Power Supply Section Not Working

[duggerd]

I just built the power supply section of the Wave Bubble (ver. 1.0a) and have a problem with the 28v supply section. I am going to use the 5v VCOs, so I did not install any of the 12v boost section. I jumpered C9 to C13, as stated on one of the posts in this forum. The 3.3v section and 5v section work fine but when I soldered in the 28v section, I hear a buzzing sound and my power supply drops down to ~2v (I am supplying 4v). I looked and I think there are no shorts, and I think that all the components are correct. I replaced all of the ICs, and it still continues to not work.

Attached is a picture of the (not working) power supply section.

http://w35ktn5.com/WB_Power_Supply.jpg

Does anyone know what the problem could be?

Thanks,

Daniel D.

[lightningserpent]

Take a very close look at the resistor that sets the 28v boost (R13 on your board) and check its resistance with a volt meter. I had some issues with my resistor here (i think I used a 10Mohm instead of a 1M) and it shorted out the entire board after pumping out about 58v.

You may need to replace the resistor if it burned out after you powered it up. The ~2v tells me you are shorted out somewhere (possibly inside one of the components if they also burned out).

[duggerd]

Take a very close look at the resistor that sets the 28v boost (R13 on your board) and check its resistance with a volt meter. I had some issues with my resistor here (i think I used a 10Mohm instead of a 1M) and it shorted out the entire board after pumping out about 58v.

You may need to replace the resistor if it burned out after you powered it up. The ~2v tells me you are shorted out somewhere (possibly inside one of the components if they also burned out).

I took it out already and checked it and it reads 1MΩ. The marking is 1004 which is 1MΩ as well.

Any other ideas?

[lightningserpent]

Only other idea is to test the connections of each component and check to see if its grounded. Double check your jumper and make sure its not grounded.

[duggerd]

Only other idea is to test the connections of each component and check to see if its grounded. Double check your jumper and make sure its not grounded.

Does a sound like a disposable camera's capacitor charging sound like anything that could be happening? I took out the jumper and still has the problem.

[lightningserpent]

Check the voltage of the 28v boost at D4. My 28v boost was putting out +50v and it was attributed to the boost resistor. I realize you replaced it already, but check and see what voltage level you are getting at the D4/C20 junction and see where you are at.

[duggerd]

Check the voltage of the 28v boost at D4. My 28v boost was putting out +50v and it was attributed to the boost resistor. I realize you replaced it already, but check and see what voltage level you are getting at the D4/C20 junction and see where you are at.

I get 2.04V at that point.

[lightningserpent]

It sounds like you have a short somewhere on the board. This is the point I would start removing components one-by-one starting with the last one placed if checking the connections systematically does not yield any answers.

[INSEAD]

Please look at my post. A multi-tap transformer will simplify construction and headaches.

[TheFallen]

Please look at my post. A multi-tap transformer will simplify construction and headaches.

I'm afraid it won't, please see my response in your thread.

[duggerd]

Well, I fixed it and it was something I was not expecting. Some traces on the PCB under the 28v DC boost converter were shorted together, causing the issue. I took off most of the 28v DC boost converter passives and took it to work to have a look under the microscope when I saw it. The board had a electrical test stamp - I doubt it actually passed. Ten seconds with a scalpel fixed that. I soldered all of the passives back on and everything works now.

Just information - I don't think anyone else will have this problem happen anytime soon.

Next are the VCOs which arrived today. Progress!

[soram]

Are you sure?

I had a very similar problem this week with the 28V section. It turned out to be the inductance. From your picture this is soldered in wrong. It is 90 degrees off and the same for the other one on your board. If you look at the bottom of the inductor the conductive area spans the full side. You soldered in the inductor with the conductive side spanning the two pads on the board hence it was shorting across the pads.

Mine did the same. Worked for a while but then eventually shorted out and burned out the IC.

Perhaps you resoldered it back properly by chance.

Anyway, I would check the other one too. It can work and then some pressure on it by handling can cause the short to appear intermittently!