Try to convert Compaq Presario 425 to Compaq Prolinea net 1/25 \ VOGONS

Try to convert Compaq Presario 425 to Compaq Prolinea net 1/25

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First post, by tabm0de

Posted on 2019-09-20, 07:44

tabm0de Offline

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Joined: 2016-12-18, 19:33
Location: Stockholm, Sweden

So basiclly its hard to find the "business" version of "Compaq Presario 425".

Compaq Prolinea net 1/25 are identical to Compaq Presario 425 except it comes with network module instead of gamepad port / modem.

I own two Compaq Presario 425 which has the "port" for the network module, i luckily found two NOS network modules for the Prolinea but never did have the luck to get them working on my Compaq Presario 425's, so finally i was able to purchases the just the board part of a Compaq Prolinea from ebay.

After receiving the Prolinea board with harddrive i swapped it with my board in Compaq Presario 425 board and booted up to windows and connected to the internet without problems, at this point i also wanted to check that my NOS network module worked and replaced the network module on the Prolinea board. And ye it worked without any problems also 😉

As i dont see any REAL differences on the boards, so i decided to the easiest and clone the bios 😉 which sadly the computer just boots up but still dont get the network module working, computer can find the card but there is no communication going on what so ever.

As i cant find any motherboard diagram of the boards and the only thing that do find is different is that my boards have two chips for the gamepad:

1The TLC556 series are monolithic timing circuits
2fabricated using the TI LinCMOS process, which
3provides full compatibility with CMOS, TTL, and
4MOS logic and operates at frequencies up to
52 MHz. Accurate time delays and oscillations are
6possible with smaller, less-expensive timing
7capacitors than the NE556 because of the high
8input impedance. Power consumption is low
9across the full range of power supply voltages.

Which i will try to remove to see if those interfere with the network card, since they are linked and connected just next to the bios.

https://i.imgur.com/moEVLxl.jpg

Here are the boards ( yes these are different revs, but my other presario is the same rev with exactly the same chips except the gamepad chips ):
Presario

https://i.imgur.com/NIWH6y9.jpg

Prolinea

https://i.imgur.com/RuguUYJ.jpg

* also to add the WHY is because presario only have two isa slots 😉 which i use one for soundcard and one for scsi 😉 and network is always fun to have hehe

naa, nothing yet...

Reply 1 of 4, by tabm0de

Posted on 2019-09-20, 12:54

tabm0de Offline

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Rank: Member
Posts: 434
Joined: 2016-12-18, 19:33
Location: Stockholm, Sweden

After looking around the board again i found a "0" ohm resister next to a chip that i cant find any information about on the prolinea which dont exist on the two presarios, i will wait for that on until monday 😀

naa, nothing yet...

Reply 2 of 4, by reflexve

Posted on 2025-12-20, 01:00

reflexve Offline

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Rank: Newbie
Posts: 8
Joined: 2025-10-30, 16:06

tabm0de wrote on 2019-09-20, 12:54:

After looking around the board again i found a "0" ohm resister next to a chip that i cant find any information about on the prolinea which dont exist on the two presarios, i will wait for that on until monday 😀

Hey there tabmode, it does not yet permit me to direct message anyone, but I've got my original Presario 425 here and had a few questions if you have any time. Thanks!

Reply 3 of 4, by tabm0de

Posted on 2025-12-20, 22:08

tabm0de Offline

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Rank: Member
Posts: 434
Joined: 2016-12-18, 19:33
Location: Stockholm, Sweden

reflexve wrote on 2025-12-20, 01:00:

tabm0de wrote on 2019-09-20, 12:54:

After looking around the board again i found a "0" ohm resister next to a chip that i cant find any information about on the prolinea which dont exist on the two presarios, i will wait for that on until monday 😀

Hey there tabmode, it does not yet permit me to direct message anyone, but I've got my original Presario 425 here and had a few questions if you have any time. Thanks!

Sure

naa, nothing yet...

Reply 4 of 4, by reflexve

Posted on 2026-01-27, 01:30

reflexve Offline

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Rank: Newbie
Posts: 8
Joined: 2025-10-30, 16:06

tabm0de wrote on 2025-12-20, 22:08:

reflexve wrote on 2025-12-20, 01:00:

tabm0de wrote on 2019-09-20, 12:54:

After looking around the board again i found a "0" ohm resister next to a chip that i cant find any information about on the prolinea which dont exist on the two presarios, i will wait for that on until monday 😀

Hey there tabmode, it does not yet permit me to direct message anyone, but I've got my original Presario 425 here and had a few questions if you have any time. Thanks!

Sure

Sorry it took so long to respond! I've been busy with work and I was also resolving a different issue with my unit, the internal vga cable needed some resoldering. I was able to read your DM, but I cannot respond to it yet it seems due to my low post count.

This computer was my original PC that I learned on and which launched my tech career. I live in Portugal these days and on my last trip to Seattle chose to bring it back to Lisbon with me. TSA unfortunately trashed the case, it's severely damaged so I'm on the lookout for a dead unit I can steal the case from (or a live one that just becomes the parts PC for future failures), but otherwise it works fine.

I have some thoughts on the primary areas I'd like to see if there is any path to updating:

1) The 20MB memory limit. The docs for the chipsets show an upper limit of 64MB, and other Compaq models with this chipset support up to that limit. I have seen it try to count up past 20 when higher amounts are installed (and sometimes some odd lower number like 5MB), but it always fails on an odd number and won't boot past the BIOS. I am curious where the limit is implemented. The attempts to count the full amount imply to me it's not the BIOS, although it potentially could be (I suspect this system does not use flash so it's not clear that it would be easy to do a hacked BIOS), but I've also wondered about some of the small chips down near the memory itself, I noticed three of them and there are three banks, wondering if those are some form of refresh/redriver that could be the limiting factor. I was wondering if you had any ideas or thoughts on this, those chips I can't really find any information on, unfortunately.

2) The CL-GD5420 graphics chip. This has one irritating limitation, 256 colors. It is the only version of the chip with that limitation, and documentation says the 542x line is pin compatible. Curious if replacing the chip with a 5421 (I am not sure it was ever used despite being in the spec doc) or 5424 could potentially get past that limit.

3) Enabling write-back cache. Back in the 90's I found a voltage regulator and managed to install an AMD 5x86 133Mhz. It works just fine that way. However it appears the CPU runs by default in write-through mode, and write back mode is a simple jumper on most other Compaq 486's of the era. There are projects to build voltage adapters that include jumpers for this but I've had difficulty finding one. This would be a significant performance boost however, and wondered if you had any suggestions.

4) Getting the front side bus to 40Mhz. The clock chip seems to support FSB speeds, and in 25Mhz mode if you pull down pin 20 it should switch to 40Mhz. Currently pin 20 is not connected to anything so far as I can tell. It would be nice to figure out if it would be possible to bring the speed up, which obviously gets the CPU to 160Mhz.

Anyway it's a shot in the dark. Currently I've got it modified with a Gotek with FlashFloppy firmware and a XTIDE boot rom on 3com card so I can use large drives (CF card adapter). Unlike you I don't have the proprietary ISA connector on the motherboard for a network card, it would have been nice to free up one more slot. But I was inspired by your post to consider others may be interested in pushing this past it's historical limits.

Also, if anyone has any clue where I could find a replacement for the case or where I could get one of the Net1/25/33 motherboards with network adapters I'd love to know. Tougher and tougher to find this stuff on eBay these days.

Thanks again, and I apologize for any naïvety here!

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