troubleshooting method for micro-controller board ?

that you are not

rail. So now that you

(was it ?), can you

place ? Measure the

if you get a

(but the

to GND. The LM317

operating current of

enough to draw

OUT pin, or

whew , less complications is a welcome occurance to me more good news please thanks, rob

Ignore all that.

1. As Arfa suggested, isolate the L387 output from the 5V rail. (Probably doesn't matter if you lift Pin 5 or disconnect some other way.)
2. Replace the 5V fuse (and only that fuse? or do you also need the 30V fuse to feed the L387?).
3. Power up.
4. If the fuse didn't blow, measure the voltage from Pin 5 to Pin 3 of the L387 (5V OUT to GND).
5. If you got ~5V, reconnect the 5V rail and test again. If not, connect a 470-1k ohm resistor from Pin 5 to Pin 3 and test again.
6. If still no 5V, measure the voltage from Pin 1 to Pin 3 (Vin to GND)

- it should be ~30V.

1. If ~30V was present on Pin 1, the L387 is bad. If not, the 30V bridge is probably bad.
2. If the fuse(s) blew, test the resistance of the bridges.

TM

Pin 3

not,

again.

to

thanks TM,

i'll try that tonight.

thanks, robb

Have you looked at the bridge rectifier and filer cap before your regulator?

wrote

your regulator?

yes, that was the first thing i considered just because it was there next to the fuses

i desoldered the bridge and then

i tested the bridge by using diode tester on the DMM so i chose the combination of pin checks that tests each of the diodes AC1 to (+) .,AC2 to (+), (-) to AC1, (-) to AC2 and each gets ~.596 (+- .007) volts till turn on

and there is no "continuity" between aany combo of bridge pins

thanks for help and reply, rob

Yes. All agreed. This is basically the first set of tests that I was suggesting, which Tony has usefully now converted to specific measurement points for you.

Just to try to help you understand the points about the regulators that we were making. Without being too 'blanket', there are two types of linear regulator chips in common use. These are fixed, and variable. The fixed ones are typically three pin, IN - GND -OUT, and come in many different voltages eg 5v 8v 9v 10v 12v 15v and so on. They come in both positive and negative flavours. In general, they don't care too much whether their output pin is loaded or not, but they do have a minimum load figure specified to

The variable ones also often have just three pins, such as the LM317, but sometimes have more. The main pins that are generally of any concern, are IN - SET - OUT. The output voltage is determined by a potential divider comprising two resistors, one strung between OUT and SET and the other between SET and the circuit common ground. By altering the ratio of the two resistors, any voltage to within a couple of volts of the input, can be set as the output. Clearly, for this setup to work, the 'top' resistor of the voltage-set divider, *must* remain connected to the output pin. What Tony was saying, is that if you just disconnect the output pin from the board, you will also be disconnecting it from the v-set resistors, which could lead to all manner of nasties ...

The good thing about these regulators is that they are pretty bomb-proof. They are safe area protected, short circuit protected and thermally protected, and will go into a voltage foldback condition if any anomalies in their operating conditions are detected. That is not to say that they don't fail themselves. They do. But often, the measured conditions, particularly the parameters measured by the Mk 1 finger-thermometer, are a big clue to what's going on. Example. 5v fixed regulator - say a 7805 1 amp version. Measured output voltage 1.8v. Measured device temperature, using Mk 1 finger = Ouch. Conclusion ? More than an amp is being drawn, the device has overheated, and gone into thermal voltage foldback, to keep within its SOA. Example 2. Same regulator, same set up, same measured ouput voltage. Measured device temperature = cool. Conclusion ? The regulator device itself is faulty. Before there are lots of cries of anguish, a bit simplistic, I know, and yes, there could be other reasons for the measured conditions, but those two examples cover probably 90% of problems around those regulator types.

Arfa

Pin 3

not,

again.

to

hi TM, I tested the L387 and i think it must be bad as i get more than

i had already desoldered it from some previous suggestions about isolating the different supply rails

so i tested by connecting 5V/1A DC source between Vin and GND-Pin3 and i checked the voltage with DVM between Vout and GND-Pin3 and i was getting 3.47 V

i changed to a 18 v/3.5A DC source and i was measuring 8.67 V between Vout and GND-Pin3

L387 is cool and when i connected an LED load to Vout the L387 got very hot very quickly so i suppose i at least need to get an L387 ?

thanks again for help, robb

From that, it sounds as though the '387 is not doing its job correctly, so replacing it would probably be a good move.

Arfa

I was

measurement

regulators that we

of linear

The fixed ones

different voltages

and negative

output pin is

to

the board,

usually be

regulator

LM317, but

concern, are

divider

the other

ratio of the two

input, can be set

resistor of the

What Tony

the board,

which could lead

bomb-proof.

thermally

anomalies in

that they don't

particularly

big clue to

version.

using Mk 1 finger

device has

within its SOA.

voltage.

device itself

simplistic, I

conditions, but

regulator

Hi Arfa, thanks for all the useful help and iinformatin i really do appreciate your's and everyones helpful advice and information. I started this project as a learning exercise guess its more a workout.

Regarding the L387, since i had already removed it hat was asy to test.

I am pretty sure it is bad from what you explained. that is 5V regulators only output 5V .

when i applied a 5V/1A DC source to Vin/GND i measured 3.47V between Vout/GND. when i applied a 18 V / 3.5A DC source to the Vin/GND i measured

an LED load between Vout/GND caused the L387 to get very hot quickly.

so a new L387 is in order so that i can complete the other tests that you TM and others have suggested

thanks again for help, robb

How much more ? A couple of hundred millivolts, says 5.25 V is OK.

Pointless. It won't operate correctly with only 5V in. 3.47V is sort of what I'd expect under those conditions. A linear voltage regulator has to have several volts more on the input than the output to function correctly.

What value resistor did you have in series with the LED ?

He didn't say if he had a resistor in series with the LED ! Could explain a lot.

Graham

With a load or no load ? If there was no load on the regulator output then that's quite possible even for a good L387. You must have a load resistor of around 470 ohms on the 5V output for testing for the chip to regulate properly.

An LED with no series current limiting resistor might well do that ! You should have a resistor of ~ 150 ohms in series with the LED.

It may not be necessary. Your testing used flawed methods.

Graham

and

sort of what I'd

to have several

hi graham, just being cautious and i do not have much in the way of handy power sources, various wall warts.

L387 got very hot

you need to use a resistor ???

just joking it was 100 Ohm 1/2 watt (Brwn Blk Brwn Gold)

would you expect 8.67 Vout with 18V DC Vinput ?

thanks for help, robb

asy

measured

output then

load resistor of

regulate properly.

ok, i set it up as you suggest a 470 Ohms between Vout and GND (Pin3) with 16v/3A DC source connected to Vin and GRD. The measurement between Vout and GND was 8.03 V when i put a LED in series with 470Ohms i get 7.92 V measured accross Vout and GND.

that is why i am seeking help from "the group", "the fountain" of electronic knowledge :(

thanks for help graham, robb

Not under those conditions.

You do need a new L387.

Graham

So while you're waiting for the new L387 (or better yet, before you even order it), replace the 30V and 12V fuses, connect your (5.2V) lantern battery to the 5V rail, and power up. Does the board work? Fuses blow?

TM

Agreed.

Some need 1-2V more, others around 1/2V (I think I've seen LDOs down to 0.2V dropout [i.e. Vout-Vin]). I didn't find a spec sheet for the L387, but the L387A has a max dropout of 0.8V (and that's from 4.9V, so Vin[min] is 5.7V). Don't know whether dropout is one of the improvements in the A version.

In most cases it's safe to test with Vin=Vout+2V, but with an adjustable LDO operating near the top of the Vout range, that may result in Vin exceeding spec. Checking the data sheet first is always a good idea.

(LDO = Low DropOut, a category of linear regulator)

TM

Sure, I was generalising somewhat for brevity.

As you say the value may vavy from several hundred millivolts for true LDO types to as much as 3V in rare cases. 2V is typically a safe value to ensure correct operation.

Graham

I can only work on this in short segments of time and am usually tired ... so i am moving backwards.

Anyway the revisit.

The last diagnostic consensus was to remove voltage regulators and inject a good 5v power into the 5v lines and look for warming components to get a fix on problems to repair.

Since my 5.2V *aged* lantern battery power supply did not impress many i cobbled a simple 5v power supply from a 18 VAC/2.5A wall wart, a 100V/1.5A bridge and 7805 5V regulator plus some resitors and a 6V bulb to test.

I connected the 5v (through 450 Ohm) to the PCB 5v and 0v lines. i measured ~60 mA curent nothing warmed ...i idecremented the resistance by 100 for each iteration of testing the measured currernt increased slightly until i made it to (100 Ohms) and then the current spiked to ~+ 1.5A and the 7805 fried ?

but still no heat on the board anywhere, no trace no component no IC ?

do i need to do something different with power supply test ? thanks for any help, robb

Do you mean that the 7805 got hot and shut down ? One of those should never "fry", because they are SOA protected. I suspect that something else happened there, because if you do the math, it is impossible for 1.5 amps to flow through a 100 ohm resistor, with only 5v driving it ... Apart from that, most variations of the 7805 are only rated to 1 amp, although there are exceptions.

When you cobbled together your test supply, did you mount the regulator on a heatsink, and most importantly, did you place a 4u7 cap, paralleled with a

The more I think about the 'problem' that this board has, the more non 'real-world' it seems. I can't really see any reason why three unrelated fuses, on three unrelated rails, should have blown, unless there was a serious and easily visible problem. The only thing that did occur to me was input voltage. You're not by any chance firing the thing up on UK 240v power, and its transformer is actually rated for 100 or 110v ? That would do it ...

Arfa