Voltage Increase, failed component?

[shakalnokturn]

Had another look and the lm7805 regulator seems to be getting very hot.. could this be a symptom of it failing and drawing too much current? Or is it more likely to be a failed component on the 5v rail?

Bearing in mind the 5v side is working perfectly

In my experience statistically (not exclusively) it's down stream from the regulator and should show as heat.
If it is the regulator by itself it should be even easier.

[fzabkar]

Had another look and the lm7805 regulator seems to be getting very hot.. could this be a symptom of it failing and drawing too much current? Or is it more likely to be a failed component on the 5v rail?

Bearing in mind the 5v side is working perfectly

Being a linear regulator, there would be a 7V differential between input and output. A load current of 140mA would dissipate 1W in the regulator.

Meaning..?

I'm just saying that it doesn't take much current to heat up the regulator, so a warm regulator may be normal.

[ajp8868]

So, I thought I'd made great progress. I found a shorted smd capacitor!

I couldn't find any 10uf caps on my donor boards so I went for a 5uf thinking it might not make much difference and might get it at least working.

Slight success.. I got the pan/tilt working!

However none of the other steppers are working now!!

Could it be that cap..? I've circled it on the attached image - could 5uf make that much difference??

[ajp8868]

Had another look and the lm7805 regulator seems to be getting very hot.. could this be a symptom of it failing and drawing too much current? Or is it more likely to be a failed component on the 5v rail?

Bearing in mind the 5v side is working perfectly

Being a linear regulator, there would be a 7V differential between input and output. A load current of 140mA would dissipate 1W in the regulator.

Meaning..?

I'm just saying that it doesn't take much current to heat up the regulator, so a warm regulator may be normal.

Ah that makes sense, yeah they both get hot, this one just gets a tad hotter. It's working though so wasn't the fault.

[ajp8868]

So it seems that a 74HC04 has now blown which I believe is from me disconnecting a stepper driver while powered up... I'm not exactly sure of it's function but it definitely is controlling these steppers.

Swapped one from a working board and it seems to have sorted it (for a brief moment until I pulled a stepper driver while powered on again, which is how I know that was the cause of it blowing)

Ordered a couple of replacements and a new driver chip, so I'll keep you guys updated!

[shakalnokturn]

Well it can't have been a dead short surely? If it was is there more than one linear regulator for the 5V supplies?
I doubt 5μF is enough to make the difference but then again if the 5V regulator has been running hot for ages it may not be giving the optimal output any more.
Ideally you'd measure DC voltage and ripple or scope at the capacitor pins (CPU decoupling I assume) .
If in doubt you can always stack a second 5μ on top of the one you fitted.
As for other steppers... Re-check wiring, I'm the first to neglect obvious things when rushing to test after replacing components.
Are the other steppers controlled by the same CPU?

[ajp8868]

Actually you're right, it measured a very slight resistance so not fully dead short. But when measured out of circuit it had no capacitance (DMM) and my little ESR tester thought it was a resistor.

What would I be looking for when measuring ripple at the caps? Sorry for noob question but I don't have a scope yet, bidding on one so finger crossed.

Fairly certain it's not wiring as it broke as soon as I removed the stepper controller, while live, for the second time. This unit was fully working, I've swapped the board into it to rule out things like wiring, motors etc.

[ajp8868]

Just to update, light is now fully working!

So I think the original issue was simply that capacitor, and I've just blown chips by unplugging steppers while powered up.

Replaced one 74HC04 which fixed colour/gobo and then replaced the other which was causing issues with prism and gobo rotate.

Thank you for all your help and suggestions. Another light saved from landfill!

[shakalnokturn]

As for the ripple question it's a bit of a tough one...
When scoping a power rail you wouldn't want the min / max values too close to the absolute min / max supply values stated for correct operation of any device powered by that rail.
For 5V or 12V rails on a linear regulator I'm usually satisfied with 10-15mV RMS or 100mV p-p but then again it depends where you measure.
Such values won't be acceptable for a 1.8V rail though.
It really depends on system requirements... You wouldn't tolerate the same amount on an instrumentation amplifier as on your stepper motor supply.