Problem with STEPS - something died

[RHMMMM]

I built a STEPS a few months ago and it has been running fine, plugged in 24x7 for ~4 months and all of a sudden yesterday, it just stopped working.

I need some help as I'm not *that* good with diagnosing problems with my own DIY electronics, but I was able to build both the PPA and STEPS so far.

I got out the 'ole multimeter and the test points 1&2 and 3&5 are showing the right voltages but 4&5 are not - the LED isn't on and the pin from the bottom of the voltage regulator & TP5 (like 22mV, which is the same as the output to the cable, of course) Nothing visibly looks wrong with any of the components and I tested all the resistors and they are fine, but beyond that I don't know what to do.

I assume so far that my voltage regulator has up and died on me. What else should I look for and test?

 

[yokoda]

From Tangents STEPS Assembly Guide:

"Next, measure DC volts between test points 4 and 5. This is the output voltage of the regulator."

So I guess it sounds like your regulator died. I've just finished my STEPS and I was curious as to why the heatsink is so hot when running for 10 mins or so. I can only touch it for a few seconds before it starts to hurt. Was yours running as hot as this? I guess if it was, it possibly burnt itself out. Possibly a nice surprise is instore for me in the future.......

 

[tangent]

Quote:

it sounds like your regulator died

I agree.

The LM317 isn't indestructible, especially the off brands. I killed a Fairchild LM317 the other day.

While you're working on the board, test the protection diodes to make sure they're still good. If they've been killed, a dead regulator is "collateral damage".

Quote:

I can only touch it for a few seconds before it starts to hurt.

How much current are you pulling from the supply? How high is the unregulated voltage?

Given those two values and the thermal resistance of the heat sink (3.7deg/C, as I recall), you can calculate the temperature the heat sink is supposed to be. (See the LT1086 datasheet for a very readable explanation that applies to all linear regulators.) You can reduce heat sink temperature by reducing one of those two values.

EDIT: You can also reduce the temperature by raising the output voltage to be closer to the regulator's dropout voltage. If that's practical in your situation, it's probably the easiest thing to do.

 

[RHMMMM]

Yep, I had some more time this morning to play with it - sure enough it was the voltage regulator. Put a new one in there and it works now.