Electronics > Repair
Power Input to Noritake Itron VFD GU128X64-800B seems shorted?
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qcarver:
Hello All.

The story: I found a convection oven out-back next to a grease dumpster. Eeprom had a `Dunkin sticker on it. SOOOPER greasy, took it home dissasembled. Found (see subj) cleaned it gently w/ dishsoap and a fine brush, then later rubbing alcohol. Left to dry for a week. Tried to power it with 5VDC from a liberated ATX power supply. Nope, noth'n! I start poking around and find that the 3 pin power connector 5V and DC seem to be shorted.

The questions. I'm a sw guy but not afraid of tinkering in hw. I have used two different meters (connectivity and ye olde beep mode on multimeter.) If power and ground are shorted, they are shorted right? I mean, I'm not charging caps "C33" or "C34" (see pic) right? So this is bad right? Is there some classic thing that might be a problem? FUSE1 and FUSE2 (pic) are conducting okay. Ideas. I mean, it could be some grease somewhere, but as you can see - she cleans up nice. Thanks a ton.



QC

https://www.eevblog.com/forum/repair/noritake-display-dead/?action=dlattach;attach=137475
macboy:
Seems like your continuity tester is backwards, with positive on the gnd. Many ICs will present a short circuit when connected backwards. Also keep in mind that a basic continuity tester is a very simple device with a simple output, don't assume that if it lights up, there must be a short circuit.

I have used several Noritake VFD displays (but not this exact one), and none of them show anything on the screen when only powered up. You need to send the commands to initialize the display and some data to be displayed.
qcarver:
Hello, thanks. So I took your advice and assumed I just wasn't getting the GPIO data right. Lol, lead to me buying a 4-channel scope and reeeeeally getting to know the spec sheet. Alas. no phosphor is excited.

So... I went back to the scrap heap where the rest of the convection oven was, and cleaned up the CPU and the connected it to the VFD and the front panel. I also probed the power supply to see what was expected. Bear in mind that the VFD connects to the CPU board with both a 26-lane ribbon cable and a two wire power line. I checked that it was 5 Volts.

My thinking was, if the CPU still works and even it can't drive the VFD then the issue is w/ the VFD hardware. video: https://drive.google.com/file/d/1A_RRZevqIPgm2I1jqORPFBvMSUdyTUnP, you can see the CPU is working b/c it responds to keypresses, alas, no gorgeous VFD blue-ness was to be seen.

I started probing and scoping the VFD, and here's what I notice. Hopefully I can get some advice on this. The 21 or so pins that go from the Noritake backing board to the phosphor matrix DO SHOW BEAUTIFUL SQUARE WAVES at 5 volts! Yay! However, the 3 pins on either side that excite the mesh show no voltage at all. Typically w/ a VFD those alternate a higher volrage... like 17? Volts DC.

So my question is, do you have any ideas how to repair the power supply? I guess I could go through and readup on all the components I see on the back. Maybe there is a quicker way?
macboy:
The 3 pins on either side if the VFD glass are for the filament, not grid. This should be powered by approximately 3 or 4 volts AC, not DC (though rarely it is DC). You need to measure the voltage with AC mode, as it will likely show zero in DC mode. And it's likely that the DC-AC converter operates at a few kHz, so the meter needs to be have at least several kHz AC bandwidth. Many modern cheaper meters go to about 1 or 2 kHz, not high enough.
qcarver:
On a scope, yeah, there is around 4-to-7Volts of excitation running about 7kHz. Interesting that most of the time captures look like the top picture but about 8 times a second I see the ringing that is in the bottom picture (see attachment.)

Settings are AC coupled Probe 1 goes to the left side trio, and Probe 2 goes to the right side, I also connected the scope ground to ground line - wasn't too sure what AC means in this case, but ground wire doesn't seem to change anything.

So to review, I have data on the parallel inputs to the glass and I have excitation on the filament inputs. Still no blue magic. Does that excitation look okay? and more thoughts? -thx
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