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Comparing Altair 680 motherboards

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  by Bill Degnan - 06/20/2009 23:58
First of all the power requirement the SWTPc MP-M boards is 3amps 5V. So far I was not able to find an adequate power supply. I am going to try to find a better solution for RAM.

Strangeness comparing Altair 680 motherboards.

Worked with Herb Johnson on this project, he provided detailed analysis vs. my shot gun repair approach.

The ePROMS on the Altair 680 with the flat paddles and 1-6 motherboard - not working. DC voltage problem. Should have +5 on pins 15, 12, 13, 23 of each 1702 PROM. Also should have -9 to pins 16 and 24.

Took a look at the transistor near Q1 and zener diode to see if it's correctly helping set voltage ..

I need to replace transistor Q1's associated SZ 10.9V Zener Diode and the nearby voltage regulator. Tried a 5.1 Zener from Radio Shack, a little low to power the PROMS.

This motherboard is a 1-6 (not a 1-6x like my other Altair 680).

Side note -

Wonder why my other, working Altair 680 with the 1-6X motherboard has a 7805 regulator in Q1, and not a TIP30 pass transistor to regulate the -9 voltage for ROMS.



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