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/ >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> ~ >>>>>> *[email protected]* >>>>>> >>>>>> >>>>>> On Wed, Oct 20, 2021 at 4:16 AM GEK <[email protected]> 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 <[email protected]> >>>>>>>>>>>> wrote: >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> On Oct 18, 2021, at 7:53 PM, Gary Kaufman <[email protected]> >>>>>>>>>>>> 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 [email protected]. >>>>>>>>>>>> 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 [email protected]. >>>>>>> >>>>>> 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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