Ludlum model 3 issues

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Sarmad suseyn
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Ludlum model 3 issues

Post by Sarmad suseyn » Mon May 04, 2020 6:18 pm

Hi
I just bought ludlum model 3 counter. It counts good with the
Probe 44.3
The issue is that the high voltage screw is not adjusting the voltage. The only voltage that i can get is 750 v.
When i opened the box i noticed : see pictures
1-There is two wires were cut(brown and red)
2- the high voltage points gives 750,900,1600,2000 volts
3- a white wire is should it be there?
Please help .
If any one have the same model can you send pictures of his own
Many thanks
Attachments
20200503_205224.jpg
20200503_205137.jpg
20200503_205057.jpg

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Richard Hull
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Re: Ludlum model 3 issues

Post by Richard Hull » Tue May 05, 2020 4:20 am

See last photo..Easy to answer. Inline plug seen on bottom of board has 8 points. count them. cable is 10 conductor. Two wires are superfluous and just cut off. No problem.

Richard Hull
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Fusion is the energy of the future....and it always will be
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Rex Allers
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Re: Ludlum model 3 issues

Post by Rex Allers » Tue May 05, 2020 7:53 am

Richard, not sure your easy answer is correct.

I've never had a Ludlum Model 3 so have zero direct knowledge but here's a version of that pic that I modified.

Lud3 pic.jpg
So I added two outlines of possible connections on the board, one is orange, one is green. You propose an inline set of connection nodes for the cable. In my picture that would be the section outlined in orange. Yep, 8 pins, hence 8 wires.

Now look at the section I outlined in green. To me it seems to be more aligned with the cable and has two rows of 5 nodes. 10-pins for the 10 wires in the flat cable. Flat cables often terminate in two-row connectors. So I think the two cut wires do have pins into the board, but are they used? Dunno.

I haven't taken any more time than looking at this pic, but Ludlum does share a lot of info. The manuals usually have schematics. I checked and there is a model 3 manual with schematics here...

https://ludlums.com/documents/product-manuals

There could be version issues, but with some studying a motivated student might find if those two wires should go somewhere.

One other observation. The soldering job for the blue wire at the bottom of the pic between two front panel terminals looks pretty poor. I would take this as a hint that someone has hacked at this device for some reason.
Rex Allers

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Re: Ludlum model 3 issues

Post by Sarmad suseyn » Tue May 05, 2020 9:18 am

Thanks for the help guys

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Re: Ludlum model 3 issues

Post by Richard Hull » Tue May 05, 2020 6:56 pm

In defense of my original point.

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correct.jpg
correct.jpg (218.73 KiB) Viewed 671 times
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Ludlum model 3 issues

Post by Sarmad suseyn » Tue May 05, 2020 11:46 pm

Hi Richard
Thanks for the picture. My only concern is that i can't regulate
The high voltage screw. Its stuck on 750v . Mean while the high voltage ports are giving 900 ,1500, 2000 v. Tried to change the variable resistor without luck. Any wonderful ideas?
Thanks for your time
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20200506_024521.jpg

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Re: Ludlum model 3 issues

Post by Richard Hull » Wed May 06, 2020 10:25 pm

Without seeing the thing or having a schematic, I have no clue.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Ludlum model 3 issues

Post by Rex Allers » Thu May 07, 2020 2:10 am

Sarmad,
I spent a bit of time today trying to understand the Model 3 circuits. It seems that the Mod 3 manual on the Ludlum page I linked earlier has schematics and board layouts that don't match yours. I assume the doc is for a newer version.

One significant difference is the shape of the board that has the row of adjustment pots on it. Looking at other manuals I found boards with the same basic shape in manuals for other '3' models (3A, 3-97, 3-98). These shouldn't be the same, though, because they have more than 5 adjustment pots. So similar but not the same.

In these other manuals, the main board has a similar shape but not the same component layout. The main board is the one where you showed the voltage steps.

To really understand what is up with your unit, you need to get the proper Model 3 manual with schematic section that matches yours. If you contact Ludlum with your model and serial number you may be able to get the proper manual. My attemps at web searches today didn't find any documentation that seemed to match your boards.

I do think that your suspicion about the white wire may be valid, as it may be a mod that was added for some reason. It does seem to me that if the HV adj signal (from the HV pot to the main board) is unmodified then the HV should adjust through some range even if the white jumper has been added.

If you can find the proper documentation for your model, I am willing to try to help you figure out the details about what could be going on.

Oh, and I looked at the documentation for the 3A that has a board shaped like the one in your pics (with the adjustment pots). Not the same circuit but similar, so the connections in the area that I outlined in green in an earlier post may actually be two connectors, one 5-pin and one 4-pin.

A guess from me. Assuming the top adjustment pot on the front panel is HV, then I would guess the signal at the purple dot in the following pic would be a low dc voltage (maybe 0 to 1.2V) that changes as the HV pot is turned. That signal should connect directly to some input pin on the main board. The HV out should change proportionally with that voltage. If you have a DVM maybe you can check out voltage and connection to the main board.

Good luck.
maybe hv adj.jpg
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Re: Ludlum model 3 issues

Post by Sarmad suseyn » Thu May 07, 2020 5:46 pm

Dear Rex Allers
Thanks a lot. Now i can adjust it.

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Re: Ludlum model 3 issues

Post by Rex Allers » Fri May 08, 2020 12:05 am

Did you find something that made it start working? Does it go beyond 750 V?
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