Given how far you have gone I'd lift pin 2 of U17 (leaving it unconnected) and measure the grid voltage. Then connect PIn 2 of U17 to POS5D and measure it again. The voltage should be more positive with the pin connected to POS5D. That would answer one and for all if the grid control is functional. It would also help to know which CRT model you have. On Thursday, October 28, 2021 at 12:39:19 PM UTC+10 GEK wrote:
> I'm getting approximately: > Astig +124v > Focus/A2 -852v > Cathode/Bright -1210v > Grid -1262v > > The manual suggests that the Brightness has about -1300v, focus about > -900v and Astig +300v > I can adjust the Astig from 0 - 240 but the image is sharpest at 124v. > > - Gary > > On Wednesday, October 27, 2021 at 10:48:16 AM UTC-4 GEK wrote: > >> 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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