Looks like your power supply is too weak – I think the 8.96V you have measured is without load, right? As soon as you connect it to a circuit, the voltage drops to 5.8V and this is not enough for the regulators. Try another one.

So at which point do you get 5.8V?

What are the voltages on the I / O / (-) pins of the 7805 and I / O / (+) pins of the 7905?

Hmmm, this is not really what I asked…

What are the voltages on the I / O / (-) pins of the 7805 and I / O / (+) pins of the 7905?

like this:

!http://imageshack.us/photo/my-images/651/shruthi4pms.jpg!

edit: not sure, if imageshack allowes to ebedd images this way.

Argh! I am also having power test problems now. I’m using a 12-volt power supply, 500ma, that’s putting out 17v at SW. The readings at the indicated coloured dots, with the LT1054 (IC7) in are minimal, .06v, and are reversed polarity. I checked the polarity of the polarized caps and they seem to be in the right place, and I assumed the long lead of the 4.7u caps was positive. The regulators are installed with the heatsinks facing the outside of the PCB.

Any ideas? Someday, maybe when I do my 20th Shruthi, I’ll actually get one to work first time.

Randy

Looks like you have fried the LT1054.

I may have fried the chip. Is there a way to test it?

The first power supply I tried, also rated at 12V put out nearly 20V! I’ll see if I can find another LT1054.

Randy

At least I’ve learned to ignore whatever is written on the wallwarts and test them first.

Randy

The Shruthi doesn’t need more than 150mA. The problem is that it’s common to see wallwarts rated 300mA fail to deliver the 150 or 160 the Shruthi needs :/

I picked up another (well, a pair, just in case) LT1054 and tested with the power supply I’m using for the other Shruthi, same result. Minimal power getting through to anything.

I checked all of the caps again and they seem to be oriented correctly. The only thing I’m not sure of is the orientation of the 4.5u caps that Olivier provides with the kit. As I mentioned, I assumed the long lead was positive, but I can’t see any markings on those caps that would let me check the orientation after-the-fact.

So, I’m back to looking for ideas.

Randy

I used pin 3 as ground and I’m getting +0.2v at pin 5. All of the red points on the photo are getting +0.4v and all of the blue are +0.3v.

I checked continuity between all of the green, red and blue points and everything seems okay. The odd one has the meter “hunting” a bit but it settles down to 1 quickly.

Randy

Depends on which probe I use. I have 15.3 at SW, then if I leave the + on SW, I get 15 on both sides of D1. If I leave the – on SW, I get essentially nothing on both sides.

What is the best point to get a ground?

Smartass! Good point ‘though! Following Titus’ suggestion, I get the same results, 0 on one side of the diode and .4 on the other.

It’s okay to be a smartass when you’re right. I appreciated the advice, just giving you a bit of a hard time, hope you don’t mind. I’m wondering if I’ve screwed up D1?

This is strange, one side of the diode should be at the same voltage as your power supply…

The power supply flow is the following:

• Arrives at the connector.
• The circuit is eventually opened / closed by a switch if you solder it at the SW switch (it’s kept close if you solder a jumper here).
• When the polarity is wrong, D1 blocks the current. Otherwise it just causes a small voltage drop (a few tenths of volt) across it.
• Then the input voltage is sent to the LT1054 and the few caps around it – and a negative voltage is generated from it (if the input is 10V, the output, on pin 5 of the LT1054 will be -10V).
• The the 7805 (7905), brings the 10V (-10V) to 5V (-5V). Excess power (input voltage – 5V times consumed current) is dissipated as heat.

Thanks pichenettes!