The default display brightness is fairly dim, and in a bright room, the display can appear as if it is inactive. I recommend reducing the amount of ambient light when testing the tube. I do trust your observations, but I have also witnessed intelligent people mistake a working clock for one with no display in a well-lit work environment. Just something to be aware of.crispytwo wrote:...my display is dark.
I have not personally tried this solution, but remember another forum user trying it successfully about a month ago. If I can find the time this weekend, I will do this myself, and post the results here.crispytwo wrote:I also attempted the long jumper wire in case that would help -- It didn't in my new circumstance. :-( -- However, I did see " .. b. b. " faintly. I've remove the wire and spent time devising the above.
I think 12v is fairly typical, despite the troubleshooting information. I can say with certainty that 12v is enough to drive the display.crispytwo wrote:I went through the standard trouble shooting and came to this measurement:When I tested this and I'm getting 12.6v at D3 -- which seems potentially too low.Low Boost Voltage.
With no tube or VFD chip installed, you should measure between 40 and 70v on the striped end of D3. With a VFD chip installed, you should measure approximately 14-16v.
This looks like the problem. The Q3-R3 connection is where the MAX6921 VFD driver chip draws power, and the MAX6921 needs at least 3.0v for reliable operation. There's a good bit of manufacturing variation among IV-18 VFD tubes, but I would put the absolute minimum filament voltage in the 1.8v to 2.5v range.crispytwo wrote:@PhilD13
In reference to 'Russell 27' method, it seemed to me that he is testing the voltage drop across the resistor R3 to ground.
So, my in-circuit voltages (with the tube connected):His values were 4.26V and 2.96V respectively (although his are measured at 70 brightness -- which I expect that mine is the default 30)
- connection at Q3-R3 is 1.97V
- connection at R3-tube is 1.19V
For the moment, there still seems to be a problem with Q3. I would recommend taking Adafruit up on their offer of a free ZVP2110A, and then test that with your solder-free test setup. That would also rule out the possibility of Q3 heat damage from all the board rework.crispytwo wrote:Is there anything I could test to show that the VFD chip is damaged?
Or test that the voltage coming into or out of it is incorrect?
Is it possible that the tube failed?
I know you've already tested your repaired board traces for continuity, but perhaps you could check them for resistance also. A dodgy connection or damaged trace with high resistance could explain the unusually low voltages you see coming from Q3.
I would only look for a different problem once you know Q3 is working properly, and right now, it doesn't seem to be.
Since it's the same clock with the problem, I think it's appropriate to continue posting to this thread.crispytwo wrote:I'm wondering if I should start a new thread since it is no longer the original problem?
When you jumper Q3 now, what is the voltage at the jumper? The R3-tube connection?crispytwo wrote:Now the jumper has no positive effect. This leads me to believe that I screwed up something else.
If you look at the schematic (below) or board design (posted earlier), you'll see that output of Q3 powers both the tube and VFD driver chip:crispytwo wrote:It is good to know that the transistor voltage is only the filament.