Facit 1132 Nixie Calculator restoration

[agent_power]

Hi community

I've got a Facit 1132 desktop calculator that I'm currently afraid to turn on. I've got no experience with tech of this vintage and I don't want to be the one that blows it up (it's unknown if the previous owner plugged it in).

Does the variac / dim bulb treatment apply here?

Anyone have service documentation for these or any other tips?

Attached are some pictures

Thanks

[pqass]

The only technical info I found looking up the NEC ICs is this: https://dopecc.net/calculators/burroughs/c3317/tech/
There is a lot in common (power supply, ICs) with this model from Burroughs OEM'd by Sharp (from parent page), although the keyboard is different.

My first instincts is to test the power supply first since the ICs are unobtainium.  The transistors on the other hand, if necessary, can likely be substituted with modern general purpose, power, and high-voltage NPN and PNP types (like MPS42, MPS92).

Fortunately, it looks like you can separate the logic and display PCBs by removing the screws either side of the blue keyboard connector and pulling it off.  Then opening the black PCB ejectors (pulling on the black metal wedges toward you) and sliding out the PCBs.  Also, you will likely need to remove the screws on top of the metal nixie bracket to release the display PCB.

The PS looks like a standard linear and doesn't look too complicated.  Will likely need to reverse-engineer it to determine ground and the [looks to be at least four] output voltages it produces (based on number of TO-3s). MOST IMPORTANTLY, it will produce at least one 170V high-voltage output!  And notice the two 450V blue caps.  This is LETHAL!  Find the wires that go to the edge connectors for the logic and display boards hidden below the PS PCB and short them to ground with a resistor (1K or so) and/or check with multimeter before touching (after having energized it).

Check fuses if they are still okay and capacitors for bulges or leaks (they look fine to me) before powering-up with a variac or at least dim-bulb.  Measure the outputs for DC and AC (ripple).  The problem here is that you don't know what voltages to expect if it isn't written on the PCBs.  The most I could find is "...Japanese MOS IC NEC uPD105C. Logic states are 0 and -24V" (https://groups.google.com/g/oldcalculatorforum/c/GOUukTKy2tI).  And I couldn't find any datasheet to help identify the power pins to work back to the PS.  In reverse-engineering the PS, maybe you can identify zeners that can confirm the exact voltages.  You can load down the outputs with resistors to determine if the voltages sag (say a few mA to 100mA).  If there is low ripple (<50mV) and no voltage sag, you could try your luck and power up.  But don't forget to bleed the PS outputs to zero before putting the logic and display PCBs back in.

EDIT:
Found this http://madrona.ca/e/eec/calctd/Casio121B_MMNotes.html link on a Casio calculator of that era that uses similar NEC ICs.  Note the power supply outputs; -24V, +180V, +90V(?).  This may be what you can expect in yours.  Also some info on how it works.  Similarly, this link https://www.oldcalculatormuseum.com/comp241.html although it may be less relevant.

[Haenk]

I'd suggest testing the large caps before switching it on. 50+ years is a rather long time, and it probably has not been switched on for 50 years. That's just to make sure there is no noisy voltage which might or might not kill your chips.
However these japanese calculators are built like a tank and use only quality components. I bet it just works.

[HarryDoPECC]

I play with quite a lot of these things and you have a combination with special risk:
 - early generation ICs with low over-volt tolerance
 - unobtanium ICs
 - series pass regulator transistors that can fail short
In this situation at a minimum I recommend that you
 - remove the boards (careful with ESD if there is any early MOS in there, I cannot recall just now)
 - test that power supply with a reasonable dummy load.
Myself, after seeing an early Victor with 10% of its ICs actually exploded and blown apart after a series pass short -> overvoltage, I install simple fuse-zener-power transistor volt clamps on vulnerable supply rails.  That transistor might be OK today, but tomorrow.....

Good luck, if you want further info then you could contact me via the dopecc.net site mentioned above.  My site, it's nice to see that someone else has read it (!)

[strawberry]

looks like brand new
looks like more modern couple chip calculators
dimm bulb wont protect unobtainable IC's
dimm bulb is for SMPS or high power expensive transistors you dont want to blow when you dont know 100% about control circuit functionality
carbon resistors may go open circuit or drifted out of spec.
it is possible to recreate IC's with modern components

[agent_power]

I play with quite a lot of these things and you have a combination with special risk:
 - early generation ICs with low over-volt tolerance
 - unobtanium ICs
 - series pass regulator transistors that can fail short
In this situation at a minimum I recommend that you
 - remove the boards (careful with ESD if there is any early MOS in there, I cannot recall just now)
 - test that power supply with a reasonable dummy load.
Myself, after seeing an early Victor with 10% of its ICs actually exploded and blown apart after a series pass short -> overvoltage, I install simple fuse-zener-power transistor volt clamps on vulnerable supply rails.  That transistor might be OK today, but tomorrow.....

Good luck, if you want further info then you could contact me via the dopecc.net site mentioned above.  My site, it's nice to see that someone else has read it (!)

Thanks for all the replies everyone!

Very useful site, and nowadays with all the lost documentation I'm happy for every bit of preserved knowledge.

It looks like someone has been in there as the screws were slightly stripped and two are missing, but otherwise it looks untouched. It could be that it was too scary inside.

How do I load test this power supply? I usually fix old computers and there I just use old hard disks as ballast, but these voltages are nothing I ever worked with. I don't have any load resistors nor would I know their values.

I took the boards out of the backplane thing and am now slowly ramping up the power supply (to give the capacitors a chance, but they'll be replaced if out of spec). The circuit boards look pretty wild compared to what I'm used to seeing.

Additionally, which Zener diodes do I use and where do you place them? Across the supply rail to ground? I guess they need to be stronger than the fuse they're meant to blow?

[pqass]

How do I load test this power supply? I usually fix old computers and there I just use old hard disks as ballast, but these voltages are nothing I ever worked with. I don't have any load resistors nor would I know their values.

I took the boards out of the backplane thing and am now slowly ramping up the power supply (to give the capacitors a chance, but they'll be replaced if out of spec). The circuit boards look pretty wild compared to what I'm used to seeing.

Additionally, which Zener diodes do I use and where do you place them? Across the supply rail to ground? I guess they need to be stronger than the fuse they're meant to blow?

I'd put those boards aside for now. 
It would be helpful if you could get top and bottom shots of the power supply board too.

Given the complexity of the PS board, I would expect to see a design similar to the attached.
Try to reverse-engineer the PS board to identify, number of transformer secondaries (incl. center taps), rectifiers (half or full wave), bulk cap, and pass transistor circuits.  There is a chance that the +180V supply may not be a transformer secondary but directly from the mains (diode+cap).  You need to confirm this before attaching an oscilloscope to any output!

The object to testing the power supply is to confirm:

(a) the rectifier diodes are okay; not shorted or open.

(b) the electrolytic capacitors are okay; low ripple under no load and loaded down. 

(c) the series pass transistors aren't shorted (passing the input directly to the output). With multimeter, measure across the bulk cap and after the pass transistor; there should be >2V difference.

(d) determine that the output voltages seen are consistent with what we would expect.  What we know: the NEC ICs work on -24V logic, and the nixies need +180V.  So two outputs should be at least those.  Regarding zeners, I'd said that you should look for any zeners on the PS board. If there is a part number we could lookup, that would help you confirm the output voltage to expect. 

It was also mentioned by HarryDoPECC that a crowbar circuit should be added to each output to protect the display and logic PCBs in case the PS series pass transistors ever go short circuit.  This is a future nice to have; see: https://www.electronics-notes.com/articles/analogue_circuits/thyristor-scr-triac/overvoltage-protection-crowbar-circuit.php  They typically use zeners to trigger on an overvoltage situation.

(e) output voltages are stable (little sag) under a modest load, however, we don't really know how much current the PS is capable of sustaining so we'll start modestly; say 10mA to 100mA per output. EDIT: Actually, we do have a clue, the fuse ratings.  Make a note of them and on which output then load that output to at most 80% of that.

To do a load test, we first use a multimeter to identify the voltage on the output under test. Then using ohm's law we determine what resistor we would need to load down that output (to ground) with, say 10mA, 50mA, 100mA, etc. eg: testing the  +180V output for 10mA, we'd use a 18k resistor, for ~50mA, we'd use a 3.3k, for 100mA we'd use a 1.8k. Keep in mind the power rating needed; eg. for the 18k, 1.8W, for the 3.3k, 8W, for the 1.8k, 18W.  You can use lower rated resistors if you're quick (<5secs) to check for voltage sag.  Given there are 16 tubes, and typical nixie anode resistors can be between 22k to 82k, we should expect the PS to supply about 130mA (high end) to 35mA (low end).

For the -24V output, you can use 2.2k, 220ohm, 100ohm, 47ohm, for 11mA, 110mA. 240mA, 510mA, respectively.  I would guess his output would need to sustain more current (than the nixie supply) given the number of ICs on the logic and display PCBs.


Then,
only after all the above to confirm stable output voltages under load, would I put the logic and display boards back in and power it all up.

[strawberry]

crowbar is better because zener diode have series resistance/slope(1W 24V ~30ohm) similar for TVS diodes
need some transient bench tests with oscilloscope

what does that core memory do on display module?

[agent_power]

I'd put those boards aside for now. 
It would be helpful if you could get top and bottom shots of the power supply board too.

Given the complexity of the PS board, I would expect to see a design similar to the attached.
Try to reverse-engineer the PS board to identify, number of transformer secondaries (incl. center taps), rectifiers (half or full wave), bulk cap, and pass transistor circuits.  There is a chance that the +180V supply may not be a transformer secondary but directly from the mains (diode+cap).  You need to confirm this before attaching an oscilloscope to any output!

The object to testing the power supply is to confirm:

(a) the rectifier diodes are okay; not shorted or open.

The diodes measure ok...see attached pictures, it will probably take a bit to complete the (amazing) drawing.. I'm also not sure about some parts, the PCB isn't silkscreened and I've never seen some of these components.

crowbar is better because zener diode have series resistance/slope(1W 24V ~30ohm) similar for TVS diodes
need some transient bench tests with oscilloscope

what does that core memory do on display module?

Thanks for the input... I don't know the calculator but I would guess the core memory is to store results judging from the keys it supports storing two totals

[pqass]

See attached for my partial reverse-engineering notes and observations below. 
You'll need to open it in a new window to see the text.

- From your earlier shots, the large TO-3 packaged pass transistors appear to be 2SC1030 80V NPNs.  I can't read the other smaller pair.  Likely at least one is a PNP?
- There are four pass transistors (suggests four regulated outputs) but I could only track three of them to the output terminals on the right side of the PCB. 
- The +180V output appears to be unregulated and not coming from the mains-side of the PCB (a good thing).  I can follow the brown secondary lead to the fuse to a [likely] diode to a HV cap to a resistor/inductor to the other HV cap then exits just above the 200mA fuse.  I couldn't trace the circuit just to the right of the pot (I'm assuming pot case is the wiper).
- I didn't see a bleed resistor for the high-voltage caps (could it be the 100K?).  BE CAREFUL!!!
- Each pass transistor has a small driver transistor (represented by circles); likely in a darlington arrangement with the pass transistor.
- At least for the regulated output from the negative bridge leg, it follows the basic design I posted in my previous message (though I would expect the pass transistor to be a PNP).  That is, GND to zener to pass transistor base to resistor to pass transistor collector (unregulated side).   The other positive bridge leg is a bit more complicated involving two driver transistors.  The positive diode pair secondary involves an unknown (to me) 4-legged brass spider-looking device (some exotic zener?).
- I'm assuming the gray lug eye terminal on the right is connected to the GND PCB trace and brown wire to the edge connectors and was attached to the chassis?
- There's a divider network output in the 2nd lowest output on the right side of the PCB.  The pot wiper (lower right) seems to adjust the 4-legged brass spider-looking device that controls the positive diode pair secondary regulation.

What does this all mean?
A:
- you probably don't have to do a thorough reverse engineering of all components.  You just need to find out what the last pass transistor does (4th regulated output?) and identify where all the regulated outputs exit (wires to the edge connectors).
- then you can load test these outputs (see my previous message) to confirm that the voltages don't sag.  Don't bother load testing the un-regulated outputs since they'll sag; just note their voltage for future reference.
- you can check voltage across the devices that I've identified as zeners. And if you can get a number off of them, we can look them up.  If I'm correct, then the regulated output should be about two diode-drops lower (~1.2V due to the darlington arrangement).  One of these regulated outputs should be -24V (for the NEC logic ICs). However, if the +180V output is truely unregulated, then there are potentially three other regulated outputs that we can only compare the zener voltage with their output voltage; that is, output=~1.2V below zener and the pass transistor collector >2V (likely more) than the emitter (regulated output).
- since there doesn't appear to be any minimal load resistors (to GND) on those output terminals - those from pass transistor emitters (ie. regulated outputs leading to the edge connectors) - before measuring any output voltage, you'll need to add high value resistors to each of the regulated outputs (100K or 1M (if the +180V is regulated)). The pass transistor emitters can't be left open (when logic and display PCBs are removed) otherwise they won't regulate.
- for future reference, I would document:
  = the VAC on all transformer secondaries relative to the GND (black) lead.
  = the VDC on positive and negative diode bridge legs, and positive diode pair leg; ie. the unregulated side.
  = the voltage across the two zeners that I've identified; I don't know what to measure on the spider-looking thing.
  = all regulated and unregulated outputs (right side of PCB) that go to the edge connectors.


EDIT: Regarding your schematic... 
The items marked ? on the mains-side are inductors (302M=3mH +/-20%, 200K=20uH +/-10% maybe).
The one item marked ? after the diode on the secondary-side may also be an inductor (though, no matches found for "mb2k0").  Is this the device barely visible below the pot and between the two HV caps positive leads? Or do you mean the black rectangle to the right of the pot?  If it's the latter, then it may be a zener because it's attached to a resistor to GND and may be part of the +180V regulation (I can't see much in this area).

[agent_power]

See attached for my partial reverse-engineering notes and observations below. 
You'll need to open it in a new window to see the text.

- From your earlier shots, the large TO-3 packaged pass transistors appear to be 2SC1030 80V NPNs.  I can't read the other smaller pair.  Likely at least one is a PNP?
- There are four pass transistors (suggests four regulated outputs) but I could only track three of them to the output terminals on the right side of the PCB. 
- The +180V output appears to be unregulated and not coming from the mains-side of the PCB (a good thing).  I can follow the brown secondary lead to the fuse to a [likely] diode to a HV cap to a resistor/inductor to the other HV cap then exits just above the 200mA fuse.  I couldn't trace the circuit just to the right of the pot (I'm assuming pot case is the wiper).
- I didn't see a bleed resistor for the high-voltage caps (could it be the 100K?).  BE CAREFUL!!!
- Each pass transistor has a small driver transistor (represented by circles); likely in a darlington arrangement with the pass transistor.
- At least for the regulated output from the negative bridge leg, it follows the basic design I posted in my previous message (though I would expect the pass transistor to be a PNP).  That is, GND to zener to pass transistor base to resistor to pass transistor collector (unregulated side).   The other positive bridge leg is a bit more complicated involving two driver transistors.  The positive diode pair secondary involves an unknown (to me) 4-legged brass spider-looking device (some exotic zener?).
- I'm assuming the gray lug eye terminal on the right is connected to the GND PCB trace and brown wire to the edge connectors and was attached to the chassis?
- There's a divider network output in the 2nd lowest output on the right side of the PCB.  The pot wiper (lower right) seems to adjust the 4-legged brass spider-looking device that controls the positive diode pair secondary regulation.

- I marked the transistors in the attached picture
- One transistor's emitter(?) is grounded and the grey wire with the ground lug also goes to the PCBs, otoh the brown wire is connected to the ground plane where all the caps' negatives are. Are there two grounds (chassis/signal ground?)
- The voltage bleeds from the caps, anyway at 230VAC input there was around 270V on them, but to be verified under load
- The brass device doesn't read as diodes, still no idea what it is

What does this all mean?
A:
- you probably don't have to do a thorough reverse engineering of all components.  You just need to find out what the last pass transistor does (4th regulated output?) and identify where all the regulated outputs exit (wires to the edge connectors).
- then you can load test these outputs (see my previous message) to confirm that the voltages don't sag.  Don't bother load testing the un-regulated outputs since they'll sag; just note their voltage for future reference.
- you can check voltage across the devices that I've identified as zeners. And if you can get a number off of them, we can look them up.  If I'm correct, then the regulated output should be about two diode-drops lower (~1.2V due to the darlington arrangement).  One of these regulated outputs should be -24V (for the NEC logic ICs). However, if the +180V output is truely unregulated, then there are potentially three other regulated outputs that we can only compare the zener voltage with their output voltage; that is, output=~1.2V below zener and the pass transistor collector >2V (likely more) than the emitter (regulated output).
- since there doesn't appear to be any minimal load resistors (to GND) on those output terminals - those from pass transistor emitters (ie. regulated outputs leading to the edge connectors) - before measuring any output voltage, you'll need to add high value resistors to each of the regulated outputs (100K or 1M (if the +180V is regulated)). The pass transistor emitters can't be left open (when logic and display PCBs are removed) otherwise they won't regulate.
- for future reference, I would document:
  = the VAC on all transformer secondaries relative to the GND (black) lead.
  = the VDC on positive and negative diode bridge legs, and positive diode pair leg; ie. the unregulated side.
  = the voltage across the two zeners that I've identified; I don't know what to measure on the spider-looking thing.
  = all regulated and unregulated outputs (right side of PCB) that go to the edge connectors.


EDIT: Regarding your schematic... 
The items marked ? on the mains-side are inductors (302M=3mH +/-20%, 200K=20uH +/-10% maybe).
The one item marked ? after the diode on the secondary-side may also be an inductor (though, no matches found for "mb2k0").  Is this the device barely visible below the pot and between the two HV caps positive leads? Or do you mean the black rectangle to the right of the pot?  If it's the latter, then it may be a zener because it's attached to a resistor to GND and may be part of the +180V regulation (I can't see much in this area).

Thanks, I didn't know about inductor numbering. mb2k0 refers to the pot, but I'm confused how it's wired up and I assumed it's for trimming the regulated voltages. The black rectangle is a regular disk shaped diode.
Don't know what to make of the zener diodes, they're labelled ZR212 Stanley 084 and ZR210 Stanley 083.

I'm going to put the inner chassis back together and try to find some load resistors. What do you mean with the high value resistors? Is this in addition to the load you mentioned before?

[pqass]

- I marked the transistors in the attached picture
- One transistor's emitter(?) is grounded and the grey wire with the ground lug also goes to the PCBs, otoh the brown wire is connected to the ground plane where all the caps' negatives are. Are there two grounds (chassis/signal ground?)
- The voltage bleeds from the caps, anyway at 230VAC input there was around 270V on them, but to be verified under load
- The brass device doesn't read as diodes, still no idea what it is

See attached for a schematic of what I've deduced so far.  I don't see a -24V output based on the parts values.  Maybe the NEC MOS chips have a large voltage range like modern CMOS?  We won't know until you measure it.

Since the transformer secondary is floating, yes, I think signal ground (brown wire) is isolated from the chassis and chassis ground (grey wire) may be carrying +10.8V WRT brown wire (see schematic on how I arrive at that). eeek!

EDIT: Could the brass mystery device be an optocoupler?  With LED on left, photo-transistor on right? 

EDIT: In my schematic I deduced the following output voltages:
RED (1)      +180V  (adjusted by pot)
WHITE? (5)   +5.5V  (adjusted by pot)
BROWN (4)    0V     (measure other outputs WRT this ground)
GREY (3)     +10.8V
ORANGE (2)   +2.75V (unregulated)
ORANGE? (6)  -8V

However, since the transformer secondary is floating, alternatively, you can use the chassis as the ground reference.  The output voltages would then be:
RED (1)      +180V  (adjusted by pot)
WHITE? (5)   -5.3V  (adjusted by pot)
BROWN (4)    -10.8V
GREY (3)     0V     (measure other outputs WRT this ground)
ORANGE (2)   -8V    (unregulated)
ORANGE? (6)  -18.8V

Thanks, I didn't know about inductor numbering. mb2k0 refers to the pot, but I'm confused how it's wired up and I assumed it's for trimming the regulated voltages. The black rectangle is a regular disk shaped diode.
Don't know what to make of the zener diodes, they're labelled ZR212 Stanley 084 and ZR210 Stanley 083.

I'm going to put the inner chassis back together and try to find some load resistors. What do you mean with the high value resistors? Is this in addition to the load you mentioned before?

Oh, the "mb2k0" is on the pot, so it makes sense: m=?, b=linear, 2k0 ohms value.  I couldn't find an exact image of these old-style trimmers on-line but I think the metal body is attached to the wiper, and each end leg is isolated below the body and 45° apart.

The black disk on the left is the diode but I was refering to the black rectangle on the right of the pot. I think that's the 2SC641 plastic transistor; I thought it was a zener earlier.  I still can't make out the 3rd leg. Looks like a 2-lead device in the photo.

Since you're powering-up the PS without any logic or display PCB installed, you'll need to provde some miminal load on each regulated output; ie. pulling the transistor emitters (and one collector) to GND (brown wire). Something that only draws a milliamp or so (100K for the HV, 10K for the LV outputs). Not enough to burn up while you are measuring various test points.  Once you've noted the voltages at minimal load, then you can parallel resistors with lower ohm values to really load down the outputs to 10mA to 100mA or higher (on the low voltage outputs) to see if (when) the outputs sags.  These low-ohm value resistors either have to be beefy since 180V@100mA=18W or you can use a lower power resistor but be very quick (<5secs) for your load test.

Once you confirm that the regulated outputs don't sag much under load, we can conclude that the PS is probably working within specifications.  Especially so if my deductions are correct.  Then you can re-install the logic and display PCBs.

Be careful.

-------------------
FYI: some info on the transistors and the zener diodes.
ZR210: https://vetco.net/products/8-7-volt-1-watt-zener-diode-nte5073a
ZR212: https://vetco.net/products/12-0-volt-1-watt-zener-diode-nte142a
2SC641: https://pdf1.alldatasheet.com/datasheet-pdf/view/108439/HITACHI/2SC641.html
2SA618: https://alltransistors.com/transistor.php?transistor=8634
2SC857: https://alltransistors.com/transistor.php?transistor=17209
2SC515A: https://datasheetspdf.com/pdf-file/637523/SavantIC/2SC515/1
2SC830: https://alltransistors.com/transistor.php?transistor=17180
2SC1030: https://datasheetspdf.com/pdf-file/637543/SavantIC/2SC1030/1

[agent_power]

I can't thank you enough for all this work! It's really interesting learning about this and well explained too

- for future reference, I would document:
  = the VAC on all transformer secondaries relative to the GND (black) lead.
  = the VDC on positive and negative diode bridge legs, and positive diode pair leg; ie. the unregulated side.
  = the voltage across the two zeners that I've identified; I don't know what to measure on the spider-looking thing.
  = all regulated and unregulated outputs (right side of PCB) that go to the edge connectors.

Voltages relative to GND / with no load:
Brown: 200 VAC
Red: 10 VAC
Blue: 16 VAC
D4: 43.6 VDC
D2/D3: 13.8 VDC
D5 ZR212: 14 VDC
D6 ZR 10.4 VDC

The brass device, I measured the voltage across the left legs is 20 VDC, but it was not conducting at the time of measurement. There is a white dot next to the upper left leg, supporting the theory it is an opto coupler, but 20 volts for an LED is a bit much no...

I found resistors in my stash of radio parts and some of them look beefy enough for load testing, tomorrow I'll go find some suitable ones to test the the regulation under load

EDIT: The two lead device 2SC641 has a third leg in the middle but it's just a stub

[agent_power]

I tried loading the supply rails down (one by one, not all at the same time), but the results are not what is expected. Possibly a fault?

Red: about 210 V unreg, 206 V with a 5K load
White: 0 V with 10K attached (something wrong with the "opto coupler" / mystery device?)
Grey: 13.5 V (unloaded, can I load this the same way as the other non-HV rails?)
Orange (2): 8.1 V (unloaded, I wasn't sure if I'm supposed to load test it when it's a reference?)
Orange (6): -9.7 with a 60 Ohm load

I went through the schematic, the RV2 5K pot is a 500R I believe. I also measured the resistors (in-circuit) and they're all either barely within spec.. worst offenders R8 at 580R and R3 at 2.3K

Any tips? Should I try the pots to see if it gets better? Measure the transistors too?

EDIT: closest I could find is this TIL108: https://www.radiomuseum.org/tubes/tube_til108.html

EDIT2: It seems the internal power supply design is same as the Sharp Compet 361, there is a Dutch thread about it and it seems the capacitos were the problem and an IC popped: https://www.circuitsonline.net/forum/view/116228
I probably want to make sure this PSU is in order before I connect any boards

[pqass]

I tried loading the supply rails down (one by one, not all at the same time), but the results are not what is expected. Possibly a fault?

Red: about 210 V unreg, 206 V with a 5K load
White: 0 V with 10K attached (something wrong with the "opto coupler" / mystery device?)
Grey: 13.5 V (unloaded, can I load this the same way as the other non-HV rails?)
Orange (2): 8.1 V (unloaded, I wasn't sure if I'm supposed to load test it when it's a reference?)
Orange (6): -9.7 with a 60 Ohm load

I went through the schematic, the RV2 5K pot is a 500R I believe. I also measured the resistors (in-circuit) and they're all either barely within spec.. worst offenders R8 at 580R and R3 at 2.3K

Any tips? Should I try the pots to see if it gets better? Measure the transistors too?

EDIT: closest I could find is this TIL108: https://www.radiomuseum.org/tubes/tube_til108.html

EDIT2: It seems the internal power supply design is same as the Sharp Compet 361, there is a Dutch thread about it and it seems the capacitos were the problem and an IC popped: https://www.circuitsonline.net/forum/view/116228
I probably want to make sure this PSU is in order before I connect any boards

You should put a minimum load on all regulated outputs at the same time, however, leave the unregulated divider output ORANGE (2) unconnected to any load resistor. 
Why? A:Because two outputs seem to be inter-dependent in some way (through that mystery device).  If one is not minimally loaded, the other may not regulate. 
Output at ORANGE (2) is unregulated and adding a load resistor will bring the output voltage down and may affect the regulation of WHITE (5).

Attached, you will see how to connect loads to all regulated outputs. ONLY IMPLEMENT ONE SET of four resistors; either taken from the power transistor terminals or from the right-side output terminals. Note that the output on the power transistors is usually the white wire (emitter) but on the right-most power transistor, the output is the body (collector).    Your choice is to solder (if you are able) or use aligator clip (or tightly wrap) wires from the power transistor terminals as shown to a suitable resistor (1/2 watt).  If you only have 1/4 watt resistors, double the resistance values.  The aim is to draw about 1mA on each output so the exact ohm values to those shown isn't strickly necessary.   All resistors should be attached on one side to one common point (GND) which is attached to output terminal BROWN (4) or clipped to the negative cap lead as shown.

I've also numbered the outputs with a "(n)" label so we're clear on which output terminal we're talking about.

Then, with you multimeter set to DCV, measure across these minimal load resistors (ie. between a given output and GND) and note the voltage readings.
Later on, when conducting the real load test, you'll just clip, one by one, a lower value ohm power resistor in parallel with the minimal load resistor and note the voltage reading.

In other words, first fill-out this table to establish what the voltages are under minimal load:

Multimeter red lead on:	Multimeter black lead on:	Reading under no load:	Reading across 10K load:	Reading across 100K load:
RED (1)	BROWN (4)	not applicable	not applicable	fill in
ORANGE (2)	BROWN (4)	fill in	not applicable	not applicable
GREY (3)	BROWN (4)	not applicable	fill in	not applicable
WHITE (5)	BROWN (4)	not applicable	fill in	not applicable
ORANGE (6)	BROWN (4)	not applicable	fill in	not applicable

Now, answering your specific questions...

206V (loaded) seems high for nixies.   The 5K load represents 41mA which is a good start. You should be able to load it down with 2K (which corresponds to 100mA).  If you use less, like 1K, you may blow the 200mA fuse.  So don't go below 2K for now.  Lets work on the other outputs first to confirm they're okay before we tweak the pot since voltage is relative and the true value may not be between (1) and GND but (1) and (3) chassis!  We'll get back to this later.  The good news here is that it didn't move much from 210V to 206V so it appears to be regulating.

0V on WHITE (5) may be because output GREY (3) isn't loaded down and therefore inhibits WHITE (5).  See above for how to load down all regulated outputs.

GREY (3) must be loaded down to GND like other regulated outputs.  Not doing so may be inhibiting WHITE (5).  Don't be confused that it connects to the chassis.

ORANGE (2) is the divider output and MUST NOT be loaded down with any resistor otherwise it may affect regulation of WHITE (5).  Just measure its value with your multimeter.

ORANGE (6) being -9.7V is in the ball park.  Remember, I was only able to lookup the zeners because they were listed as a replacement for a newer device.  I couldn't find their actual datasheet; they're that old!  I was assuming the modern replacement zener has the same Vz as yours.  This may not be a valid assumption. 

As for R8 being 580R vs. 500R and R3 being 2.3K vs. 2K; that's not much of a change, 15% or so. 
I'll have to recalculate expected WHITE (5) and ORANGE (2) outputs based on RV2 being 500R vs. 5K. FIll-in the above table first.

Don't change the pots just yet until we understand more. 

Good catch on that optocoupler find. What if you load down all regulated outputs as directed above and then measure across both left and then right pairs of the mystery device. Maybe the LED is on the right side?  I would expect 1.2V to 2V on whichever side the LED is on.  Also, with regulated outputs loaded down, measure the DCV across leads of both zeners D5 and D6.

Yes, lets fully test this PS before risking the logic and display boards!

[pqass]

I can't thank you enough for all this work! It's really interesting learning about this and well explained too

- for future reference, I would document:
  = the VAC on all transformer secondaries relative to the GND (black) lead.
  = the VDC on positive and negative diode bridge legs, and positive diode pair leg; ie. the unregulated side.
  = the voltage across the two zeners that I've identified; I don't know what to measure on the spider-looking thing.
  = all regulated and unregulated outputs (right side of PCB) that go to the edge connectors.

Voltages relative to GND / with no load:
Brown: 200 VAC
Red: 10 VAC
Blue: 16 VAC
D4: 43.6 VDC
D2/D3: 13.8 VDC
D5 ZR212: 14 VDC
D6 ZR 10.4 VDC

Brown: 200VAC (RMS) becomes ~280VDC after the diode (200V*1.414-0.7V).  You verified this to be ~270V (close enough) in your subsequent message. Good.

Red: 10VAC (RMS) becomes 13.8VDC after the diode (10V*1.414-0.7V). And therefore we should expect the regulated output after the power transistors be at most ~2V lower.

Blue: 16VAC (RMS) becomes ~22VDC after the bridge (16V*1.414-0.7V).  This is what is expected between GND and one pole. However, you have D4 reading 43.6V which is what I would expect between + and - of the diode bridge (there are two halfs, so double one pole to GND).

D5 ZR212: 14VDC.  Is this across the zener leads directly?  Or, one lead and GND?  Because there are components on both legs (R3 or Q1) and that may be affecting your reading.  If this is the reading across the zener leads directly, then this zener cannot be replaced with the 12V zener that lists it as replacing (see link in the FYI section of my earlier message).  If so, we should expect the regulated output GREY (3) be +12.8V instead.

D6 ZR210: 10.4VDC.  Hmm... good to know. This zener cannot be replaced by the 8.7V zener that lists it as replacing (see link in the FYI section of my earlier message).  If so, we should expect the regulated output ORANGE (6) be -9.7V instead (which you verified in your last message).

The brass device, I measured the voltage across the left legs is 20 VDC, but it was not conducting at the time of measurement. There is a white dot next to the upper left leg, supporting the theory it is an opto coupler, but 20 volts for an LED is a bit much no...

Agreed. 20VDC is too much for a LED.  What's the VDC across the right pair?  Maybe the LED is there.

I found resistors in my stash of radio parts and some of them look beefy enough for load testing, tomorrow I'll go find some suitable ones to test the the regulation under load

EDIT: The two lead device 2SC641 has a third leg in the middle but it's just a stub

I suspected that the transistor is being [ab]used as a zener!  ie. emitter to +HV (unreg) and base to 150K R5 to GND.
C641 and A618 form a constant current source that regulates a constant current through the 100K R7.  And therefore,
a constant voltage at the base of Q8 driver transistor. The regulated RED (1) output is then 1.2V below that.
See https://sound-au.com/ism.htm#p5 for an explaination on current sources/sinks.

[agent_power]

Blue: 16VAC (RMS) becomes ~22VDC after the bridge (16V*1.414-0.7V).  This is what is expected between GND and one pole. However, you have D4 reading 43.6V which is what I would expect between + and - of the diode bridge (there are two halfs, so double one pole to GND).

D5 ZR212: 14VDC.  Is this across the zener leads directly?  Or, one lead and GND?  Because there are components on both legs (R3 or Q1) and that may be affecting your reading.  If this is the reading across the zener leads directly, then this zener cannot be replaced with the 12V zener that lists it as replacing (see link in the FYI section of my earlier message).  If so, we should expect the regulated output GREY (3) be +12.8V instead.

Ah yes you're right, I measured it wrong. I can verify it after I do the setup explained in your previous post but It'll probably be as you wrote.

Measurements were taken across the zener diode, yes.

Agreed. 20VDC is too much for a LED.  What's the VDC across the right pair?  Maybe the LED is there.

I'll have to check again with the proper load, but it was barely a Volt. On the other hand, if it is a TIL108 it says the breakdown voltage is 35V so it would make sense again? Maybe I can try downloading that datasheet...

I suspected that the transistor is being [ab]used as a zener!  ie. emitter to +HV (unreg) and base to 150K R5 to GND.
C641 and A618 form a constant current source that regulates a constant current through the 100K R7.  And therefore,
a constant voltage at the base of Q8 driver transistor. The regulated RED (1) output is then 1.2V below that.
See https://sound-au.com/ism.htm#p5 for an explaination on current sources/sinks.

Interesting 

I'll come back once I have everything set up, I'm gone for the weekend (1-2 days or so)

[pqass]

Attached is an updated schematic based on your latest input.

Please connect all [minimum] resistor loads as suggested (HV:100K or LV:10K or ones with values in the ball-park) and let me know your multimeter readings at the points marked with a voltmeter symbol in the schematic.

Q:What lead you to TIL108 as being the Mystery Device?  Was the device marked as such?  Or, were you just going on the general shape?

EDIT: I found the datasheet for TIL108. 
See page 110 in http://www.bitsavers.org/components/ti/_dataBooks/1978_TI_The_Optoelectronics_Data_Book_for_Design_Engineers_5ed.pdf
Currently, the schematic shows incorrect orientation of phototransistor; just flip the pair.
However, based on your photos of the IR-diode pair, it doesn't make sense that the center pin (anode) is connected to the transistor base (or collector) with the diode cathode to the 2K to +22V (unreg).

[agent_power]

Ok, minimal load results:

Multimeter red lead on:	Multimeter black lead on:	Reading under no load:	Reading across 10K load:	Reading across 100K load:
RED (1)	BROWN (4)	not applicable	not applicable	209 VDC
ORANGE (2)	BROWN (4)	8.14 VDC	not applicable	not applicable
GREY (3)	BROWN (4)	not applicable	13.9 VDC	not applicable
WHITE (5)	BROWN (4)	not applicable	0 VDC	not applicable
ORANGE (6)	BROWN (4)	not applicable	-9.8 VDC	not applicable

D5: 13.9 VDC
D6: 10.3 VDC

MES14: 195.7 VDC
MES15: -13.5 VDC
MES16: -13.5 VDC
MES17: -5.4 VDC
MES18: -23.4 VDC

Regarding the mystery device: It is not a TIL108, the datasheet you found mentions a black stripe which mine doesn't have. I've only got a white dot on the upper left leg. When put the common on the dotted lead, I get:
21.5 VDC between the upper left and lower left leg
0 VDC between the upper left and upper right leg
10 VDC between the upper left and lower right leg

3.9something VDC between the upper right and lower right leg, but my multimeter freaks out after some seconds and it seems to affect the circuit (..device, regulation...)

Q1 should be oriented as follows if I got it right:

ZR212 - Base, which would make GND - E and upper leg of supposed optocoupler - C ?? I do get the .68V drop from the leg of ZR212 to ground and dotted leg

EDIT: I guessed from here, the little tab points towards the cap/zener: https://www.web-bcs.com/transistor/tc/2sc/2SC857.php

[pqass]

I think the 195.7VDC is a bit high for nixies (it may have drifted up with age) but you can always (later) turn down the red trimmer to save tube life.

I don't think the power transistors are shorted or open since there is a significant voltage difference between the un-regulated and regulated sides of three of the four regulated outputs. However, the 0V WRT GND for WHITE (5) is concerning.  What is the voltage WRT GND at the base of the driver transistor Q6? (ie. upper-right pin of mystery device WRT GND)   If it is also 0V then that darlington pair isn't being turned on at all and you may have a mystery device problem.  If there is a non-zero voltage on the base of Q6 then you'll need to check/test Q6 and Q7 out-of-circuit.

I don't think the zeners would change much as they age so ORANGE (6) and GREY (3) regulated outputs should not have changed.  Notice ORANGE (6) is about -24V WRT chassis as expected/needed for the NEC ICs.  This is a good sign.

If all the carbon resistors increased in value by, say, 15% over time, I don't think that would affect the zeners Vz nor the divider network.

Given the voltages you're seeing on the mystery device left & right pairs, I don't really understand it. Is it behaving as it should? It looks like a hermetically sealed semiconductor so it's probably okay given that it's only managing micro power levels.  I agree with your Q1 orientation assessment.

Other than WHITE (5), I think if you can demonstrate that if the regulated outputs can sustatain a significant load, then that would be enough to to verify those outputs.  To test them, for each regulated output at a time, add a low resistance (power resistor) in parallel with the minimum load resistor and see if the regulated output changes significantly (say, anything more than 0.5V).
For RED (1), apply a 2K 20W load resistance and measure MES14 (100mA).
For WHITE (5), apply a 33ohm 5W load resistance and measure MES15 (~400mA).  Although, it'll probably still be 0V WRT GND.
For GREY (3), apply a 33ohm 5W load resistance and measure MES11 (~400mA).
For ORANGE (6), apply a 33ohm 5W load resistance and measure MES18 (~300mA).
If you don't have 20W or 5W resistors, you can use a lower wattage one but you have to be quick in your measurement otherwise you risk burnout.   Don't go lower than 2K on the HV output as that risks blowing the 200mA fuse.  If there is no significant sag with the 33ohm, you can try 22ohm down to 12ohm for the LV outputs but now you're getting into 600mA and >1A, respectively.

It's likely that the regulated outputs will sustain the above power resistor loads, however, we need to clear up the WHITE (5)  0V issue before powering up the device with all PCBs installed.

I've updated the schematic with actual voltage readings. See attached.

[agent_power]

What is the voltage WRT GND at the base of the driver transistor Q6? (ie. upper-right pin of mystery device WRT GND)   If it is also 0V then that darlington pair isn't being turned on at all and you may have a mystery device problem.  If there is a non-zero voltage on the base of Q6 then you'll need to check/test Q6 and Q7 out-of-circuit.

I don't think the zeners would change much as they age so ORANGE (6) and GREY (3) regulated outputs should not have changed.  Notice ORANGE (6) is about -24V WRT chassis as expected/needed for the NEC ICs.  This is a good sign.

If all the carbon resistors increased in value by, say, 15% over time, I don't think that would affect the zeners Vz nor the divider network.

Given the voltages you're seeing on the mystery device left & right pairs, I don't really understand it. Is it behaving as it should? It looks like a hermetically sealed semiconductor so it's probably okay given that it's only managing micro power levels.  I agree with your Q1 orientation assessment.

There's barely any voltage at the base of Q6 (~.015 V). This is the biggest question, is it behaving at it should...

Q6 measures OK with a multimeter in-circuit.

I could desolder the mystery device and check if there is a marking underneath. Tomorrow I'll try to procure the power resistors to verify the other rails.

[pqass]

What is the voltage WRT GND at the base of the driver transistor Q6? (ie. upper-right pin of mystery device WRT GND)   If it is also 0V then that darlington pair isn't being turned on at all and you may have a mystery device problem.  If there is a non-zero voltage on the base of Q6 then you'll need to check/test Q6 and Q7 out-of-circuit.

I don't think the zeners would change much as they age so ORANGE (6) and GREY (3) regulated outputs should not have changed.  Notice ORANGE (6) is about -24V WRT chassis as expected/needed for the NEC ICs.  This is a good sign.

If all the carbon resistors increased in value by, say, 15% over time, I don't think that would affect the zeners Vz nor the divider network.

Given the voltages you're seeing on the mystery device left & right pairs, I don't really understand it. Is it behaving as it should? It looks like a hermetically sealed semiconductor so it's probably okay given that it's only managing micro power levels.  I agree with your Q1 orientation assessment.

There's barely any voltage at the base of Q6 (~.015 V). This is the biggest question, is it behaving at it should...

Q6 measures OK with a multimeter in-circuit.

I could desolder the mystery device and check if there is a marking underneath. Tomorrow I'll try to procure the power resistors to verify the other rails.

Yeah, it doesn't look like that's normal that there's [virtually] zero volts on the base of Q6.  There's no equivalent to R3 to default the darlington to on hence zero output.

Measure the VDC across cap C4.  If the mystery device connects the RV2 wiper to the base of Q6, then the output would be 1.2V below that of C4 VDC.  If it's zero, bad pot?  But I don't want you to exercise it (back and forth) otherwise you'll lose the setting.  I guess you could mark it (knob with body) before using cleaner.

It could also be that Q1 is bad.  That is, it still exhibits a B-E diode drop yet the collector is always open?  An LED across the left pair of the mystery device should be able to confirm that.

Look for dry/cracked solder joints (by inspection or continuity) and re-flow.

You could try to lift the two upper leads off the board.  Then you can conclusively test which side has a diode drop (or not) and in which direction.   And also check if there are any markings underneath.

[agent_power]

Sorry for the late reply, the weather was nice and I spend the weekend outside (gasp )

Before desoldering anything I clipped in the load resistors (I found a 2.2K, 33R, 22R with appropriate wattages).

I tried to do an experiment: Loading down WHITE and GREY at the same time and there appears to be a voltage now on WHITE: around 1-1.5 V WRT GND, around .4 V on the base of Q6, ORANGE(2) dropped down to 7.9V ~7.97V (closer to your calculated voltage)

Here the requested values:

For RED (1), apply a 2K 20W load resistance and measure MES14 (100mA).
For WHITE (5), apply a 33ohm 5W load resistance and measure MES15 (~400mA).  Although, it'll probably still be 0V WRT GND.
For GREY (3), apply a 33ohm 5W load resistance and measure MES11 (~400mA).
For ORANGE (6), apply a 33ohm 5W load resistance and measure MES18 (~300mA).
If you don't have 20W or 5W resistors, you can use a lower wattage one but you have to be quick in your measurement otherwise you risk burnout.   Don't go lower than 2K on the HV output as that risks blowing the 200mA fuse.  If there is no significant sag with the 33ohm, you can try 22ohm down to 12ohm for the LV outputs but now you're getting into 600mA and >1A, respectively.

RED: MES9 = 169 DCV, MES14 155 DCV - could be in the ballpark with the real Nixies attached, no?
WHITE: MES10 = 1 DCV, MES15 -13.5 DCV
GREY: MES11 = 13.2 DCV
ORANGE(6): MES13 = -9.7 DCV, MES18 -23.3 DCV - remains pretty stable, also with the 22R load

I have to get up early tomorrow so no more time for further tests, but let me know if you still want me to desolder the mystery device or we can conclude that it's doing "something" and the voltages look alright (+/- 13.5, ~ -24 WRT chassis).

PS: I only reflowed the output terminals because they were crumbling away as I was attaching more and more things to them (see attached modern art installation)

[pqass]

Sorry for the late reply, the weather was nice and I spend the weekend outside (gasp )

No worries...

Before desoldering anything I clipped in the load resistors (I found a 2.2K, 33R, 22R with appropriate wattages).

I tried to do an experiment: Loading down WHITE and GREY at the same time and there appears to be a voltage now on WHITE: around 1-1.5 V WRT GND, around .4 V on the base of Q6, ORANGE(2) dropped down to 7.9V ~7.97V (closer to your calculated voltage)

I can't explain why WHITE (5) VDC > base of Q6 VDC. Bad Q7 possibly?  Q7 emitter should always be 1.2V lower than Q6 base.
ORANGE (2) is lower because you've loaded down GREY (3). And it isn't down by much +8.14V to +7.97V.
My calculated number was based on the assumption of the Q1 being oriented differently than currently shown; collector on zener and base to mystery device (I forgot to update the prediction).  Showing Q1 as it is now adds an extra 0.7V to the zener voltage causing the output to be predicted higher by 0.7V to +13.5V.  Working backwards, seeing +7.97 means there is +13.3V on the GREY (3) output which is good with the 22R/33R (whichever) you loaded it down with (7.97÷(2000÷(2000+330+500+500))=13.3).

Here the requested values:

For RED (1), apply a 2K 20W load resistance and measure MES14 (100mA).
For WHITE (5), apply a 33ohm 5W load resistance and measure MES15 (~400mA).  Although, it'll probably still be 0V WRT GND.
For GREY (3), apply a 33ohm 5W load resistance and measure MES11 (~400mA).
For ORANGE (6), apply a 33ohm 5W load resistance and measure MES18 (~300mA).
If you don't have 20W or 5W resistors, you can use a lower wattage one but you have to be quick in your measurement otherwise you risk burnout.   Don't go lower than 2K on the HV output as that risks blowing the 200mA fuse.  If there is no significant sag with the 33ohm, you can try 22ohm down to 12ohm for the LV outputs but now you're getting into 600mA and >1A, respectively.

RED: MES9 = 169 DCV, MES14 155 DCV - could be in the ballpark with the real Nixies attached, no?
WHITE: MES10 = 1 DCV, MES15 -13.5 DCV
GREY: MES11 = 13.2 DCV
ORANGE(6): MES13 = -9.7 DCV, MES18 -23.3 DCV - remains pretty stable, also with the 22R load

RED(1): MES9 = 169VDC (2.2k load)  is in the right ball-park for nixies but that's come down quite a lot from +209VDC (100k load).  I'm not too worried about this because it has just occurred to me that the nixies are multiplexed so only one nixie cathode should ever be lit at one time.  And they shouldn't have used anything lower than 10k for an anode resistor.  (ie. kept the current to single digit mA).  My 2.2k suggestion was based soley on the 200mA fuse; thinking this output should do at least half that.  But really, that fuse is way over spec'd by at least 10x.

WHITE(5): see my comment above

GREY(3): MES11 = 13.2 DCV is looking good.

ORANGE(6): MES13 = -9.7 DCV, MES18 -23.3 DCV is also looking very good.

I have to get up early tomorrow so no more time for further tests, but let me know if you still want me to desolder the mystery device or we can conclude that it's doing "something" and the voltages look alright (+/- 13.5, ~ -24 WRT chassis).

I still think there is something wrong with WHITE(5) because the Q6 base isn't 1.2V > Q7 emitter.  But the other outputs seem just fine.  And the -24V WRT chassis really confirms it since that's what the NEC ICs need.

Re-read my last message. Report back the VDC across C4; this is the blue 33uF cap next to the mystery device.  It could be a bad wiper contact, dry solder joint (area around mystery device, Q1,R1,Q6, pot wiper), bad Q1, bad Q7, (unfortunately) bad mystery device, or combination.   When you report back, we can dill-down further and eliminate/confirm Q6/Q7 is the culprit.

[agent_power]

I can't explain why WHITE (5) VDC > base of Q6 VDC. Bad Q7 possibly?  Q7 emitter should always be 1.2V lower than Q6 base.
ORANGE (2) is lower because you've loaded down GREY (3). And it isn't down by much +8.14V to +7.97V.
My calculated number was based on the assumption of the Q1 being oriented differently than currently shown; collector on zener and base to mystery device (I forgot to update the prediction).  Showing Q1 as it is now adds an extra 0.7V to the zener voltage causing the output to be predicted higher by 0.7V to +13.5V.  Working backwards, seeing +7.97 means there is +13.3V on the GREY (3) output which is good with the 22R/33R (whichever) you loaded it down with (7.97÷(2000÷(2000+330+500+500))=13.3).

I'll check Q1, Q6, Q7 during the course of the next days out of circuit.

Re-read my last message. Report back the VDC across C4; this is the blue 33uF cap next to the mystery device.  It could be a bad wiper contact, dry solder joint (area around mystery device, Q1,R1,Q6, pot wiper), bad Q1, bad Q7, (unfortunately) bad mystery device, or combination.   When you report back, we can dill-down further and eliminate/confirm Q6/Q7 is the culprit.

With GREY (33R) and WHITE (60R) loaded down:
C4: 9.8 DCV (always), mystery device right leg pair: 8.6 DCV, or virtually no voltage?

minimal loads:
C4: 10.0 DCV, mystery device right leg pair: OL, 3.98 DCV, flashing bar graph?

Not sure if something is intermittent and I'm getting different results on the mystery device, but it's probably wise to exercise the pot and reflow some joints. If you think it's a good idea I could also try to scope the voltages around that area, maybe the multimeter doesn't like the output.

Btw, R1 = 1k (if it's the "dog bone" style resistor) and measures as such, R3 = 2k and is at 2k3