Core voltage check problems

[tonysnail]

Hi all..

I've just soldered together my first Core module, and I'm going through the checks before I stuff the PIC and Optocoupler.

To power the board so that I can take voltage readings, I'm using the 5v DC power from a C64 power supply, wired directly into J1 (Positive at the top, looking at the board like in Thorsten's photos).

I haven't built an external power board yet, so I've got my core stuffed exactly as shown on the core walkthrough..

I checked the following:

IC1:MCLR(1) - IC1:Vss(12)

IC1:Vdd(11) - IC1:Vss(12)

IC1:Vdd(32) - IC1:Vss(31)

IC2(8) - IC2:(5)

- they all read 2.5 V - half what they should be!

These are the only places I can find anything close to 5V:

5.25v coming in on J1.

The positive lead of the bridge rectifier reads 4.7V.

The leg closest to the board's centre of the 7809 reads 4.7V.

Every other place where the schematic indicates a +5V supply is only receiving 2.5V.

Why could this be? I've done a pretty extensive search for short-circuits on my soldering, and dodgy connections but so far I can't find any more faults..

Is this because I haven't built a proper power board?

Hope you can help a budding new synth tinkerer!

Carl Hudson

[philetaylor]

Hi.

My first guess is that you didn't read the bit in http://www.ucapps.de/mbhp_core.html where it says that J1 should be connected to A 7-10V AC Transformer (DC can also be used, I usually use a 9V DC supply).

The reason for this is that the core has its own 5V regulator and full-wave bridge rectifier, a voltage drop of 2.5V over these is quite likely!

This would explain why you are only seeing 2.5V :)

Phil

EDIT: If you are sure that your supply is 5V, you could connect it to J2 instead which bypasses the Rectifier/Regulator.

EDIT2: The CORE module doesn't have a 7809, it should be a 7805!

Edited November 17, 2009 by philetaylor

[tonysnail]

Ahh! Thanks a lot!

Carl

[philetaylor]

No problem

I should also point out that you are best to remove the regulator (7805) if you are powering from 5V via J2 as putting 5V on the output of the 7805 probably wouldn't do it much good!

Phil