Pioneer RX-570 keeps blowing fuses

first, dont go poking around with a meter with a needle. Get a digital meter if possible, or know where you are poking. The reason being that the needle type meters can cause current to flow where it shouldn't. That is you might blow things by just looking at the resistance across them. This is especially true with mosfets, but it sounds like you don't know what those are.

If you really want to learn electronics, get the service manual to this thing. It might be available on the net somewhere for free or a small fee. just google it. Then figure out what the symbols in the schematic of the service manual mean and what they do. know what a transistor does. This is a good start.

To directly answer your question, the round thing is a resistor. Get a resistor color code guide (free on net) and it will show you that red red green (in that order with a 4th band after green) is 2.2 mega ohm. thats a lot, and probably wont make the needle move much, but a digital multimeter should be able to read it ok. Usually resistors are ok unless they look bad, but not always. I usually asume they are fine and only test them when i get really stumped.

Hope this helps.

Matt Evans wrote:

I honestly don't want to put you off learning about the subject some, but you have picked a mighty tough repair project here, to cut your teeth on. The reason that the fuse is blowing, is most likely to be as a result of a bad output stage - although there are other causes, such as a bad bridge rectifier in the power supply. Pioneer amps are notorious for making the most experienced of us cry, so I think that the liklihood of you ever getting to the bottom of this problem, particularly just armed with a multimeter, is slim to zero. You will probably find that your inexperienced probing ultimately leads to additional damage, which will do you no favours with your friend. Believe me when I tell you that you've only got to look sideways at these DC coupled amps, to make them blow their output stages. Your best bet would be to bow out of this quickly, and advise your friend to take the item to a good repair shop, with properly qualified people who specialise in repairing this type of equipment. Then, get yourself some beginner's electronics books, and build up some basic understanding of principles, and above all, personal safety when dealing with line-powered equipment.

Arfa

Arfa Daily ha escrito:

I thoroughly agree with Arfa. Don't keep probing around if you haven't so much as the basic component knowledge necessary- you will make things worse, possibly putting the appliance beyond economical repair, and may do yourself an injury. IMO there is nothing worse from a tech's point of view, than trying to sort out the aftermath of someone's inexperienced poking (which often transforms the original straightforward fix into an expensive component swapping mess). Some repair shops even refuse to deal with such items. Do yourself and your mate a favour and put the top back on it!

-b.

surely the deals the same with dmms, no?

Arfa Daily wrote:

oh, horrors. The only thing you'll learn on dc coupled stuff is how frustrating tronics can be.

NT

This unit was designed to blow the audio output transistors if a short is detected on any of the B + lines. If the cassette motor shorts, for example, the audio amplifier blows. These units can be modified so this doesn't happen, but I wouldn't recommend repairing one of these and I spent over 20 years in the consumer audio field. Chuck

These models are NOT for newbies or beginners. I have a lots of experience on these - my old posts on them still come up from time to time. Trust me and the others here who have advised you to get out of this one. If you're wanting to learn electronics, don't do it with one of these.

Mark Z.

Thanks for the replys guys. I'm wondering though what i would physically have to do to repair this thing...solder on some transistors? I have a soldering iron and experience using it, so if that's all that the repair intails, i think i could do it. If its really that difficult i probably won't attempt it, but i would still like to know what i would have to do. If you know of something on the web describing it, please post a link. Thanks again.

ISTM that the general opinion is that you probably have 1940's Ford repair skills and you are trying to fix a Prius. Probably not looking at a good result here.

...have you paid *any* attention to what people have posted in response to your original question??

-b.

It doesn't hurt to ask. I can can look up anything that i don't know. But if it's such a big problem, forget it. JEEZ! o_0

No, you're right - it doesn't hurt to ask. You did, and we answered you with what we considered to be honest advice. We really aren't trying to be obstructive or offensive to you, or to drive you away from the group. You could learn much by hanging out here. However, although soldering some transistors will, almost without doubt, be involved in the repair, without detailed knowledge of how to repair DC coupled amplifiers, you will only gain lots of skill in replacing and soldering output transistors, because you will be replacing them again, and again, and again, until your wallet is empty, or your supplier has run out of them.

Trust me when I tell you, with 35 years experience in fixing these things, that with the level of skill that you currently possess, you WILL NOT succeed in repairing this amplifier.

If you are determined to take it a bit further, you could check the bridge rectifier for shorts, but you will have to remove it to check that you are not reading across a fault elsewhere ( do you even have desoldering equipment / skills that will allow you to remove multi-leg items from a board without damaging the print ? ) If it's not the bridge, then you could try measuring on ohms across the two main smoothing caps, where you will almost certainly read a short, from bad output transistors. This will only be the tip of the iceberg though. As well as bad output transistors, there will be bad drivers, open resistors, maybe bad diodes, and a trail that can end you up in the preamps.

If these things can make experienced engineers cry, I hesitate to think what effect they might have on a beginner. Keep up the interest, but please take well-intentioned advice from everyone, and walk away from this one.

Arfa

I'm fond of saying that Pioneer's engineers should go to jail for this one. (even though it was really Mitsumi who made those amp modules)

There is a so-called "protection" circuit which operates to INTENTIONALLY destroy the output transistors if any fault is detected. A power supply voltage down, a bad cassette motor, bad op-amp IC, etc can cause the output transistors to fail. All this to make the fuse blow, so the unit cannot continue under the fault condition.

Sort of like designing a car engine to throw a rod if a brake light goes out, so that you cannot continue to operate the unsafe vehicle.

Mark Z.

That looks like a no to me. OK then, look up design of dc coupled amps. Get back to us in 2 years time.

NT

Ok, i guess it really is something that is way over my head. I appreciate that you guys took the time to explain it to me in more detail. My dad is a retired electician. He gave me some books to read as well as an old multimeter, so i've got a start learning about this stuff. I'm going to try googling some of the terms you guys were talking about in your replys to see if i can make heads or tails of it. I'm more than likely NOT going to try to fix it though, although my friend to whom it belongs to is way in debt and won't be able to take it to a repair shop. It will go back to its duty of filling a hole in his entertainment center for aesthetic value only. Cheers.

If you seriously want to understand this one, google for the schematic of a dc coupled amp and try and follow it thru, see how it works. Just make sure youre not in any way suicidal beforehand.

NT

Try learning to repair simpler things - small appliances or basic radios. Work your way up to nasty stuff like this.

You need to tell the OP.

And not top post. This is how confusion like has happened here, as to who you're replying to, occurs. Homer was not the original poster, just one of the respondents ...

Arfa