Megadisk wrote on 2022-08-21, 16:21:

Another happy customer here!. Everything works good after the cpu transplant. I decided to go all out so I could close this chapter. All new caps, IDE to Cf card (can acess all 2GB with HD overlay) and coin battery mod. Believe it not, my Amstrad 386sx mega pc board with the Cyrix Cx486SRx2 clip on cpu upgrade still performs somewhat better.

excellent!!!!

Are there any recommendations for quieter fans that are compatible and fit inside the Mega PC PSU? I'm considering trying to reduce the volume a bit!

IIRC the original fan is 40x40x20mm
I could not find a good replacement so I ended up using a 40x40x25mm Noctua fan but I had to do 2 things so it could fit:
a. bend a heatsink on the pcb
b. make some grooves on the fan so it can fit inside

it is more quiet but still noticeable , I do not think it's possible to make it more quiet with the way the PSU is made....

maybe someone else has a better solution?

keropi wrote on 2022-10-22, 07:33:

IIRC the original fan is 40x40x20mm
I could not find a good replacement so I ended up using a 40x40x25mm Noctua fan but I had to do 2 things so it could fit:

Looks like you've got a 60x60x25mm fan there if it's the NF-A6x25 FLX as per the label.

Looks like most 60mm fans are 25mm thick. This one I found (https://www.quietpc.com/gel-silent6) is claiming only 15mm thick, it takes a 3-pin power supply, does that look a plausible replacement?

Ah yes it needs 60x60 not 40x40 my bad
3 pins is no issue, you will leave the tach cable not connected anyways, the PSU does not monitor RPM
If you get just make sure the CFM are enough , that's the only concern really...

Such a cool place and so incredibly heart warming to see that the Mega PC lives on. I hope i'm not late to the club. I also hope the thread is just taking a rest.

I recently found my old Mega PC (with the 486SLC 25MAB chip) in my storage facility and with it all my original games and disks. I still think i have the keyboard, joystick and game pad somewhere but i was lucky to have found both the system and monitor in very original condition. You can imagine my delight when i discovered it all working again when powered up. The (noisy!) sound of that 40MB drive almost had me tearing up, honestly. The Mega PC, which i had from new, was my last in a whole string of Amstrad systems i bought into before moving on to Dells starting with their first Pentium 60. Goodness, we even had each one of Amstrad's first and send generation Emailers!

However (and yes, the tone drops a little), the dead battery was so kind to do its thing and cause some greenish blue fuzziness around the board which did eat up some of the traces. I have attempted to repair some and it's been largely successful but i may return to this in the future. The main problem at the moment is that whilst it POSTS fine, there is clearly something wrong with the disk controller: errors on bootup are the two Diskette Drive A error and Fixed Disk Controller Failure messages.

Curiously, i do vaguely remember having this problem over 20 years ago and i think my simple workaround was use of the IDE header on an ISA sound card but my memory fails me. I really want to try and fix this.

I obtained the service manuals (my thanks too to @dioxaz) and am probing the WDC76C20 for faults. It appears to be powering up fine and traces to/from it are also fine. Those traces around the battery affected some of the power conditioning but with some repaired, it is not seemingly affecting the controller. I don't have an oscilloscope but i suspect i am going in that direction. That both the chip is controller for both floppy and hard disk suggests it is either a problem upstream or that the actual chip is faulty. However, this chip was hugely popular for PC clones at the time and i have not come across other stories of it failing.

I hope to post up pictures of another saved Mega PC but in the meantime, is anyone able to shine a light as to what i could do to troubleshoot the onboard controller?

Cheers!
Pops

popolou wrote on 2024-02-02, 22:28:

Such a cool place and so incredibly heart warming to see that the Mega PC lives on. [...]

welcome!!! always nice to see another megapc getting saved 😀
maybe the issues you have are bad traces under the fdd/hdd connectors, I had removed mine and took some photos - maybe they help you find the issue , I am attaching the relevant photo in this post

I seemed to have missed the service manual for the WD 386sx based mobo, can you link it here? I too have a dead 386sx mobo that I am attempting to revive ....

Ah kala, thank you for the welcome! Yes, i am probably going to have to lift the headers to examine their condition - some of the pins appeared to have weakened over time so those were replaced. I suspect i am going to have to follow the trail and see where it takes me.

It seems my copy of the 386SX Service Manual is some 30MB in size so couldn't attach it - luckily there is a copy available from here. I believe there may well be a later revision of it because i have come across some inaccuracies with a few of the schematic diagrams (but the PCB layout appears to be correct and reliable).

It's quite intriguing there is so little on the actual error itself available online; I'd have thought there would have been some analysis of this controller what with it being so common. Perhaps that would have been too easy!

Pops

thanks for the link of the SM , it will really help with troubleshooting!
yeah, removal or the headers is probably the only way to make sure there are no issues under them, please update on your progress and good luck!