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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details.

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Old 24th Dec 2017, 2:14 am   #21
Refugee
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Default Re: Magic Eye on Precision Aneroid Barometer stopped working

Those blue display calculators that were every ware at one time had one in them.
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Old 24th Dec 2017, 7:28 am   #22
TonyDuell
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Default Re: Magic Eye on Precision Aneroid Barometer stopped working

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Originally Posted by Ambientnoise View Post
The old methylene chloride paint strippers did a good, if slow job on many epoxy encapsulants. It did remove paint, markings and some plastic from components too so frequently you had a real mess to decipher, if that was the intent. Dont know about the current safer formuations.
I seem to remember that it is illegal to sell (and use?) methylene chloride (dichloromethane) as a paint stripper. But you can still get it as a plastic welding solvent.

I am not sure what the law says about using it to de-pot encapsulated electronics, but who is to know
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Old 24th Dec 2017, 7:31 am   #23
TonyDuell
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Default Re: Magic Eye on Precision Aneroid Barometer stopped working

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Originally Posted by Refugee View Post
Those blue display calculators that were every ware at one time had one in them.
Those DC-DC converters (often, but not always a daughterboard on the main calculator PCB) generated about 30V. Enough for a DM160 indicator but probably not enough for a DM70/DM71.

Incidentally, some of those old calculators are of interest to collectors so it would be a good idea to check what you've got (particularly if it has more than the standard 4 functions) before stripping it.
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Old 24th Dec 2017, 11:08 am   #24
ms660
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Default Re: Magic Eye on Precision Aneroid Barometer stopped working

In the instructions, the change in the length of the display between Pattern A and Pattern B doesn't look a lot so I wonder if the grid bias needed for Pattern B is by contact potential bias, eg: no separate -ve grid bias supply?

A resistance measurement between the grid and supply -ve might give a clue?

Lawrence.

Last edited by ms660; 24th Dec 2017 at 11:26 am.
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Old 30th Dec 2017, 1:06 pm   #25
elanman99
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Default Re: Magic Eye on Precision Aneroid Barometer stopped working

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If anyone can help me return this to working order I would be very grateful. The DM70 magic eye is powered by a single 1.5volt D cell. Up until a week ago it was working well then it became unreliable, sometimes failing to light up when the button was pressed to take a reading. In dim light the heater element can be seen glowing when the valve is supposed to operate. I presume the DC/DC converter has broken as no HT is being produced. There are no user serviceable parts as it is encased in a block of resin.
I do not have a suitable circuit and am not electronically savvy enough to come up with one myself. I am able to assemble and solder components but cannot produce printed circuits. The space inside the instrument is limited.

If I can't get the magic eye working I would look for a circuit which changed an LED from red to green when a contact was broken but would much prefer to keep it as original as possible. It is a very accurate instrument but at the moment is completely unusable.
Steve

I may have an original potted inverter that will fit your Baromec. From memory two different types were used but the one I have is 24x30x60mm with yellow/blue 1.5V input wires and red/black for the 120VDC output.

Somewhere I may have the small pcb with the DM71 on it as well as some other Baromec parts.

Ian
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Old 3rd Nov 2023, 3:15 pm   #26
Steve Browne
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Default Aneroid barometer Magic Eye update...

Thank you all for your comments. I used 5 x A27 12 volt batteries for the HT. They needed replacing for the first time this week.

The plastic holders were a bit weak for the springs and they had all split. This time round I used bakelite discs and penny washers to keep them together. All set for a few years and looking forward to the next low pressure system!
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Old 4th Nov 2023, 5:41 pm   #27
matthewhouse
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Default Re: Magic Eye on Precision Aneroid Barometer stopped working

Good to see you have kept it running!
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Old 5th Nov 2023, 9:54 am   #28
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Default Re: Magic Eye on Precision Aneroid Barometer stopped working

As a former user of several precision and sometimes "ancient" barometers I can say every service effort was followed by a sometimes time and cost intensive re-calibrating laboratory process. Often some tiny corrosion on contact surface caused malfunction. A close look was rewarding. DM 70 or DM 71 (just different in wiring) are still available, so I would prefer to get it back to original. These instruments are made much better than any today's stuff.
If it was mine I'd want to contact the Met office and ask who does calibration/certification. These folks will know who can repair it - if they do not offer that service, too. Over here in Germany I'd contact DMT Exam, TÜV West. Got to admit I have been out of this for many years now.
Joe
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Old 5th Nov 2023, 11:45 pm   #29
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Default Re: Magic Eye on Precision Aneroid Barometer stopped working

I picked up one of those barometers in one of Chas Miller's Radiophile ferreting boxes. Made by mechanism Ltd. Mine is a bit different, probably older. I used 6 12 v fob batteries in series giving 72v. & s 1 1/2 v D cell. The switch contacts inside short a 1 meg grid resistor so display is either fully open or closed. Easy to set to local air pressure, I set mine against a Fortin mercury barometer. If memory serves, you just remove the knob, slacken the screw in middle of shaft, and adjust the inner shaft relative to the outer till the contacts open at the desired reading. Nip the screw back up & refit the knob. Note they read from low to high, i.e when contacts open, not closing. It was reading 954 mb on sat, never seen my barometers so low.
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