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Fuse Resistors - The where's, why's and how's

Hi All, congrats for this great thread skippy124 ! it's still a reference for Sansui lovers.
Just for information I found 2 more FR on the AU 317 II on the small mic input board, respectively R601, R602, both 120 Ohm.
 
Very informative thread! Anyone by chance know the locations of the fuseable resistors on a AU-7700? I am trying to see if they are the cause for horrible loud buzzing in one I m trying to diagnose for a friend. I have a thread started on it, if you would rather reply to it.
 
Vinylbeast said:
Anyone by chance know the locations of the fuseable resistors on a AU-7700?
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If there are any they are likely to be on the F-2097 Main Amp Board, possibly R23 & R24, 180Ω and R37 & R38, 100Ω according to the schematic, however your unit could have a somewhat different value for these.

Edit
Post corrected after rechecking schematic values, on very blurry copy of schematic. :(
 
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LBPete said:
The service manual lists all the parts for each board. The fuse resistors are clearly called out. You need to do your homework.

- Pete
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Under the abbreviations for the parts types I dont see a “fuse resistor” listed. It has abbreviations for carbon, solid, cement and metal film.
 
Hyperion said:
If there are any they are likely to be on the F-2097 Main Amp Board, possibly R23 & R37, and R24 & R38 - all 100Ω according to the schematic, however your unit could have a somewhat different value for these.
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In my service manual it shows R23 &R24 as 180Ω and R37 & R38 as 100Ω
 
The manual I'm looking at shows R31/32 and R41/42 on board F-2596 for an AU-7900 as 220 ohm fuse resistors in the parts list. It spells out fuse resistor, no abbreviation. The schematic for the AU-7900 also shows these 220 ohm resistors as fuse type. They identify them with a stylized x1. The legend at the bottom of the page calls out the stylized x1 as fuse resistors.

It's very unlikely that these 4 resistors have anything to do with your hum problem but if their values have drifted they should be replaced.

- Pete
 
LBPete said:
The manual I'm looking at shows R31/32 and R41/42 on board F-2596 for an AU-7900 as 220 ohm fuse resistors in the parts list. It spells out fuse resistor, no abbreviation. The schematic for the AU-7900 also shows these 220 ohm resistors as fuse type. They identify them with a stylized x1. The legend at the bottom of the page calls out the stylized x1 as fuse resistors.

It's very unlikely that these 4 resistors have anything to do with your hum problem but if their values have drifted they should be replaced.

- Pete
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I am working on an AU-7700 not a AU-7900…they arent same boards/layouts are they?
 
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Sorry, my bad. They are different. The AU-7700 probably doesn't have any fuse resistors. They are not called out in the service manual. The AU-7700 predates their use. What is the serial number of your unit? If it's late production, Sansui may have sneaked in a few. Take a look on the power supply/amp board. They have a distinctive gray/blue color.

- Pete
 
Would a small plume of acrid, white smoke that rose from my Sansui R50 twice, in rapid sucession at turn-on, be a hint that two fusible resistors may have burnt? There are no visible indications on any of the boards that any burning occurred.

And does a burnt fusible resistor have a characteristic smell?
 
bwv1 said:
Would a small plume of acrid, white smoke that rose from my Sansui R50 twice, in rapid sucession at turn-on, be a hint that two fusible resistors may have burnt? There are no visible indications on any of the boards that any burning occurred.
And does a burnt fusible resistor have a characteristic smell?
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Look closely, you should be able to spot the burned component, possibly burnt on the under side.
 
Hyperion said:
If there are any they are likely to be on the F-2097 Main Amp Board, possibly R23 & R24, 180Ω and R37 & R38, 100Ω according to the schematic, however your unit could have a somewhat different value for these.

Edit
Post corrected after rechecking schematic values, on very blurry copy of schematic. :(
Click to expand...

FWIW an AU-6600 I'm working on does indeed have fuse resistors here, on board F-2097. Not labelled F-2097A in the amp.
 
Adding a snippet from a G-4700 servicer manual showing the "F. R." abbreviation for the F-3066 board.

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Off topic:
I have recapped a wide variety of 70s vintage receivers/amplifiers/tuners and in my experience Sansui amps far and away have the most issues.

Examples include the notorious 5000A F-1040, the 9090 (which I think I counted almost 20 total fuses including the in-line ones rather sloppily added to the amp boards) and then the liberal use of these really nasty fusible resistors like in the G-4700 (no less than 10 used).

I guess folks like Kenwood, Pioneer, Marantz and Harman Kardon did not push their amplifier designs so close to the edge?
 
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