Facit 1132 Nixie Calculator restoration - Page 1
Forum section: electronics / repair

author: agent_power
author_rank: Regular Contributor
timestamp: May 21, 2023, 07:26:54 pm
content: Hi communityI'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 picturesThanks

author: pqass
author_rank: Super Contributor
timestamp: May 21, 2023, 10:04:07 pm
content: 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 thishttp://madrona.ca/e/eec/calctd/Casio121B_MMNotes.htmllink 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 linkhttps://www.oldcalculatormuseum.com/comp241.htmlalthough it may be less relevant.

author: Haenk
author_rank: Super Contributor
timestamp: May 22, 2023, 08:58:29 am
content: 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.

author: HarryDoPECC
author_rank: Regular Contributor
timestamp: May 22, 2023, 10:56:47 am
content: 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 shortIn 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 (!)

author: strawberry
author_rank: Super Contributor
timestamp: May 22, 2023, 12:18:25 pm
content: looks like brand newlooks like more modern couple chip calculatorsdimm bulb wont protect unobtainable IC'sdimm bulb is for SMPS or high power expensive transistors you dont want to blow when you dont know 100% about control circuit functionalitycarbon resistors may go open circuit or drifted out of spec.it is possible to recreate IC's with modern components

author: agent_power
author_rank: Regular Contributor
timestamp: May 22, 2023, 08:48:07 pm
content: Quote from: HarryDoPECC on May 22, 2023, 10:56:47 amThanks 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?

author: pqass
author_rank: Super Contributor
timestamp: May 22, 2023, 11:25:06 pm
content: Quote from: agent_power on May 22, 2023, 08:48:07 pmI'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.phpThey 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.

author: strawberry
author_rank: Super Contributor
timestamp: May 23, 2023, 06:09:11 am
content: crowbar is better because zener diode have series resistance/slope(1W 24V ~30ohm) similar for TVS diodesneed some transient bench tests with oscilloscopewhat does that core memory do on display module?

author: agent_power
author_rank: Regular Contributor
timestamp: May 23, 2023, 09:28:30 pm
content: Quote from: pqass on May 22, 2023, 11:25:06 pmThe 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.Quote from: strawberry on May 23, 2023, 06:09:11 amThanks 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

author: pqass
author_rank: Super Contributor
timestamp: May 24, 2023, 07:40:02 am
content: 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  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).

author: agent_power
author_rank: Regular Contributor
timestamp: May 24, 2023, 08:00:43 pm
content: Quote from: pqass on May 24, 2023, 07:40:02 am- 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 isQuote from: pqass on May 24, 2023, 07:40:02 amThanks, 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?

author: pqass
author_rank: Super Contributor
timestamp: May 25, 2023, 07:14:01 am
content: Quote from: agent_power on May 24, 2023, 08:00:43 pmSee 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) +10.8VORANGE (2) +2.75V (unregulated)ORANGE? (6) -8VHowever, 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) -10.8VGREY (3) 0V (measure other outputs WRT this ground)ORANGE (2) -8V (unregulated)ORANGE? (6) -18.8VQuoteOh, 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-nte5073aZR212:https://vetco.net/products/12-0-volt-1-watt-zener-diode-nte142a2SC641:https://pdf1.alldatasheet.com/datasheet-pdf/view/108439/HITACHI/2SC641.html2SA618:https://alltransistors.com/transistor.php?transistor=86342SC857:https://alltransistors.com/transistor.php?transistor=172092SC515A:https://datasheetspdf.com/pdf-file/637523/SavantIC/2SC515/12SC830:https://alltransistors.com/transistor.php?transistor=171802SC1030:https://datasheetspdf.com/pdf-file/637543/SavantIC/2SC1030/1

author: agent_power
author_rank: Regular Contributor
timestamp: May 25, 2023, 11:24:40 pm
content: I can't thank you enough for all this work! It's really interesting learning about this and well explained tooQuote from: pqass on May 24, 2023, 07:40:02 amVoltages relative to GND / with no load:Brown: 200 VACRed: 10 VACBlue: 16 VACD4: 43.6 VDCD2/D3: 13.8 VDCD5 ZR212: 14 VDCD6 ZR 10.4 VDCThe 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 loadEDIT: The two lead device 2SC641 has a third leg in the middle but it's just a stub

author: agent_power
author_rank: Regular Contributor
timestamp: May 26, 2023, 10:48:43 am
content: 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 loadWhite: 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 loadI 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 2.3KAny 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.htmlEDIT2: 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/116228I probably want to make sure this PSU is in order before I connect any boards

author: pqass
author_rank: Super Contributor
timestamp: May 26, 2023, 08:02:22 pm
content: Quote from: agent_power on May 26, 2023, 10:48:43 amYou should put a minimum load onall 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, firstfill-out this tableto 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 applicablenot applicablefill inORANGE (2)BROWN (4)fill innot applicablenot applicableGREY (3)BROWN (4)not applicablefill innot applicableWHITE (5)BROWN (4)not applicablefill innot applicableORANGE (6)BROWN (4)not applicablefill innot applicableNow, 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 youload 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!

author: pqass
author_rank: Super Contributor
timestamp: May 26, 2023, 09:24:39 pm
content: Quote from: agent_power on May 25, 2023, 11:24:40 pmBrown: 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).QuoteAgreed. 20VDC is too much for a LED. What's the VDC across the right pair? Maybe the LED is there.QuoteI suspected that the transistor is being 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.Seehttps://sound-au.com/ism.htm#p5for an explaination on current sources/sinks.

author: agent_power
author_rank: Regular Contributor
timestamp: May 26, 2023, 10:31:22 pm
content: Quote from: pqass on May 26, 2023, 09:24:39 pmAh 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.QuoteI'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...QuoteInterestingI'll come back once I have everything set up, I'm gone for the weekend (1-2 days or so)

author: pqass
author_rank: Super Contributor
timestamp: May 28, 2023, 10:46:15 pm
content: Attached is an updated schematic based on your latest input.Please connect all  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 inhttp://www.bitsavers.org/components/ti/_dataBooks/1978_TI_The_Optoelectronics_Data_Book_for_Design_Engineers_5ed.pdfCurrently, 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).

author: agent_power
author_rank: Regular Contributor
timestamp: May 30, 2023, 11:58:23 pm
content: 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 applicablenot applicable209 VDCORANGE (2)BROWN (4)8.14 VDCnot applicablenot applicableGREY (3)BROWN (4)not applicable13.9 VDCnot applicableWHITE (5)BROWN (4)not applicable0 VDCnot applicableORANGE (6)BROWN (4)not applicable-9.8 VDCnot applicableD5: 13.9 VDCD6: 10.3 VDCMES14: 195.7 VDCMES15: -13.5 VDCMES16: -13.5 VDCMES17: -5.4 VDCMES18: -23.4 VDCRegarding 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 leg0 VDC between the upper left and upper right leg10 VDC between the upper left and lower right leg3.9something 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 legEDIT: I guessed from here, the little tab points towards the cap/zener:https://www.web-bcs.com/transistor/tc/2sc/2SC857.php

author: pqass
author_rank: Super Contributor
timestamp: June 01, 2023, 07:29:38 am
content: 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.

author: agent_power
author_rank: Regular Contributor
timestamp: June 01, 2023, 03:50:56 pm
content: Quote from: pqass on June 01, 2023, 07:29:38 amThere'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.

author: pqass
author_rank: Super Contributor
timestamp: June 01, 2023, 05:47:52 pm
content: Quote from: agent_power on June 01, 2023, 03:50:56 pmYeah, it doesn't look like that's normal that there's  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.

author: agent_power
author_rank: Regular Contributor
timestamp: June 05, 2023, 09:14:47 pm
content: 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:Quote from: pqass on June 01, 2023, 07:29:38 amRED: MES9 = 169 DCV, MES14 155 DCV - could be in the ballpark with the real Nixies attached, no?WHITE: MES10 = 1 DCV, MES15 -13.5 DCVGREY: MES11 = 13.2 DCVORANGE(6): MES13 = -9.7 DCV, MES18 -23.3 DCV - remains pretty stable, also with the 22R loadI 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)

author: pqass
author_rank: Super Contributor
timestamp: June 06, 2023, 03:31:04 pm
content: Quote from: agent_power on June 05, 2023, 09:14:47 pmNo worries...QuoteI 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).QuoteRED(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 aboveGREY(3): MES11 = 13.2 DCV is looking good.ORANGE(6): MES13 = -9.7 DCV, MES18 -23.3 DCV is also looking very good.QuoteI 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.

author: agent_power
author_rank: Regular Contributor
timestamp: June 06, 2023, 08:59:12 pm
content: Quote from: pqass on June 06, 2023, 03:31:04 pmI'll check Q1, Q6, Q7 during the course of the next days out of circuit.QuoteWith 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

author: pqass
author_rank: Super Contributor
timestamp: June 06, 2023, 11:16:52 pm
content: Quote from: agent_power on June 06, 2023, 08:59:12 pmBefore pulling off the transistors to test out-of-circuit...If C4 is about 10V WRT GND (when both loaded and miminally loaded), then I suspect the mystery device IS NOT transmitting that through to Q6 base. If it were, then WHITE (5) should be +8.8V (unless the mystery device was adding a Vdrop of its own). But you also said that the right leg pair was 8.6VDC or virtually zero at times. That sounds intermittent. The problem could be on the right side of the mystery device but it also could be that the left legs aren't receiving a signal and therefore the right legs are open (seen as 0.4V on base of Q6). I still suspect the mystery device is an optocoupler.(a) Lets start with reflowing the solder on the leg pads of the mystery device and traces to all other immediate devices (Q1 collector, R1 (both sides to diode-bridge unreg. positive rail), Q6 base, and to the C4 cap and RV2 pot wiper).(b) You could exercise the pot, although the wiper reports 10V under both load and minimal load, so it may not be necessary. BUT IF YOU DO, mark the spot on the screw and body so you can return it to that same point. ie. output of wiper to GND should go back to 10VDC. We don't want to lose this calibration!(c) If the above reflow (a) doesn't produce a real voltage on WHITE(5) of +8.8V WRT GND (my prediction), then you can lift the two upper pins of the mystery device (on left and right sides, leaving the lower pins connected) and then short the RV2 pot wiper/C4 positive leg to Q6 base (tack/clip a jumper wire). Then measure WHITE(5) and GREY (3) (loaded and minimally loaded). If you see +8.8V WRT GND on WHITE(5) then that confirms Q6 and Q7 are okay. BUT MAKE SURE there is NOTHING CONNECTED at the other end of the WHITE (5) wire (NO logic and display BOARDS INSTALLED in the edge connectors).(d) While you have the upper legs of the mystery device lifted, check underneath for any markings.(e) Also, use the diode-check on your MM to find on which pair (left or right) of the mystery device the LED is on and in which orientation (cathode on upper or lower).(f) You can then remove the temporary jumper wire (c) and put the upper legs back into their holes and re-solder in place.WRT using an oscilloscope, I'm not sure you'll see much since all the points to measure will be VDC. If you want, you could see if the unregulated side of the diode bridge (positive and negative) or the unregulated side of the diode-pair (positive) don't have excessive ripple (>2V) but you can do this later once we get WHITE(5) working. DO NOT ATTACH your scope probe anywhere from the brown HV transformer winding to the RED (1) rail. I don't want you to blowup your 'scope. Of course, all measurements should be WRT (probe ground clip on) GND.WRT R1 measuring 1K instead of 2K, that would just double the current through the left legs of the mystery device to ~22mA from ~11mA; that's not an unreasonable current through an LED (which I suspect is in the mystery device).WRT R3 being 2.3K vs 2K, thats just a 15% increase so the current through the zener goes from 4mA to 3.5mA which, for my taste, seems a bit low for a zener bias but GREY(3) is regulating properly so I wouln't worry about that.

author: agent_power
author_rank: Regular Contributor
timestamp: June 07, 2023, 08:51:51 pm
content: Alright:a) didn't solve the problemb) didn't solve the problemc) does make a difference, WHITE with minimal load: 8.9 DCV, with 60R load: 8.5 DCV (Q6 + Q7 confirmed working?)d) no markingse) no voltage drop in any directionf) should I put it back in, or desolder it completely and test it in another circuit?Is the mystery device or Q1 possibly faulty?

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 07, 2023, 11:04:01 pm
content: Subscribing to a very interesting thread.

author: pqass
author_rank: Super Contributor
timestamp: June 08, 2023, 03:02:36 am
content: (a) bummer.(b) bummer.(c) YES, it looks like Q6 and Q7 are working. The big questions are now: is this the correct output voltage given that we bypassed the mystery device? Or does it add a Vdrop to lower WHITE (5) by some amount? And is the mystery device just a means to delay enabling WHITE (5) behind GREY (3)?Q: While you've shorted the C4 positive to Q6 base, and WHITE (5) is +8.5VDC, is GREY (3) still outputing +13.3VDC?If so, then it confirms that Q1 is correctly modeled (collector to mystery device) in my last (May 31) schematic.Nevermind, WHITE(5) won't be producing anything if GREY(3) didn't have a voltage on it since we're feeding part of that back to Q6 base. Further, if the zener D5 was disconnected then GREY(3) would be just a couple of volts below its unregulated side which would make WHITE(5) a lot higher than the predicted +8.8VDC.(d) bummer.(e) bummer.(f) The dot on the left leg sure smells like it's indicating the cathode to me.But there is zero chance that it has an LED with large Vdrop like a modern white LED. And your MM isn't measuring it properly. EDIT: I just checked if my bench meter's diode-check can measure a red LED. It can't. So you'll have to do it out-of-circuit. See "...report back the Vdrop on the left pair..." below.Q:You said that R1 measures 1K but is it marked 2K?If true, then that changed the current from 11mA to 22mA (based on 22V unreg. rail) but this should not be enough to kill the LED (if it exists) in the mystery device because many old optocouplers have robust LEDs that can take 40+mA continously.I guess you can try to test Q1 out-of-circuit.Q: Are you using one of those component testers that shows transistor type, EBC pinout, hFE, etc?When you do remove Q1, confirm from the underside (based on the tab) exactly which pin is going to GND, zener, and mystery device upper-left leg. Datasheet:https://www.web-bcs.com/transistor/tc/2sc/2SC857.phpIf Q1 is good, then you can remove the mystery device and test it separately by connecting:i. upper left to 0V, lower-left to 1K to Vcc,ii. upper right to 0V, lower-right to 10K to Vcciii. with your multimeter on VDC on the right pair.iv. use 22VDC for Vcc from a lab power supply or lacking that a wall-wart/laptop power supply that can do any fixed value between 12VDC and 22VDC.If it's a working opto coupler then connecting and disconnecting the 1K should cause the MM to go from 0V to Vcc.Also, report back the Vdrop on the left pair when the 1K is connected.EDIT: Also, while you have the mystery device out, confirm with your MM set to ohms, that there is very high resistance between any pin on the left side to any on the right side.Good luck.

author: agent_power
author_rank: Regular Contributor
timestamp: June 09, 2023, 08:06:29 pm
content: QuoteMy mistake in the post with the picture, it's marked 1K and measures 1KQuoteSee pictures, looks good to me unless it's noisy or intermittent or something like thatQuoteOut of circuit, there's few dozens MOhms between the legsSee the picture.. not sure I'm doing something wrong but it's just measuring Vcc. Disconnecting the 1K doesn't make a difference

author: pqass
author_rank: Super Contributor
timestamp: June 10, 2023, 08:16:48 pm
content: Since the transistor looks to be working (and you earlier eliminated connection issues), therefore, I think the mystery device is probably dead. Unfortunately, we can't absolutely prove that it's an optocoupler but I can't think of any other thing it could be. It has the case style, dot mark, and high resistance between left/right leg pairs (even if one leg is broken). And is consistent with an isolated low-current switch for the WHITE(5) darlington pair. It all fits.But before we pronounce it truely dead,one last test...connect a multimeter in ammeter mode to see if the left pair is drawing any current at all. It should draw ~20mA in your breadboard setup. See attached test setup schematic. You had said it appeared to be intermittent in your earlier message. So try tapping on the device with your finger while watching the ammeter and voltage drop on the right pair.If there is still no current in the left pair and no change in the right pair (always shows Vcc) then you probably can substitute the mystery device with a 4N35 or a TIL111 optocoupler (or almost any with a ~40mA LED continuous current with phototransistor output). Note the pins of cathode/emitter in the modern part (rotated CW 90°); they're opposite to dot on the mystery device.I happen to have a TIL111 that exhibits a 100mV drop on the phototransistor when 20mA is applied to the LED. Given that the darlington pair has a high hFE, causing only a minimal drop in RV2 wiper voltage, that should result in about a +8.3V WHITE(5) WRT GND (and about -5V WRT chassis) regulated output. FYI: see attached schematic showing divider with RV2 wiper and opto driving the darlington pair; ie. how I believe WHITE(5) regulation is intended to work.Also attached is the latest schematic of the PS with updated notes and measurement table.Thanks for confirming Q1 orientation. I can only think it is being used to delay WHITE(5) after GREY(3) is up.Relative to GND, the outputs (1,5,3,2,6) are: +169V, +8.3V, +13.2V, +8.1V, -9.7VBut, relative to chassis, the outputs (1,5,4,2,6) are: +155V, -5V, -13.2V, -5.4V, -23.3VThe HV is sagging a bit since it's probably loaded too much (with the 2.2K).But it's interesting that there is a (approx) -5V and a -24V in there.As such, we may be on the right track WRT correct output voltages.

author: agent_power
author_rank: Regular Contributor
timestamp: June 12, 2023, 02:39:22 pm
content: Ok, I got some life out of it in the breadboard setup:I tried your test - didn't help. The next best thing to do with intermittent devices apart from hitting them is temperature: Spraying cold spray didn't help, but heating it up with hot air turned it on pretty quickly.The current draw was about 23mA, the voltage measured on the right pair went from 0.8V (torched) to about 0.45V (cooled down a minute), then turned off entirely (= measured voltage on right pair back to Vcc).While conducting, I could disconnect the 1K to turn it off.Can we pronounce it broken? I don't know of any optocouplers that need to be warmed up. Am I missing something? Some primitive delay circuit and it only works under load?

author: pqass
author_rank: Super Contributor
timestamp: June 12, 2023, 03:59:38 pm
content: Good thinking with the hot/cold test!Yeah it's dead. Swap-in another optocoupler and call it done.Then add the loads to GND: 10K*, 33R*, 33R, 22R, for RED(1), WHITE(5), GREY(3), ORANGE(6), respectively. (*=more realistic)Measure them WRT GND and WRT chassis and I'll update the schematic.This part doesn't do any serious power handling. Nor is there any constant switching; Q1 via zener turns on once at power up and keeps the LED lit. The phototransistor shouldn't heat up since there's <1mA to Q6 base for up to 2.5A out of WHITE(5). I guess the LED at a constant 28mW (1.2V*23mA) eventually caused a crack somewhere.The only possible issue I see is a difference in Vce across the dead vs the new phototransistor. If the new part is less than the dead part, the new part will raise WHITE(5) output by the difference; eg. Vce=450mV vs TIL111 Vce=100mV leads to an increase of 350mV. But given that the Vce of the dead part was going down (450mV) as it was cooling off (before cutting out), even at that point it would be <5% difference in the regulated output. So, I wouldn't worry about it.

author: agent_power
author_rank: Regular Contributor
timestamp: June 16, 2023, 09:38:44 am
content: I found a 4n35 (Vce=70mV, still ok?)... quick check before I power it up:Is it wired in correctly? Or do I need to swap the C / E around?

author: pqass
author_rank: Super Contributor
timestamp: June 16, 2023, 03:50:08 pm
content: Quote from: agent_power on June 16, 2023, 09:38:44 amThe 4n35 should be fine.And you have it the right way assuming the LED is on the left, phototransistor on the right.But before powering up with the logic and display boards installed, let see what the output voltages are under load.Connect to GND: 10K*, 33R*, 33R, 22R, for RED(1), WHITE(5), GREY(3), ORANGE(6), respectively. (*=more realistic)Measure them WRT GND (BROWN(4)) and WRT chassis (GREY(3)).

author: agent_power
author_rank: Regular Contributor
timestamp: June 17, 2023, 08:55:29 pm
content: Quote from: pqass on June 16, 2023, 03:50:08 pmAh, yes, I didn't have the latest schematics printed out and wasn't sure about the wiring of the phototransistor.QuoteNo 10K available (of that wattage) for the RED supply, but with 2x22k at about 10.8K I get 207 DCV WRT GND, 193.5 DCV WRT GREY respectively.With the 33R load, WHITE is: 8.8 DCV WRT GND, -4.9 DCV WRT GREY, but I noticed that it creeps up with temperature. Is this something to worry about? Is the 2SC830 failing or is this normal behaviour? It went from about 8.6ish to 8.8205-ish (sometimes creeping up, sometimes going back down, more or less remaining there now). If I blow on it changes a little...?The optocoupler is slightly warm..I think it's repaired? Time for the logic boards? Or is it better to implement the protection circuit against shorting transistors first?

author: pqass
author_rank: Super Contributor
timestamp: June 17, 2023, 11:56:45 pm
content: Quote from: agent_power on June 17, 2023, 08:55:29 pm10.8K (22K||22K) is an acceptable load for the HV output. It puts the current on that output to about 20mA. 207V/193.5V (WRT GND/chassis) still seems a bit high to me but may be warranted for a 16 digit multiplexed nixie design. Later, if you wish, you can turn down the pot with the red knob if you want to lower the brightness and prolong the life of the nixies.QuoteGood to see that the WHITE(5) output is now working. Whether it's 8.8V or 8.6V (WRT GND) is not really that important. It's only about a ±1.5% difference. Transistors and diodes exhibit a -2.2mV/°C drop in Vbe as they warm up. The transistors Q6, Q7, Q3, and Q4 (last two affects the divider which serve as a reference to regulate the first two) will change due to the regulator design; that is, one without feedback to compensate for this Vbe change. The designers thought this was acceptable so don't worry about it.QuoteA slightly warm optocoupler should be fine.Yes, I think it's repaired.As long as the other outputs still show these voltages (under 33R/none/22R loads WRT GND):GREY(3): +13.2V, ORANGE(2): +8.14V, ORANGE(6): -9.7VWe've reverse-engineered the PS circuit and determined that the GREY(3), ORANGE(6), and thus ORANGE(2) are solely regulated from fixed zeners. And zeners don't really change much with age, therefore, I'm confident that these outputs are correct. RED(1), the HV output, can likely move quite a bit (via pot RV1) since there are likely only the nixie anodes connected to it (no ICs). WHITE(5) is controlled via pot RV2 but is also linked to the fixed zener D5 via divider so as long as you put back pot calibration (after exercising it), you should be fine here too.Since we've confirmed that all the power transistors are still good and regulating properly under load, I think you can put back the logic and display boards and power it all up to see if it comes back to life.When you do power it all up with logic and display boards installed, you're going to have to take voltage readings (WRT GND and chassis) on all outputs again to establish a base-line (under the real load). We only tested it to a 400mA load on the LV outputs and 20mA load on the HV output. Then we can discuss the protection circuits afterwards.See attached for the latest schematic with updated notes.

author: agent_power
author_rank: Regular Contributor
timestamp: June 18, 2023, 09:28:21 am
content: Good and bad news:It powers up and the nixies light up too. There was even a 0 on the rightmost nixie, but after 15 seconds it showed random numbers and went comatose.Here are the voltages, with the RED pot all the way down (one dot on the nixies still lights up, I guess that's good enough voltages)WRT GND, chassis in VDC:RED: 190, 176.8WHITE: 5.6, -7.7BROWN: 0, -13.4GREY: 13.4, 0ORANGE(2): 2.9, -10.5ORANGE(6): -9.8, 23.3WHITE and ORANGE(2) deviate from the prediction.. close, but no cigarEDIT: Attached are some scope pictures.. not sure what to make of it, WHITE still looks weird compared to the others

author: agent_power
author_rank: Regular Contributor
timestamp: June 18, 2023, 02:42:36 pm
content: I swapped some boards out while trying to figure out if one drags down voltages due to a shorted component. Voltages were all over the place with some boards missing, so I'm not sure if there's additional regulation or referencing happening in the whole circuit.The last try was having all boards in but the keyboard disconnected, and it seems to work now.Almost every key was completely stuck and tried to get it going with some contact lubricant (it usually dissolves the old grease well enough).... in this case I might have addition faults in there

author: pqass
author_rank: Super Contributor
timestamp: June 18, 2023, 02:51:26 pm
content: Quote from: agent_power on June 18, 2023, 09:28:21 amWRT GNDWRT chassisMy CommentsRED(1):+190V+176.8VGood. Within acceptable limits. Nixies light-up (typ. >165V) nor excessively bright.WHITE(5):+5.6V-7.7VBad. Likely a consequence of ORANGE(2) droop.BROWN(4): a.k.a GND0V-13.4VGood. No drooping.GREY(3): a.k.a chassis+13.4V0VGood. Confirms reverse of BROWN(4).ORANGE(2):+2.9V-10.5VBad. See below.ORANGE(6):-9.8V+23.3VGood. No drooping.WHITE(5) is 2 volts below what it should be but this is very likely because of ORANGE(2) is drooping. And the +5.6V WRT GND is consistent with a +2.9V ORANGE(2). Normally, for RV2 wiper to output +10V (with GREY(3) at +13.4V) RV2 needs to be split 160R/340R. But, given that ORANGE(2) is now +2.9V, therefore, 13.4-2.9=10.5×(330+160)÷(330+500+500)+2.9=6.77 at the wiper, and therefore, 6.77-1.2=5.6V at WHITE(5).ORANGE(2) should be close to +8.1V WRT GND or -5.4V WRT chassis. Because it is derived from a resistor divider, that implies that whatever it feeds must be high impedence otherwise it will cause it to droop. Which is what is happening.Unfortunately, you are going to have to trace where the ORANGE (2) wire goes; which board(s), which component(s) it immediately touches. It is probably used as a reference (my guess) so it shouldn't be used in lots of places; probably leads to a  buffer amp that's loading it down.Q1: Immediately upon power-up, is ORANGE (2), WHITE(5) normally at +8.1V, +8.6V, respectively, and then they droop?Q2: Immediately upon power-up, can you type on the keyboard and does the machine respond normally before it goes comatose?The 'scope shots show high-frequency noise (the most on WHITE(5)) and the periodic ripple/spikes are below 20mV and likely due to transistor/IC switching. That doesn't look that bad. There should be local cap decoupling next to the ICs to get rid if it.

author: agent_power
author_rank: Regular Contributor
timestamp: June 18, 2023, 04:17:46 pm
content: Quote from: pqass on June 18, 2023, 02:51:26 pmIt looks like it stabilises at 5.6 V immediately.I traced it to yet another alien looking thing (see attachment). The second legs seems to go to a ground plane as the trace then stretches across the board connecting many other components...I haven't found out if it's one of the established grounds (BROWN or GREY). I guess to know what the voltage should be we need to figure out this component too.QuoteSee my second post after the scope pictures. It seems to power up correctly without keyboard and there is possibly a fault there.

author: pqass
author_rank: Super Contributor
timestamp: June 18, 2023, 06:05:03 pm
content: Quote from: agent_power on June 18, 2023, 04:17:46 pmThat half-dissolved pill thing looks like a cap. The '70s had some weird packages.I looked around and just see carbon resistors, green polyester film caps, glass diodes, transistors, ICs, and some kind of hybrid(?) packages (those marked "Sharp" "DP4" "DN3" etc.). I only see one blue axial electrolytic cap and no tantalum caps; the latter can go short. The carbon resistors might increase in resistance as they get old but the semiconducters should be fine if not abused.Yeah, figuring-out which is the common is hard given we don't have any datasheet on any of the ICs.I suppose it is possible that ORANGE(2) is intentionally being pulled down.QuoteSo, without the keyboard (all other boards installed), the voltages are still those below?WHITE(5): +5.6V -7.7V WRT GND/chassisORANGE(2): +2.9, -10.5 WRT GND/chassisAnd, also without keyboard, does it still go comatose after 15 seconds?If it DOES NOT go comatose without the keyboard then I'd give the keyboard a good cleaning and test each of the switches for continuity (high-resistance when not pressed, low-resistance when pressed). Then reboot with keyboard installed and see if it still goes comatose. A key may be loading down a power rail.The comatose issue or low ORANGE(2) may not be related.

author: agent_power
author_rank: Regular Contributor
timestamp: June 19, 2023, 09:05:50 pm
content: Quote from: pqass on June 18, 2023, 06:05:03 pmThe voltages remain the same with the keyboard disconnected, the only difference is the 0 doesn't show up (it only appears comatose with the keyboard connected).Working assumption: the boards regulate ORANGE(2) and WHITE somehow and there are no faulty components that influence it.Any idea how to disassemble those type of keyboards? I've never handled one like that... the wires are soldered to phenolic boards sandwiched between metal plates. Is it possible to bend those metal pieces back..? I guess that's how you un-sandwich it...I would like to throw this in an ultrasonic cleaner but I don't own one and the keyboard can't be disconnected from the backplane. Alternatively, I'll try to map out the keyboard. My hope is that maybe just one or two keys are stuck close and hinder the calculator from operating correctly.PS: There's a really bizarre connector on the back.. what could be the purpose? Remote control... factory testing?

author: pqass
author_rank: Super Contributor
timestamp: June 19, 2023, 10:22:49 pm
content: Quote from: agent_power on June 19, 2023, 09:05:50 pmThat's a reasonable assumption.QuoteMaybe you can first separate all key groups from the top of the enclosure. It looks like it can come off as one unit. I think that row of brass phillips screws above & below the blue wires (from your first message) secures them. That should give you access side-on to spray contact cleaner and exercise the keys. I don't think you should separate those plates as they are punched along the left and right edges (4 times) of each key group. It'll probably cause you grief to put back together with multiple springs and alignment points. And never be flat again.QuoteI don't have an ultrasonic cleaner so I can't say whether it will work or be non-destructive.Printer maybe?

author: Haenk
author_rank: Super Contributor
timestamp: June 20, 2023, 08:50:12 am
content: Quote from: agent_power on June 19, 2023, 09:05:50 pmIn that era, some calculators had "options" - for example a "secondary operator", a detached display and keyboard connected to the main machine. (I have no idea how this did work out, maybe one operator could lock out the other operator?) Also some had an external display option or even a line printer port.

author: agent_power
author_rank: Regular Contributor
timestamp: July 02, 2023, 09:49:47 pm
content: Quote from: pqass on June 19, 2023, 10:22:49 pmI beeped out all the keys. All of them appear to work with exception of the division key, where the readings are erratic - between .5 MOhm and few hundred Ohms when pressed down. No amount of cleaner and exercising seems to helpUnless there is an issue on a component inside the keyboard (I can see some in the sandwich) or the sliding switches, I'm not really sure how the keyboard is causing a problem.