Re-building the x0x - Problem with the VCO (Solved)

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Alexfrbc
 
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Joined: Sat Jan 24, 2015 12:51 pm

Re-building the x0x - Problem with the VCO (Solved)

Post by Alexfrbc »

Hi

I recently dug out my old x0xb0x from the attic. I built it many years ago, but it was never working. As i could see a lot of the soldering joints was not the best, i decided to desolder everything and start from scratch, to better be able to test and debug properly.

So i've taken on the project, and the first part with the Power supply went flawless, but on the VCO section i have run into a problem.

It is on this measurement in the image below that i have the issue. My meter does not read anything on this one. I get a 0.000 DC reading

To me it looks fine on the soldering joints, and i tested the resistors, capacitors, and diodes individually before putting them in. I also double checked i put the correct parts in.

Any idea what the problem could be ?

Taken from here: http://www.ladyada.net/make/x0xb0x/fab/vco.html

Image
Last edited by Alexfrbc on Sun Jan 25, 2015 7:10 pm, edited 2 times in total.

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Alexfrbc
 
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Re: Re-building the x0x - Problem with the VCO

Post by Alexfrbc »

i've tried taking out most of the parts and retested them. Everything seems to check out fine, but i still get that 0.000 VDC reading on the 8.5 VDC bias test.


I tested all the voltages on the chip. Maybe someone can tell me if it looks right or not. Could the pin with the 0.000 VDC reading be related to not getting any voltage on the bias test ?

Image

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Alexfrbc
 
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Re: Re-building the x0x - Problem with the VCO

Post by Alexfrbc »

Ok i was lucky enough to find the solution after endless searching through the forum.

Big thanks to user Maclean for providing my solution!!! (see link) I had missed the R105 was facing the opposite direction on my PCB, making me measure from the wrong side. Now i have 8.80 VDC Bias. Yay!

viewtopic.php?f=12&t=32174&p=159898&hil ... as#p159898

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