Dead 420 Help please!

Have a look here, the part which has F4A written on it is a fuse. Very likely it`s gone.

Have just checked and fuse appears to be fine. Thanks for the suggestion.

Hi,

If the fuse has gone, then rather than replacing the original (tricky on SMD parts) solder another of same rating in parallel. Plenty of choice on eBay for example - cost is peanuts.

Only do this if the original is measured to be open circuit. Use sticky tape or glue to hold the new one in place whilst you solder quickly with a SMALL iron - don't overheat and loosen the original!!

Question - why wasn't an SMD fuseholder fitted - they exist ??!! Just good design practice - fuses do age and fail if properly rated for the job.

Peter

Garth,

Have you measured voltage at PSU plug when disconnected or actually on the board itself at the back of the power socket.

I've just recovered from a PSU failure where volts were fine on the plug, but dropped to virtually nothing (<1.5V ) when connected. The control board was fully functional with a new PSU.

Peter.

Did you check your crash-stop button.

could accidentally been triggered?

Did you check your crash-stop button.

could accidentally been triggered?

Unlikely because of: "power light does not come on"

Thanks for the input guys,

CNCmiller - As Andreas points out, no power so can't be the switch. But I tried it anyway, just for completeness ! Unfortunately no effect.

Peter - If I measure the voltage on pin 5 of IC5 (LM2574 step down voltage regulator) I get 30V. When I measure the output on pin 7 I am getting nothing. I am not an electronics expert but this suggests to me that this voltage regulator is deceased. Looks too tricky to replace so have ordered another board from Rory at StoneyCNC.

I don't know why this chip should fail (if I am correct in my assumption that this is the culprit!) but will continue to investigate further down the circuit and report back anything I find. Might be useful for others as future reference.

Thanks again for all of your input. Any other thoughts would be be gratefully received!

Garth

Hi Garth,

It sounds as though your diagnosis is correct - a dead LM2574N-5. However it might be that there is a short between +5V and ground, it's worth checking just to eliminate the obvious.

If the IC is dead, then as it's a standard DIP8 dual in line package with 0.1" pin spacing it should be relatively easy to replace. The trick is not to try to unsolder everything at the same time, just cut off each pin close to the IC and then remove each one individually using a fine tipped soldering iron (2mm tip or thereabouts) on the non component (solder) side of the board

The through holes would need to be cleared before inserting a replacement part. Use a solder sucker if you have one, or failing that, sharpen a cocktail stick and gently push that into each hole when the solder is melted. This should allow the new part to be inserted easily - dont force it just in case you damage any of the through hole plating.

Resolder the new part taking care not to overheat or use excess solder. The LM2574N-5 can be bought on eBay for around £5 or so in UK.

Good luck if you try this.

Peter

Thanks Peter,

Little bit clumsy when it comes to soldering so plan is :-

New board is ordered and should be with me tomorrow (Tuesday). I will install and hopefully all should be OK and I can get on with current project.

However, I have also ordered a couple of LM2574N-5 (£4 on eBay) and when they arrive on Thursday I will have a go at replacing the dud (assumed) and will test the renewed board without reinstalling into Stepcraft.

If successful I will end up with a spare board. Expensive exercise but at least will have got to the bottom of the issue (at least the what, not the why!)

Again if successful, may be useful to others if they have a similar problem - £4 for new chip rather than £120 for new board.

Will report back later in the week on my soldering efforts!!

Many thanks,
Garfth

Good news is that new board installed and I am up and running again!

Bad news is that I have replaced the assumed culprit voltage regulator on the old board to no effect. Bit of a b****r to remove the old one but followed Peters advice and finally got there. Started using my fine point 12W iron but not up to the job so had to file down the bit on my 25W iron to get the job done.

Measuring the voltage at the JP5 pads, I don't get any voltage. Leaving the common probe on the GND tab and touching the +ve probe either side of the fuse F1 I get 30V so fuse is ok. Touching on pin 5 of the voltage regulator I get 30V (my soldering worked!). On pin 7 I get nothing.

I am at a loss to know how or where to look next. Also not sure I could replace any of those miniature surface mount components anyway without totalling the board.

So it looks like the end of the road for this thread, unless anybody can come up with a magic silver bullet?

Thanks for all your help and input.

Garth.

Hi Garth,

Glad you are up and running again, pity the replacement chip didn't solve the problem.

If you are willing, just throw the old board in my direction - I've done some SMD device work so I might be able to resurrect it.

The regulator circuit is bog standard and simple (straight out of the IC data sheet), so probably there is either an O/C inductor or a short circuit on the 5V logic supply (capacitor or diode on regulator posssibly).

Regards,

Peter

As Peter says there could be a short on the out-pin to ground or the diode is dead. So it seems that the root cause is still there somewhere.
Also it is important that PIN 3 has contact to ground otherwise the regulator is shut down.

If you want to check if the regulator is working you should think about to interupt the PCB track on it's way from PIN 7 to anywhere and then to check the output voltage. But after that you have to remove the paint on the track to get it resoldered.

Maybe there is a tiny tiny metal chip (aluminium) somewhere causing a short ... ???

Good luck!

Hartmut,

The board has worked reliably for a couple of years or so, and there is plenty of solder resist over the tracks, so I think a metal sliver is probably the least likely.

If there is no short on the logic supply, then it has to be one of the three output components (schottky diode, inductor or capacitor) - assuming the LM2574 in still good, connected and enabled.

If there is a short, then a low voltage ( < 2V or so ) current limited power supply fed onto Vcc and ground will, with care, reveal the culprit as the current is increased (slowly!!). A hot component or even smoke is a good sign. :woohoo:

Sounds as though hours of fun can be had Garth!!

I'm a very good catcher!!

Peter

Apologies for slow response gentlemen. Too busy chipping!

Ummm, my electronics goes back to the Neolithic period so a little out of my depth here. Have made an attempt to sketch out the front end of the power supply area. As Peter says, it looks very similar to the data sheet for the LM2574. However, I don't have the skill or wherewithal to play with SMD components and my understanding is that you can't check things like Schotkky diodes 'in circuit', they need to be demounted.

So, Peter, if you are still up for it, I am happy to donate the boards body to science! Still determined to understand what has failed for future reference (and feedback to Stepcraft).

If you could let me have your address I will ship it off early next week. (Not sure how to do private messaging on this forum).

Thanks again for the input and look forward to getting to the bottom of this.