PSU fried

vibes71

Hi everyone,

While reconfigurating my hardwaresetup, suddenly a burnt smell was noticable.
After a search it turned out to be my LXR that caused the smell.
Most likely the PSU of the LXR is dead. I got no 5Volt measurement as given in step 5 of the assemby instructions.
Could it be that the two capacitors are damaged ? They look a little brownish instead of black...

Any thoughts ?
Thanx in advance.

Jürgen

julian

sorry to hear this.
the capacitors look good.
they would bulge or pop if damaged.
I suspect the 7805.

the real question is why it happened.
what power plug do you use?
is there a short somewhere?
do you measure continuity between 5V and GND?

vibes71

Hi Julian,
Thanks for the reply.
I used a 9v adapter, with the + polarity in center, which I bought for my guitarpedals.
http://www.sweetwater.com/store/detail/1SpotComboPk
I will measure for shorts and continuity when I get back home.
Jürgen

julian

for further testing I would recommend to remove the mainbaord and the ICs. just to not damage them if something is really wrong and you re-apply voltage.
on the picture it looks like you already removed the ICs?

vibes71

Hi again,

I replaced the 7805 voltage regulator, but I still don't measure 5Volt like indicated in step 5.
It did when I was building it and when I did the test before proceding to the next step.
The LXR worked fine 'till the accident..
Can't find traces of a fried component...

Jürgen

vibes71

I removed the 8pin IC to measure like indicated in step 5.
As safety precaution I will remove the other IC's as well...

vibes71

I have continuity between GND and 5V...

fcd72

thats probably a suboptimal thing…..

vibes71

The fact that I don't measure 5 volts anymore as described in step 5 is bugging me. Took out the capacitors but in the shop they also said they looked fine.

vibes71

I think I found what caused the malfunction. A powered USB hub with a 9V adaptor instead of a 5V adaptor.
A USB keyboard connected to the same hub has also died.
Is there any chance I could still repair the LXR.
I allready miss it a lot

Jürgen

vibes71

It gets worse : the big chip of the motherboard is damaged as far as I can tell...

julian

ugh! that explains the smell
seems it released its magic smoke.
the USB 5V line is connected to the STM32 chip (the big one)
and everything above 5V is really bad for it.

You can contact me via email.
I think I could offer you a cheaper replacement.
I still have some used mainbaords from some prototypes here if you are interested.

do you also measure continuity between 5V and GND when the mainboard is unplugged?

vibes71

In the meanwhile...
Fried mainboard and after a long search and reassemblage found out the 1N4148 protection diode for the optocoupler input was broken.

:^)

mmarsh

Yeah, so that 1Spot is center negative.  Most guitar pedal supplies are center negative.  Did you use an adapter to switch it to center positive?

vibes71

Yes, I used an adapter to switch it to center positive. The accident happened because I used a 9v adaptor instead of a 5v one by mistake for a powered usb-hub connected to the LXR , while reconfigurating my man-cave...
All my adapters are labeled from now on...

julian

I'll try to add over voltage protection for the USB port in the next revision.
I'm surprised that it affected the diode.
The USB power is only used to detect if there is an USB cable plugged in and never forwarded to the frontpanel.
Seems the STM32 does not like 9V at all and wreaked havoc

vibes71

This morning I received my new mainboard.
Everything is working splendid as before and no data on the SD-card is lost.
Great !!!
Thanks for all the help Julian.

Jürgen

julian

glad it is working again!