Author Topic: My first YouTube video HP 8640B signal Gen  (Read 3964 times)

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My first YouTube video HP 8640B signal Gen
« on: May 24, 2014, 06:54:52 AM »
https://www.youtube.com/watch?v=ZQrnKrwrBqE&feature=youtu.be

This is my new HP signal generator I purchased from a very nice fellow up in Pikeville.  He bought it 2 years ago and was going to fix it but never got around to it.  The unit is well used. And would not power up. While checking switched I noticedthe fine tune switch is stuck and I broke the FM mode switch. That can be fixed no worries.

I addressed  the no power up issue and found that one side of the power switch did not work.  Removed the switch, drilled out the rivits, and found a spring out of posistion on that side. Put it back together and the unit powers up.

Next was to remove the range select unit so I could address the cracked gear issue. It is simple to remove but I nned to take the front panel off also to repair the broken slide switch and do some needed cleaning.  While looking at the cracked gear I noticed one of the contact fingers were missing on the front rotory switch. I cut up an old relay to make the fingers out of, took me 2 tries to get it right.

After I get the unit cleaned up I will put everything back together and start testing to see where it is. I do know it put out some signal but with the fingers missing nothing was right.
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Re: My first YouTube video HP 8640B signal Gen
« Reply #1 on: May 24, 2014, 12:39:07 PM »
I was able to fix the range selector gear. Maybe it will hold up till I can find a repalcement.
What I did was remove the brass insert.  Then put epoxy in the crack and clamped it back together. I then drilled very tiny holes in the back side of the gear.  Then rough it up with sand paper.  Nylon is hard to glue together!.

I cut a piece of perfboard to fit the rear of the gear. epoxed everything and clamped it together. After 3 hours of trying time it seems to have done the trick. After the epoxy dried I heated up the insert on a flat piece of steel.  Then pushed the gear down over it and cooled it with water.  Just had to align the 2 set screw holes then clean them out.
BTW, make sure you mark the location od all moving parts. I had the rear contact disk in the wrong location and had to disassemble everything.

On the broken FM switch there was not enough material to hold when glued together. I then cut a piece of very thin steel and formed it to the underside of the switch lever.  I then drilled holes in all pieces and epoxed it together. Seems to work fine.
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Re: My first YouTube video HP 8640B signal Gen
« Reply #3 on: May 25, 2014, 09:36:16 AM »
more pics
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Re: My first YouTube video HP 8640B signal Gen
« Reply #5 on: July 27, 2014, 01:25:45 AM »
Thanks so much for this post and video series.This is my favorite piece of test equipt on my bench,,I was a little intimidated by it at first but now seeing you tear into it helped me so much.Mine is still working perfect,,no issues as of yet,,only thing I did do was a time base alignment..the trimmer cap inside the hole of the front cover is so sensitive on mine,,almost like its worn out,,you have to be very easy when calibrating it,,maybe we can figure out an upgrade for this trimmer cap,,possibly a VC1 from a cobra 25 will work??
 Thanks RT!!

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Re: My first YouTube video HP 8640B signal Gen
« Reply #6 on: July 27, 2014, 09:26:42 PM »
Thanks Tom, I really enjoyed working on this piece. It was so much fun. They are very easy to take apart and remove stuff, although it is a bit compact in there.
HP did a great job on the design. I will have to look at that trimmer and see what is up with it. May be something we can do to make it better. Something like a 10 turn.......




Replace gears:
http://www.wb0smx.net/?p=2023
Buddy kc4umo