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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 26th Jan 2013, 6:35 am   #1
SteveSmit
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Default Levell TM14 Modern Equivalent?

Greetings,

Where I work we have quite a bit of rather old equipment that's still in use, the oldest being a B&K digital frequency analyzer from the mid seventies. The object of my post is as the title says, an insulation tester. We are down to our last working Levell TM-14, and I've been looking online for any modern equivalent, most specifically one that can work right down to the 5V test voltage that the TM-14 can use, as well as the more typical 500V range. Needs to be capable of working up to the GOhm level at least. Does anyone know of anything?

Thanks in advance.

Regards,
Steve.
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Old 27th Jan 2013, 6:04 pm   #2
John_BS
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Default Re: Levell TM14 Modern Equivalent?

Steve:

I'e got one of these: might be able to fix one of yours if you get desperate

John
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Old 29th Jan 2013, 7:26 pm   #3
SteveSmit
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Default Re: Levell TM14 Modern Equivalent?

John,

Yeah the thought crossed my mind of attempting a repair on it. It does seem as though it's something very specific that's gone on it. I switched on, got the ready neon starting to glow up then it went out. The battery check seems to still work as it should but nothing else does. On the resistance setting none of the voltage settings give out so much as a single volt from the test points. Does give the impression of something that's just fell over that could be fairly easily fixed, but I wouldn't know where to start. We just use this for testing cables that we make up, one peer into the inner workings was enough to tell me that I'd get rapidly lost if I started poking about in there. Unless of course you know of any failure these are known for, or what might be a good thing to check?

Sending the equipment might be tough though unfortunately. I might just end up getting them to bite the bullet and replace it with a similarly capable unit. 10Tohm capable insulation checkers aren't what you'd call ten a penny though!

*edit*
Having said all that, if anyone has any documentation that includes the circuit diagrams that could be very helpful indeed. Thanks again.

Last edited by SteveSmit; 29th Jan 2013 at 7:54 pm.
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Old 30th Jan 2013, 7:21 pm   #4
Roger-M0TDM
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Default Re: Levell TM14 Modern Equivalent?

Isn't one of the Robin insulation testers applicable..
Used one at college in my city+guilds electrical installation course..
Measure resistance down to 0.01 ohm forget the top end tho.
Insulation test of 100,250,500 and 1000 volts..
Or one of the new Meggar units.
Regards Roger.
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Old 30th Jan 2013, 7:50 pm   #5
WME_bill
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Default Re: Levell TM14 Modern Equivalent?

Levell TM14 insulation tester. The difficulty you will have is that I know of no other tester where you can vary the voltage down to 2.5V.
So I was wondering if you had the manual, and as you apparently haven't, I have scanned my copy and attach it herewith. I do not have the component lists, though most are marked.
Nor the semiconductors, so would be very grateful if you could perhaps let me have a note of the transistors/ diodes when you have opened your unit up.
As to what the fault may be, As all the test voltages suggests the transformer or voltage multiplier rectifier chain. I have a Comark Insulation tester (of 1971 and 1981), which is switchable 25v to 1000V. The transformer failed. The original was specified as a Radiospares economy output transformer, operating 12V to 280v x4 for 1kv. So I used a transistor radio output transformer taken of an old radio, and it has served very well.
Your TM14 only has to generate 120V and multiplies it up, so a replacement should be straightforward, if you are prepared to experiment with several strays. wme_bill m0wpn
Attached Files
File Type: pdf Levell TM14-wm.pdf (906.0 KB, 188 views)
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Old 21st Mar 2015, 6:14 pm   #6
Chris55000
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Default Re: Levell TM14 Modern Equivalent?

Hi!

Quite apart from the fact that a four-year-old could make a far neater and clearer effort than whoever draw most of Levell's circuit diagrams for all their gear, the two main issues with these are failure of the two BC184L multivibrator transistors and short-circuited turns in the secondary winding.

Do check that none of the winding leadouts have broken away from the bobbin - if any have you'll need to have a chat with Ed Dinning!

Chris Williams
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Old 21st Mar 2015, 7:58 pm   #7
Radio Wrangler
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Default Re: Levell TM14 Modern Equivalent?

Thanks, Bill, that circuit's quite interesting.

10 Tera-Ohms, eh? but no guarding tracks and all that jazz? I wonder what their PCB material and process is?

It looks like a reasonable insulation tester, but it doesn't seem to have what it would take to live up to some of the headline figures.

The most exotic part in it seems to be an LF35? opamp, probably an LF356? Transstors 11 and 12 doing the log conversion might be fancy but maybe not, they haven't gone for supermatched pairs.

As long as the meter movement is OK and no switches have been mangled, it ought to be fixable.

For one with no voltage output, then as sid above, the multivibrator and transformer are the places to start.

David
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Old 21st Mar 2015, 8:23 pm   #8
Alistair D
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Default Re: Levell TM14 Modern Equivalent?

Unless the TM14 is different to most of the other Levell products the PCB material is usually dark brown in colour which I assume to be SRBP.

I have previously offered to have a look at any faulty meters the OP has but all has gone quiet since.

Al
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