Re: ASUS Radeon 9800XT : Can I save its life ?

Posted on 2021-05-05, 00:01

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I'm still assuming that the PSU turning off when the molex is connected would be due to an overload. So if there's not a short from 12->G, 5->G or 12->5 (can you get resistances for those?), then perhaps there's one to one of the AGP connector pins. You might be able to identify which voltage is …

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Re: ASUS Radeon 9800XT : Can I save its life ?

Posted on 2021-05-04, 18:09

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Dunno if the direct photo links will work: https://i.ibb.co/9hRmsY1/Photo4518.jpg https://i.ibb.co/XSqkL3m/Photo4514.jpg Some soldering looking a bit odd by the caps near the VGA connector. [Oh, and what were the resistances from +12V to GND and +5 to GND (and +12 to +5 just for completeness sake)?]

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Re: Help identifying 486 board (495SLC rev T1, Opti 495XLC chipset)

Posted on 2021-05-04, 13:49

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Looks similar to this maybe: http://www.win3x.org/uh19/motherboard/show/7209 [doesn't seem to help much, as can't find any more information about it. What jumper settings are you missing?]

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Re: XTIDE on 3C509B card

Posted on 2021-05-03, 19:58

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

There's a bit here about the changes to make a 28 EEPROM to work in a 27 EPROM socket: https://theansweris27.com/bmw-e30-318i-engine … t-optimization/ Scroll down to the EPROM to EEPROM section for the details.

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Re: 486 will not boot from floppy; will not read from floppy either

Posted on 2021-05-03, 13:28

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Much rejoicing ! so all it was, was a 74F151 which wasn't relaying the DRQ2 signal to the chipset anymore . Correct ? Seems to be. It looks like non-DMA communication was possible for controlling the drive (so spin-up and head positioning worked) and for reading FDC status registers (so the IMD …

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Re: 486 will not boot from floppy; will not read from floppy either

Posted on 2021-05-03, 09:16

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Edited: Oh, nope I guess the leg fell off again. Resoldered it and both floppy and IDE are working again. Currently testing for stability but I think we are good. Nice, thanks for sticking with it, I learnt a fair bit. Was there any sign the problem chip had been replaced or worked on before? It …

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Re: 486 will not boot from floppy; will not read from floppy either

Posted on 2021-05-02, 20:41

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

So let me ask about IMD, because I see some clarification above about it working now? Or did I misunderstand? If IMD does recognize disk format when you enter the alignment option, and more importantly can read the sectors without timing out or freezing when you press D, and it's only DOS commands …

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Re: Need some advice before I attempt a repair on a board

Posted on 2021-05-02, 19:04

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Looks like just the two vias between those points, so probably one of those failed. I thought at first the -12V line headed up to JP32, but it looks like the via doesn't connect with that track (I lined up the front and back photos to draw in the bottom -12V traced so far). Looks like a via comes up …

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Re: 486 will not boot from floppy; will not read from floppy either

Posted on 2021-05-02, 18:11

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

On page 41 of the SIS 85C471 datasheet (an improved 460/461 with just slightly diff pinout ) it shows using 74f138 and 74f151 logic. Might help explain the board layout a bit better. or not...am still looking for the real 85c461 datasheet Thanks, that looks like it explains a lot. I noticed in the …

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Re: 486 will not boot from floppy; will not read from floppy either

Posted on 2021-05-02, 12:07

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Wow, looks like good progress. I had another read back, and this was the test you posted that I had missed and thought it suggested there was a problem with DACK2, even if the test card said DMA2 was ok (I guess it must only monitor the DRQ?): I have checked all the connections of the isa connector …

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Re: 486 will not boot from floppy; will not read from floppy either

Posted on 2021-05-01, 13:46

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

it could also be a failed or missing decoupling cap. True, line bounce could be a thing. To be honest, I would have expected the wrong track/sector numbers from IMD to be random if it were a decoupling issue, but maybe not. This is where my lack of knowledge of the ISA bus gets in my way. We know …

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Re: Serial mouse problems with 486! Please help!

Posted on 2021-05-01, 11:42

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Thanks guys, still cant get it going. According to my Mobo manual the COM header is the AT/everex type. The new ribbon cable I bought is the cross over type, whereas the old one that was in the machine was a straight through (at the level of the d-sub). I tried to re-solder the connection to change …

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Re: IBM PS/2 Model 55SX won't boot, even with reference disk.

Posted on 2021-05-01, 10:33

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

And yes, my original drive is Mitsubishi and I've found only two SMD electrolytic caps. Probably not useful, but I've been trying to get an old Mitsubishi drive to work, which had 2 SMD electrolytics that had leaked over the board, and they were way out of spec. On mine, they smooth the power …

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Re: 486 will not boot from floppy; will not read from floppy either

Posted on 2021-05-01, 10:20

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

With a freshly formatted floppy I can step between tracks and the read command seems to work but writing still fails. If the head selected is indicated by H0 or H1 then it is properly changing heads, otherwise it isn't. Ok, so I think that proves the FDC is reading data correctly from the disk. As …

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Re: T-398 turbo switch help

Posted on 2021-05-01, 08:53

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Thanks, I'd wondered about those extra pins, they had to be there for something (otherwise why got to the trouble of routeing traces to them and soldering in the pins) but forgot about a separate turbo LED. I'd guess that anything driving an LED will be current limited in some way (hence your 2V …

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Re: What retro activity did you get up to today?

Posted on 2021-04-30, 23:32

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I had to do it all with a solder wick, and that shit is tedious. Yes, good for cleaning up smd pads once most of the solder's already cleared off. Works better with lots of flux around. What is the trick to using a desoldering pump? I can't seem to lift any solder with it, but people make videos …

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Re: AQUARIUS SYSTEMS, INC. A10001 - Does not want to read from the floppy

Posted on 2021-04-30, 21:47

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I take it that originally the floppy emulator gave the same error as the physical drives. Is that still the case now that you're getting CRC errors? How do the RPM test and Alignment test in IMD behave?

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Re: Reviving a 486 MB

Posted on 2021-04-30, 21:28

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

haha, the original chip (almost for sure) is an UV-eraseable EPROM (I can feel the window through the sticker), my plan is to eventually replace this by an EEPROM temporarily for testing/educational reasons. However I don't have any idea about the pinout of this EPROM and whether compatible EEPROMs …

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Re: Motherboard BIOS wont save

Posted on 2021-04-30, 21:09

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Two possibilities might be either corroded contacts , I've considered de - soldering the battery holder because it looks like there might be some green stuff on the pins. Or the Diodes might be faulty since the other duplicate board gives a reading of 0.60V and this one does not , but I'm not sure …

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Re: Pentium 200 MMX Overdrive - Fan replacement?

Posted on 2021-04-30, 19:00

by

by snufkin

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Nice, that should be ok. Only thing I'd worry about would be if the fan stalls you might not know and the CPU might overheat. Could be worth getting a small temp display and attaching the sensor to the heatsink. Something like this (I just did a quick search on ebay): Filename Thermometer.jpg File …

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