component causing the STK to go pop! Is the hum present on both channels (L+R) or just one? Check to see if there is any DC voltage coming out of the speaker terminals.

Regards,
Lloyd
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Old 17th Jan 2017, 7:58 am   #50
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Thanks Guys,
I'm gunna go with Lloyd here as the thought of this thing having two sides adds a layer of complexity beyond what I can handle.

I found this outstanding guide about the STK465 and how to test it.

Will also check if DC voltage is present on the speakers. The issue is present on both left and right speakers equally.

I had to pack away the radio yesterday as I thought the OH was going to flip out over the mess so probably won't get anything done for the next few days.

Cheers!
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Old 17th Jan 2017, 10:18 am   #51
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Lloyd, you may be right, although I know that Sharp, Blaupunkt and others were using double sided PCBs well over 30 years ago. Some early ones used rivets to connect the tracks on one side to those on the other, and the boards weren't always green on either or both sides. Somewhere I have some old Sharp service manuals, though not the one for the VZ3000, and I'll check whether they used D.S. Boards out of curiosity.
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Old 17th Jan 2017, 1:28 pm   #52
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Missing components are common on some boards. They are for models which used the same board, but had more complex features. I have seen boards where entire sections of the board are blank. In fact when I first got into electronics I was making an old Marconiphone Radiogram, which carried the 1977 chassis and mono FM radio, into a stereo one. It used the same board as the 1978 chassis. which was stereo FM, but the 1977 left out all the stereo components. I never did succeed in making it stereo, but learned lots about electronics trying!

Doubled sided boards tend to come in when surface mounted devices started to be used more.
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Old 17th Jan 2017, 1:33 pm   #53
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

I agree with Lloyd and Grubhead on this. Definitely a single-sided board and the empty holes are nothing to be concerned about.

Great work so far, Billy, good luck.
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Old 19th Jan 2017, 9:03 am   #54
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Good morning All,

I powered it up and checked the speakers for DC voltage. It's zero on each speaker. That's good I suppose...
Here's the IC design:
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Next I checked the the IC pins for voltage and wrote them down:

1. -8.3
2. -10
3. 0
4. -27.3
5. -28.4
6. -26.1
7. -26.1
8. -8.4
9. 28
10. -26.7
11. -26
12. -28.4
13. -27.9
14. 0
15. -10
16. -8

The first seven and last seven above are basically mirrors of each other which seems correct for left and right channels. Pin 9 is the +vcc. As per the diagram, 3 and 14 are grounds and have 0 volts which is a good sign.

The only strange thing I did notice was that pin 9 also reads as 59.7 on the DC volts setting. Is that normal?

Many thanks!
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Old 19th Jan 2017, 9:59 am   #55
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

This IC, in common with many others, has what is known as a split supply - i.e. +28v (pin9) and -28v (pin 12), with respect to (wrt)ground at either pins 3 or 14, but I can't see how you would measure +59.7v wrt ground on pin 9, unless it's a quirk of your multimeter, especially if it's a digital one. Measuring between any one of pins 4,5, 6, 7, 10, 11, 12, or 13, would give a reading of around +56 to +59v, with Negative probe of the meter connected to one of the above pins and the positive one on pin 9, as would be reading the full upply voltage, i.e. +28v and -28v, 56v. total.
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Old 19th Jan 2017, 11:12 am   #56
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Looking at the state of the PCB I would be tempted to assume that it is oscillating due to a cracked ground plane between the negative of the main capacitor and pin 9.
Just try two lengths of hook-up wire between pins 3,14 and the negative terminal on the capacitor in the power supply.
A small track in the negative feedback area can also cause oscillation too.
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Old 19th Jan 2017, 1:07 pm   #57
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Pins 7 6 10 11 should read pretty much zero you are showing around 26 v on them, this points to a short Circuit in the STK chip, years ago back in the 80's i replaced hundreds of STK chips in Sharp audio equipment, nearly all damaged by shorts in the speaker wiring or the speaker DIN plugs.

We hated the VZ3000 and my heart sank if i saw one on the repair rack, although the STK will be easy enough to replace.

Steve
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Old 19th Jan 2017, 2:05 pm   #58
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Just out of interest, can you check the resistance (with the unit switched off!) of R417? It is a 100 ohm fusible resistor between pins 8 and 9, with pin 9 at 25v (or 28 in your case) pin 8 should be 24v rather than -8.4. Worth a shot before condemning the STK completely!

Regards,
Lloyd.
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Old 19th Jan 2017, 4:29 pm   #59
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Thanks Guys, Some great suggestions here. I'll give them a shot as soon as I get home tonight.

@LiveWire: I took a pic of the DMM:
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Old 19th Jan 2017, 9:56 pm   #60
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Default Re: Power Amp IC Replacement on Sharp VZ-3000

Not sure what model DMM that is, but they can all give strange readings at times. I hadn't however, taken in the fact that the reading on pin 8 was wrong, so, as Lloyd says, do check R417. Fusible resistors do sometimes fail for no apparent reason, although if it is open circuit, the STK may be faulty
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