Voltage regulator burning out

[Tommygun011198]

Hi all,

Ive been having an issue with a clone of the hydra - i drew this up in diptrace and ordered some boards from JLC. Side note that this is a one off gift for a friend lol

I already have a hydra i built with a PCB from pedalPCB, and i managed to get this one working just the same until the voltage regulator burned out.

I replaced the regulator and it burned out again, shorting itself in the process. I noticed that the silkscreen for the regulator (IC4 in the centre) might have been reversed compared to the pinout so i added a new regulator inverted but i just get a horrible loud buzzing - this was a bit of a hail mary as the circuit had been working just fine so i dont know whats causing this issue.

I thought it might be that the ground pin of the regulator isnt attached to a ground plane and so it doesnt have a decent heatsink, can anyone confirm if this is indeed the issue or if they have any other suggestions?

Any help would be appreciated!

Many thanks,
Tom

 

[finebyfine]

Your regulator is laid out backwards as you suspected. The ST data sheets are so counterintuitive and I’ve made the same mistake before and still triple check when using them. Not only is the TO-92 oriented in the way opposite of what we usually see, it’s also upside down. I imagine that the time the circuit was working was just the time it took for the components to fail.

Did you only replace the burned out regulator when you tried to reverse it or did you repopulate a new PCB?

If the former, I would guess that the regulator failing also damaged something else in the circuit but if it’s the latter I don’t see an obvious reason why. At the current draw of the circuit I wouldn’t suspect the ground plane or trace width to cause a failure - I wouldn’t recommend using a trace for ground personally but if you throw the values we use in pedals into a trace width calculator, even using the smallest size JLCPCB will fab is still sufficient most of the time.

 

[Tommygun011198]

Your regulator is laid out backwards as you suspected. The ST data sheets are so counterintuitive and I’ve made the same mistake before and still triple check when using them. Not only is the TO-92 oriented in the way opposite of what we usually see, it’s also upside down. I imagine that the time the circuit was working was just the time it took for the components to fail.

Did you only replace the burned out regulator when you tried to reverse it or did you repopulate a new PCB?

If the former, I would guess that the regulator failing also damaged something else in the circuit but if it’s the latter I don’t see an obvious reason why. At the current draw of the circuit I wouldn’t suspect the ground plane or trace width to cause a failure - I wouldn’t recommend using a trace for ground personally but if you throw the values we use in pedals into a trace width calculator, even using the smallest size JLCPCB will fab is still sufficient most of the time.

Thanks so much for the response! yeah I found that the pinout diagrams for the L78L33 voltage regulator aren't all that obvious, definitely going to be double checking from now on!

When the circuit was working it worked for about half an hour before I turned it off. It was only after I boxed it up, attached the jacks and footswitch and went to test it that it decided it didn't want to live anymore - does this change anything?

When trying to solve the issue I was only replacing the voltage regulator, so I'll try to check a few other components and see what I can find, if not I'll populate a new board. From looking at the schematic do you have any idea what components might have failed?

Thanks for the help!
Tom