Power supply test problem [RESOLVED]

Discontinued DIY products Shruthi
#1

Hello,

I’m assembling the MK2 filter, got to step 5 power test and got the following:

All 12 measured voltages are 7.64 to 7.65 V (red) and -7.64 to -7.65 V (green). I’ve measured input voltage as 9.19V. So on the plus side they’re all the correct sign and symmetrical. The downside is they’re not 5V!

I did read old threads which suggested changing batteries in multimeter which I did, but results are identical.

I’m using a switchable PS with next voltage below 9V is 6V (measures 6.14V with multimeter), so that’s not much use to compare.

I’ve checked that I put the 7805 and 7905 voltage regulators in the correct place.

Voltage readings off the voltage regulator pins are:
7805: +7.66V, +7.73V, +8.53V
7905: -7.64V, -8.4V, -7.74V

One point to note: I put the resistors on the board first (sorry force of habit; I am aware of the general principle of RTFI about reading instructions, but I presume that has no bearing on this issue).

Any ideas? Have I fried the voltage regulators?

#2

Your voltage readings are very strange… On each regulator, there’s a grounded pin that should be at 0V. Either the soldering of this pin is really bad and it’s not grounded ; or you are using the wrong point for the COM / ground probe of your meter.

#3

Thanks, will start there and let you know.

#4

Found it: short across 7805. Resoldered it and now all readings 4.98V and correct sign.

Onwards and upwards!