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Yamaha CR-420 -- fuse?

myu701

myu701

Vintage futurist
The Yamaha CR-420 was my first "real" stereo and it served me well through high school and college. I passed it on to my sister, who used it for about 5 years or so, then she deposited it back at the parent's eternal storage closet: the basement.

So, come full circle more than 20 years later, I find the thing behind some boxes. It's in pretty good cosmetic shape. However, there's no sign of power. No lights, no relay click. However, the switched and unswitched AC current sockets work.

I opened up the casing and I noticed an empty fuse holder. 250v 3A. It should be occupied, correct? Would the unit be completely inoperative without it? No lights or relay click at all?

Thanks for any advice... :)
 
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YUP! No fuse, no work! Be sure to check the filter capacitors before powering up as they tend to dry out over periods or years of non use, and may need to be replaced.

You might get lucky by replacing the fuse, but I wouldn't recommend it!
 
cademan said:
YUP! No fuse, no work! Be sure to check the filter capacitors before powering up as they tend to dry out over periods or years of non use, and may need to be replaced.

You might get lucky by replacing the fuse, but I wouldn't recommend it!
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I figured as much, but knowing my sister's lack of electronics knowledge, I wouldn't have thought she removed the fuse (unless perhaps it was a boyfriend). But you do have a good point... if the previous fuse blew, something caused it that could still be a problem. Are there any risks on testing the receiver if the filter capacitors aren't any good?


ecluser said:
There are two fuses inside the receiver, a 3A fuse close to the power transformer, and a 1A fuse.
Here is a schematic:
http://www.eserviceinfo.com/downloadsm/54540/Yamaha_CR420.html
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Excellent -- thanks very much for that link, ecluser. Good to know for future reference on other equipment, too.
 
If its no skin off of your back, and you don't really care if it works or not, put a fuse in it, connect a junk speaker (if you got one) and go for it. You got nothing to lose 'cept blowing the fuse!

Then its totally up to you if its worth fixing or hunting down the problem! Your time, your money, your hobby! :thmbsp:
 
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Before puting a new fuse, you may check for a short between the collector and emitter of each power transistor. Pinout is BCE when you look at the transistors from the top.

It is possible that one of the main rectifiers (D505~D508) is shorted.
 
If I can get it to work, I'd give it to a friend or family member as I'm lusting after a future 2020 or 2040. :)

Unfortunately, my knowledge of electronics is very weak. I do have a Fluke multimeter. I guess it wouldn't hurt to do a little short checking. THIS seems like a good reference for the novice. What do you think?
 
Good reference for novice, yes. But keep in mind one very important aspect of component testing: in circuit the other components, connected to the device under test, will affect the final reading of the multimeter. When testing transistors, it is always preferable to remove them. However, when a component is shorted, we don't need to remove it from the circuit.
 
And so if a transistor has a short, I take it that either the collector or emitter (or both) would show no current? Or is it that an unexpected circuit appears like emitter(+)/collector(-) or emitter(-)/collector(+) ?
 
When a transistor is shorted it behaves almost like a short circuit between the collector and the emitter. This transistor will conduct as much current as the rest of the circuit (power supply, load resistors...) will allow, until the circuit is broken by a failure in one component, a fuse for example.
 
ecluser said:
When a transistor is shorted it behaves almost like a short circuit between the collector and the emitter. This transistor will conduct as much current as the rest of the circuit (power supply, load resistors...) will allow, until the circuit is broken by a failure in one component, a fuse for example.
Click to expand...

Yes, in retrospect my question looks a bit silly... of course a break in the current isn't going to trip the fuse, it would be the other way around--a current when not expected or higher than it should be. Thanks. :)


Incidentally, is a "fast blow" fuse usually preferred in audio electronics applications?
 
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myu701 said:
Incidentally, is a "fast blow" fuse usually preferred in audio electronics applications?
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Yes, but it is a matter of circuit design. You may think that a 1A fuse will blow at say 1.2A, but it is not as simple as that. A 1A fast blow fuse can usually support a 1.1A current for 4 hours, 1.35A for 1 hour and 2A for 5 seconds before opening.
 
ecluser said:
Yes, but it is a matter of circuit design. You may think that a 1A fuse will blow at say 1.2A, but it is not as simple as that. A 1A fast blow fuse can usually support a 1.1A current for 4 hours, 1.35A for 1 hour and 2A for 5 seconds before opening.
Click to expand...

I see what you mean. It makes sense that circuits would be designed to handle higher amperage, but have a lower amperage fuse with a safety margin. I just hadn't heard the term "fast blow" used before.
 
Does anyone know what body type these axial fuses have, for the older CR-XXX Yamaha receivers? Unfortunately, the fuse was missing when I opened up the case (someone must have removed it). I've seen most with glass and the fuse element visible, but when I examined another Yamaha receiver (much later model), the fuse was opaque. I'm hoping that the one used in the CR-420 would be the more readily available glass type.
 
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