Broken power supply

Hi folks,

as a proud owner of a well functioning ambika with 6x 4PM since last February I was astonished when I discovered three weeks ago that my power supply (profitec AC-AC 9V 1300mA) suddenly became very hot and gave up working. Buying a new one, I had to discover the same phenomenon today with the new one as well. My ambika passed all voltage tests when I build it, though the 7805 gets pretty hot, which I thought to be normal. Any solutions?

Thanky very much for your help!


That is odd … I’ve got exactly the same power supply, and 6 voicecards (SMR4’s in my case) as well. No issues so far (and yes, the 7805 gets hot - that is normal).

One thing to do would be to measure the current (not the voltage) that the display draws - this can be the biggest single power consumer in your Ambika, so it might be worth putting in a resistor to reduce that (if the current is indeed too large).

I’ve made sure the backlight of my display draws only 50 mA (that is, picked a resistor value to get that).

I don’t know whether your 4PM card draws more power than my SMR4 one … times six might make a difference, of course.

The solution might be buying a 2A power supply …

if it is drawing too much current for the supply the output voltage will drop significantly, that’s a way to check.

“The solution might be buying a 2A power supply …”

I’d say that is unlikely unless you are using a VFD display. If you are drawing more than 1.3 AC amps than there is something else going on, mine runs fine on a 500 mA supply

So has this been solved? Does the Ambika behave now, or what was the cause for the broken power supply?

Sorry for the delayed answer, yes, its been solved (up to now at least) building a new power supply on my own with 2A!

Good to hear !

Would be interesting to know how much current a 4pm voicecard draws (compared to the SMR4 ones) …

so was your old psu just dead and the second also, by coincidence? or is your ambika really drawing juice like a hair-dryer?

I don´t know, but I do not believe in such coincidences. At least the 2A power supply works, but I do discover that the colour of the backlight led becomes a bit lighter (turning from black into green), the longer I keep the Ambika connected to the supply. But I don´t mind!


Are you able to measure the current drawn by a single 4pm voicecard ? I’d like to know (for my second Ambika …).

yes, but beeing not familiar with measuring you would have to tell me exactly on witch point of the pcb I would have to measure what … !

you’d need to disconnect the voicecard in question and connect it with jumper wires and on the power rail(s) you put a multimeter between (in A/mA mode) so that the current flows through the meter (not parallel as in voltage readings)

Ok, thanks, I’ll have a try tomorrow!

Thanks !
If you don’t manage, don’t worry, eventually I can measure the one I’m still populating with all those colourful parts :slight_smile: