Just built my Anushri. On power on, no sign of activity. Followed the troubleshooting in the power section and here’s what I have:
Point 1: After turning power switch on, starts at ~5.5V, climbs slowly to ~6.5V, jumps briefly to ~11.8V, then settles at ~9.8V.
Following measurements done after voltage at point 1 has settled at around 9.8V.
Point 2: 9.1V
Point 3: -8.5 V
Green Points: -5V
Red Points: 0.05V
Cyan Point: -4.07V
Purple Point: 0V
So looks like something’s up with the positive voltages. Where do I go from here?
Maybe it’s an incorrectly oriented IC (or the wrong IC in the wrong socket…) Remove all ICs (except the LT1054) and check that the +5V rail is alright.
OK just tried that. No change.
Unplug everything. Is there a short between the red point (you can pick any of them) and ground? If so, you need to check all your solder joints carefully because there’s a bridge somewhere between a power supply pin and a ground pin…
Hmm, my continuity tester beeps when I make a connection between a red point and ground. I assume that’s a yes, then?
That’s a yes.
Happy hunting !
(Remember to check sockets as well)
Thanks, guys. Question: could too much solder on the DC jack cause a short like this?
ok, I’ve looked over all the solder joints many times on separate occasions and I don’t see any solder bridges.
One strange thing I’ve noticed:
If I do a continuity test after the board has been powered off for a while, I get a small “tick” when I connect ground and +5V, but no sustained beep. If I power on the board to test the voltage, connecting ground and +5V will produce a sustained beep with the continuity tester. Would it be safe to assume this is due to the metal expanding slightly since the board probably warms up when connected to power, and so maybe this is a really subtle bridge?
The fading beep is because all the caps are flushed with the current from your Beeper, once they are loaded no current flows into the circuit - no Beep. Measuring continuity on a powered board is pointless as you may see “continuity” on every powered pad since there is some kind of potential.
So you assumption is false - and if your board bends due to warmup you should check if you havent accidentally connected your Shruthi to Mains Power
That seems highly unlikely, there are very few components that get hot enough to even begin expanding themselves, much less the entire board…
It may very well be a tiny bridge, possible underneath a socket, header or something nefarious like that, or it could be your DC jack - Can’t really tell from a-far…
Post some high res pictures please?
(Edit - Try checking the voltage between Ground and +5v, that should give some indication of possible shorts - If my theory holds up(kinda tired), you should get either 5v, or 0v… 0v would indicate a short, since 5v+5v = 0v difference in potential)
Thanks, fcd72 and V`cent, that makes sense.
Between Ground and +5v, I get 0.06 volts.
Here are some pics of the board
oops, forgot to attach them.
I’m guessing that what I have marked are just the light of the flash combined with the reflection of Resin, but can’t be too sure… The DC socket looks fine from underneath (neat soldering in general), but the corner looks weird… Not sure, can’t figure out how solder should have crept in there…
(I’m guessing that the 0.06 volts are when power is applied?)
Yup, that’s with power applied. I checked the joints you’ve circled, and yeah, all except the power jack was just resin+flash. The corner of the DC socket did look suspect though, so I unsoldered it. Before I solder it back to the board, I want to make sure the socket itself is okay. Is it normal to have continuity between the ground pin and the outer collar pin?
A short around the power socket would affect the entire power supply, not just the +5V bus. I don’t think this is where the issue lies. Can you measure the voltage between ground and each of the pins of the 7805 and 7905?
Continuity between ground and outer collar is normal, since the outer collar is negative/ground
check with a magnifying glass and good light. sometimes you have little, very little bridges of solder, like a hair. if you can’t find anything visually you could try the following:
switch off, take out all chips, hook your beeper to gnd and +V. so as long as there’s a short it will make sound.
then work over the solder pads again until you find the one that makes it stop.
if you go around pads the iron will pick up metal dust too.
you can also use a screwdriver or something similar with a sharp tip and scratch once or twice between pads that are very close.
and btw the solder pads of your midi sockets will have less mechanical stress if you fill all the pads. same with the power jack. just touch the lug and pad together and let the solder fill the whole thing. making a short there is hard to do, they’re quite far apart
Pin I : 9.36 V
Pin - : 0 V
Pin 0 : 0.06 V
Pin + : 0 V
Pin I : -9.17 V
Pin 0 : -4.99 V
rosch: Thanks for the tips. Went over the whole board with a jeweller’s screwdiver and scratched lightly between the pads. Didn’t fix the problem, but now that a lot of the rosin has been scraped away, I’ll have another look with the magnifying glass.
Well, I re-did every single solder joint on the board, and looked it over a million times with the magnifying glass. Still getting a short between ground and +5V. Not sure where to go from here. Any suggestions?