The protection unit of Yamaha's RX-750 is active despite perfect working power amplifier section due the absence of neg. supply voltage.
Reason therefore is the interrupt safety resistor R171 (1Ω) between transformer and rectifier diodes node D116/D118 (go to the attached schematic).
I replace it together with R172 by a 1R/5W ceramic type (after additional cleaning and polish the loudspeaker relay contacts correct working is to observe at the whole device - also the voltages are according to those from the schematic).
But I want to add an usual fuse both in the pos. and neg. voltage rail.
How I find out the correct value for ampere rating and character (ultra-rapid, super-fast, fast and slow-blow) ?
Or is this replacement impossible and only fuse resistors come into question therefore ?
If so, how do I choose the correct value here (the old ones obviously to weak) ?
Thank you very much for an advice.
Here datasheets of two companies:
CRF Series >> Safety resistors >> Products >> Vitrohm | Resistors
https://www.vishay.com/docs/31031/cmffuse.pdf
P.S.: This thread don't provide the right hints:
Suitable substiture for fusible resistor?
Reason therefore is the interrupt safety resistor R171 (1Ω) between transformer and rectifier diodes node D116/D118 (go to the attached schematic).
I replace it together with R172 by a 1R/5W ceramic type (after additional cleaning and polish the loudspeaker relay contacts correct working is to observe at the whole device - also the voltages are according to those from the schematic).
But I want to add an usual fuse both in the pos. and neg. voltage rail.
How I find out the correct value for ampere rating and character (ultra-rapid, super-fast, fast and slow-blow) ?
Or is this replacement impossible and only fuse resistors come into question therefore ?
If so, how do I choose the correct value here (the old ones obviously to weak) ?
Thank you very much for an advice.
Here datasheets of two companies:
CRF Series >> Safety resistors >> Products >> Vitrohm | Resistors
https://www.vishay.com/docs/31031/cmffuse.pdf
P.S.: This thread don't provide the right hints:
Suitable substiture for fusible resistor?
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R171 is a safety component, and as such, MMUUSSTT be replaced with the correct device.
If you chose to replace it with something else, the device has lost its safety certification, and you assume responsibilty for for the products safety.
If the product subsequently catches fire, and someone dies, you accept responsibility.
If you chose to replace it with something else, the device has lost its safety certification, and you assume responsibilty for for the products safety.
If the product subsequently catches fire, and someone dies, you accept responsibility.
The manual specifies R171 key safety spec as flameproof (carbon 1/4w) , not particularly fusible as it’s main overriding spec.
So look for that spec specifically
Like Yaego FCR-25JR-52-1R
Replacing with a 5W variant is madness
If you really want to add fuses to the rail, break into it and measure the current !! Check if it fluctuates with volume, and add a tiny bit of headroom (like 10%) to the fuse you select ,
But without doubt never replace a 1/4W with a 5W !!!
So look for that spec specifically
Like Yaego FCR-25JR-52-1R
Replacing with a 5W variant is madness
If you really want to add fuses to the rail, break into it and measure the current !! Check if it fluctuates with volume, and add a tiny bit of headroom (like 10%) to the fuse you select ,
But without doubt never replace a 1/4W with a 5W !!!
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What means for you "correct device" ?
If you are right, the datasheet of the genuine part is essential for finding the right replacement part (Yamaha's part No. for this resistor is "HV453100") and if datasheet unknown and the part no longer available a repair service is impossible.
The choice for this 5W had no specific reason and was made because I had it available to see if there were any more errors. Volume control haven't any influence, because the protect section use independent voltage rails/windings.
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Safety resistors, Fuses etc are safety devices. To maintain electrical safety, they must be replaced with devices which have identical characteristics.
Manufacturers supply part numbers so that technicians can order the correct part easily.
You do not have to use the manufacturers part to maintain safety. A 0.4W non-flamable resistor supplied form a reputable company has the same safety certification as the manufacturers part (and is probably cheaper).
Likewise, a F400mA fuse will be designated as a safety component. As long as the replacement is a F400mA fuse from a reputable supplier, it has the same safety certification as the original component.
As long as you replace like for like, wattage etc. then you are maintaining the safety of the product.
If you change a safety designated component for a standard component, then the products safety is compromised and you are on your own.
Manufacturers supply part numbers so that technicians can order the correct part easily.
You do not have to use the manufacturers part to maintain safety. A 0.4W non-flamable resistor supplied form a reputable company has the same safety certification as the manufacturers part (and is probably cheaper).
Likewise, a F400mA fuse will be designated as a safety component. As long as the replacement is a F400mA fuse from a reputable supplier, it has the same safety certification as the original component.
As long as you replace like for like, wattage etc. then you are maintaining the safety of the product.
If you change a safety designated component for a standard component, then the products safety is compromised and you are on your own.
If the developer has perform a good design that's true. If not, the last statement also applies if you replace like for like.
BTW - Safety resistors are in most cases a real security risk in terms of fire hazard - in other words, exactly the opposite of what they were supposed to do.
I heard this statement from many experienced developers in the field of battery charging technology - this has been done since the 1990s as a cheap alternative to real microfuses, which show much more exact parameters in it's datasheets than safety resistors regarding the individual characteristics for interruption.
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I just checked and as it happens Yamaha still stock this resistor , and do have stock 🙂
If however you want to go with fusible (and specified as non-flammable) , then you could try NFR2500001008JA500 which farnell for one have stock of. https://uk.farnell.com/vishay/nfr25...metal-film/dp/9473939?ost=fusible+1r&cfm=true
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You are doing/saying ANYTHING to self justify NOT meeting Safety Standards 😡 and to boot diss proper Safety suggestions by WAY more experienced Members.
Boy, you are FULL of it!!!!
Doubly so in a cutthroat Market where saving 1/4 of a cent makes or breaks a Company.
Now think about YAMAHA.
So what?
Different products for different needs.
Did I mention cutthroat competition? 🙄
In any case the proper, SAFE, Factory suggested part is available, so .....
So you think YOU are more qualified to decide on safety than **YAMAHA** Engineers?
Boy, you are FULL of it!!!!
YOU have it the exactly opposite (wrong) way.
Who cares about what is being done in an absolutely different field?
Doubly so in a cutthroat Market where saving 1/4 of a cent makes or breaks a Company.
Now think about YAMAHA.
So what?
Different products for different needs.
Did I mention cutthroat competition? 🙄
In any case the proper, SAFE, Factory suggested part is available, so .....