Sunday, August 2, 2015

Fostex Mixer/Reel-to-Reel VU meter fix


                     


I recently picked up a Fostex-R8 eight track reel-to-reel recorder, and then snagged one of these Fostex 450 mixers to go with it.  The mixer worked great except for the LED VU meters.  most of the LED's appeared dead like in the above 'before' GIF.  Lurking around the internet, in forums, and message boards,  I came to realize this is a common problem with these machines.  Luckily my R8's LED's are all working fine.  I believe the VU meter boards are all very similar between the various Fostex mixers and reel-to-reels.  So, this little tutorial might help out anyone with one or more of these machines.  With patience and a steady hand, you too can have all new fully functional VU meters!

 This is what the LED meter looks like when you get is out of the mixer.  It's held in with plastic clips, that need to be gently pushed apart to free the board.  That black button on the left is the LED driver chip.  There is no way to replace that, so if it gets damaged your out of luck.  On top of the LED's is a white plastic piece to house the LEDs and diffuse the light into nice looking rectangles.


I had to use a blade to get the plastic piece off.  The piece has four small dowels that fit through the PCB and bevel out to hold it on.  I just cut the bevel off to release it.  Now I can see the teeny tiny LED's.

 Here's a closeup of the fragile micro LED's.  Like .1mm squares with a single hair wire attached to the top of them.  No wonder these things fail!  With a small point soldering Iron I removed all the old diodes.

 And here's the replacements!  Modern 0603 surface mount LED's.  These are similar in design except they are encased in an epoxy or resin.  This protects the hair wire from braking.  If you've ever solder SMD components you probably know extra Flux is important and very helpful.  I used flux to help tin the trace pads and hold the LED's in place while soldering.

Here's one finished board.  The plastic diffuser piece fits right back over the new LED's, and the PCB snaps right back into place.  I'm not going to lie, it's a tedious job, but once your done you'll have fully functional beautiful bright new VU meters.  They should last a good long while too.  I hope this helps some people out!  Feel free to contact me if you have any questions.

cheers,


Addendum:
If anyone has dead LED's and isn't comfortable doing this procedure themselves I might offer a repair service in the future.  Ideally you'd be able to remove the VU boards yourself, and mail them to me instead of the whole machine.  I haven't worked out prices, but it would be reasonable (cost of materials and time).

21 comments:

  1. Hi,
    I have a Fostex 450 too and a Model 80 recorder, so 12 VU meters to fix , but i'm not confident in myself for these too tiny leds.
    So I need you help.
    Hope to read you soon,
    Chris

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  2. Hey Chris,
    Please send me an email if you think you'd like to have me fix your VU meters. For 12 VU meters, I'm thinking around 200$ for parts, labor, and return shipping.

    best,

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  3. Can you supply the part number you used for the replacement LEDs?

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    1. Sorry, I don't have a specific part number for the LEDs I used. I just bought a pack on the bay when I did this mod. I think any 0603 size LEDs should work, but if you're buying from mouser or digikey or something I would go for low current ones (under 50ma).

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    2. Cool, that's what I was looking to know. Thanks =)

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    3. This comment has been removed by the author.

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  4. https://www.facebook.com/Magneto-shop-1388419874796661/

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  5. Might have to hit you as I'm going to test out a Model 80 tomorrow and I have a feeling...

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  6. I have a about 12 I'd like to get fixed. I'm good with an iron and through hole, but no experience whatsoever in surface mount. Let me know how much to fix 12 if you are interested. rob@leftofthedial.com

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  7. I commented here back in April. That machine I got had all it's LED's working which was awesome except for the fact that it could barely rewind. I sold it off and recently and ended up with another M80 with dead LED's scattered throughout it's VU meter. I have a soldering gun and am ready to take this on but I just had couple questions (stupid as they may be). One, is the color you used clear? Also, what is Flux? Thanks in advance for putting this page up in the first place. You rule.

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    1. Hi, when you say soldering gun do you do mean one of those trigger style soldering guns? I would not recommend you use one of those. You really need a decent fine tipped soldering station to do this job.

      The LEDs look clear but glow different colors.

      Flux is a liquid or paste that helps solder flow, helps make good connections, and prevents solder bridges. I used a liquid flux that comes in a syringe ( bought it on the bay )

      I will warn you, this is like delicate surgery. It takes a steady hand, practice and a lot of patience to do this fix. If you've never soldered surface mount components before, I recommend you practice on some junk PCBs first. Try removing tiny resistors and capacitors then try to put them back.

      Those LEDs dimensions are .8mm x 1.6mm! Super tiny and hard to put in place. I've replaced hundreds of those LEDs and it still takes me about 20-30min to do one VU board.

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    2. I have a Weller soldering iron and am ordering the Flux. I have experience soldering capacitors and wires but nothing this intricate. I'm confident that with this instruction and a little more direction, that I will be able to fix it. Can you describe the application of the Flux? Do you apply it where you want the solder to go, or is it the opposite?

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    3. Flux is great for lots of reasons. I use it to help tin the tiny solder pads and get them ready for the new LEDs. Clean the boards with alcohol after you do this. Then place a small dot of flux on and in-between the solder pads. The flux helps stick the tiny LED in place and will help prevent solder bridges under the LED.

      I recommend watching SMD soldering videos on youtube. You can see how people use flux to solder there.

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  8. This is my first time i visit here. I found so many entertaining stuff in your blog. Keep up the good work.
    Plastic Flow Meter

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  9. Thanks for the info and write-up! I ended up rebuilding a total of 8 meters. The first one took me like 45 minutes, but by the time I got down to the last few they were only taking me 8-10 minutes.

    I used the following LEDs from Mouser:
    696-SMLFM0603SICTR (red)
    696-SMLFM0603SUGCTR (green)

    FYI to anyone else doing this... These ended up being SIGNIFICANTLY brighter than the original LEDs. Normally not a bad thing, but if you are looking to match working meters, or just wanting a "stock" look, you may want to get some that aren't as bright.

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    Replies
    1. Hi John! glad you found the write-up useful. One thing you can do to adjust the brightness is to up the resistance of the resistors on the individual boards. I think I changed the resistance value on my boards to 270K.

      The LEDs you used are 20ma. That's a pretty common current rating and probably what I used on my own meters. The last boards I fixed I ended up using 10ma LEDs, and they turned out only slightly brighter then the originals.

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    2. Ah, that's good to know, thanks!

      PS, would you happen to know how to drive one of these boards without installing it back into its original unit (tape deck/mixer)? I'm thinking about selling the extras off and would like to re-test them beforehand.

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  10. Got it figured out. If you just want to make sure all 12 LEDs work, supply 0v to pin 1, and +9v to pin 2. Pins 3 and 4 control the scale (-3.3v to 0v).

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  11. This is my first time i visit here. I found so many entertaining stuff in your blog. Keep up the good work.
    Plastic Flow Meter

    ReplyDelete