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 Post subject: Sencore DVM38 DC range problem
PostPosted: Dec Sat 26, 2020 5:52 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7884
Location: Toledo, Ohio
When this meter is in the DC volts position the display starts incrementing on its own and eventually gets to the point where it flashes as if it's overranged. It does not red any voltage. Anybody ever encounter this type of problem before?

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Last edited by Jim Dutridge on Dec Sun 27, 2020 5:46 pm, edited 1 time in total.

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 Post subject: Re: Sencore DVM32 DC range problem
PostPosted: Dec Sun 27, 2020 3:53 pm 
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Joined: Mar Sat 25, 2017 3:44 am
Posts: 147
Location: Kennesaw, GA 30152
Does the problem reset each time it's moved from DC to another function and back again?


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 Post subject: Re: Sencore DVM32 DC range problem
PostPosted: Dec Sun 27, 2020 4:20 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7884
Location: Toledo, Ohio
Nope, only happens on the DC range and I found the culprit. There is a small switch that is activated when the main DC range switch is selected. Problem is that this smaller switch does not completely engage when the DC range is selected. If I depress the range switch slightly past its stopped position, the display goes back to its normal display and I can read voltages normally.

Now, how to address this problem. I was thinking of trying to somehow elongate the switch shaft but I'm unsure of how to go about this. Any ideas? At most the switch would only have to go a 1/16" further.

Attachment:
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Jim
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I have flying monkeys and I know how to use them.


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 Post subject: Re: Sencore DVM32 DC range problem
PostPosted: Dec Sun 27, 2020 4:31 pm 
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Joined: Mar Sat 25, 2017 3:44 am
Posts: 147
Location: Kennesaw, GA 30152
Good troubleshooting!
Good luck with the repair. I take it the tip of the shaft is worn down or the button that activates it is worn a bit? Some plastic repair epoxy might do the trick. PlasticWeld from JB Weld would be a good choice I think.


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 Post subject: Re: Sencore DVM32 DC range problem
PostPosted: Dec Sun 27, 2020 4:44 pm 
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Joined: Mar Sat 25, 2017 3:44 am
Posts: 147
Location: Kennesaw, GA 30152
One other thought. If the switch can come apart, maybe the contacts just need a good cleaning. Probably has some corrosion at the position it normally sits.


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 Post subject: Re: Sencore DVM32 DC range problem
PostPosted: Dec Sun 27, 2020 5:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7884
Location: Toledo, Ohio
The shaft of the switch actually fits into the rear of the main DC function switch so that when DC is selected , its movement pushes the shaft of the switch. This is what the setup looks like:

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IMG_20201227_110031004.jpg
IMG_20201227_110031004.jpg [ 206.67 KiB | Viewed 1191 times ]


Yes, I tried cleaning the switch but that didn't change anything.

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Jim
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I have flying monkeys and I know how to use them.


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 Post subject: Re: Sencore DVM32 DC range problem
PostPosted: Dec Sun 27, 2020 5:19 pm 
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Joined: Mar Sat 25, 2017 3:44 am
Posts: 147
Location: Kennesaw, GA 30152
Maybe the problem lies with the main DC function switch. It obviously is working in and of itself, but has it worn so that it no longer pushes the other switch to the correct position?
I'm sure you will find a solution. Just yell at me if I'm off track. :mrgreen:


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 Post subject: Re: Sencore DVM32 DC range problem
PostPosted: Dec Sun 27, 2020 5:34 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7884
Location: Toledo, Ohio
As I look at the rear end of all of the range switches, they all appear to be reaching the same position when they are pushed so I don't think the main switch is the problem. I don't know why they decided to go with 2 separate switches when one switch with the correct number of sections would have been better. Someone must had a brother in the switch making business.

I have decided to use a drop of super glue and a small square piece of paper match to extend the shaft. Now to just let it dry.

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Jim
KE8GMW
---------------------
I have flying monkeys and I know how to use them.


Last edited by Jim Dutridge on Dec Sun 27, 2020 5:44 pm, edited 1 time in total.

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 Post subject: Re: Sencore DVM32 DC range problem
PostPosted: Dec Sun 27, 2020 5:41 pm 
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Joined: Mar Sat 25, 2017 3:44 am
Posts: 147
Location: Kennesaw, GA 30152
I'm looking at a pic of the DVM32 and I don't see any push buttons. It looks very similar to the DVM37 I used to have. I never had occasion to open it up so I'm not familiar with the switch arrangement. But it looks as if they are rotary switches - same as the DVM37?


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 Post subject: Re: Sencore DVM32 DC range problem
PostPosted: Dec Sun 27, 2020 5:45 pm 
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Joined: Mar Sat 25, 2017 3:44 am
Posts: 147
Location: Kennesaw, GA 30152
I see now. Yours is a DVM38. At least based on the board number from your pics. It makes a lot more sense to me now.


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 Post subject: Re: Sencore DVM38 DC range problem
PostPosted: Dec Sun 27, 2020 5:48 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7884
Location: Toledo, Ohio
Yea, sorry about that. Don't know how I got the wrong model number. I have corrected the title.

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Jim
KE8GMW
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I have flying monkeys and I know how to use them.


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 Post subject: Re: Sencore DVM38 DC range problem
PostPosted: Dec Tue 29, 2020 10:12 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7884
Location: Toledo, Ohio
My little adjustment to the shaft length worked. No more incrementing display in the DC range.

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Jim
KE8GMW
---------------------
I have flying monkeys and I know how to use them.


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 Post subject: Re: Sencore DVM38 DC range problem
PostPosted: Dec Tue 29, 2020 10:15 pm 
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Joined: Mar Sat 25, 2017 3:44 am
Posts: 147
Location: Kennesaw, GA 30152
Good news!


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 Post subject: Re: Sencore DVM38 DC range problem
PostPosted: Dec Wed 30, 2020 1:10 am 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11527
Location: Sunbury, Ohio 43074
Im glad to hear you got it fixed. Those particular switch types are notoriously difficult to clean. I run across them all the time in instruments and most frequently in HiFi gear. About all you can do is try and shoot contact cleaner down the shaft and hope it gets where it needs to go inside, then follow up with air the same way.

I have once or twice drilled a tiny hole (hand drill of course-a pin vise that I use to drill PCB holes) in the end to shoot cleaner in. That's a last resort, since your chances of hitting something vital are, imho, approximately 96.88%

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 Post subject: Re: Sencore DVM38 DC range problem
PostPosted: Dec Wed 30, 2020 1:22 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7884
Location: Toledo, Ohio
I have drilled holes in the past also. Actually I used a pin heated with a soldering iron to make a small hole. In this case though the switch has an open back so no drilling was needed.

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Jim
KE8GMW
---------------------
I have flying monkeys and I know how to use them.


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