Power Supply Circuit Not working

MIDIbox SID
1

Hi I’m setting up the optimised power supply for 2 sid one core

http://ucapps.de/mbhp/mbhp_8xsid_c64_psu_optimized.pdf

I’ve connected all the parts But when I connect the cable that joins 5v + 9v to make 14 v

it is dragging down the power supply

I am getting 9v out of pin 3 of the 7809

and 5 v out of the bottom output

I connect the wire between the two and it drags it down

I am using a 7pin din chassis socket

and a uk power supply

checked every part of my circuit and everything connected fine

Continued Question

So for the core I need 5v dc

For the two sids which are the newer sids 8580 need 9v dc

So If I left out the wire that bridges the 5vdc with the 9vdc on pin 2 and 3 of the 7809

and just connected to the 9vdc sid and core 5vdc, there would be a drop in voltage on the sid end?would there?

Is it better to have the 14vdc and 5vdc for noise reduction? and then ofcourse it gets regulated at the sid end,

I’m a little confused but the main question why is it dropping the voltage when I connect the 5vdc to the 9vdc at pins 2 and 3 of the 7809?

any ideas

much appreciated

PJ

2

Thank You

3

Yes, you can just use one 7809 and provide 9VDC if you only have 6582/8580 SIDs. In that case, the middle pin of the 7809 would just be tied to ground. Since it’s powering all your SIDs, you may need to put a heatsink on it. Based upon your explanation, I am not sure why you are not getting 14VDC unfortunately :confused:

4

Hi M00dawg

ye if you look at the schematic for the power supply optimised, the output for the sids is 14vdc

http://ucapps.de/mbhp/mbhp_8xsid_c64_psu_optimized.pdf

now looking at it today and testing it, I’m saying you get 5vdc from the bottom output 5vdc going to the core

now there is a connection from the 5vdc going to pin 2 of the 7809 and my observation tells me the reason why this is because its adding the 5 vdc to the 9vdc and giving a 14vdc output to the sids,

now when im testing this it is not working basically

when i connect the wire that brideges 5vdc with 9vdc to get 14vdc it is dragging down the voltage and getting me a lot less than 14vdc

do you get me?

thank you man

5

Dragging down by how much? That’s not very specific and a number would be helpful there. Be sure you’re checking the voltage against the 5V GND and not the GND connected to the 7809 (since that’s actually 5V).

Also, not to be the grammar fanatic, but grouping your thoughts into paragraphs and proper sentence punctuation will make your responses much easier to read and understand. That will likely get more people to help you out because I actually had somewhat of a hard time reading your initial response.

Anyways hope that helps!

6

Hi M00dawg

thank you for your response,

I will explain in a better format.

Ok I have tested the whole circuit.

Looked at the different connections, tested them with a multimeter, all is ok.

Now I disconnected the wire that runs from pin 2 of the 7809 to the positive 5 vdc.

when I check the output from pin 3 of the 7809 and touch the 5v earth I get 9vdc

when I touch the 5v positive and negative i get 5vdc

Now when I connect this wire and touch the positive wire of the meter to the output to the sids (or pin 3 of the 7809)

and to the earth of the 5vdc, I am getting between 7 and 8 volts or less it varies, now everything is connected fine, and its just the circuit im testing, it is not connected to anything else.

apologies for bad punctuation and bad grammer, im a newbie here.

what do you think?

thank you

7

Now I disconnected the wire that runs from pin 2 of the 7809 to the positive 5 vdc.

when I check the output from pin 3 of the 7809 and touch the 5v earth I get 9vdc

i think it’s strange that you read 9V between output of 7809 and the GND of the 5V rail when the two circuits are not even connected to each other, as there’s no clear reference between both (which is achieved by making the bridge).

just thinking out loud here, i haven’t built this.

edit:

are you sure there’s no other connection between the 2 parts? maybe a component at the wrong place?

8

Hmm something odd is afoot and I don’t have a clear answer for what it is. The typical “check your solder joints and wiring” suggestion comes to mind. More often than not I’ve seen it be a bad solder joint causing weirdness (I’ve had weirdness on my own PSU designs caused by that) so even though it’s a typical response, it’s still good advice. Are you sure you have the bridge rectifier connected correctly?