Nixie Clock

[elchucko]

I have an IN-12 VFD clock I assembled from a kit a few years ago. Recently after a loss of ac power to my home the clock circuit would overheat and shut down the clock. There are 2ea MC34063A ICs in the circuit that get very hot. If I set the brightness of the IV-12 display tubes to half the circuit runs cooler. After removing all tubes voltages test OK. As I plug in each tube the Mc34063A ICs get warmer and warmer as additional tubes are plugged in until the ICs are too hot to touch. Can you assist? Thank you

 

[Gryd3]

sounds like a current draw issue, the simplest method I can think of is the addition of a heat-sink.

 

[davenn]

elchucko
welcome to the forums

I'm assuming it hasn't always been getting so hot like this ?
but it's only been occurring since the power cut ?

Its possible a component has been damaged by an excessive voltage spike when the power was restored

a circuit diag and a photo or 2 of the unit would help

cheers
Dave

 

[KrisBlueNZ]

Hi and welcome to Electronics Point

As Dave says, it's reasonable to assume that something was damaged by a voltage spike.

I would suspect the MC34063s first. It's also possible that the output diodes were damaged; these are connected between pin 1 and the output smoothing capacitor on each MC34063.

(Gryd3, the MC34063 is a DIP-8 and can't really be heatsinked.)

If you can provide a link to an online copy of the schematic diagram, or upload one as an attachment to a post in this thread, we may be able to suggest other components to check or replace.

 

[elchucko]

Attached is the schematic of the clock. I've added a heat sink to IC 3 and IC4. I've set the display brightness to about midpoint (value of 1 thru 10). I have R2 jumpered as it opens with display set at 10

 

[KrisBlueNZ]

Have you replaced the MC34063s? They're cheap and still readily available. They would be my first suspect.

 

[elchucko]

This may be a (stupid) question. What if I "piggybacked" each IC with another? Would that handle the load better?

 

[KrisBlueNZ]

This may be a (stupid) question. What if I "piggybacked" each IC with another? Would that handle the load better?

No.
Hey, I have a question...

I would suspect the MC34063s first.

Have you replaced the MC34063s?

HAVE

YOU

REPLACED

THE

MC34063s

???

 

[elchucko]

No but I'll order some today

 

[elchucko]

I'll install MC33063. Better heat range.

 

[KrisBlueNZ]

Knock yourself out

 

[elchucko]

The MC34063 is soldered on the PCB. When I remove the IC I plan to use an 8DIP socket and insert the MC33063. Is this a good idea or (because of heat) not?

 

[KrisBlueNZ]

Is it IC4 you're replacing? That one shouldn't even get warm. You could use an IC socket for it.

BTW when you're removing the old one, cut off the leads one by one with a side cutter, flush with the sides of the IC. It's a lot easier to remove the leads individually than to try to remove the whole IC. Then solder-suck the holes. Sorry if this was already obvious to you.

 

[elchucko]

Thank you!