Magnavox 386SX-16 Upgrade options?

[[Chris]]

I'm sure you remember my earlier post about this PC

I've been considering maxing out the ram to 8MB via the SIMM bank, but what confuses me is in the service manual, it mentions that this pc can expand up to 16MB of total RAM via expansion boards.

Is this expansion board the service manual mentions is one of those expansion modules that uses one of the ISA slots? or how?

Oh and here's the sole SIMM bank it provides for the 8MB module which i plan on getting (currently in use by a 4MB module)

As for the FPU, what kind of socket is this so i know which 387SX Math Co-processor to get? Are there any processor upgrade kits that uses this socket (like an AMD Am486 or Am5x86?)

I also plan on sticking in a CF card adapter for extra space (at least 256MB) and for easier addition/removal of files from/to this PC, while keeping the original HDD (40MB Seagate ST157A) for the OS. Here's the specifications from the service manual:

Which CF card adapter would you guys recommend to use as i see various adapters on eBay but don't know which one would work best?

Last but not least, if i decide to stick with just 8MB of RAM, what would be a recommended ISA Ethernet card that would work best for Windows 3.11, as well as a graphics card for at least 24-bit color, as i'm ditching the modem card (it's not original to the PC which i added a few years back)

A quick look at the internals:

 

[krebizfan]

The square FPU socket will take a 387SX-16. 387SX-25 might be easier to find and has no problems running slower. Any CPU upgrade would require unsoldering the 386SX.

ISA memory expansion card is the only way to add RAM beyond what is stuck on the motherboard. Some 8MB SIMMs didn't work with some SIMM sockets because of design changes and I have no idea how to determine which 8MB SIMM will work on your motherboard. ISA cards can do 8 MB with a few capable to do 12MB with a even harder to locate daughtercard.

Network card: 3Com Etherlink is common, reliable, cheap, and has drivers for most of the major operating systems that could run on this system.

 

[Stone]

Some 8MB SIMMs didn't work with some SIMM sockets because of design changes and I have no idea how to determine which 8MB SIMM will work on your motherboard.

Since the manual says 'PS/2 type' I'd go with that.

 

[PeterNC]

RAM: you could install this unit: http://www.memory4less.com/m4l_itemdetail.aspx?itemid=1463985928&partno=3DHP1818-4702. I installed one in my 286 (same MOBO / case).
VGA: Diamond Speedstar 64 2MB ISA will give you 800*600 24BIT.
FPU: any 80387SX should work as long as it is >= 16MHZ.
CPU: I am not sure there are ISA cards that would supersede the MOBO CPU. I am also not sure a faster CPU would be supported by the Philips BIOS.
NIC: NE1000 / NE2000 / 3COM EtherLink II / 3COM EtherLink III (all ISA) are good bets. The older: the better is usually supported by Windows 3.11.

Drivers for this machine: https://drive.google.com/file/d/0B1s--ZfwkGSMZlhWTDZFb1QwRXc/edit?usp=sharing.

Good luck!

 

[vwestlife]

The square FPU socket will take a 387SX-16. 387SX-25 might be easier to find and has no problems running slower. Any CPU upgrade would require unsoldering the 386SX.

Cyrix did sell "486SRx²" CPU upgrades that were designed to clip on top of a 386SX chip without needing to unsolder it. However, these upgrades are exceedingly rare, and I have no idea how reliable the clipped-on connection is.

 

[raifield]

I read on Walsh's IBM Model 25 site that most of the 16MHz 386SX chips cannot be upgraded with a clip-on. Later revisions of the 16Mhz chip will work, but you need a certain stepping level. The site states that a 386SX running at 20MHz (and presumably faster) will accept the upgrade and I assume this advice works for all 386SX systems, not just the Model 25.

 

[smeezekitty]

Cyrix did sell "486SRx²" CPU upgrades that were designed to clip on top of a 386SX chip without needing to unsolder it. However, these upgrades are exceedingly rare, and I have no idea how reliable the clipped-on connection is.

I can't see how that would possibly work because the onboard cpu would still continue to try to execute code
and surely the signals would clash

 

[[Chris]]

Gave the OS a little facelift, surprised Calmira doesn't eat up too much memory:

 

[Unknown_K]

I can't see how that would possibly work because the onboard cpu would still continue to try to execute code
and surely the signals would clash

I would think one of the leads turns off the old processor. I have one of those Cyrix CPUs and sold one to a member here years ago and it worked for them (if you have the overhead clearance).

 

[lowen]

I can't see how that would possibly work because the onboard cpu would still continue to try to execute code
and surely the signals would clash

Pin 28 on 386SX processors after the SX-16 is a signal called 'FLT#' and is the mechanism that allows this to work. Basically, the Cyrix clip-on acts as an on-circuit emulator (ONCE) in Intel's terminology (in-circuit emulation typically requires removal of a emulated chip; Intel's FLT# signal allows this to happen with the processor soldered in). See the section in the Intel386SX datasheet about 'Float' (starts on page 60 in the PDF I have here).

 

[RWallmow]

I would think one of the leads turns off the old processor. I have one of those Cyrix CPUs and sold one to a member here years ago and it worked for them (if you have the overhead clearance).

I think that was me, it didn't work for me, those upgrade CPUs come in specific bus speeds, the one I got from you was a 25/50Mhz chip, my bus speed was limited to 20mhz and it didn't work for me. It did work for the person I passed it along to though.

To the OP on the topic of CF cards, the adapter matters much less than the CF card itself, not all CF cards support true IDE mode, I have known Lexar, Transcend, and Sandisk to usually work, don't cheap out too much on the card, you will likely regret it. Also one other thing to think about your BIOS almost certainly has a 520MB limit, so cards larger that will have wasted space unless you install a DDO or extended/modded BIOS (XT-IDE BIOS chip in a BOOT-ROM socket on a NIC card is popular choice).

 

[smeezekitty]

CF cards seem very hit in miss with the BIOS. For example my 486DX/33 would never work right with a CF but my 486DX4/120 works great with the same cards

 

[[Chris]]

Also anyone here good at soldering SIMM slots? I'm going to admit, getting this machine prepared isn't an easy task when the SIMM slot for the RAM is very temperamental if not enough pressure is applied (it spits out false positives as a result). Note that the ram isn't actually failing, but due to lack of enough pressure to make proper contact, the BIOS detects this so-called failure.

This is what i mean about having to apply enough pressure as the two pieces that hold the RAM was too worn out to hold it properly

A peek at the VGA BIOS:

 

[vwestlife]

I wonder who made that "Philips" ROM BIOS... Phoenix? Award?

 

[PeterNC]

Very hard to say. The chipset is UMC. The BIOS supports many EU languages. The BIOS is also very different from other systems. Definitely not a standard clone BIOS. Philips used to be big in industrial automation / semiconductors and so on (before semiconductors were spun off as NXP).

 

[[Chris]]

Picked up a 3Com Etherlink III ISA ethernet card. Works wonders. Now to just get the ISA video card. I'm debating whether i should get an ISA to PCMCIA card adapter (which would give me 1 or 2 PCMCIA card slots) or not.

 

[SpidersWeb]

Why would you want PCMCIA? It's mostly all modems and network cards out there.

 

[[Chris]]

Why would you want PCMCIA? It's mostly all modems and network cards out there.

Planning on throwing in a CD-ROM drive but unsure if replacing the 5.25 diskette drive or using an external one as I have a Panasonic external CD-ROM drive with the provided PCMCIA card laying around and the second slot to use an Ethernet card should I decide on an external. Then again I could always go the Paralell port route.

 

[SpidersWeb]

hmm PCMCIA would probably be faster than parallel - might not be a bad option.

The ideal solution is SCSI, but finding the card + cables + enclosures + drive - probably not worth the hassle unless you come across it.

 

[RWallmow]

hmm PCMCIA would probably be faster than parallel - might not be a bad option.

The ideal solution is SCSI, but finding the card + cables + enclosures + drive - probably not worth the hassle unless you come across it.

All the PCMCIA ISA adapters I have come across have all had odd limitations or quirks, or were SLOW as molasses, I don't think its a very ideal solution for expansion on a desktop.

I too would say SCSI gives decent external expansion, CD, HD, Zip/Jaz, Scanners, quite a bit of expansion options. However it too is not without quirks, like termination and cabling issues, but there's a lot of SCSI gear out in the wild, you can do quite a bit with it, and its pretty fast and quite reliable once you get termination and cabling sorted out.