VOGONS


Reply 20 of 25, by franky52

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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.

Reply 21 of 25, by adalbert

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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
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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/

Reply 22 of 25, by franky52

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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?

Reply 23 of 25, by LightStruk

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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!

Reply 24 of 25, by adalbert

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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.

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Reply 25 of 25, by franky52

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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.