Sammich SID voltage problem **FIXED**

[Sine Square Saw]

Hey all, just completed my sammichSID, really nice straigtforward design. Many thanks to Wilba.

Got as far as loading the patches on and the firmware, but just went through the final voltage check before installing the SIDs and discovered a few oddities. The voltage between pin 28 (top-right corner) and pin 14 (bottom-left corner) of each SID's IC socket is not what it should be. I'm using 6582A SIDs and the voltage there should be 9V, instead I'm getting around 5V (4.16v to be exact).

I've tried it with both the 12v AC powersupply that Wilba sent me and a 12v DC regulated supply which I had already and I get the same voltages.

J20 should be 9v I get 8.16v

J2 should be 5v I get 4.16v

J1 should be 12v I get 11.11

On the voltage regulator 7809(9v) where I should get 12v I get 9.76v

On the voltage regulator 7809(9v) where I should get 9v I get 8.16v

I've double and triple checked everything in the guide. I was also very careful to solder everything quickly and there don't seem to be any dry solder joints, but who knows I may have botched something.

Has anyone else experienced this or have an idea as to what I may have done wrong?

Thanks all, glad to be starting in this wonderful world of SID synths.

Benji

[Wilba]

I don't see how it could be working if instead of 5V you have 4.16V supplying the PIC. That's too low for it to even start up I think.

Assuming your multimeter is working, 9.76V going into the 7809 is too low.

Can you test your multimeter against a known good voltage, like your regulated 12V DC supply?

And is this 9.76V reading when using the regulated supply too? Because it should be much higher.

Possibly the LCD backlight current is interfering. Remove JBL shunt so there's no current being drawn by the backlight (esp. taken out of the "12V" supply before it goes into the 7809). Retest the voltages and let me know if anything changed.

[Sine Square Saw]

I don't see how it could be working if instead of 5V you have 4.16V supplying the PIC. That's too low for it to even start up I think.

Assuming your multimeter is working, 9.76V going into the 7809 is too low.

Can you test your multimeter against a known good voltage, like your regulated 12V DC supply?

And is this 9.76V reading when using the regulated supply too? Because it should be much higher.

Possibly the LCD backlight current is interfering. Remove JBL shunt so there's no current being drawn by the backlight (esp. taken out of the "12V" supply before it goes into the 7809). Retest the voltages and let me know if anything changed.

Tested the 12v regulated PSU, multimeter measures it as 11.12v.

Replaced the battery in the multimeter, no change in measurements.

Measured the power again this time using the 12AC PSU that you sent with the kit and got the following measurements:

J20 should be 9v I get 8.19v

J2 should be 5v I get 4.61v

J1 should be 12v I get 13.23v

On the voltage regulator 7809(9v) where I should get 12v I get 16.35v

On the voltage regulator 7809(9v) where I should get 9v I get 8.19v

Definitely booted, loaded firmware and transferred all the patches OK. Maybe my trusty multimeter isn't so trusty. Could I have cooked the voltage regulator?

Cheers mate,

Benji

[Wilba]

I don't think you cooked the regulators.

A 12V regulated PSU should measure 12V on your multimeter. Maybe +/- 0.1V. 11.12V is way below what I'd expect.

That could mean the multimeter is giving you bad measurements. Are you sure you have it set to DC? :)

The thing is, you could probably just install SIDs and everything will work fine... the regulators are outputting roughly correct voltages but considering regulators are designed to output exact voltages, the fact that they don't could mean something is wrong. e.g. A short between 5V/ground might cause so much current draw that the regulator outputs sag under the load. However, I still don't think the PIC would be happy with only 4.61V supply, or the LCD. Just a guess.

Retry your voltage measurements with the regulated 12V DC PSU and the JBL shunt removed.

However, at this stage there might be no point until you truly validate your multimeter is working by comparing with a known good one.

[Sine Square Saw]

I don't think you cooked the regulators.

A 12V regulated PSU should measure 12V on your multimeter. Maybe +/- 0.1V. 11.12V is way below what I'd expect.

That could mean the multimeter is giving you bad measurements. Are you sure you have it set to DC? :)

The thing is, you could probably just install SIDs and everything will work fine... the regulators are outputting roughly correct voltages but considering regulators are designed to output exact voltages, the fact that they don't could mean something is wrong. e.g. A short between 5V/ground might cause so much current draw that the regulator outputs sag under the load. However, I still don't think the PIC would be happy with only 4.61V supply, or the LCD. Just a guess.

Retry your voltage measurements with the regulated 12V DC PSU and the JBL shunt removed.

However, at this stage there might be no point until you truly validate your multimeter is working by comparing with a known good one.

Picked up a new multimeter today. Everything is in fact hunky-dory. Did the voltage tests again with the regulated supply and everything was as it should be. Crazy. I wouldn't have expected that. Thanks for all your help Wilba.

I'll install the SIDs and see how it goes.

Benji

[Wilba]

Cool... I was worried I might have convinced you to buy a new multimeter for no reason :whistle:

[Sine Square Saw]

Cool... I was worried I might have convinced you to buy a new multimeter for no reason :whistle:

nah everything works a treat. Put the SIDs in and gave it a burl. All good. Thanks again for designing such a nice piece of kit. I definitely owe ya a beer.

Edited April 6, 2010 by Sine Square Saw