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. 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/e09371dd-6503-4d38-bcde-5e30e81a35dcn%40googlegroups.com.
