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Old 14th February 2008, 06:22 PM   #1
Bluto is offline Bluto  United States
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Default Electrocution not an option ...

No one believes it but it's just a fact. I've gotten burned 5 times in a row on used receivers on Ebay. All arrived non functional despite confirming e-mails that they were as advertised... working.

I really want to keep one of them, a Sansui QRX 7500.

I'm in Wisconsin. I won't ship these things anywhere but will drive them 150 miles for repair.

Someone qualified is welcome to all but the big Sansui as trade for repairing it or I'll pay for those services . The rest is scrap in my mind only because I have zero idea regards fixing it. It all powers up. I'll even throw in the Aiwa cassette deck that also arrived non functional.

That brings me to parts. I'm just beginning study on Amps and am certain some of these parts are worth keeping. Knobs, attenuators, transformers, resistors, capacitors, etc. I really don't want to get fried and have never taken a receiver even out of it's case.

Is it dangerous for me to start gutting these things? Any Primer I should read someone could suggest?

Bluto
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Old 16th February 2008, 12:10 PM   #2
Nanook is offline Nanook  Canada
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Default niot an option...

I agree.

First, sorry to hear of you being burnt re: ebay. If purchasing something for any "real" money, use an escrow service. It's relatively cheap insurance.

As long as the receivers are solid state, there really little to worry about. The biggest threat comes from non discharged , large capacitors. You can always use a 10 watt, 10 Ohm resistor to bleed down the caps, but most SS amps already incorporate something like this.

If tubes, a whole different animal: If uncertain about high voltages, just don't do it. As above , the caps are the most dangerous, because the stored energy (as high voltage) is often several hundred volts, and can KILL you dead.

My rule if thumb: if you think you should be worried about working on a piece of gear, and won't unless someone else is around (for safety) , then you probably should not be working on it.

Pretty much everything else is pretty benign, but even a small cap can back a wallup (re photo flashes use caps to store energy until required).

stew
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Old 16th February 2008, 12:36 PM   #3
kaan is offline kaan  Denmark
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Caps don't hold the charge forever.
If you don't know how to discharge them safely the just let them sit for about 3 months without power, that ought to do the trick.

Edit: Discharging smallish caps is just a matter of shorting them a few times till the sparks stop flowing
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Old 16th February 2008, 06:57 PM   #4
Bluto is offline Bluto  United States
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Stew -

" I am not worthy!".

Been a Fan of your's ever since I discovered this Forum and sometime before as I'd read reviews you'd done.

May I say you always present as a true Gentleman with a real degree of humility as well despite your obvious qualifications. Those attributes are sincerely refreshing in this study of interest. Just refreshing period and it truly makes Guys like me who are just beginning on the learning curve a good deal more comfortable.

Never thought of an escrow service and I'll check into it. I really don't want to give up entirely on vintage equipment and I'm out enough I could have bought a new Jolida hybrid ! All for love of 70's equipment.

Grandpa was an Electrician and taught me enough that I tore every bit of wiring and box out of a 3 story Victorian and replaced it with a buddy in 2 and 1/2 days. Saved 2K in 1980 dollars. What I have no knowledge of is Theory regards electronics and 110 ain't much compared to what's inside Amps. Tubes terrify me and plans are to start with a small kit when I have learned enough to feel comfortable. I've read enough so far to know you shouldn't solder connections with a tire iron while sitting in the swimming pool. I think a Pioneer amongst the group might be a hybrid, I'll research it before I open it up.

Much appreciated- Bluto
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Old 16th February 2008, 07:03 PM   #5
Bluto is offline Bluto  United States
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Kaan -

Thanks - I've read a few threads on discharging the caps but nice to know I should be O.K. after a few months.

'Short til the sparks stop flying'? Encouraging .... LOL.

Bluto
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Old 17th February 2008, 12:10 AM   #6
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A few months? What are those supercaps? Regular caps will autodischarge in a matter of minutes, max an hour.
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Old 17th February 2008, 05:31 PM   #7
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Back in the day when I used to repair these things (amplifiers), I never worried about the caps. They'll discharge fairly quickly once the power is off and the voltages that they work with are relatively harmless.

That being said, the best zap I ever recieved was from a cap on a tube type 100 watt FM transmitter. I was removing a burned resistor, had the solder wick in one hand, iron in the other. As I was wicking up the solder, I layed my wrists down on the case which provided the perfect discharge path for the rather large cap that was tied to the leg of the resistor. 400 volts to ground, through the finger tips down the hand and out the wrist.

After the wick landed on the other side of the room, I looked over at the schematic again and kicked myself, the resistor was the discharge path for the cap.
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Old 17th February 2008, 05:53 PM   #8
Netlist is offline Netlist  Belgium
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The proper way to discharge the big caps in an amplifier is with a resistor. I use something like 20 ohm 10Watt. Don't use the brute force screwdriver method. Bad for the screwdriver and the caps.
Always measure the residual voltage after discharging.
To me 3-4V is the maximum allowed remaining voltage.

I agree that small cans are not an issue, certainly not after a few minutes.

All this as a rule of thumb.

/Hugo
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Old 17th February 2008, 07:14 PM   #9
AuroraB is offline AuroraB  Norway
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Well, there are cap's - and there are CAP's.....

Many years ago, a got kicked real hard from the multiplier caps in a radar scope.... 40 hrs after switch off.
Never take easy on safety!
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Old 27th March 2008, 09:16 PM   #10
240z4u is offline 240z4u  United States
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Hey Bluto, please contact me. I am in southern WI and have some suggestions and may be able to offer a hand.

I am not a "tech" but a DIY guy who knows some folks who can help you out.

Thanks - Evan

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