I probably do have a 10meg resistor down in my cellar, time to dig. I wasn't sure if I'd need to create an actual voltage divider with 2 resistors/ground wire so that's helpful. I'd hate to destroy a Fluke...
On Wednesday, October 27, 2021 at 1:06:19 AM UTC-4 gregebert wrote: > Most DMMs have 10Meg input impedance, so you can put a 10meg resistor > in-series with your meter, and measure double the voltage. It wont be > exact, but pretty close. If you really need an exact measurement, then > measure a stable lower voltage without the resistor, then again with it. > Dividing those 2 measurements will give you a ratio close to 2.0, and you > can use that when measuring your high voltage. > > > On Tuesday, October 26, 2021 at 8:40:54 PM UTC-7 GEK wrote: > >> Thanks everyone for the hints, I'll look more closely at the HV - I'm a >> bit shy about measuring as I don't have a meter that will go to -1300v for >> the bright. >> >> - Gary >> >> On Tuesday, October 26, 2021 at 3:17:49 PM UTC-4 Bartek Ogryz wrote: >> >>> I'm not familiar with that project and that circuit, but based on my >>> experience in CRT TV repairs, if you have a proper blanking signal, >>> something must be wrong with HV as Tristan said. >>> Grid1 - negative voltage on this grid allows electrons to flow (brighter >>> picture), 0V blocks them (darkness). This grid can be driven by the >>> blanking signal, >>> Grid2 - is the screen grid, high voltage accelerates the electrons and >>> brightens the screen. If that voltage is too high, it can "force" electrons >>> to flow, regardless of the Grid1 voltage. >>> Chceck the main power supply first - if it's voltage is too high, all HV >>> voltages will also be too high. >>> wtorek, 26 października 2021 o 05:02:21 UTC+2 Tristan napisał(a): >>> >>>> The brightness pot needing to be turned right up still suggests that >>>> you have a problem with grid voltage control. I'd expect to see some >>>> higher >>>> frequencies much higher than 60Hz on the BLNK- signal as well though. I'd >>>> be surprised if the problem was in the supply sections for the cathode or >>>> anode given that it is mostly working in your photo but there could be an >>>> issue with the specific section of the supply dedicated to the grid and it >>>> is referenced to the cathode. Although you have now replaced most of the >>>> potentially offending components unless you have an open winding on the >>>> transformer. You could check the resistance across pins 4,5 and 6 of the >>>> transformer. I'd expect them all to read fairly low. >>>> On Tuesday, October 26, 2021 at 10:20:26 AM UTC+10 GEK wrote: >>>> >>>>> Ok, so I'm stumped (again)... >>>>> >>>>> I have replaced D35-38, C52, C53, C54, C55, Q1, C51 and U17. >>>>> R67, F68, R69, R70 and R71 measure correctly in circuit. >>>>> I've confirmed pulsing on the BLNK- signal at 60hz >>>>> I've also swapped U5 (74HC74) and U4 (74HC151). >>>>> I've swapped the CRT. >>>>> >>>>> Curiously I need to have the Bright potentiometer (R11) at maximum to >>>>> get an image. >>>>> Could something in the High Voltage Supply be causing problems with >>>>> the blanking? >>>>> >>>>> On Thursday, October 21, 2021 at 3:05:10 PM UTC-4 Paul Andrews wrote: >>>>> >>>>>> Hah yes. I have one of its brethren that is even more 'eclectic'. >>>>>> >>>>>> On Wednesday, October 20, 2021 at 8:04:03 PM UTC-4 Terry S wrote: >>>>>> >>>>>>> >>>>>>> That may just be one of the worst PCB layouts I've ever seen. >>>>>>> On Wednesday, October 20, 2021 at 8:33:41 AM UTC-5 martin martin >>>>>>> wrote: >>>>>>> >>>>>>>> Here's a simple one >>>>>>>> >>>>>>>> https://www.tindie.com/products/howchon/osc45-oscilloscope-clock-kit-for-many-crt-types/ >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> ~ >>>>>>>> *mcve...@gmail.com* >>>>>>>> >>>>>>>> >>>>>>>> On Wed, Oct 20, 2021 at 4:16 AM GEK <geka...@gmail.com> wrote: >>>>>>>> >>>>>>>>> Will do, Hopefully parts will be here by Friday. I may try and >>>>>>>>> shotgun D35-38 and C52-53 before then as I should have spares around >>>>>>>>> here. >>>>>>>>> >>>>>>>>> Finger's crossed! >>>>>>>>> >>>>>>>>> - Gary >>>>>>>>> >>>>>>>>> On Wednesday, October 20, 2021 at 1:19:58 AM UTC-4 Tristan wrote: >>>>>>>>> >>>>>>>>>> Hi Gary, >>>>>>>>>> >>>>>>>>>> That's a bit odd. While I'm no EE I would have expected that >>>>>>>>>> removing U17 would have blanked the display if the rest of the >>>>>>>>>> circuit was >>>>>>>>>> working correctly. It looks Q13 should be conducting without U17 >>>>>>>>>> fitted and >>>>>>>>>> the grid should become more negative with respect to the cathode to >>>>>>>>>> ensure >>>>>>>>>> cutoff. I think you may need to look at the D35-38 and C52 & C53. >>>>>>>>>> >>>>>>>>>> - Tristan >>>>>>>>>> >>>>>>>>>> On Wednesday, October 20, 2021 at 12:42:53 PM UTC+10 GEK wrote: >>>>>>>>>> >>>>>>>>>>> Tristan - >>>>>>>>>>> >>>>>>>>>>> Thanks for those hints. the BLNK signal is pulsing at 60hz, and >>>>>>>>>>> I swapped Q13 without any change. I also socketed U17 (6N137) >>>>>>>>>>> while >>>>>>>>>>> waiting for a replacement to arrive. Removing U17 from the circuit >>>>>>>>>>> leaves >>>>>>>>>>> the display unchanged, so it does appear that the blanking circuit >>>>>>>>>>> is the >>>>>>>>>>> culprit. >>>>>>>>>>> >>>>>>>>>>> I'll swap U17 once it arrives - and if that doesn't fix things >>>>>>>>>>> start shotgunning the passives. >>>>>>>>>>> >>>>>>>>>>> Thanks again for the guidance, very appreciated! >>>>>>>>>>> >>>>>>>>>>> - Gary >>>>>>>>>>> >>>>>>>>>>> On Tuesday, October 19, 2021 at 10:04:24 PM UTC-4 Tristan wrote: >>>>>>>>>>> >>>>>>>>>>>> Also the voltage between the cathode and the blanking section >>>>>>>>>>>> should be checked (I.e. the voltage across C51) and R65 and R67 >>>>>>>>>>>> should be >>>>>>>>>>>> checked (or potentially replaced along with C51 if shotgunning >>>>>>>>>>>> it). The >>>>>>>>>>>> rest of the high voltage supply appears to be working. >>>>>>>>>>>> >>>>>>>>>>>> - Tristan >>>>>>>>>>>> On Wednesday, October 20, 2021 at 11:50:56 AM UTC+10 Tristan >>>>>>>>>>>> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> I agree. The blanking is not working and as a result the beam >>>>>>>>>>>>> is also faintly visible as it moves quickly between the >>>>>>>>>>>>> characters as well >>>>>>>>>>>>> drawing the arcs. It would be a good idea to check the BLNK >>>>>>>>>>>>> signal on a >>>>>>>>>>>>> scope and at least see that is is toggling but my money would be >>>>>>>>>>>>> on the >>>>>>>>>>>>> analogue blanking section. Given the other side of the >>>>>>>>>>>>> optoisolator in the >>>>>>>>>>>>> blanking section is at a fairly high negative voltage potential >>>>>>>>>>>>> (as this >>>>>>>>>>>>> reduces the need for the deflection amps to handle higher >>>>>>>>>>>>> voltages) you >>>>>>>>>>>>> will need to be careful when probing around there but I would >>>>>>>>>>>>> start by >>>>>>>>>>>>> checking the voltages across C54 and C55 (as long as you are >>>>>>>>>>>>> confident >>>>>>>>>>>>> doing so safely with the HV potential to ground). The correct >>>>>>>>>>>>> voltages >>>>>>>>>>>>> aren't specified on the schematic but they will be based on the >>>>>>>>>>>>> grid cutoff >>>>>>>>>>>>> voltage of the tube. If you wanted to avoid probing while the >>>>>>>>>>>>> clock is on >>>>>>>>>>>>> I'd be inclined to shotgun replace that section starting with the >>>>>>>>>>>>> power >>>>>>>>>>>>> supply diodes, caps and Q13 and then U17 and finally the passives >>>>>>>>>>>>> and see >>>>>>>>>>>>> how you go. >>>>>>>>>>>>> >>>>>>>>>>>>> - Tristan >>>>>>>>>>>>> On Tuesday, October 19, 2021 at 4:24:11 PM UTC+10 iavine wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> From what I remember: >>>>>>>>>>>>>> the characters are generated from circles, ellipses or lines >>>>>>>>>>>>>> which in turn are created using sun or cosine waveforms >>>>>>>>>>>>>> To make a character the beam is blanked for certain parts eg >>>>>>>>>>>>>> C is a circle with a bit cut out. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Looks like the blanking is not working as you’ve got a lot of >>>>>>>>>>>>>> circles and ellipses there. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Looks cool though >>>>>>>>>>>>>> >>>>>>>>>>>>>> Cheers >>>>>>>>>>>>>> Ian V >>>>>>>>>>>>>> >>>>>>>>>>>>>> On 19 Oct 2021, at 06:08, Mac Doktor <themac...@gmail.com> >>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> On Oct 18, 2021, at 7:53 PM, Gary Kaufman <geka...@gmail.com> >>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>> I've now got a stable, but scrambled display (see pic's). I >>>>>>>>>>>>>> think I have a problem with the shape generators but would >>>>>>>>>>>>>> appreciate any >>>>>>>>>>>>>> help or suggestions you could offer. >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> Nah, that's just Cyrillic Neu Sans. >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> Terry Bowman, KA4HJH >>>>>>>>>>>>>> "The Mac Doctor" >>>>>>>>>>>>>> >>>>>>>>>>>>>> "If only you could see what I've seen with your eyes."—Roy >>>>>>>>>>>>>> Batty, *Blade Runner* >>>>>>>>>>>>>> >>>>>>>>>>>>>> -- >>>>>>>>>>>>>> You received this message because you are subscribed to the >>>>>>>>>>>>>> Google Groups "neonixie-l" group. >>>>>>>>>>>>>> >>>>>>>>>>>>>> To unsubscribe from this group and stop receiving emails from >>>>>>>>>>>>>> it, send an email to neonixie-l+...@googlegroups.com. >>>>>>>>>>>>>> To view this discussion on the web, visit >>>>>>>>>>>>>> https://groups.google.com/d/msgid/neonixie-l/3FBEDB26-E97C-44E2-B088-BDA7DAE4A020%40gmail.com >>>>>>>>>>>>>> >>>>>>>>>>>>>> <https://groups.google.com/d/msgid/neonixie-l/3FBEDB26-E97C-44E2-B088-BDA7DAE4A020%40gmail.com?utm_medium=email&utm_source=footer> >>>>>>>>>>>>>> . >>>>>>>>>>>>>> >>>>>>>>>>>>>> -- >>>>>>>>> You received this message because you are subscribed to the Google >>>>>>>>> Groups "neonixie-l" group. >>>>>>>>> To unsubscribe from this group and stop receiving emails from it, >>>>>>>>> send an email to neonixie-l+...@googlegroups.com. >>>>>>>>> >>>>>>>> To view this discussion on the web, visit >>>>>>>>> https://groups.google.com/d/msgid/neonixie-l/00c69936-4f04-4a88-8343-f2f7d860135fn%40googlegroups.com >>>>>>>>> >>>>>>>>> <https://groups.google.com/d/msgid/neonixie-l/00c69936-4f04-4a88-8343-f2f7d860135fn%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>>>>>> . >>>>>>>>> >>>>>>>> -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. 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