qprhooligan
Well-Known Member
should I get 1% or 5% tolerance?
Fuse Resistors - The where's, why's and how's
- Thread starter skippy124
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qprhooligan
Well-Known Member
Not sure what happened to what I typed out but it got truncated. now I have to start over.
Sansui service manuals seem to suck. The parts lists are incomplete. Or am I missing something?
bobrown14
Super Member
The manual is a "guide"
you can use it but be ready to make another order. Another reason for getting extra parts .. sooner or later you will have the spare parts when the manual screws you. They don't really suck per se but they are not always 100% - the thing that messes me up is the PCB printing when the caps have a + sign where it's a negative so not only do you need to watch out with the manual but pay attention when taking parts out and the orientation. That will really bite you..Cheers,
Bob
ConradH
Lunatic Member
The AU-717 uses 82 ohm fusible resistors (schematic note 3) in the RIAA phono section- the emitter resistors for the output pair. It also has a couple in the filter section and on the power amp boards. There are non-flammable resistors (schematic note 2) in the power section and elsewhere. In general, where you find a low impedance small signal NPN/PNP output pair, there's a good chance that the emitter resistors will be fusible. Not decided what I'll replace them with yet.
The unit I'm working on developed bad phono performance and the resistors ranged from over 200 ohms to over 500 kohms. They can probably rise by 10X before you notice a problem, but it just ain't right!
edit- And after replacing the resistors with 1/4W metal films, I found several noisy transistors in the phono section. The 82 ohm fusibles on the filter/tone board were in spec, but the 150 ohm fusibles on the power boards were not.
The unit I'm working on developed bad phono performance and the resistors ranged from over 200 ohms to over 500 kohms. They can probably rise by 10X before you notice a problem, but it just ain't right!
edit- And after replacing the resistors with 1/4W metal films, I found several noisy transistors in the phono section. The 82 ohm fusibles on the filter/tone board were in spec, but the 150 ohm fusibles on the power boards were not.
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Dannybartman
New Member
Hey,
I know I may be really late to this, but I was going over your pictures. I need a 330 ohm variable resistor for my sansui 551 and I can not find one for the life of me. I was wondering if you could point me in the right direction of where to find one? I'm very knew to repairing vintage gear. Thank you for any help! I added a picture and made an annotation around said resistor.
I know I may be really late to this, but I was going over your pictures. I need a 330 ohm variable resistor for my sansui 551 and I can not find one for the life of me. I was wondering if you could point me in the right direction of where to find one? I'm very knew to repairing vintage gear. Thank you for any help! I added a picture and made an annotation around said resistor.
Attachments
I would get 500 ohm, Bourns types are very popular and very good - available from Mouser, Digikey etc.
Note the orientation of the adjuster - you want 'top adjust' for that position - otherwise you'll find it impossible or very difficult to turn the adjuster.
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sKiZo
Hates received: 92644 43.20°N 85.50°W
This particular beast is a VR ... which brings to mind the question ... why replace it, unless it's obviously failed? Most aren't prone to the typical aging problems, and can be cleaned and retuned without any issues. Just keep in mind some of them are VERY twitchy, and it doesn't take much to throw the circuit out of spec into dangerous territory.
SoundOfSound
Super Member
There are some cases out there were a fusible resistor is the only protection you have. There are also unobtainable parts with these little guys trying to protect them.
I think the new technology has gotten much better.
Here are some fusible resistors to use if you need fusible replacements. They are metal film and flame proof.
Vishay 1/3W and 1/2W with a prefix of NFR25 for 1/3W and NFR25H for 1/2W.
http://www.mouser.com/ds/2/427/nfr25-239840.pdf
Yago 1/4W to 3W with a prefix of FRM.
http://www.mouser.com/ds/2/447/Leaded-R_FRM_2011-12977.pdf
I think the new technology has gotten much better.
Here are some fusible resistors to use if you need fusible replacements. They are metal film and flame proof.
Vishay 1/3W and 1/2W with a prefix of NFR25 for 1/3W and NFR25H for 1/2W.
http://www.mouser.com/ds/2/427/nfr25-239840.pdf
Yago 1/4W to 3W with a prefix of FRM.
http://www.mouser.com/ds/2/447/Leaded-R_FRM_2011-12977.pdf
Oh yes they are - they need to be replaced, and to address the twitchiness multi turn replacement types are a good idea.
I found 4 bad fuse resisters on a TA-500 phono board a couple days ago.
The TA-300 uses the same board.
They are labeled in the service manual as "FR" type (fuse resistor). 68 ohm.
Although the actual resistors look like 47ohm but maybe they are that dis colored.
The TA-300 uses the same board.
They are labeled in the service manual as "FR" type (fuse resistor). 68 ohm.
Although the actual resistors look like 47ohm but maybe they are that dis colored.
DrDreas
Member
Excellent thread, thanks guys!
I have an AU-117 that is only putting out the faintest amount of sound in both channels, both through headphones and speaker outputs (not distorted though, curiously enough). Also, I noticed the volume spikes along with some distortion when turning it off with a source playing music through it. After seeing this thread I was sure I may have found the reason...
I have so far replaced the 4x 220ohm resistors as these were the ones that seem to have drifted the most, but the amps behavior has not changed...and none of the 13 fuse resistors that are circled in the first pic are open circuit either. Can they be intermittently out of spec?
What I'm wondering is whether there is a rule-of-thumb percentage of drift that is acceptable or would indicate a resistor is problematic, and am I barking up the right tree here with my amp or should I look elsewhere? There doesn't seem to be a service manual available for the first version either...only the 117II
I have an AU-117 that is only putting out the faintest amount of sound in both channels, both through headphones and speaker outputs (not distorted though, curiously enough). Also, I noticed the volume spikes along with some distortion when turning it off with a source playing music through it. After seeing this thread I was sure I may have found the reason...
I have so far replaced the 4x 220ohm resistors as these were the ones that seem to have drifted the most, but the amps behavior has not changed...and none of the 13 fuse resistors that are circled in the first pic are open circuit either. Can they be intermittently out of spec?
What I'm wondering is whether there is a rule-of-thumb percentage of drift that is acceptable or would indicate a resistor is problematic, and am I barking up the right tree here with my amp or should I look elsewhere? There doesn't seem to be a service manual available for the first version either...only the 117II
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Karl vd Berg
Super Member
Gentlemen,
Although this is a very specific thread on Fuse Resistors, I'd like to ask permission to add this post on a particular resistor, common in (almost) all the AU-x17 series: the NFB resistor, which in these models also seem to be vulnerable to "a fair amount of voltage and power", like the fuse resistors.
I asked in a thread at diyAudio about the AU-317 schematics on its design and any possible "improvements" to see what folks there think about it. I got few good replies, and one of them - diyAudio member jcarr - replied the following:
(Click to expand, and see the #5)
The R31 resistor that Jonathan refers is from the AU-317 schematics, but it can be found in every other following model (27k ohm in the AU-717). I'm pretty sure the experienced ones here know about the importance of this resistor, but few others who are or will be fixing/upgrading these models still don't.
So, I thought I could share it for those who are and will be in the process of recap/upgrading one of the AU-x17 series amps.
Below, a few schematics with the NFB resistors circled / highlighted.
Although this is a very specific thread on Fuse Resistors, I'd like to ask permission to add this post on a particular resistor, common in (almost) all the AU-x17 series: the NFB resistor, which in these models also seem to be vulnerable to "a fair amount of voltage and power", like the fuse resistors.
I asked in a thread at diyAudio about the AU-317 schematics on its design and any possible "improvements" to see what folks there think about it. I got few good replies, and one of them - diyAudio member jcarr - replied the following:
(Click to expand, and see the #5)
jcarr said:
The R31 resistor that Jonathan refers is from the AU-317 schematics, but it can be found in every other following model (27k ohm in the AU-717). I'm pretty sure the experienced ones here know about the importance of this resistor, but few others who are or will be fixing/upgrading these models still don't.
So, I thought I could share it for those who are and will be in the process of recap/upgrading one of the AU-x17 series amps.
Below, a few schematics with the NFB resistors circled / highlighted.
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I have been thinking about the feedback resistor for a while now, and have bought some nice ones for my AU-D11 II, but haven't got round to fitting them yet. I have come to the conclusion that fitting the best resistor you can get in this position is a good idea.
Nice post Karl
Nice post Karl
ConradH
Lunatic Member
IMO, feedback resistors are critical because any subtle flaw in that resistor becomes part of the transfer function of the amp. Don't forget that the feedback resistor is part of a divider, so you have to pay just as much attention to the other leg to ground, plus any caps that might be present.