Voltage check in SID connected to core: low volts, help!

[tarzan boy]

Hello,

I've gone through every step leading up to the point I am at now,

Ensure the following voltage levels:

IC1:Vcc(25) - IC1:Vss(14) = 5V

IC2:Vdd(16) - IC2:Vss(8) = 5V

IC3:Vdd(16) - IC3:Vss(8) = 5V

but when I read these levels I get a little less than 2 volts.

In all previous steps everything was fine:

All voltages on CORE are fine without chips inserted (when applying 7.5 volts from wall-wart)

All voltages on SID are fine without chips inserted (when applying 15 volts from another wall-wart)

Then I inserted the ICs into the CORE and applied power and everything is still ok when I check voltage.

Now when i connect J2 and J10 from CORE to SID J2 (and yes I was sure to use the schematic for my ribbon cable as described in mbhp_sid_c64_psu.pdf) I get this low voltage (1.7 or so) on all the places that I should recieve 5v on the CORE and the SID module, and the regulator on the CORE gets extremely hot within 20-30 seconds.

I've done continuity checks on each wire in my ribbon cable, i've made sure that the bottom of the core board where the IC socket is soldered connects electrically with the corresponding pin on the bottom of the SID board when the ribbon is connected.

(i've also made continuity checks after every single solder i made to make sure every component had an electrical connection with the board!!  :o )

I've done some forum searches and most people have said that when they check this voltage it is ok. One person said they had a similar problem but realized they didnt solder a pin on J1 of the core. I checked and yep, its soldered!

However I did find this which seems to contradict http://www.ucapps.de/mbhp_sid.html and what others have said about their success with these voltage checks:

TK said in http://69.56.171.55/~midibox/forum/index.php?topic=2877.0

Quote

Also, where does the 2.5VDC come from? I notice that on the SC pin of J2 on the core, there is 2.5V instead of 5V - is this normal?

the shift clock SC is a fast switching signal, therefore no DC. You cannot measure the voltage with a common multimeter.

[end quote]

Could someone clarify, or maybe help me?

[TK.]

First of all it would be interesting, from which chip this failure is comming from. This should help to locate the error.

So, just put out the ICs from the sockets (each time only one), and check which one does lower the voltage. Please do the measurements quickly, because depending on the type of error the ICs could be damaged when they are powered too long (hopefully all ICs are still ok)

Best Regards, Thorsten.

[tarzan boy]

its not an error from any chip, i still havent (for fear of damage) put in any of the chips in the sid module.

all the chips in the core module give the right voltages, and when i do not have the sid module plugged in, I check the J2 of core and its steady at 5v.

Would a short in the Sid module make a lower voltage or would it simply just make the voltage zero?

When i do a continuity check it doesnt seem that I have a short there though (the plug coming from J2 on sid to J2 of core); I get a resistance like the one across the voltage regulator.

[later...]

I've just tried taking out the 2 ICs from my core module and I still get the same behavior: voltage goes way down to 1.7V when I plug the sid module into the core module (both with no ICs plugged.)

I just came back from the weekend and I've double checked all my connections and placement of capacitors. The only slightly strange thing is that hte Joergs Mididshop included a 2200uF polarized cap instead of a 1000uF like the schematic for the SID module calls for. I cant see this making a difference since its connected to the 12V input... I hope at least this reasoning is right!

[TK.]

The different cap value cannot cause a problem.

its not an error from any chip, i still havent (for fear of damage) put in any of the chips in the sid module.

very good! This increases the chances to get the module running :)

Would a short in the Sid module make a lower voltage or would it simply just make the voltage zero?

It depends on the type of error. A solder clump between two tracks of the SID module could cause such a problem.

In principle such errors can be found visually, but is very time consuming. There is a radical, but very effective method which saves some time, but which requires a good oversight over the schematic and the PCB: cut the power rails (e.g. with a screwdriver) at some places where you think that they could be critical, and measure the voltage after each cut. This helps you to find the area which is affected. Try to find the error without too much cuts... after you've located the error, you can repair  these cuts with solder...

Best Regards, Thorsten.

[tarzan boy]

TK,

thanks! i didnt actually get as far as destroying any of the PCB, but your suggestion made me second guess the placement of the crystal (where i would have made my first cut into the PCB) and I realized that I soldered it in backwards! I had soldered it so the text was in the right position but not the sharp angled corner (the part that matters!)

So i just removed the crystal, resoldered it correctly, and everything checks out.

Now i can continue. thanks for the help.

[TK.]

Cool! I haven't expected such an error, I will improve the schematic

Best Regards, Thorsten.

[tarzan boy]

i think if i hadnt been soldering for 5-6 hours straight i wouldnt have made the error.

But as far as changing the schematic, doesnt the layout of the text on the crystal solely depend on the brand of crystal you buy? i.e. noting "text should go this way" is irrelavent, or am i wrong and all crystals have the same text design principles?

The way it is now (placement by shape) corresponds to how you denote the placement of the ICs however; the little indent indicates which way to insert...

ah- and I wanted to say that this morning i finally got the first sounds out of my 6581R2!

A little bit of guesswork uploading the sysex files (i'm on a mac and I don't have Tiger so I cant use Java 1.5 which enables me to use the MIOS Studio) since I have no real feedback using SysEx Librarian. I had to attempt upload of MIOS a few times before it stuck...

when i do more intricate uploads (patches, control surface files ,etc) i will probably use a friend's PC...

so excited; now on to the LCD.