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!