Home › Forums › Altura Theremin MIDI Controller Forum › Altura FAQ & Support › No Power at D2… What am I missing?
- This topic has 15 replies, 2 voices, and was last updated 1 year, 5 months ago by brach.
Hi all. I finished my Altura build and it went quite smoothly. Everything looks great. All solder joints look clean. However, when I attempted to power her up… nothing (with battery or wall adapter). Here’s the troubleshooting steps I tried so far…
– Metered the 9V battery, it’s delivering 9.3V
– Metered the A/C adapter, it’s showing 9.6V – tip neg
– Metered where the 9V wires attach to the board, solid 9V there
– Metered the contacts on the bottom of the A/C jack – I’m seeing 9V there
– Metered at D2, virtually no current (about .02V) showing there
– Metered between ground and both sides of the LED (thinking maybe it was in backwards) – no current on either side of the LED
So, it appears the power is getting to the board, but not to D2. If I’m reading the schematic correctly, the only thing between the jack and D2 is the switch… and that’s on (BTW, I also metered wit the switch off just to make sure the switch wasn’t crossed somehow). What am I missing?
Sorry for the frustration.
If you are certain that your power supply is correct (it doesn’t give AC voltage and the polarity is correct) and you are sure the ground reference that you are using for your meter is really at ground potential, then there is a good chance all the current is being shunted to ground via a short somewhere on the 9V bus. What resistance do you get across D2?
As you suspect, another possibility is the switch. Do you get continuity between C8 and the square pad of D2 (the 9V bus)?
Let me know.
You need to check with your voltmeter between ground and the contacts on the On-Off switch. With the switch ‘Off’ there should be 9volts on one side and nothing on the other. With the switch ‘On’ there should be 9 Volts on both sides.
Check that the power switch is not rubbing on the case. Sometimes the switch can appear to be latched ‘On’, but the contacts are not touching because the button has not latched properly (i.e. it has been pushed in and held by the case, but has not dropped back to the ‘Latched-on’ position. With the power button in the ‘On position, gently pull it out from the case.
If the switch is operating freely, but 9Volts does not appear on both sides of the switch when latched ‘On’, either the switch connections have a dry joint or the switch is faulty.
Thanks for the help guys. Great suggestion by Roy.
I checked and I’m not seeing 9V on either side of the switch. Hmmmmmm. So I guess something is going on with the DC jack??? I’ll try desoldering that from the board and see if there’s a glob of solder or something like that on the underside that’s shorting it out. I’m not really sure what else it could be.
I might be better off to just buy another port and try again. Does anyone know the Mouser part# for this port?
I wouldn’t jump to that conclusion yet (that your dc jack is bad). Didn’t you say you were getting 9V on the solder joints of the 9V jack? If so then your jack is fine.
The “sides” of the switch that Roy was talking about are the front and back side. You should be getting 9V on the center lug of the switch (the center lug on the half closest to the DC jack). When the switch is on (pushed in) you should then get 9V on the lug of the switch furthest away from the front edge of the board (closest to C1). These lugs should be connected when the switch is in, check this with your continuity tester.
I get your logic Brach, it makes perfect sense, but I think you missed the part where I said there is no voltage on EITHER SIDE of switch. So, the power is not getting from the power jack (or battery… I tried with both) to the switch. I can see 9V at the actual terminals of the jack (so I don’t think the jack itself is bad), but it could still be shorted where it meets the board (sloppy solder, stray wire, who knows).
So, unless you can think of something else (I’m certainly open to other ideas), I’m assuming the jack needs to be removed, cleaned off, and re-soldered. I was going to try that today. The reason I wanted a replacement part is because I think that jack is going to be difficult to remove from the board and I may damage it in the process.
Okay… I just did some more troubleshooting. I checked for continuity across the switch. The only place I’m seeing continuity is across the diagonal posts (furthest forward and backward). I’m assuming those are both ground and that’s why but I have no continuity across any of the other 6 pegs. I tried all combinations of L and R. Also, I discovered there is 9V power at C8. So maybe it’s not the jack… great suggestion Brach.
Sometimes a picture is worth 1000 words. The green line indicates continuity. The red arrows are the places where I can see 9V.
Thank you for the picture. That is very helpful.
Here is a picture of the traces on the PCB (in red). Make sure you are getting continuity between all the points on the switch and power jack which should be connected. It seems like there may be a broken trace from the jack to the switch. You probably will need to use the pointy end of the meter’s probe to dig into the solder joint to get past the layer of flux, so you can get an accurate reading. If you do find there is a broken trace somewhere then you’ll have to run a jumper wire between the 2 pads that the trace is supposed to be connected to.
The 2 pads on the switch that have traces attached to them are the 2 pins that should be connected when the button is pressed in. Test those for continuity.
Let me know what you find.
I’ll be out of town for the next week, but I’ll try to follow up when I get the chance in a day or 2.
Thanks so much Brach. Some great suggestions. After testing all the continuity joints, I used a jumper wire to make the connection below and now the power light comes on. Progress! Alas, I’m not seeing any lit segments on the LCD screen. I’m checking the Troubleshooting Guide now to see what it says about that. I guess the fun just doesn’t stop on this one. Sheesh. Is Mercury in retrograde?
This is probably a case of the 5V rail shorting to ground somewhere/somehow. With the power removed from the board measure the resistance between the 5V pin on the regulator (the one currently at .8V) and ground. I’m guessing it’s probably some very low resistance. If so, scan the entire board with a magnifying glass looking for any speck of solder or short that could be keeping that rail at ground potential.
If it’s not some very low resistance then the voltage regulator may be bad. Un-solder and pull up the 5V lead off the board and measure the voltage on that pin when it’s not connected to anything. If it is still not at 5V then the regulator is most likely bad.
But also make sure the center pin of the regulator is really connected to ground.
…before everything else make sure the voltage regulator is orientated properly and it’s the correct part (not a 2N3904).
Thanks for the great suggestions Brach. I think I found the problem. I unplugged the 2 mic/speaker daughterboards during the switch/jack troubleshooting and then plugged them back in again after we fixed that. Somehow, I got one of them reversed when I plugged them back in. I just unplugged both from the board, powered it up and bam… 5V at the left side of U5. I plugged them both in correctly, powered it back up and… you guessed it… I see digits on the LCD.
That’s good to know for future reference. If one of the 2 daughterboards is backwards, you’ll see low output at U5. Ugh… that was frustrating. I was so focused on looking at the solder joints, I completely missed the fact that one of the ribbon cables was backwards. D’oh.
In any case, thanks for your help on the switch issue. That one was legit and not just me being absent-minded.