LightStruk wrote on 2020-11-11, 17:10:

An update for anyone watching this thread - I finally checked the voltages on the PCI slot, and the +12V signal rail is live, but the -12V rail is not.

I also checked the pins of the serial ports, and at least two pins had voltages like -10.5V.

Ideally, I would still rather populate the riser card correctly, since that's less cumbersome than running a bodge wire from somewhere on the motherboard. But that requires knowing what to populate it with.

Any update with -12v rail? I´ve got the same sound card and in my HP T5720 that rail is also missing. I was about to buy a -12v converter but it would be a better choice if I can get that current from somewhere else.

I am 99,9% sure that it is meant for MC34063A converter. It used to be very popular and cheap, I also used it in custom PCB design some time ago.

Compare these two:

https://www.ebay.com/itm/MC34063A-Reverse-Vol … kgAAOSwiZpdfKZe

You can buy this module and try to resolder components (hard way) or just install new module with extension wires (easier way). You would need to carefully figure out where to place appropriate components and replace potentiometer with resistors when you want to populate the original board. Or buy brand new components if you can get them from local electronic store (otherwise shipping may cost too much to be worth it).
You can use this design tool to figure out the values http://www.nomad.ee/micros/mc34063a/

Thank you for the info!

Due to my skills, I´m more prone to solder one of those converters to the PCI riser. Searching for one of those, most of them need to supply positive and negative current.

Does the MC34063A converter supply only negative (-12v) current?

adalbert wrote on 2021-01-12, 19:36:

I am 99,9% sure that it is meant for MC34063A converter. It used to be very popular and cheap, I also used it in custom PCB desi […]
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I am 99,9% sure that it is meant for MC34063A converter. It used to be very popular and cheap, I also used it in custom PCB design some time ago.

Compare these two:
mc34063_compare.png

https://www.ebay.com/itm/MC34063A-Reverse-Vol … kgAAOSwiZpdfKZe

You can buy this module and try to resolder components (hard way) or just install new module with extension wires (easier way). You would need to carefully figure out where to place appropriate components and replace potentiometer with resistors when you want to populate the original board. Or buy brand new components if you can get them from local electronic store (otherwise shipping may cost too much to be worth it).
You can use this design tool to figure out the values http://www.nomad.ee/micros/mc34063a/

I was building a cart to order a bunch of things from Mouser anyway. Multiple manufacturers have MC34063-type ICs for less than a dollar there, and I imagine it's similar at other stores. I'll trace the circuit to see what the intended V_in is, and using that tool you linked, I'll have values for the discretes!

franky52 wrote on 2021-01-12, 19:55:

Does the MC34063A converter supply only negative (-12v) current?

Yes, this module has only 3 pins: +voltage input, GND, -voltage output. It will only output negative voltage. But after you solder positive voltage wire (may be +5V OR +12V) and GND, you need to calibrate correct voltage output (-12V) with screwdriver and voltage meter. Then you can solder a wire to the -12V output.

That’s perfect! I will buy one and maybe this will solve the troubles with the HP T5720 width some audio cards and there won’t be any necessity to populate the pci riser, although I’m not 100% of this.

adalbert wrote on 2021-01-12, 20:11:

franky52 wrote on 2021-01-12, 19:55:

Does the MC34063A converter supply only negative (-12v) current?

Yes, this module has only 3 pins: +voltage input, GND, -voltage output. It will only output negative voltage. But after you solder positive voltage wire (may be +5V OR +12V) and GND, you need to calibrate correct voltage output (-12V) with screwdriver and voltage meter. Then you can solder a wire to the -12V output.

Today I got some of those modules and I’m not able to get negative voltage. It’s acting like a step-up.

I tried with +12V and +5V input but the results are the same ... +12V from the Vout pin.

I’m I doing something wrong?

Did you buy proper version of this converter? Because there are listings for different versions - step up, step down and inverting. It depends on the wiring, resistors and capacitors used on the board. You can also try setting the voltage with little screw on the potentiometer.

Make sure that you measure with black probe on GND and red on Vout. If everything is working properly, you should be able to set fixed -12V voltage on the output. You will always get -12V output, no matter if you connect +5V or +12V on the input.

You can take a photo of the module with visible components, then we can check if it is the proper version. Maybe you just got a wrong one from the store.

This is the one I’ve got:
https://es.aliexpress.com/item/32969938755.ht … .cf5563c05h4zHE
I can set the voltage from 12v to at least 20 something when the Vin is 12v, but I can’t go lower than 12V.

You are not measuring from input to output with your voltmeter? Because of course if you measure from +12v input to -12v output the total difference will be 24v…

No. 😀. I measure from GND to VOUT.

I achieved 24V after turning the screw several times. But never got a negative voltage .

If I measure from GND to VIN I get the +12v I’m supplying

Quick update.

I bought the wrong converter. The right one seems to be this one https://es.aliexpress.com/item/4001133889934. … searchweb201603

When I get one in the coming weeks I will post my results. Anyway, I managed to get -8V from one of the COM pin ( on the Futro S400 but not on the HP T5720) and the sound card is working without any noise and as loud as it should be.

So I think populating the pci riser is useless to this kind of sound cards as they need the -12v rail to work as intended.

I got a Neoware CA10 1Ghz version, after reading everyone's comments here about -12v and some sound cards so here's what I did to get my Aopen AW744L II working on it with a cheap 1U PCI riser.
First I bought this https://www.amazon.ca/gp/product/B07SG375XZ voltage converter with neg 12 output, then soldered it in like so (see below)
https://youtu.be/pclt4k6G7yk Video of it working