Modular Nixie Clock Rev3 keeps restarting

More
9 months 1 week ago #10483 by Ty_Eeberfest

jjansen wrote: Thanks for the explanation. Very nice to learn more about how things work!
No, unfortunately I don't have such a mosfet at hand. The current one is a IRF640, Vds is 200V, is this enough?


Oops, forgot that the kits now ship with a 640, not the 840 shown on the schematic. Ian made some changes to the HV generator calibration code a while back that eliminate voltage excursions beyond about 180V during HV calibration. Thus the 200V IRF640 is fine since the running voltage is about 170V. The 840 was only needed because HV calibration used to briefly run the circuit up to 230 (or was it 250?) volts.

If you were thinking of buying a new MOSFET there are many different ones that will work. You want to get one with specs generally similar to the IRF640 or 840, mainly these specs:

VDS >= 200v
ID max = at least a couple amps
VGS(th) max <= 4v
RDS(on) the lower the better (lower RDS -> runs cooler)

The reason I list those specs instead of just saying "buy an IRF640" is that if you're buying a MOSFET you might want to pick one of the newer ones with super low RDS so heat / heat sinks never become an issue. Or not... I don't mean to complicate things!

Look into it later when the dust is clearing off the crater.

Please Log in or Create an account to join the conversation.

More
9 months 1 week ago #10484 by Ian
I think the controller clock circuit is the problem. The controller is in charge of turning the MOSFET on and off, and if the controller clock stops (even momentarily), then the MOSFET might get stuck in an ON state. As Ty said, this shorts out the supply.

Please re-flash the solder joints around the crystal, the 22pF capacitors and pins 9 and 10 of the controller. Please take out the controller and then re-seat it, making sure that none of the pins are tarnished.

We can move on to the MOSFET later if that doesn't help.

Please Log in or Create an account to join the conversation.

More
9 months 6 days ago #10485 by jjansen
Ian, I took out the controller, brushed all pins, and re-flashed all solder joints of the controller, the 22pF caps and the crystal.
Still resetting.

When I touch pin 10 with an insulated screwdriver it also reboots / crashes directly. With pin 9 this is not really the case (or less). But I am not sure if this is 'normal' behaviour when touching pin 9/10 of an ATmega ;-)

btw, R18 measures 3 kOhms

Please Log in or Create an account to join the conversation.

More
9 months 6 days ago #10486 by Ty_Eeberfest

jjansen wrote: When I touch pin 10 with an insulated screwdriver it also reboots / crashes directly. With pin 9 this is not really the case (or less). But I am not sure if this is 'normal' behaviour when touching pin 9/10 of an ATmega ;-)


Normal? Maybe. In my experience it depends a lot on what your other hand is touching, whether or not your body is grounded, and so on. The caps and crystal form sort of a tuned circuit running at a pretty high frequency, so body capacitance and conductivity can easily upset it. In short, crashing when those pins are touched doesn't necessarily mean anything.

I am rather stuck at the moment. If you have any other observations let me know! I imagine Ian will be checking the forum in a few hours so maybe he will see something I am missing.

Look into it later when the dust is clearing off the crater.

Please Log in or Create an account to join the conversation.

More
9 months 6 days ago #10487 by jjansen
I would guess that the next step would be replacing the mosfet?

Please Log in or Create an account to join the conversation.

More
9 months 6 days ago #10488 by Ian
I have seen this once or twice in the past: When it has appened, I have solved it by replacing the 22pF caps and the crystal. I don't know which of the components it is really due to. I'll send you a replacement set of the suspect components. Please try to replace the 22pF first (this is my first suspect) and then if that does not work, the crystal as well.

As I always repeat: if you are taking something off for replacement, sacrifice it. In the case of the 22pF caps, cut the body off and remove the leads individually.

Please Log in or Create an account to join the conversation.

Moderators: AccutronTy_EeberfestIan
Time to create page: 0.169 seconds

Search

Tube Suppliers

Go to top
JSN Boot template designed by JoomlaShine.com