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Author Topic: MSF5000BWhiskers Removal done right  (Read 1185 times)

AF6D

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MSF5000BWhiskers Removal done right
« on: June 05, 2019, 09:50:03 PM »

Hey gang! I'm pretty sure I've got metallurgical WHISKERS inside my preselector of my VHF msf5000. In the past we've always taken compressed air and stuck it in a hole and just blown it around but I know that doesn't get it out. Is there a proper way to disassemble the preselector to properly clean it out? Can one safely remove each tuning core and blow it around? Is there actually any way of removing it or it seems like whenever we clean it it just displaces it.

We seem to have drifted off frequency as well suggesting the VFO may have the same issue. The VFO on the VHF model is not the same as the UHF model. It does not require tuning.  Basically open and shut I guess. What is the best way to clean it out? I'm not even sure where it is on the board to be honest with you.

We're not going to have these much longer. We were ill-advised when we bought five of these years ago only to find out they had 30KHz front ends in a 15KHz band plan. But for now we keep them running. We may put mmdvm boards on them but that's a conversation for a future time.

Thank you in advance.
« Last Edit: June 05, 2019, 09:54:49 PM by AF6D »
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N2AYM

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RE: MSF5000BWhiskers Removal done right
« Reply #1 on: June 06, 2019, 11:50:43 AM »

if you really do indeed have whiskers in your preselector they
are usually crystalin and not metallurgical. I have always had
good luck by taking a small hammer and slightly banging on the
side of the preselector dislodging the whiskers and using a very
powerful but small mini vacuum cleaner with a crevice tube to
suck out all the dislodged crystalin whiskers after you have taken
apart the preslector exposing the deeper wells where the small
dislodged crystalin shards collect. And I must assume you are
speeking about VCO's and not VFO's!  :)
« Last Edit: June 06, 2019, 11:55:10 AM by N2AYM »
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AF6D

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RE: MSF5000BWhiskers Removal done right
« Reply #2 on: June 06, 2019, 09:15:30 PM »

I use speech to text and I didn't catch the error - yes, VCO::) I manually typed it this time.  ;D

I don't work with metal and assumed it was metallurgical. Not that it matters. I can tell you that before blowing condensed air in the sensitivity will drop considerably. Afterwards we can get a good tone at -125dBm. It's only rated at -119dBm so we have a bit better.

What kind of vacuum did you use? I've had that idea but no clue as to what to use.

We're going to be phasing these MSF's out. They're great and rugged but out-dated. We may or may not go digital (and could use a MMDVM with the MSF's if desired) but think it's time to upgrade. We need something with 20 KHz channel spacing due to the output of a repeater right up next to our input. Don't ask...  >:(
 The VHF MSF's are 30 KHz.
But for now $$$ say that we use the MSF's and keep them running.
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K4JJL

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RE: MSF5000BWhiskers Removal done right
« Reply #3 on: June 07, 2019, 05:39:38 AM »

There are maybe 30 Torx screws to remove to take apart the preselector.  There's a number pattern for removal and reinstallation screws (like an engine head).  If you don't do it in the right order, you can warp the cover.

In the past, I've used a q-tip to dislodge the whiskers and an air compressor to blow out the remnants.  If you want to go to the extreme, you can mask off the edges, back out the tuning slugs, and hit it with a clear coat to keep them from growing again.  I've done that with GE Mastr II preselectors before.

If I may make a recommendation, I'd replace all the electrolytic capacitors on the uniboard.  They always leak and can cause trace damage.  I keep a bag of tantalum caps just for that purpose.  There's also 2 large caps that go bad on the control board.  Change those, too.

The VCOs are the 2 metal boxes in the top left and right (TX and RX) above the uniboard in the drawer.  The intermediate power amp is between them.  They have an RCA jack and a 5-pin molex connector tied to them.  I've had to short the laser-etched tuning strips to bring them down to lock in the ham band before.  They do not have a tuning slug like the UHF/800/900 models.  The frequency tuning is not done with the VCOs anyway.  It's done on the uniboard via a tuning slug on the 14.4 MHz crystal package.  There will be a hole in the top of the metal lid of the drawer marked as the frequency adjustment.  Use a plastic tool, otherwise the metal in the tool will throw off the tuning and it'll take 3x as long to set it.

If you're interested, I may have a high power amp from a high-band PURC station available for purchase.  It'll plug right in to the MSF.  Let me know and I'll see if I can dig it out of storage.
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N2AYM

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RE: MSF5000BWhiskers Removal done right
« Reply #4 on: June 07, 2019, 10:07:48 AM »

"What kind of vacuum did you use? I've had that idea but no clue as to what to use."

Sorry - it's been too long since i did this to remember exactly what i had back then.
All i remember is that it was a handheld mini-vacuum cleaner with small plastic sucker
tube extensions.
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AF6D

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RE: MSF5000BWhiskers Removal done right
« Reply #5 on: June 11, 2019, 08:21:16 PM »

There are maybe 30 Torx screws to remove to take apart the preselector.  There's a number pattern for removal and reinstallation screws (like an engine head).  If you don't do it in the right order, you can warp the cover....

This is a lot of work to open the preselector but if I had the pattern it could be done. Reminds me of rebuilding a carburetor for some reason. But Clear Coat? I'd think that would change things. I think removing the tuning slugs and hitting it with air and a vacuum would do but then 6 months from now...

I can do each of these tasks but maybe it's time to bite the bullet and somehow get 5 Quantars. Right now only one repeater is acting up.
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K4JJL

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RE: MSF5000BWhiskers Removal done right
« Reply #6 on: June 12, 2019, 09:46:35 AM »

This is a lot of work to open the preselector but if I had the pattern it could be done.

The numbers are stamped right next to the corresponding screw.
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