SammichSID: Final pre-flight checks failed :(

MIDIbox SID
1

Hi guys,

This seems to be a common problem for me when I’m building electronics - everything during the construction goes fine, the testing is fine, but somewhere right near the end, there’s a problem.

I’ve built my sammichSID, following the instructions carefully. The voltage tests in section 5 went fine, and I’ve got as far as the final checks before installing the 6582s in section 8. The build guide says:

“Test voltage between pin 28 (top-right corner) and pin 14 (bottom-left corner) of each SID’s IC socket… For 8580 or 6582, this must be exactly 9V.”

The multimeter says: “8.8” (that’s with the red probe top-right and the black bottom-left). All the other voltages check out. The voltage between GND and “12V” is 10.8, which I think for 6582s should be adequate (although obviously I haven’t tested that with the 6582s in place yet).

So… What do I do now?

2

hi

my English is very very bad!!

sorry!

What type of power supply do you use?

if your power supply is 12V regulated

to measure the 12V pins must be bridged JBP

This is what happened to me, I use 6581

The JBP prevents the voltages passing through the diode bridge, as you continued imposition of the JP in 6582 or 8580 if this is your type of SID.

I hope, have helped

best regards

Lucas

3

With no SIDs or LCD backlight draining the current, you really should get closer to 9V.

It could be that your multimeter is not that accurate, or the power supply is a little bit weak.

What power supply are you using? i.e. unregulated 12V AC 500mA? etc.

What do you measure for the 5V supply?

You should try to work out why you aren’t getting closer to 9V (i.e. 8.95V or higher), but it’s probably close enough to plug in SIDs and get sound out of them. This voltage check is more to make sure you have the JP header shunt installed correctly and won’t fry your SIDs with anything higher than 9V. So don’t worry too much.

4

My power supply is one of these:

http://www.maplin.co.uk/Module.aspx?ModuleNo=32746

i.e. a regulated, 500mA, with a little trimpot thing to switch between voltages. It’s currently set to 12 volts, and the multimeter reads that it’s putting out 12.2V, which I figure is acceptable. The multimeter is quite a cheap one, but has seemed easily accurate enough in the past.

The 5V supply measures as 5.0V, so bang on. I’ve just re-checked the other 9V points on the board, and they all come out as 8.8V. So… Something odd with the 7809, or earlier in the chain? Here are the voltages I’m seeing from testing a bunch of random points

With the black probe at GND:

end pin of power socket: 11.5V

top left pin of switch: 11.5V

middle right pin of switch: -0.7V

positive pin of C5: 10.8V

right pin of 7809: 10.8V

left pin of 7809: 8.8V

top right pin of IC1L and IC1R: 8.8V

With the black probe on the left pin of the power socket:

end pin of power socket: 12.2V

Top left pin of switch: 12.2V

middle right pin of switch: 0.0V

Positive pin of C5: 11.5V

right pin of 7809: 11.5V

left pin of 7809: 9.6V

top right pin of IC1L and IC1R: 9.6V

Does that give any clues?

5

I just did some tests using my own regulated 12V 500mA supply…

There are only 3 relevant measurements

A. straight out of the plug (i.e. at J1 pins)

B. voltage between GND (middle pin) and input pin of 7809

C. voltage between GND (middle pin) and output pin of 7809

For me, I get A=12.06V, B=10.6V, C=8.94V

For you, it’s A=12.2V, B=10.8V, C=8.8V

It’s a little low but OK.

Since you’re using a regulated DC power supply which is tip positive, you can try putting the shunts in JBP to bypass the bridge rectifier (it’s not needed). That will get rid of the 1.4V drop from the two diodes in the bridge rectifer, giving a little more voltage to the 7809, and you should probably see the 7809 output closer to 9V. You would need these shunts if you were using 6581 SIDs anyway, but it’s completely safe to do for 6582/8580R5 use. Just check the power supply really is tip positive.

6

I tried the shunts in JBP but they didn’t seem to make a difference. In the end I figured “what the hell?” and put the SIDs in. I need to get a chance to really properly test it (have to spend some time with The Missus first, 'cos she got lonely whilst I was building it) but the initial impressions are that it seems to work just fine and sounds nice and fat :smiley:

It’s an awesome bit of kit, and apparently it creates beer for you as well. Bonus!

7

Thanks!

If it’s no difference with JBP shunts, I can’t explain it… if there is exactly 12V going into the 7809, there should be exactly 9V coming out. So I’m tempted to blame the 7809 being at fault, and/or it’s sagging under heavy load (which it shouldn’t be with no SIDs and no LCD connected). Strange.

But if it works, and you’re not getting any audio artifacts then fuggetaboutit :wink: