Jenny Reloaded problem :(

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2 years 5 months ago #7129 by Pacman223
Hi everyone. I built a Jenny re-loaded about 6 months ago.

nixiekits.eu/

I thought everything was good, until a couple of weeks ago, and it just stopped working. The back lights would come on, but not the Tubes.

in opening it up, I found the C-13 was blackened and looked bad.. I got a replacement cap and replaced it.. turned it back on and everything looked good.

about 1 - 2 hours later, the clock failed again. This time C-13 looks fine. but t-2 gets instantly hot when plugged in.. soo hot as to burn you. I might try to replace it, but since it was working with c-13 replaced, I don't know that t-2 is really the issue, and I'm thinking I might need to replace something else.

I e-mailed Jürgen (Mr Nixie) and he might be able to help. But I know there are lots of very smart people here that might know what might have happened.

I would be grateful for any ideas of what I might be able to do to fix the clock.. I really LOVED the clock.. if I can't fix it, I'll have to replace it.

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2 years 5 months ago #7130 by Pacman223
Ok..

more information.. after writing the above, I took the clock apart again, I noticed when I replaced c-13 I shorted it out :(.. I bet I ruined T2.. and it needs to be replaced.

next question about t2.

T2 is described as
RFD3055L MosFet DPAC

is that the same as this mouser part?
512-RFD3055LE
?

Thanks,

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2 years 5 months ago #7133 by Ty_Eeberfest
That Mouser part certainly looks like an identical replacement for the original mosfet. I suspect the E on the end is something specific to Fairchild that doesn't matter here.

More to the point I'm puzzled about 2 things:

1) Why would C13 burn in the first place? It's not like it's passing any current worth mentioning or seeing high voltage across it. Voltage at that node should be 47vdc per the manual, that's nothing to a ceramic disk cap.

2) If you shorted out the replacement C13 how did the clock manage to work for several hours? If truly shorted, the short takes your HV straight to ground = no HV at all!

So I'm not quite sure what to say. Because of point 2 above I'm not quite convinced there was a short. Though I must say, T2 getting hot certainly suggests some sort of excessive load on the HV, like maybe a short.

Overall, I think you better wait to hear back from Jürgen on this one. That note in the manual about de-soldering parts from the 4-layer board has me nervous because I'm not quite sure what he means... and then it says to see de-soldering tips at end of manual but there are no tips that I can see...

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

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2 years 5 months ago - 2 years 5 months ago #7136 by Pacman223
Ty,

Thanks for your quick reply.

I wonder if I have one of the resistors near c-13 wrong...

In looking at the diagram, I'm now wondering if I messed up in a resistor. I wonder if putting in a resister of the wrong value caused added stress to the original c-13 cap? thats why it burned up? those ceramic caps don't usualy go bad do they?

I will check them when I get home from work today.

I'll order a new T2 today also.. just in case that is the issue. (I can't beleive how much I miss that clock now).
Last Edit: 2 years 5 months ago by Pacman223.

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2 years 5 months ago #7138 by Ty_Eeberfest
If you got R4 and R7 swapped it would never have worked in the first place. If the boost converter managed to run at all it would put out something like 1/20 of the expected voltage, which would not light up the tubes.

You are right that ceramic disk caps don't often fail and especially don't burn up. However... having said that I just took another look at the parts list and realized that C13 is NOT an old school ceramic disk like I thought. It looks more like an MLCC type which will not have the insanely high voltage rating of an old school ceramic. Small MLCCs can have really low- to medium-voltage ratings. See for example this: www.mouser.com/catalog/catalogusd/648/1099.pdf The voltages range from 6.3 to 200, so IF C13 is a 50V cap and IF the high voltage was running a little bit above spec, the it becomes at least conceivable that C13 could burn.

It looks like the purpose of C13 is to get rid of whatever high frequency noise makes it past C5 / C6. While the DC voltage should be 47v it's hard to say what the peak voltage of the noise could be. Looking at the HV test point with a scope could prove interesting.

Lastly. If it was my clock this is what I'd do. Remove C13 and clean up so there is no short. Plug in the clock and see if it works. If not, replace T2. If it does work, get a 0.1u 200v capacitor and install it in C13's place. Then I'd probably put a scope on the high voltage as mentioned so maybe I could figure out why it broke in the first place.

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

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2 years 5 months ago #7143 by Pacman223
after cleaning up c13 still, the clock still doesn't work.

T2 gets instantly super hot

I have its replacement on order.. as soon as it gets here I'll replace it.

I'm still worried that I mixed up one of the resisters. when I replace T2.. I'll check all the resisters around it.

Thanks for your advice Ty.. I might have been better off with a higher voltage c13 cap?

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2 years 5 months ago #7145 by Ty_Eeberfest
I guess we'll see what happens when you get a new mosfet. Somehow getting super hot sounds more like a mosfet that's being overloaded badly - by driving into a short maybe - than like a bad mosfet.

The warnings in the manual about de-soldering parts from the 4-layer board still nags at me too. Not sure what he had in mind, wish he would drop in here and tell us.

With power off of course, check the resistance from the HV Test Point to ground and let me know what you get.

I can't say much about the voltage rating of C13 since I have no idea what the voltage rating of either the original or the replacement was. 100v or higher would be ideal, but I can see where there would be a temptation to use a 50v since it would be smaller and maybe cheaper. In theory a 50v should work but since the working voltage of the circuit is 47v that leaves basically no headroom, margin for error / drift / whatever.

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

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2 years 5 months ago #7146 by lcc
HI
i know that your clock has being running ok for some time
i can remember when i built one of these clocks i had trouble with the super cap it was solders to close to the board and solder had built up under neath it and shorted out stopping the clock from working just thought i would mention it just in case you had the same problem and it has only just started to give you trouble

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2 years 5 months ago - 2 years 5 months ago #7147 by Pacman223
I'm working on it tonight

The ground to high voltage reading is .723 k ohms.
(odd reading.. but I think that tells me something isn't exactly right.

I had to halt working on it until later tonight. (family needing my attention). but I received the T2 replacement from Mouser (they were very fast).

I think I'll check the resistors to see if I may have mixed one of those up originally, replace t2, and see where that takes me.

I'm worried about un-soldering the T2, but I don't think I have much of a choice on that.

Thanks I'll keep everyone informed on how this works.

oh.. when replacing c-13.. I believe it was 50v. ceramic cap.
Last Edit: 2 years 5 months ago by Pacman223.

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2 years 5 months ago - 2 years 5 months ago #7148 by Pacman223
bad news.

after replacing t2.. which I worry I damaged one of the t2 holes getting the new part in...

the clock still does not light up.

HV -> Ground reads 5 v

very odd reading.. on R4 (22k resistor).. measuring just that resistor.. while in the clock reads 1.7k ... yea very odd...
removing R4.. still reads 1.7k .. i.e. nothing in the resistor's place, measuring from pin hole to pin hole.. .. which leads me to believe there is some sort of short..

measuring R4 outside of the clock.. reads 22k.. all other resistors read correctly

Short of some sort of miracle I don't think the clock will work again :(.. which is REALLY sad..

As a last measure.. I even got my wife involved (she has a bs in electrical Engineer, but hasn't messed with circuits since collage).. she can't figure out how r4 would read 1.7k resistance with nothing in place (I try not to bother her too much, she doesn't like me building Nixie clocks much, and gets really grumpy when I talk to her about them).
Last Edit: 2 years 5 months ago by Pacman223.

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