Test Equipment Anonymous (TEA) group therapy thread

[Vince]

Nixie DMM update

As always while everybody was on Discord, I was at the bench working hard.

So, progress has been made ! There is some good some bad, it's been a roller coaster working on this thing this evening.

....snip....

I wanted to set the meter to "Manual" Trigger, so that it does not generate a ramp at power up, so I can see if the output of the ramp was valid, as if it's not it might well play havoc with the comparators hence ripple that garbage to the Gate logic hence it would explain my free running counter.

That's when I eventually realized that the switch that selects from AUTO or MANUAL.. is dodgy ! It's a SPDT switch. In AUTO mode, the contact close and open as they should. However in NORMAL mode, it's neither clearly open nor closed. This no doubt explains why I noticed that in AUTO mode the meter displayed (once warmed up and working I mean, of course) normal/sensible results, but in MANUAL mode, the result of the measurement would be good only 10% of the time. 90% of the time it would be absolute garbage, even illegal values ( >= 5000 counts ! ).
The switch looks to be the same type/style/construction as the mains/power switch which, I remind you, is ALSO failed (open circuit). They looks like sealed plastic body stuff, so I can't open them to refurbish them.

So, for my troubleshooting purposes, I shorted that switch so that it's hard wired to MANUAL mode. Then I realized that when I depress the push-button, I also get sometimes weird results... so this switch is probably also dodgy.  Nowhere near as bad as the MAN/AUTO one, but still a little bit.

I've had a closer look at the switches in the teardown pictures and that style of switch (well the chrome push-button one) are familiar, yes we used them at work, BR used them for a reset switch on one product and they did occasionally fail, can't remember if they were just intermittent, or failed completely.
I doubt I have any, due to someone from a another company rummaging & pillaging through all the parts, before I was allowed to buy them as surplus. 

OK OK... so they might have failed out of age and use then, they may not necessarily have soaked humidity.. that's a plus, I guess.
If you can figure out the brand of these switches, or similar looking ones so as to retain the original look, don't hesitate ! 

For now, I maybe have a plan, sort of... since I have nothing to lose and both the Power switch and the MAN/AUTO switch are dead... might as well try to see if I can open them up, or at least drill a tiny hole in their plastic body to try to get them to drink a drop of contact cleaner.

Re: the symbol tube with blue glow, this is normal for tubes with a tiny amount of Hg inside, it shouldn't be visible once the filter is back in place. If a tube fails due to a crack, they die very quickly, I think with a pinkish glow before they EOL.

Oh thanks for that, that's rather good news, one less problem !!   

[mnementh]

...R.I.P.

Heh... so I'm not the only one who has a collection of laptop battery BMS boards in the scrap PCB bin, ehhh...?

Great source of high-current FETs and Schottkeys... sometimes even useful values of shunt resistors and Polyfuses. 

I harvested the cells, and threw the BMS boards away, not planning to remove any components from them. But they'll stay there until the scrap box is full and wouldn't be the first thing to be drawn out of the scrap again ...

I guess I'm weird. I look at that pic and I see a wealth of scrappy bits to file away in my drawer unit for future use. 

Little speaker? Into the PC case modding bin; modern PC cases never come with a speaker anymore. Old calculators? source of carbon pads to slice off and fix remote controls or equipment keypads with. Okay, I already have a little container with several dozen membrane keypads just for this... prolly wouldn't save those. But I would probably snag the PV cells. Condenser mic for repairs and speaker module in phone for similar hacks.

BMS modules have, depending on unit, tactile switch, high-current FETs (sometimes Dual FETs in single package), thermistor, high-precision high-power shunt resistors and SMD LEDs and Schottkeys, and Circuit Protectors/Thermal fuses all on a pretty tiny PCB that takes up little space in the scrap PCB bin. That little PCB with a USB jack on it would def go in the "Random Electrical Bits" drawer.

That tempered glass scale would probably get the electronics shaved off and upcycled into a shelf or with strategically placed rubber feet to put between equipment on the bench to ensure proper airflow. I'd probably try to find a way to hack those fiber patches into TOSLINK cables; Jeebus they are stoopit expensive for what they are, which is the worst possible grade of polyester optical fiber. And any dual or tri-color LED gets harvested and put in a little divider box for future deviltry.

Yeah, I'm a junk collector. Thankfully, SWMBO has helped me to see the light; I now sort through my bins of junk and "cull the herd" on a pretty regular basis. 

mnem
Oooooh... is that a Qi-compliant wireless charging base...?   

[med6753]

Re: the symbol tube with blue glow, this is normal for tubes with a tiny amount of Hg inside, it shouldn't be visible once the filter is back in place. If a tube fails due to a crack, they die very quickly, I think with a pinkish glow before they EOL.

Oh thanks for that, that's rather good news, one less problem !!   

Beam power pentode vacuum tubes used in output of audio amplifiers and the horizontal output of analog TV's have a characteristic, and normal, blueish glow around the plates when in operation. 

[mnementh]

Yes, and that is the main reason for all the stoopit Chinesium choob AudioPhool gear with a blue LED under the base of the choob. 

mnem
Just say no, thank you.

[TERRA Operative]

I for one HATE LED's under tubes.

[factory]

Nixie DMM update

As always while everybody was on Discord, I was at the bench working hard.

So, progress has been made ! There is some good some bad, it's been a roller coaster working on this thing this evening.

....snip....

I wanted to set the meter to "Manual" Trigger, so that it does not generate a ramp at power up, so I can see if the output of the ramp was valid, as if it's not it might well play havoc with the comparators hence ripple that garbage to the Gate logic hence it would explain my free running counter.

That's when I eventually realized that the switch that selects from AUTO or MANUAL.. is dodgy ! It's a SPDT switch. In AUTO mode, the contact close and open as they should. However in NORMAL mode, it's neither clearly open nor closed. This no doubt explains why I noticed that in AUTO mode the meter displayed (once warmed up and working I mean, of course) normal/sensible results, but in MANUAL mode, the result of the measurement would be good only 10% of the time. 90% of the time it would be absolute garbage, even illegal values ( >= 5000 counts ! ).
The switch looks to be the same type/style/construction as the mains/power switch which, I remind you, is ALSO failed (open circuit). They looks like sealed plastic body stuff, so I can't open them to refurbish them.

So, for my troubleshooting purposes, I shorted that switch so that it's hard wired to MANUAL mode. Then I realized that when I depress the push-button, I also get sometimes weird results... so this switch is probably also dodgy.  Nowhere near as bad as the MAN/AUTO one, but still a little bit.

I've had a closer look at the switches in the teardown pictures and that style of switch (well the chrome push-button one) are familiar, yes we used them at work, BR used them for a reset switch on one product and they did occasionally fail, can't remember if they were just intermittent, or failed completely.
I doubt I have any, due to someone from a another company rummaging & pillaging through all the parts, before I was allowed to buy them as surplus. 

OK OK... so they might have failed out of age and use then, they may not necessarily have soaked humidity.. that's a plus, I guess.
If you can figure out the brand of these switches, or similar looking ones so as to retain the original look, don't hesitate ! 

For now, I maybe have a plan, sort of... since I have nothing to lose and both the Power switch and the MAN/AUTO switch are dead... might as well try to see if I can open them up, or at least drill a tiny hole in their plastic body to try to get them to drink a drop of contact cleaner.

Those switches were made by SECME, just had a rummage and found some much smaller ones that are ex-military in my spares.
I dread to think how much they cost, same for those used at work.

A quick Web search and the 10mm ones seem to be DJET series, available in push-button & toggle switch variants.

David

[Specmaster]

Totally agree, those Chinese AD584-M really are great little units and excellent value for money, if only they also did current and AC units like them, or could even build a unit with all three tests for a bit extra cash, it would be a great device to add into the toolkit.

Agree, as long as it is the one's with a legitimate label on the back indicating it's actual measured voltage. Both mine are. The one's with no label or "cookie cutter" label should be considered suspect.

I'm not sure how trustworthy the chinese devices are w.r.t. drift over time.

I'd look at Ian Johnson's devices https://www.ianjohnston.com/index.php/onlineshop He's on this forum He's evaluating whether his stock will allow him to offer more

We had some considerable conversation on this subject in here a year or three ago... I thought the consensus was that as long as the Vref was one of those obviously made using a reclaimed AD584x, they should be considered to be pretty well-aged and therefore pretty stable...?

mnem
 

Yes, we did indeed, and considering the huge price gulf between the Chinese AD584-M devices and those that Ian produces, I'd challenge anybody to get a better bang per buck performance ratio. Ian also has a Mastech MS7221 voltage and current calibrator in his arsenal which I also have, and he likes those as well. He paid £45 on eBay as a faulty unit and mended it, I also got mine on eBay but as a working unit and IIRC for a bit less as the seller had never used it and it was indeed like brand new in its case.

[Kosmic]

I was not going to let Robert and Bean having all the fun with the thermal imagers, so I decided to start scanning ebay for a cheap one.
...

So I finally took the time to make the Bullard TIx thermal camera a little bit more useful. I previously found the NTSC video out but still had 2 problems:

1. The camera came with no battery.
2. As it is, the camera can't record anything.

To fix problem #1, I could have bought a replacement battery (they are still for sale) but they are old crappy Nicd and they are super expensive for what they are. So, I decided to convert to Lithium Ion. I strapped together 3 x Samsung 18650 batteries with a cheap balancing / protection board. Charging will be done like the original battery via the DC connector on the camera.





Now problem #2. I used a cheap (16$) video recorder. The video out of the thermal camera was connected to the recorder and led / button of the recorder removed and replaced by a led / button on the camera.



The new recording button controlling the recorder.


The unused transmitter led on the top left of the screen was repurpose for recording.


For now, I just pushed everything in the old battery compartment. I need to 3d print a holder for the battery and recorder.


A little test I done with the camera reassembled. The recorder is working pretty well  Interesting to see the thermal reflection on the tiles.

[m k]

Was 12AX7 something old Tek was missing many times?
If so is that Slovak version a reasonable alternative?
If so I didn't have a problem picking 10 in local estore.

BTW,
my AD584-M has a label with printed values.
Around 2C below the printed temp my 4 decimal HP 34401A is a spot on.

[Kosmic]

Totally agree, those Chinese AD584-M really are great little units and excellent value for money, if only they also did current and AC units like them, or could even build a unit with all three tests for a bit extra cash, it would be a great device to add into the toolkit.

Agree, as long as it is the one's with a legitimate label on the back indicating it's actual measured voltage. Both mine are. The one's with no label or "cookie cutter" label should be considered suspect.

I'm not sure how trustworthy the chinese devices are w.r.t. drift over time.

I'd look at Ian Johnson's devices https://www.ianjohnston.com/index.php/onlineshop He's on this forum He's evaluating whether his stock will allow him to offer more

We had some considerable conversation on this subject in here a year or three ago... I thought the consensus was that as long as the Vref was one of those obviously made using a reclaimed AD584x, they should be considered to be pretty well-aged and therefore pretty stable...?

mnem
 

Yes, we did indeed, and considering the huge price gulf between the Chinese AD584-M devices and those that Ian produces, I'd challenge anybody to get a better bang per buck performance ratio. Ian also has a Mastech MS7221 voltage and current calibrator in his arsenal which I also have, and he likes those as well. He paid £45 on eBay as a faulty unit and mended it, I also got mine on eBay but as a working unit and IIRC for a bit less as the seller had never used it and it was indeed like brand new in its case.

Ian devices use a LM399 voltage reference. You can't really compare them to a AD584 or Mastech MS7221.

I had mostly bad luck with cheap AD584 references. Ordered 3 and were all off from each other. Like I said previously they are probably ok to check 4.5 digits meters.

[TERRA Operative]

Now problem #2. I used a cheap (16$) video recorder. The video out of the thermal camera was connected to the recorder and led / button of the recorder removed and replaced by a led / button on the camera.

That little widget is intriguing, do you have some more info on it?

[Kosmic]

Now problem #2. I used a cheap (16$) video recorder. The video out of the thermal camera was connected to the recorder and led / button of the recorder removed and replaced by a led / button on the camera.

That little widget is intriguing, do you have some more info on it?

https://shop.runcam.com/runcam-mini-fpv-dvr/

Manual is here https://www.runcam.com/download/RUNCAM-DVR-S-Manual.pdf

[mnementh]

      

It's used in FPV quadcopters; most of the sub-250-gram models use a stack of such PCBs for the Flight Controller, VTX, ESCs, and receiver/Telemetry. This is another board that adds onboard video recording from the FPV camera; RunCam are usually reasonably HD video.

mnem
 

[Kosmic]

It's used in FPV quadcopters; most of the sub-250-gram models use a stack of such PCBs for the Flight Controller, VTX, ESCs, and receiver/Telemetry. This is another board that adds onboard video recording from the FPV camera; RunCam are usually reasonably HD video.

mnem
 

Yep. I was wondering if it would accept the low resolution signal coming out of the Raytheon 300d module (NTSC at 320x240). Working really well in the end.

[Vince]

Now problem #2. I used a cheap (16$) video recorder. The video out of the thermal camera was connected to the recorder and led / button of the recorder removed and replaced by a led / button on the camera.

Wow I didn't even know such tiny cheap modules existed for such purposes, incredible ! 
You learn a little something new every day on TEA !

Those Chinese are so nice spitting out all sorts of cool useful cheap tiny modules and stuff, what would we do without them... long live the Chinese !

[Vince]

Yes, and that is the main reason for all the stoopit Chinesium choob AudioPhool gear with a blue LED under the base of the choob. 

Ah OK ! Didn't know about that.. not being into audio stuff at all, other than having a CD player in the lab and cheap 10 Euro Sony amp I fixed so I can hear what comes out of the CD player...

I assumed this "passion" for LEd'ed tubes was simply due to the.. well the modern love for LED lighting everything these days, especially with horrible BLUE freaknig LEDs.

It's not just the Chinese though ! Over here, on Leboncoin.fr there is a constant stream of people selling Nixie clocks, 99% of them having crappy ugly uncalled for LED lighting at the base of the tube !
Like these, random pick of the day :

Even uses RGB LEDs so you can change the colour as you wish.
https://www.leboncoin.fr/decoration/1899620687.htm

https://www.leboncoin.fr/decoration/1905109272.htm

This one has a NIxie tube that fails to light up (he says the Nixie is fine, he swapped it) but the buy still wants top dollar for it because he says the Nixies alone are worth a lot of money and are hard to find currently with the situation in Ukraine ! Guy deserves a beating.

https://www.leboncoin.fr/decoration/2137621559.htm

[med6753]

Was 12AX7 something old Tek was missing many times?
If so is that Slovak version a reasonable alternative?
If so I didn't have a problem picking 10 in local estore.

BTW,
my AD584-M has a label with printed values.
Around 2C below the printed temp my 4 decimal HP 34401A is a spot on.

Any 12AX7 or European ECC83 equivalent will work just fine in Tek gear except where matched pairs are required. It will still work with unmatched pairs but you may have some DC offset that you can't fully adjust out. But other than that no worries.   

[med6753]

I don't mind blue LED's but under vacuum tubes is just stooopid. 

[Vince]

Those switches were made by SECME, just had a rummage and found some much smaller ones that are ex-military in my spares.
I dread to think how much they cost, same for those used at work.

A quick Web search and the 10mm ones seem to be DJET series, available in push-button & toggle switch variants.

David

Wow you are my hero Factory, UI love you !!! 

Gooled for that, indeed that's exactly it !! 

I looked on Ebay, and found a couple ads, one for a push-button that's ultra-luxurious, being a DPDT where I need only SPST, but well that will do it just as well !

Only 2.50 Euros ON OFFER at that !, and the seller is in France so no customs BS and reasonable cheap shipping, 6 Euros. 

https://www.ebay.fr/itm/125250689134?hash=item1d2985d86e:g:g0MAAOSwcGNiUb0x

Then there is this SPDT toggle switch, the one I need for the AUTO/MAN switch :

Only 2 Euros and from the same seller, so maybe I can combine shipping and get the two switches for only 10 Euros delivered !! 

https://www.ebay.fr/itm/125252164816?hash=item1d299c5cd0:g:X9MAAOSwwt5iUvzQ

So I just need to keep digging to find another toggle switch, for the power switch, and I will be sorted !! 


EDIT : Google found me this, English translated version for your convenience.

http://www.eozonline.com/en_EN/DJET

So looks like SECME still do these switches today ?! Under a new name, now called " EOZ " .
So maybe one can still buy these brand new but... do they sell to retailers 
Says these DJET switches are recommended for Military and Aerospace applications, must be good then ! 

That's encouraging anyway, will keep digging.

EDIT #2 : Oh, on their site they list their resellers, there are 4 in France, including RS !!
Will check them out immediately !

http://www.eozonline.com/en_EN/reseau-de-vente.html

EDIT #3 : just checked the ir German retailer :

https://www.buerklin.com/de/search/?text=djet

Like.. 50 Euros for one push-button, and that's before tax I presume ! So ONE switch costs as much as I paid for the instrument itself ! And I need 3 of them 
The ones on French Ebay at 2 Euros are much more in my budget !  Used they are probably, so it's a gamble, but at that price I am willing to take a chance !

EDIT #4 : oh, found another SPDT one on Ebay, also in France, only 2 Euros and only 2 euros shipping ! I am sorted, have all the switches I need now !! 

https://www.ebay.fr/itm/333773747983?_trkparms=amclksrc%3DITM%26aid%3D1110018%26algo%3DHOMESPLICE.COMPLISTINGS%26ao%3D1%26asc%3D20140616153302%26meid%3D003a0cbdf0534d6988be513e9a247555%26pid%3D100168%26rk%3D4%26rkt%3D15%26sd%3D125252164816%26itm%3D333773747983%26pmt%3D0%26noa%3D1%26pg%3D5411%26algv%3DOrganicCompBase&_trksid=p5411.c100168.m2941

[Robert763]

I was not going to let Robert and Bean having all the fun with the thermal imagers, so I decided to start scanning ebay for a cheap one.
...

So I finally took the time to make the Bullard TIx thermal camera a little bit more useful. I previously found the NTSC video out but still had 2 problems:

1. The camera came with no battery.
2. As it is, the camera can't record anything.

To fix problem #1, I could have bought a replacement battery (they are still for sale) but they are old crappy Nicd and they are super expensive for what they are. So, I decided to convert to Lithium Ion. I strapped together 3 x Samsung 18650 batteries with a cheap balancing / protection board. Charging will be done like the original battery via the DC connector on the camera.





Now problem #2. I used a cheap (16$) video recorder. The video out of the thermal camera was connected to the recorder and led / button of the recorder removed and replaced by a led / button on the camera.



The new recording button controlling the recorder.


The unused transmitter led on the top left of the screen was repurpose for recording.


For now, I just pushed everything in the old battery compartment. I need to 3d print a holder for the battery and recorder.


A little test I done with the camera reassembled. The recorder is working pretty well  Interesting to see the thermal reflection on the tiles.

Nice work.
That Bullard uses the same BST imaging engine as the Talisman Wasp I have. Mine has 625 line 25 FPS video output of course.
I wasn't aware of the mini DVR for drones. Looks like a nice solution and give a digital output format too.
My Wasp is currently on loan to a friend who is a professional videographer. He want's to add a bit of thermal video to a job.
Any modern camera with >9 fps and video recording are expensive.

[Kosmic]

Nice work.
That Bullard uses the same BST imaging engine as the Talisman Wasp I have. Mine has 625 line 25 FPS video output of course.
I wasn't aware of the mini DVR for drones. Looks like a nice solution and give a digital output format too.
My Wasp is currently on loan to a friend who is a professional videographer. He want's to add a bit of thermal video to a job.
Any modern camera with >9 fps and video recording are expensive.

320x240 at 25/30 fps is pretty good indeed. The only problem with those cameras is that they can't focus at close distance. I want to try some Zinc Selenide lens available on aliexpress. Not sure if it's a good idea to order from China right now though.

[Neomys Sapiens]

Nixie DMM update


...
That's when I eventually realized that the switch that selects from AUTO or MANUAL.. is dodgy ! It's a SPDT switch. In AUTO mode, the contact close and open as they should. However in NORMAL mode, it's neither clearly open nor closed. This no doubt explains why I noticed that in AUTO mode the meter displayed (once warmed up and working I mean, of course) normal/sensible results, but in MANUAL mode, the result of the measurement would be good only 10% of the time. 90% of the time it would be absolute garbage, even illegal values ( >= 5000 counts ! ).
The switch looks to be the same type/style/construction as the mains/power switch which, I remind you, is ALSO failed (open circuit). They looks like sealed plastic body stuff, so I can't open them to refurbish them.

So, for my troubleshooting purposes, I shorted the that switch so that it's hard wired to MANUAL mode. Then I realized that when I depress the push-button, I also get sometimes weird results... so this switch is probably also dodgy.  Nowhere near as bad as the MAN/AUTO one, but still a little bit.

APEM makes identical switches.
They are a metricized derivate of MIL-DTL-83731 switches respectively MIL-PRF-8805 pushbuttons, which have either 15/32" or 1/4" bushings.
(Honeywell, Eaton, ITW, Otto controls, Alcoswitch)
Depending on the space behind your panel, you could substitute a more robust one as per MIL-DTL-3950 for the power switch.

[Neomys Sapiens]

Won a bid on a lot of adaptors today (which contains ZERO cut-off PL connectors).
What made me go for them is when I looked at the detail pics, I saw that there are several adaptors for Combo-D or VG RF contacts included (erroneously described as SSMB). The attenuators, Tektronix terminations and the Pomona BNC-to-mini Banana I regard merely as bonus. And a lot of standard BNC stuff too, which I would not have needed. The Combo-D are something where I was not covered except 1 or 2.
Not a bad haul for 26.- all inclusive.

[factory]

Mnem, is this the kind of cheap Chineseum BMS 8S board that could be used in the Tek 422 scope & why only 7sections on the board? Would have been nicer to find something in the UK, but all those seem to be for larger solar/battery charging.

   

Original battery pack was 24V Ni-Cd D cells, I'm thinking of using LiFePo4 cells, I would need to modify the existing charger & low battery circuits on the scope.


David

It's an active balancing circuit; instead of bleeder resistors it shunts current from the highest cell to the lowest. It only needs active elements on B1-B7 to do so.

LiFePo4 tends to not like high current draw; you want to design around a 1-3C discharge rate. I see a 3A fuse in the battery circuit so pretty much any 18650-32650 Lixx cell of 3000mAH capacity or more should be a good match. Obviously you're going to need to make sure your BMS is either LiFePo4 firmware or programmable for LiFePo4. 20S Nixx application is a great candidate for a 8S LiFePo4 pack upgrade.

I suggest something like these, if you can get them where you are and have room for 2-7mm longer cells (32mm x 65-70mm), as they are sanely priced and have a nice 3C discharge rating, so you're definitely not going to be beating them very hard, and they should give you many many cycles. They are very close to the dimensions of a D-cell, which comes in at approx 34mm x 63mm:

https://batteryhookup.com/products/100-brand-new-lifep04-32650-3-2v-6000mah-cells

If your original pack was 10x2 configuration, that would be somewhere around 340mm x 68mm x64mm tall. Turned sideways in a 4x2 configuration, these would be ~270-280mm x32mm, so you could double-stack for 8S2P config at 270-280mm x64mm x 64mm "tall". This would still leave ~ 64mm x 64mm x 60-65mm deep at the end of the pack for the BMS board. Typical for these cells is 3.8-6AH capacity, so you'd be right around 7.6-12AH vs 8-10AH capacity for a full D-cell NiMH/NiCd battery.

Do you know what the actual float voltage and charge current of the existing charge circuitry is? From looking at the circuit... it appears ~27.1V less ~.6Vfd of that diode, so 26.5V / 8 =3.31V/cell... Hmmm. You really need to be charging at 3.4-3.5V/cell minimum, even if short-cycling to prolong battery life.

What's the Low-Batt light threshold? I see 11.5-35V operating voltage; if that reflects LVC (0.58V/Cell for the NiCd does seem a wee bit low) but the light comes on at a more conservative 1V/cell or 20V, you might actually be right in the ballpark at 2.5V/cell or 20V for the LiFePo4 pack. Then you'd just let the LVC in the BMS stop you from over-discharging the pack.

mnem
*juicy*

Thanks for that Mnem, it's helped a lot. 

I've had a read through relevant sections of the manual for the later version with no nuvistors, as mine is an older one with the three nuvistors, the quoted figures will be slightly lower.

Power consumption on DC is 26W max, current = 26 divided by the input voltage (11.5V to 35V) = 2.26A to 0.74A. 1.09A at 24V, will be higher with older version.
It takes 16 hours to charge the 20 series D NiCds, 5 hours operating time, 30 mins less with scale illumination fully on.
Charge rate is 400mA on mains charging only, 30mA when operating at the same time, no charging on external DC, the thermal cut-out also cuts charge rate to 30mA.
The low voltage indicator circuit flashes the power light when battery voltage is below 22V.

I've done some tests on mine earlier today, it appears the charging circuit is a current limiter only, open circuit voltage goes up to 62.5V, I also managed to smoke the 180Ω resistor for the 30mA trickle charge during testing, more on that below. 

First I wanted to test the charger was functioning correctly at the two charge rates, a 24V 12W lamp was used as a load, the fast charge rate was 400mA and crept up & stabilised at approx 413mA once run for a while, voltage across the load was approx 18V. The slow rate (30mA) was then selected, current was a bit higher than the book stated at 48mA after running for a while.



Then I stupidly decided to find out if it would overcharge the potential replacement 8S LiFePo4 batteries, I swapped the lamp for a 240V 150W one, the current at fast charge was 272mA and 47.4V was measured at the battery connector, looks like I will need to add OVP to the replacement battery pack.


The slow charge was selected again and I got a smell of something cooking, I quickly turned it off, separating the PSU I found the 180Ω carbon comp resistor that is added in series for the slow charge rate had got a bit burnt, it now measured 76Ω with the charred casing. 



I'm not sure what happened, maybe the test exceeded it's power rating, or it was already on it's way out? It took a while to locate my spares, I could only find a slightly larger metal film type.
In it went & retesting with the 24V lamp, it appeared no other damage was caused. 

The next test was to run it on DC and find measure the current draw at various voltages, with the scale lighting on & off, intensity was set at a sensible level, with the internal setup signal selected for both inputs.


Measurements were taken with two DMMs, as the Sorensen PSU meters need calibrating.


Looks like the maximum current for the 8S LiFePo4 would be 1.2A, I probably don't need to go above 6AH capacity to meet the run time of the NiCd pack, not sure I need more run time, as it would increase both the costs of the replacement battery pack & charge time.

Last test was done at the same time as the current measurement, the low voltage indicator circuit is currently set at 21.8V, it latches the power lamp in a flashing state.

Need to work on the case next, the battery pack would have been attached inside, an old D cell is shown for scale, measurements have not yet been taken.



David

[Vince]

Nixie DMM update


...
That's when I eventually realized that the switch that selects from AUTO or MANUAL.. is dodgy ! It's a SPDT switch. In AUTO mode, the contact close and open as they should. However in NORMAL mode, it's neither clearly open nor closed. This no doubt explains why I noticed that in AUTO mode the meter displayed (once warmed up and working I mean, of course) normal/sensible results, but in MANUAL mode, the result of the measurement would be good only 10% of the time. 90% of the time it would be absolute garbage, even illegal values ( >= 5000 counts ! ).
The switch looks to be the same type/style/construction as the mains/power switch which, I remind you, is ALSO failed (open circuit). They looks like sealed plastic body stuff, so I can't open them to refurbish them.

So, for my troubleshooting purposes, I shorted the that switch so that it's hard wired to MANUAL mode. Then I realized that when I depress the push-button, I also get sometimes weird results... so this switch is probably also dodgy.  Nowhere near as bad as the MAN/AUTO one, but still a little bit.

APEM makes identical switches.
They are a metricized derivate of MIL-DTL-83731 switches respectively MIL-PRF-8805 push buttons, which have either 15/32" or 1/4" bushings.
(Honeywell, Eaton, ITW, Otto controls, Alcoswitch)
Depending on the space behind your panel, you could substitute a more robust one as per MIL-DTL-3950 for the power switch.

Thanks for the leads.
I just had a super quick look on Ebay for APEM switches. Did find a nice one to replace the push-button, but the toggle switches I have not found one that has a "bat"/lever with the same shape, which is quite distinctive I find. A subtle mix of curves and flats. Most switches have a 100% rounded bat. I did see a APME with a bat with some sharp angles to it, but too sharp, they over did it.
Well they look nice regardless, so would consider them if the price is cheap enough that I can contemplate replacing both toggle switches, so that the looks is consistent. The finish is not negotiable though, must be chromed, other wise it won't blend with the rest of the front panel.

Metric derivatives of English stuff ? Well I guess I could easily fit an imperial size switch. If the switch is a tad smaller, it's fine : the retaining nut will keep it in place. OTHO if the hole in the chassis is a bit too small, I can easily enlarge it a bit, no big deal.

Thanks for giving more options ! 

For now... I sent an e-mail to that French Ebay seller that has a couple of SECME DJET. He already replied, saying no worries he can do combined shipping AND he added : I have SIX more of DJET 10mm available that he didn't list on Ebay ! He said he would make a new Ebay ad to sell the entire lot, so I can pay shipping only once.  At only 2 Euros a pop, and only 4 or 5 Euros shipping, I must try this before anything else. If all these switches are dodgy well I will then look into getting new ones from APEM for example.