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

Discussion in 'Exclusively Sansui' started by skippy124, Mar 13, 2012.

  1. skippy124

    skippy124 AK Subscriber Subscriber

    Messages:
    1,623
    Location:
    Sydney Australia
    Hi,

    After working on quite a few Sansui amps and encountering the dreaded fuse resistors on many of them, I thought it might be worthwhile to post up some information on where they are in various amps and receivers, what symptoms are typically present when these go faulty, and what to do about replacements.

    Contributions are welcomed from other AK'ers, and I will index these in this first post.

    Starting at the end.... it has been well documented by others here that the typical 1/4W fuse resistor used by Sansui in many of their amps and receivers can be replaced by either good quality 1/4 or 1/2 Watt Metal Film resistors, and that is the path I have taken on many occasions and have yet to encounter any problems with this approach.


    The typical fuse resistor that gives problems can a light grey , greyish blue or light green colour, and looks like these ones shown below

    [​IMG]

    The following posts will show the position of fuse resistors in the AU117 through AU717, plus the AU 2900/3900/4900 series. As stated above posts are welcome on other amps/receivers, and any comments are more than welcome.

    Some of the typical symptoms of out of spec (high resistance) or open circuit fuse resistors are (in the affected channel) - distorted output, low bias reading and/or inability to set correct bias, low gain and pops/crackles/noise.

    I hope this is of use and gives a little back to the excellent Sansui fraternity we have here on AK.

    AU117

    AU217II

    AU417

    [URL="http://www.audiokarma.org/forums/showpost.php?p=5544295&postcount=18]5050[/URL]


    Cheers

    John
     
    Last edited: Mar 25, 2012
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  2. skippy124

    skippy124 AK Subscriber Subscriber

    Messages:
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    Here are the fuse resistor locations on the AU117 I have (Note some have been replaced in the photos, some not). For reference the S/N on this unit is 037110888.

    On the AU117, the board is mounted upside down, so this is really the bottom view.

    [​IMG]

    Photo showing the bulk of the fuse resistors

    [​IMG]

    Photo showing the last two fuse resistors

    [​IMG]


    If anyone has photos of an AU117II and could post them up or email them to me that would be appreciated. I will add them to this post.

    Cheers

    John
     
    Last edited: Mar 15, 2012
  3. skippy124

    skippy124 AK Subscriber Subscriber

    Messages:
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    Location:
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    reserved for AU217 - if anyone has a 217 and can post up some pics in this thread, or email some pics that would be appreciated, I will use them in this post.


    My AU217II

    Top view of the 217II, all of the fuse resistors are on the main amp board (and there are 12 of them). This Amp has just hit the bench, it was purchased as "going". A quick check of the resistors show the 6.8 ohm are all in tolerance ( seems the 6.8 ohm base drive resistors rarely drift high), and the others are all way out of tolerance to a couple that are open circuit. This particular amp will have all these resistors replaced, given a good clean/service, possibly a recap and then be put into the collection.

    [​IMG]


    10 of the 12 resistors are shown here


    [​IMG]


    And the other two in this photo


    [​IMG]


    Cheers

    John
     
    Last edited: Mar 15, 2012
  4. skippy124

    skippy124 AK Subscriber Subscriber

    Messages:
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    Location:
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    AU317

    Main amp board fuse resistors R35, R36, R45, R46

    [​IMG]

    These are 150 ohm resistors, this is the resistance reading of one of them (the others measured anywhere from 250 ohms to 400 ohms)

    [​IMG]

    Fuse resistors replaced with 1/2W metal film

    [​IMG]

    Tone Control Board F-2752

    There are two fuse resistors on this board - R17 and R18 and they are 68 ohm. The are mounted "upright" with a ceramic tube spacer (these are the only resistors on the tone control board with the ceramic tubes). The resistors have been replaced in the following pic

    [​IMG]




    AU317II

    The 317II is almost identical to the 317, but the fuse resistor R35, R36, R45, R46 value for the main board is 82 ohm (shown with fuse resistors replaced)

    [​IMG]

    The tone control board F-2752 is the same as used in the 317, the fuse resistors R17, R18 are 68 ohm and are the only resistors on this board mounted with a ceramic tube standoff (arrowed in the following pic)

    [​IMG]
     
    Last edited: Dec 26, 2012
    dedero likes this.
  5. skippy124

    skippy124 AK Subscriber Subscriber

    Messages:
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    Location:
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    The AU417 has eleven 1/2W fuse resistors. There are two on each of the main amplifier modules F2721 and F2722 - R36 and R37 (150 ohm), and 4 on the Head Amp board F2723 located on the right hand side of the amp (mounted vertically) - R47, R48, R49, R50 (82 ohm), and the three in the power supply I'll detail later

    a view of the AU417 from the top

    [​IMG]

    The fuse resistors on one of the amp modules

    [​IMG]

    Amp module removed and fuse resistors shown

    [​IMG]

    The other amp module with the fuse resistors replaced

    [​IMG]

    The Head Amp board (with Amp modules removed) and fuse resistors circled

    [​IMG]

    Pictures of the power supply board fuse resistors to come shortly
     
    Last edited: Mar 13, 2012
  6. skippy124

    skippy124 AK Subscriber Subscriber

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    reserved for AU517/717
     

     

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  7. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
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    I vote sticky :thmbsp: :yes: - already ! :yes: - and I'll delete this post if it gets in the way !

    Really good idea for a thread.
     
  8. EchoWars

    EchoWars Hiding in Honduras

    Messages:
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    FYI, the manual says they are 1/4W fuse resistors, but they are actually 1/3W. Seems that most that I encounter are a pale green color.
     
  9. Pepa

    Pepa Well-Known Member

    Messages:
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    @skippy124...great thread :thmbsp:
     
  10. skippy124

    skippy124 AK Subscriber Subscriber

    Messages:
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    Location:
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    Thanks John, as I have most of these units here at the moment I thought it would be a good idea to take some pics and identify where these are and what they look like. And no need to delete, I will reference any new information in the first post re specific models that I or others post in the future.

    Thanks Glenn, I'll add this info to the first post.

    I also need to add some comments in the first post re service manuals vs actual units... whats in the service manual doesn't necessarily agree with what is fitted...


    Cheers

    John
     
  11. roger2

    roger2 . Subscriber

    Messages:
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    indiana
    +1

    IMO this thread is Sticky-worthy. I will be glad to follow Hyperion's lead and delete this post to clean up the thread

    BTW I have a couple 317's waiting in the wings...but it could be a while before I get to one or both :sigh:
     
    Last edited: Mar 13, 2012

     

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  12. Glenz75

    Glenz75 Sansui and Pioneer Freak

    Messages:
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    Great thread Skippy, this one is worth keeping up :yes: I have fixed several Sansui's that have had problems caused by these resistors, also interesting to note that I've seen these exact same ones in Hitachi amplifers as well and they too are always bad. Cheers Glen
     
  13. KingBubba

    KingBubba "Too Much Stuff" Subscriber

    Messages:
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    In most cases, knowing full well Sansui's problematic Service Manuals, are these resistors identified in the SM or on the schematic or silkscreen on the board itself?
     
  14. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
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    Mostly

    Almost always

    No

    That is my experience anyway.
     
  15. kevzep

    kevzep Its all about the Music Subscriber

    Yes, the ones I have come across are this color..........they are not necessarily the bluish gray ones....

    I have observed people getting confused between "fusible" resistors and "Non Inductive" resistors. Mostly in the advice given....
    A lot of the bluish gray resistors you find on the driver boards and Power supply boards are actually as the service manual designates, "NIR Resistors", Non Inductive Resistors, some have the "S" bends in the legs too so they stand up off the circuit board.

    They use these "NIR Resistors" for their low noise properties in certain parts of the circuit...

    This should definitely be a sticky....Great idea....Good to have this kind of reference.
     
  16. skippy124

    skippy124 AK Subscriber Subscriber

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    Thanks for the contributions!!

    With respect to the Service manuals detailing the fuse resistors, it has been my experience that.... sometimes yes.... sometimes no (maybe I am being a bit hard.... mostly yes). It may be that there are differences in build state over the time and factory where a model range was built, e.g. the 3900/4900 service manual I have shows no fuse resistors, but the two AU4900's and 4 AU3900's I have had across the work bench all had fuse resistors in the usual places in the main amp (the output transistor base drive resistors - 6.8 ohm, and the associated 220 ohm resistors to ground).

    Kev,

    I always thought that NIR stood for "Non Inductive Resistor", but it appears in Sansui language these stand for "Non Inflammable Resistor", and from what I have seen they look and fail exaxtly the same as those designated fuse resistors when they are the 1/4W size (the larger wattage NIR's don't appear to have the same failure problems in my experience so far)

    [​IMG] [​IMG]

    I will amend the first post to include some of the extra info posted.

    Also looking for some photos of fuse resistors in an AU117II and an AU217 ( I have the AU117 and AU217II).

    Cheers

    John
     
    Last edited: Mar 15, 2012

     

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  17. LBPete

    LBPete Rolling Along Subscriber

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    Most fuse resistors are classified as 1/4 watt with a few called out as 1/2 watt. Sansui used fuse resistors in locations that were likely to pass high current during a component failure. The idea is that the fuse resistor will open and shut down the amp. They didn't consider that these amps would still be in use nearly 40 years later. They have a tendency to fail over time.

    It is important to use nonflammable (metal film, not carbon) replacements because these resistor can overheat in a failure. Keeping the 1/4 watt resistor value during replacement will give a slightly higher level of protection during a failure because it will be more likely to open than a 1/2 watt resistor. Is this necessary? Hard to say. I generally use 1/2 watt.

    There are also some cases where increasing the value to 1/2 watt is probably a good idea. R33/34 on the F-2624 driver board in the 9090DB/8080DB 7070 and QRX9001/8001. These were 1/4 watt fuse resistors and very prone to failure. It's likely their value was marginal so going to 1/2watt will increase reliability.

    This board is a good example of Sansui using both 1/2 and 1/4 watt fuse resistors. R33/34 and R34/36 are listed as 1/4 watt, the rest are listed as 1/2w.

    - Pete
     
  18. skippy124

    skippy124 AK Subscriber Subscriber

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    Sansui 5050 receiver.

    Had a 5050 on the bench today with a protection fault, and found there are 5 fuse resistors of interest in this receiver (and possibly the 6060 as well). This 5050 has the F-2700/2701 Power Supply/Protector boards (not the F-2648 board).

    Top view

    [​IMG]

    Close up of the F-2700/2701 power supply board (components circled in red were the cause of the protector fault, diode was short and this took out the associated smoothing cap, this diode and cap make up the power supply rail for the relay and protector), with the F-2647 driver board plugged into this board on the left hand side

    [​IMG]

    F-2647 driver board removed, 220 ohm fuse resistors circled in red (all measure around 300 - 330 ohm)

    [​IMG]

    Bottom cover removed, and 220 ohm resistor (R601) on the F-2646 tone control board circled (this one measured around 4K ohms)

    [​IMG]

    I have not replaced any of these as yet, the amp runs and sounds *OK*, will report back on any improvements after the changes have been done.

    Cheers

    John
     
  19. SmitterDave

    SmitterDave Audio Preservation through Restoration. Subscriber

    Messages:
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    Location:
    Where the F%*# is Norway Maine
    I have found the same 220 ohm resistors on the G-8000,9000 and AU-7900 that are used as a fuse. Quite annoying as you cannot tell they are burned open.

    I like my resistors to look good and toasty if they are going to open up

    SmitterDave
     
  20. Trnsfmr

    Trnsfmr Well-Known Member

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    additional fusibles in QRX9001

    Here's a few that most people miss, in the QRX9001. If the power meter lamps are dim, or vary in brightness, change out the 22 ohm fusible on each of the little meter boards. This resistor acts to drop the voltage to the lamps and I have found them as high as 48 ohms. Usually it will bring all the lamps brighter and equal.
     

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