Image Map Image Map
Page 1 of 2 12 LastLast
Results 1 to 10 of 15

Thread: Tandon TM848-2 fuse

  1. #1
    Join Date
    Jan 2012
    Location
    Zurich, Switzerland
    Posts
    275

    Default Tandon TM848-2 fuse

    I have a Tandon TM848-2 8" floppy drive where the fuse next to the power connector has blown. No idea yet where the cause is, but I can find no info on the rating of the fuse, and it doesn't appear on the schematics, at least that I can find. Does anyone know what a suitable replacement would be? I read in the specs that there can be as much as 2.5 amps drawn on the 24v line as the spindle motor starts, so in the absence of any further info, I've found some 4A slo-blow axial fuses. Does this sound reasonable?

    cheers, Rob

  2. #2
    Join Date
    Dec 2005
    Location
    Toronto ON Canada
    Posts
    7,162

    Default

    Quote Originally Posted by crock View Post
    I have a Tandon TM848-2 8" floppy drive where the fuse next to the power connector has blown. No idea yet where the cause is, but I can find no info on the rating of the fuse, and it doesn't appear on the schematics, at least that I can find. Does anyone know what a suitable replacement would be? I read in the specs that there can be as much as 2.5 amps drawn on the 24v line as the spindle motor starts, so in the absence of any further info, I've found some 4A slo-blow axial fuses. Does this sound reasonable?

    cheers, Rob
    Hi Rob,

    Only two out of my four TM848s actually have that fuse installed and it certainly looks like an afterthought; FWIW it is a BEL 3A, no indication to suggest that it's an SB type.

    m

  3. #3
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    31,997
    Blog Entries
    18

    Default

    One of the reasons that the fuse on the 848 can blow is that the 4.7uF cap C6 can short or the 7812 regulator that follows it has failed. You might also check out the 4.7 uF cap at C2. I've had drives fail twice because of the 7812 being run too hot. It's a lousy design and probably an afterthought. If you have a separate 12V supply, you may want to consider bypassing the regulator entirely.

    Consider, at a draw of 2A, that regulator has to dissipate 24 watts in heat!

    A more pragmatic approach would be to use a "simple switcher" to drop the 24V. Such as the LM2576, which would take a few more components, but eliminate that hot spot.
    Last edited by Chuck(G); February 11th, 2017 at 12:56 PM.

  4. #4
    Join Date
    Jan 2012
    Location
    Zurich, Switzerland
    Posts
    275

    Default

    Quote Originally Posted by Chuck(G) View Post
    One of the reasons that the fuse on the 848 can blow is that the 4.7uF cap C6 can short or the 7812 regulator that follows it has failed. You might also check out the 4.7 uF cap at C2. I've had drives fail twice because of the 7812 being run too hot. It's a lousy design and probably an afterthought. If you have a separate 12V supply, you may want to consider bypassing the regulator entirely.
    You were bang on the money Chuck, the C2 capacitor was shorted. That's been replaced and the fuse bypassed and the drive at least runs now. It's still not able to format a disk yet, but I suspect that might be the controller board.

  5. #5
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    31,997
    Blog Entries
    18

    Default

    Just curious--did the bad capacitor have a yellow jacket? Mine did--and I'm wondering if that's one of the first things to replace.

  6. #6
    Join Date
    May 2006
    Location
    Melbourne, Australia
    Posts
    6,290

    Default

    I do not know which model of TM848 that you have, but the photo at [here] shows a particular make/value cap that I often found faulty when diagnosing my newly acquired TM848's. On careful inspection, some were visibly leaking. I ended up just replacing them all.

  7. #7
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    31,997
    Blog Entries
    18

    Default

    Got photos of C2 and C6? Those are the ones most prone to failure, it seems.

  8. #8
    Join Date
    May 2006
    Location
    Melbourne, Australia
    Posts
    6,290

    Default

    Quote Originally Posted by Chuck(G) View Post
    Got photos of C2 and C6? Those are the ones most prone to failure, it seems.
    [Here].
    C1 was what went short circuit on one of my drives.

  9. #9
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    31,997
    Blog Entries
    18

    Default

    I guess it's safe to posit that if you've got a problem with an 848, the capacitors might be the first place to check...

  10. #10
    Join Date
    Jan 2012
    Location
    Zurich, Switzerland
    Posts
    275

    Default

    Quote Originally Posted by Chuck(G) View Post
    Just curious--did the bad capacitor have a yellow jacket? Mine did--and I'm wondering if that's one of the first things to replace.
    Nope, black bullet shaped ones. Here's photos of the failed caps and fuse, plus my ugly repair until I receive some axial 4.7 uf caps.

    DSCN0126.jpg
    DSCN0128.jpg

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •