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/a94090c0-4c5c-4710-b9f7-a0736acc0947n%40googlegroups.com.
