So another possibility is that one of the amplifiers is clipping, usually because the input signals are trying to drive the output beyond the supply rails. BTW, most op-amps are not rail-to-rail, but they can get pretty close. It will show up quickly on a scope.
On Saturday, June 22, 2024 at 3:35:15 PM UTC-7 Dekatron42 wrote: > So what happens if you put this Teensy in the other working board, does > the error follow the Teensy? > > If so, have you tried to reprogram the Teensy or even erase it to set it > to its original setup condition? > > /Martin > > On Saturday 22 June 2024 at 22:48:49 UTC+2 Max DN wrote: > >> @Martin, if I try to bypass the DAC using POTs for NEG5 and POS5 it all >> seems fine (the dot goes across the whole X axis and Y axis). >> @gregebert, no Z-axis. >> >> I am probing X and Y just out of the DAC and not connected to anything >> else. I can see the image on the oscilloscope as a full round circle, but >> as I try to center it to what would be the center of the CRT then thr >> circle flatlines. >> >> It feels as though past a certain point on the vertical axis, the dots >> are just collapsing into the same line and cannot go past (on one end of >> the Y vertical axis, X axis is fine). >> >> Very odd as I have already used same code and same pcb for another scope >> clock. After 10 hours on it today, I'm going to let go until I have any >> other ideas. I have tried replacing the processor, the DAC (3 times), >> checked all resistors and bypass caps and triple checked all soldering >> points. Maybe it's time to bin this pcb, but I do like a challenge! >> >> >> Il giorno sabato 22 giugno 2024 alle 16:38:19 UTC+1 gregebert ha scritto: >> >>> Is there a Z-axis ??? That would be my first suspect; if the trace is >>> still visible, then the appropriate grid needs to be driven a bit more >>> negative. >>> >>> If the CRT uses rapid movement for dark (technically dim) regions, and >>> slower movement for bright regions, then my best guess is some kind of >>> software tweak would be needed to get the beam to move faster, or off the >>> phosphor-coated area (or both). >>> >>> On Saturday, June 22, 2024 at 3:49:04 AM UTC-7 Dekatron42 wrote: >>> >>>> Can you remove the processor and feed the amplifiers directly from a >>>> potentiometer connected to NEG5 and POS5 and see how the dot moves on the >>>> screen? You need one potentiometer for X & Y so that the dot will appear >>>> on >>>> screen. This way you will test out the amplifier chains without the DAC >>>> involved. >>>> >>>> /Martin >>>> >>>> On Saturday 22 June 2024 at 12:10:54 UTC+2 Max DN wrote: >>>> >>>>> Martin, that's what I am thinking... however I don't think it's the >>>>> amplifier chain as I get the same issue if I just display X and Y signals >>>>> straight out of the DAC on the oscilloscope. That brings it down to a few >>>>> components only: 2 potentiometers for centerting X and Y, their two >>>>> bypass >>>>> capacitors, the DAC and its 1 bypass capacitors, the +3.3V Linear >>>>> regulator, the +5V supply to the DAC. I'm going to try and replace >>>>> everything once more by one by one... Not the smartest way of doing it >>>>> but >>>>> let's see what it brings... >>>>> >>>>> Il giorno sabato 22 giugno 2024 alle 11:01:12 UTC+1 Dekatron42 ha >>>>> scritto: >>>>> >>>>>> Could it be the that any of the power lines sags as the signal tries >>>>>> to increase to the right (in the picture right where the line is) or >>>>>> that >>>>>> any of the resistors in the amplifier chain has an incorrect value? >>>>>> >>>>>> /Martin >>>>>> >>>>>> On Saturday 22 June 2024 at 11:32:21 UTC+2 Max DN wrote: >>>>>> >>>>>>> Tried to replace a few more parts, including potentiometers for >>>>>>> Focus and Intensity, made no difference. So, back to basics: using an >>>>>>> oscilloscope I see that the X and Y signals straight out of the DAC >>>>>>> look >>>>>>> exactly the same as in the picture I had attached. Maybe a faulty DAC? >>>>>>> Tried to replace the DAC twice with new ones and made no difference. >>>>>>> Looks >>>>>>> like I'm hitting some sort of physical limits... More debugging to do... >>>>>>> >>>>>>> Il giorno venerdì 21 giugno 2024 alle 18:31:51 UTC+1 Max DN ha >>>>>>> scritto: >>>>>>> >>>>>>>> Hello, >>>>>>>> >>>>>>>> I'm building a scope clock, same board as another one I built >>>>>>>> before with no issues (after some help I got on this group, thank >>>>>>>> you!) and >>>>>>>> I'm getting a flat line on the display. >>>>>>>> >>>>>>>> I have tried replacing the CRT, the DAC, the Op Amps and the MPSW42 >>>>>>>> deflection amplifiers but made no difference. CRT is 3RP1A. Code and >>>>>>>> circuitry have been fully tested on another working board. >>>>>>>> >>>>>>>> I do recall having a similar issue before with a DH3/91 CRT and I >>>>>>>> seem to recall that I just needed to adjust the pot for Astigmatism >>>>>>>> that >>>>>>>> controls the voltage on A2. Schematics as in here: >>>>>>>> http://www.cathodecorner.com/sctv/sctv-schem-2.png >>>>>>>> >>>>>>>> I'm a bit at a loss here, although I'm sure it's something simple >>>>>>>> that I'm missing. >>>>>>>> >>>>>>>> Pic attached. >>>>>>>> >>>>>>>> Any suggestions welcome, >>>>>>>> >>>>>>>> Max >>>>>>>> >>>>>>> -- 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/bf0395e2-308c-4f60-b210-6877d527cb98n%40googlegroups.com.
