Thanks also for your results and explanation. Quite high ISA
1) VLSI SCAMP 311 | 386SX25@TI486SXLC2-50@60 | 16MB | CL-GD5428 | CT2830| SCC-1 | MT32 | Fast-SCSI AHA 1542CF + BlueSCSI v2/15k U320
2) SIS486 | 486DX/2 66(@80) | 32MB | TGUI9440 | LAPC-I
I have finished upgrading the 486slc33 amstrad megapc motherboard using a custom interposer specifically designed for this mobo and a 486SXLC2 cpu. The CPU is fed 3.6v for it's core and the 5v I/O pin is used so the upgrade is operating 100% within the TI recommendations for the 66mhz SXLC2 cpu (ofcourse the 50mhz cpu used is overclocked at 66mhz).
The flex interposer isolates the needed pins and takes care of core voltage and 5v i/o , it demands a good amount of experience to assemble and install correctly. The end result really makes the effort worth it, it won't make the system a DOOM machine but games that used to lag are now perfectly playable (realms of chaos, discworld CD stuff like that that needed a little more power to run without lag).
Another side effect is the cpu temperature: the original 5v TI486SLC33 was a furnace , this 3.6v SXLC2 is half the temp or something, definitely a welcome byproduct 😀
I did some benchmarking:
3DBENCH for fast PCs is 33.2fps
wolf3d is 51.1fps
Doom max window with status bar is 23,88fps at low detail and 16,22fps at high detail
BIOS settings for cache/ram are very limited so not much can be tinkered, even AMISETUP does not reveal any hidden options of worth
the motherboard is this: https://theretroweb.com/motherboards/s/amstra … lc-vio-a-rev1-0 , winbond chipset with onboard vga.
Excellent ~
T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜
Fantastic job
1) VLSI SCAMP 311 | 386SX25@TI486SXLC2-50@60 | 16MB | CL-GD5428 | CT2830| SCC-1 | MT32 | Fast-SCSI AHA 1542CF + BlueSCSI v2/15k U320
2) SIS486 | 486DX/2 66(@80) | 32MB | TGUI9440 | LAPC-I
keropi wrote on 2025-04-26, 14:48:I have finished upgrading the 486slc33 amstrad megapc motherboard using a custom interposer specifically designed for this mobo and a 486SXLC2 cpu.
I'm impressed. I considered lifting some pins of the package and running a wire around, in the air, with perhaps 3-4 SMD caps to nearby GND pins, to provide the lower Vcc voltage. This already has a VRM integrated? SMPS as far as I can tell?
I gotta ask, how much did it cost to have this interposer manufactured and what service did you use? The EU services are a bit on the expensive side compared to China, so much in fact that I think twice before starting a new PCB project.
yep, the vrm in on the top right corner and it's the AP62250WU-7
the flex was made by JLC, it was pretty cheap - I think there was also a promotion or something
