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 Post subject: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 7:53 am 
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Joined: Mar Tue 24, 2020 3:06 pm
Posts: 13
Hi, all.

This is a variable air gap cap. Can I assume it’s functional if the plates separate while adjusting the trimmer? I ask because I’m in the middle of aligning it and turning the trimmer has no effect. In fact the only time I see the eye tube’s bars adjust is when touching the screwdriver’s tip to the trimmer’s adjustment screw. I’m new to this and need some guidance. I’ve already replaced the 100pf connecting the trimmer to the 6c4. Thanks in advance!

Cheers,

Frank


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 Post subject: Re: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 8:54 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2443
Location: Saskatoon
Make sure that C1 is wired correctly. The solder lug that is electrically connected to the adjusting screw should go to ground. If it's wired the other way, then the capacitance will change when you touch it with a metal screwdriver and it will be impossible to adjust it correctly.


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 Post subject: Re: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 9:01 am 
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Joined: Mar Tue 24, 2020 3:06 pm
Posts: 13
Thank you very much. I’ll update this soon.


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 Post subject: Re: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 9:10 am 
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Joined: Mar Tue 24, 2020 3:06 pm
Posts: 13
Looks correct. Curious why the capacitance is changing with the tip of the screwdriver then. The schematic shows c2 as 100 MFD, but the instructions refer to it as MMFD (100PF). Which is correct? I’ve used a 100PF cap here.


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 Post subject: Re: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 6:59 pm 
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Joined: Mar Tue 24, 2020 3:06 pm
Posts: 13
Ok C1 is working and the screw is electrically connected to ground - but so is the other end of C1, as it is connected to one leg of the coil, which is grounded through its other leg.


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 Post subject: Re: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 7:55 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2443
Location: Saskatoon
It appears that the 100MFD in the schematic is a typo, and 100 pF is correct.

When you checked to see if the adjusting screw side of the trimmer is grounded did you just measure it with an ohmmeter, or did you trace the connection. Connection to ground through a coil winding is not the same as a direct connection to ground, even though the ohmmeter will give the same reading. The fact that the screwdriver affects the capacitance, tells us that the screw side of the trimmer is not connected directly to ground, or else the trimmer is defective.


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 Post subject: Re: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 8:16 pm 
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Joined: Mar Tue 24, 2020 3:06 pm
Posts: 13
I used the continuity test on my DMM. Is there any way to rule out the trimmer if this was correct?


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 Post subject: Re: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 8:36 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 6884
Location: Sunbury, Ohio 43074
Well, a few things. If you try and test the trimmer with your DMM or any other ohmmeter, it is going to read shorted because it's across the coil.

Question .... are you using the original test leads .. the 40" 93 ohm line with the clips on the end? Wrong length or wrong type of cable might affect this. The test leads are part of a tuned circuit that includes the coil and trimmer capacitor you've mentioned. According to the manual, it's operating at approximately 40MHz. so a little changes a lot.

Doublecheck the resistors in the front end of the instrument as well, and make sure the switch contacts are clean, and the wafers are not doused with cleaner.

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Last edited by Barry H Bennett on Mar Thu 26, 2020 8:46 pm, edited 1 time in total.

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 Post subject: Re: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 8:44 pm 
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Joined: Mar Tue 24, 2020 3:06 pm
Posts: 13
Ok, after removing and reinstalling the trimmer, it’s perfectly functional. It’s in the same position, so my mind is boggled lol. Thank you.


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 Post subject: Re: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 8:47 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 6884
Location: Sunbury, Ohio 43074
Possibly just a dirty ground connection, or maybe you just scared it!! :shock:

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


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 Post subject: Re: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 9:03 pm 
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Joined: Mar Tue 24, 2020 3:06 pm
Posts: 13
I was threatening to use the “southern hammer” technique that was so successful for my dad. That’s where you curse your life and slash your fist into the side or top of the non-functional object. Lol

Barry: forgot to respond to you. She’s been fully serviced inside and out. New cable/test leads @ 40”. Added a few more little things to spruce the place up a bit. Pics soon.


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 Post subject: Re: PACO c-25: 3-30mmf trimmer
PostPosted: Mar Thu 26, 2020 9:32 pm 
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Joined: Mar Tue 24, 2020 3:06 pm
Posts: 13
COMPLETEDDDDDDDDdddddd.....d

Added top handle and rear cable wrap. Well, that's a handle, too.

Image

Image

Image

Image

Image


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