VOGONS


First post, by Vaylo

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Hello folks,

I have a QDI P5I430VX v1.0 motherboard which seems to be totally dead. There's no video out signal when a GPU is connected, it does not beep, it does nothing at all. I tried to investigate the cause and so far i focused on the tantalum caps. None of them shows any visible damage like burns or cracks so i did some primitive measurements using my DMM. There's 21 tantalums in total and 19 gave me more or less same readings when using continuity measurements and resistance measurements (scale set to 2000 Ohms).

Two of them however - TC16 located next to PSU connector (i think its negative leg is connected to pin 3 of the P9 connector (-5V?)) and OC22 (probably incorrect designation, should have been TC22?) gave me way different readings.

TC16 - continuity test displays off limits either way; resistance test - scale must be set to 20M Ohm to display at least something, otherwise off limits. Could this one be open?

OC22 - continuity test with correct polarity (Red probe on +, black on -) reads off limits, reverse polarity beeps constantly, displays negative 785; resistance test - correct polarity displays off limits, reverse polarity displays negative(?) 760 Ohms.

Should i assume that TC16 is open and OC22 is shorted? Do my measurements make any sense at all or are they a complete non sense?

Thanks for any help in advance.

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Reply 2 of 13, by Vaylo

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Nexxen wrote on 2024-06-03, 18:12:

CPU voltages are ok?

Should i measure with CPU inserted? I did some measurements now with CPU and RAM removed and measured zero volts on the highlighted pins.

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Reply 3 of 13, by rasz_pl

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Vaylo wrote on 2024-06-03, 17:57:

Do my measurements make any sense

no, thats not how capacitors work, those tantalums are ok

Open Source AT&T Globalyst/NCR/FIC 486-GAC-2 proprietary Cache Module reproduction

Reply 4 of 13, by Vaylo

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rasz_pl wrote on 2024-06-03, 18:35:
Vaylo wrote on 2024-06-03, 17:57:

Do my measurements make any sense

no, thats not how capacitors work, those tantalums are ok

Hi,

thanks for the feedback. While i understand what capacitors are and what they do i may not know how to measure them properly while they are soldered in a circuit. That's why i tried to apply some common sense here - when 19 out of 21 gave me some similar readings and two gave me something completely different then i naturally suspected those last 2 were bad. In the meantime i did some measurement on the ISA slot but that's probably of no help here - all voltages are present where they are expected to be - that means +/- 5V and +/-12V.

Thanks.

Reply 5 of 13, by Nexxen

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The 2 components wiht heatsinks are responsible for the Vcore and Vio of the cpu.
Measure those without the cpu in.

Your board is single voltage cpus only, Being dual voltage test different voltages: I/O it should be 3.3V and Vcore whatever ypu set it..
They are Vcc2 and Vcc3 on the socket schematic.

https://theretroweb.com/motherboards/s/qdi-p5 … vx-250-explorer

PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 6 of 13, by Vaylo

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Nexxen wrote on 2024-06-03, 19:20:
The 2 components wiht heatsinks are responsible for the Vcore and Vio of the cpu. Measure those without the cpu in. […]
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The 2 components wiht heatsinks are responsible for the Vcore and Vio of the cpu.
Measure those without the cpu in.

Your board is single voltage cpus only, Being dual voltage test different voltages: I/O it should be 3.3V and Vcore whatever ypu set it..
They are Vcc2 and Vcc3 on the socket schematic.

https://theretroweb.com/motherboards/s/qdi-p5 … vx-250-explorer

Thank you very much. Both VCC2 and VCC3 give 0.2V.

I also measured those two darlingtons (both TIP102) and their readings are following:

Base: 5.85V
Collector: 5.10
Emitter: 0.2V

Reply 9 of 13, by Nexxen

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I had 2 boards with dead TIP102.
Probably you have to replace them.

You can desolder them and test.
https://pdf1.alldatasheet.com/datasheet-pdf/v … OLA/TIP102.html

PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 10 of 13, by Vaylo

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Thank you, will do tomorrow. If i find them to be dead would a BDW93C be a proper replacement? All parameters appear to be the same except it only has 12 Amps collector current rating instead of TIP102's 15 Amps. Not sure if that matters that much.

https://www.tme.eu/Document/0183d6be97ac41f90 … 6264/BDW93C.pdf

Reply 11 of 13, by rasz_pl

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Vaylo wrote on 2024-06-03, 19:13:

how to measure them properly

The only failure condition you could detect by measuring resistance of a capacitor is a dead short.

Open Source AT&T Globalyst/NCR/FIC 486-GAC-2 proprietary Cache Module reproduction

Reply 12 of 13, by Nexxen

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Vaylo wrote on 2024-06-03, 20:16:

Thank you, will do tomorrow. If i find them to be dead would a BDW93C be a proper replacement? All parameters appear to be the same except it only has 12 Amps collector current rating instead of TIP102's 15 Amps. Not sure if that matters that much.

https://www.tme.eu/Document/0183d6be97ac41f90 … 6264/BDW93C.pdf

I'd say yes but IDK if those cpus can go up to 15A, maybe less is ok.
Sorry.

PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 13 of 13, by majestyk

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These transistors died for a reason. The tiny heatsinks attached to them are far too small for Pentium MMX class, let alone K6-2 CPUs.
If you just replace the transistors make sure you choose a good CPU cooler that directs it´s airstream right at the heatsinks, not just to the left and right. Don´t use "silent" or undervolted fans.
If you have the means equit the transistors with larger heatsinks.