SMR4 mkII - Yet more power supply test fails


I’m a complete hamfisted amateur and I think I’m killing my Shruthi…

In the first SMR4 power supply test I’m getting the following readings on the TL1072P

p4: -0.48
p5: 3.63

I’m getting the same readings for all the other points indicated in the test.

Any ideas what’s wrong? I’ve tested my psu and its doing 9.27v

First, read your Meters instructions, to be shure you are measuring the right thing (DC Voltage with the correct Range. If you measure -0,48 i dont knwo what you have measured? Average Frog Population in your Pond per square Foot? Relative Moon Humidity?)
Then check the soldering at every point of the Power Supply. 99% of the problems are due to the fact you solder the PSU firs and your soldering skills are just evoked or totally rusted. Check if you have scrambled up the 7805 with the 7905 (second common failure)

Ahh, I’d set the meter to detect sarcasm but now the needle’s bent.

I had the 7805/7905 switched, good call. Sorted that out, now +ve readings are all good, but the -ve points all read 0v. Hmmm.

This is not as much fun as I was hoping.

Are the voltages going into the 7805 and 7905 right, means somewhat above 5V and somewhat below -5V?

Not at the moment - should I be testing 7805/7905 with all the other ICs inserted or not?

Thats not sarcasm - you stated you are “hamfisted amateur” and many noobs just turn on their meter and measure whatever the switch is pointing to - and we breaking our minds what this should mean…

Your rails should show plain ±5V a small deviation is OK, sometimes its just the battery of your meter beeing near its end of life that shifts your readings.

You will have to insert the LT1054 for having a negative rail since it generates the negative Voltage the 7905 has to generate…

See the Manual

*Step 5: power supply, testing

You can now insert IC1 (LT1054). Be careful with the orientation, this IC is oriented unlike the other ICs on the board! The LT1054 does not have a notch, but a round mark to indicate its first pin. This round mark must be near the IC1 marking on the PCB.

The power supply is now ready to be tested. Connect a DC supply (unregulated, any voltage between 7.5V and 9V, center pin positive) and check the voltages at the following points of the PCB:*

You need the 1054 inserted. I did the very same thing on my first build, no big deal.

Sorry I was getting a bit stressed. no offense taken, or given I hope :slight_smile:

The meter was set to DC voltage, 20k scale. I think this is ok because it’s showing +5v at the points where it should…

20kV DC? ! be careful please :wink:

YO, on a 20k scale a 5,0 reading would mean 5000V…

Maybe it’s set for milliamps? If you can, check the negative 5 volt points as well. If they also are good, then you’re golden.

Ok…back to serious mode… Besides from the jokes we all really want that Shruthi to function
You probably had the meter on the right setting… 00.0 to 19.9 V range … because your measurement makes sense.
So next step make sure you inserted the TL1045 (read above post by fcd72) and do the measurements again.

Also make sure the 1054 is oriented correctly - it’s not always very clear because they have this dot instead of a notch - and do the same orientation check for all polarized components (the diode and the caps, especially the tantalium one which is very hard to see without a magnifier).

MANY THANKS to all of you. Power tests passed, Control board test PASSED.

Best of all, I plugged it in and it’s making the right noises.

I am super chuffed. Thanks again!



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OMFG that’s a fat synth

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