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Old 30th November 2006, 09:52 PM   #1
Mguth is offline Mguth  United States
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Default Half-dead Rotel RB-850 resurrection

Hi all! Glad I found this board.

I'm trying to figure out what is wrong with my girlfriend's dad's old Rotel RB-850.

It has a dead right channel. It blows fuses as soon as you press the power button. I left the lid off, pressed power, and watched them both sizzle.

I'm good at electrical and mechanical things, but I know nothing about what might cause this. If I can figure out what it is though, I'm sure I can fix it.

I looked for the obvious things like crossed/bare wires and couldn't see anything. There are no visible burn marks on any of the system boards... it all looks good.

Any ideas what might cause this and if it can easily be resurrected? I'd really like to repair it as an extra Christmas gift rather than buying a new one.

Thanks much!

Michael
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Old 1st December 2006, 03:51 PM   #2
anatech is offline anatech  Canada
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Hi Michael,
You may want to do some studying first. A good electronics technician takes years to study, things are not that simple. If they were, technicians would be worthless.

So, to start, what test equipment do you have? Have you taken any electronics courses?

-Chris
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Old 1st December 2006, 08:11 PM   #3
Mguth is offline Mguth  United States
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Hey Chris,

I realize it's not 'that simple', but I'm no fool when it comes to technical items. I have a natural understanding of most of these things. I suppose I was thinking that if someone could say check "this, this, and this", I could figure out how to do that via Google, this board, and elsewhere. I'd teach myself.

I have a soldering iron, a de-soldering tool and a volt meter. I've had no classes for eletrical work outside of DIY stuff around the house or in a car.

Worst case scenario: I don't fix it and it remains as-is. If I don't even attempt it, it's probably going in the trash anyways.

Thanks!

Michael
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Old 1st December 2006, 08:36 PM   #4
anatech is offline anatech  Canada
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Hi Michael,
Well in that case, check the output transistors for a short C-E. Also have a look at the rectifiers.

-Chris
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Old 2nd December 2006, 12:10 AM   #5
Minion is offline Minion  Canada
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Sometimes a Bad or burnt out component is not easy to find from looking at it....I have had several Electrolytic caps go bad that showed no signs of it from looking at them, I have also had several Burnt resistors and transistors that didn"t look much different than the Good ones so it is not allways easy to tell these things without haveing some real test equipment and a first hand knowlege of how Circuits and Components interact....

Also a schematic of your unit is allmost allways necessary for troubleshooting a problem like this and without it fixing a problem like this will be next to impossible especially if you know very little about audio electronics....

You could replace every component on the Circuit board and still not have a working amp when you are done, especially if there is an unseen short in the PCB it"s self.....

You might try takeing it into a shop and ask them to find out what is wrong with it and then once you know you could try fixing it yourself, a Lot of Places will do free estimates which should tell you what is wrong with it, and Knowing is half the Battle.....


Good luck
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Old 2nd December 2006, 01:03 AM   #6
anatech is offline anatech  Canada
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Minion,
Quote:
You might try takeing it into a shop and ask them to find out what is wrong with it and then once you know you could try fixing it yourself, a Lot of Places will do free estimates which should tell you what is wrong with it, and Knowing is half the Battle.....
I can't believe you just said that. You are abusing the kindness of others!

Besides, a free estimate is worth exactly what you paid for it. Nothing. Often they are just plain wrong.

It doesn't take a genius to replace parts, although some skill and knowledge is required. The finer points will make a large difference. The value is knowing what parts to change, whether to match them (and how) plus many other things. Even down to how tight a transistor mounting screw should be. Amazing how many people get that wrong.

-Chris
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Old 2nd December 2006, 05:38 PM   #7
Minion is offline Minion  Canada
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Quote:
Originally posted by anatech
Minion,

I can't believe you just said that. You are abusing the kindness of others!

Besides, a free estimate is worth exactly what you paid for it. Nothing. Often they are just plain wrong.
-Chris

I can"t believe you just said that....Companies don"t give free estimates because they are "Kind" they do it because if they didn"t there buisiness would suffer...

No one is going to pay $xxx to find out there gear isn"t worth fixing and companies know that that is why they do free estimates.....

I recently took my TV to the shop to get an estimate for repair and they told me what was wrong with it and how much the Part would cost and how much labor would be and I decided that the Labor was too expensive so I bought the Part from them and took the TV home and Fixed it myself, They even told me how to Install the New Part ...They didn"t seem to mind ,If they did mind they wouldn"t have been so helpfull in telling me how to replace the Part.....

It"s all Part of doing business......
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Old 2nd December 2006, 05:54 PM   #8
anatech is offline anatech  Canada
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Hi Minion,
Quote:
It"s all Part of doing business......
I disagree completely with you.

I ran a service shop for 16 years and spend much longer as a technician. Our policy was different (due to people like you ).

We would give you an estimate and repair the item if the labour was less than 1 hour, seems perfectly reasonable to me. If the item was not repairable, or not worth repairing we would tell you so and there was no charge. If a reasonable estimate was refused we charged you 1/2 hour labour. We also didn't repair anything with a handle unless it was a Revox open reel. The customer was given no details on a refused estimate.

Our biggest losses were repairing items that were attempted by:
- bad repair shops
- the friends of the customer
- techs who specialized in other types of electronics
- the customer
- any engineer who figured they were smarter

We assigned an aszhole tax to units that had been tampered with and the customer concealed that fact (read: lied about it). The units that were too badly damaged to repair were the cause of the above problem, or a natural disaster (lightening, water ...).

It is tough enough to run an honest business without guys with your reasoning running around. Good shops do not want you as a customer, believe it. They do not make a lot of money, believe that too.

I really hope you open a service shop some day. That will change your tune big time!

-Chris
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Old 2nd December 2006, 07:00 PM   #9
Minion is offline Minion  Canada
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I do run a Shop that repairs computers, and I do free estimates, and I will also tell a person how to fix there own PC if they buy the parts from me...Either way I make a Sale....


It"s the Price of doing business, and I understand that and that is why I run my business that way I do and my customers luv me for it.....

The old Moto "The customer is allways Right" holds true even today were many companies think that the world owes them something......

A Free estimate is exactly that "A FREE estimate"..Now if you want to try to squeeze money out of your customers to cover your cost of a free estimate then don"t call it a free estimate cuz you simply lieing to your Patrons, and if you feel you are being taken advantage of because you offer free estimates then don"t offer them, but saying you give a free estimate when you are really trying to squeeze money out of them is plain dishonest....

There is no Law that says a Customer has to be honest but there are laws that say a buisiness person does have to be honest, so if you don"t like the water get out of the pool.....

Enuff said.....
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Old 2nd December 2006, 07:39 PM   #10
anatech is offline anatech  Canada
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Ahhh, you're a computer guy!

That explains why you don't value your technician or their knowledge. Trust me, a proper amplifier repair is far more involved. I deal with computers on a daily basis but don't repair TV's (thank goodness).

You will find that that model of doing business may work for you, but it doesn't for audio service, insterment service or telephone service. The average "okay" test bench for audio may easily have $10K in equipment on it and more. Never mind parts stock and training.

-Chris
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