New 486dlc build problem.

Discussion about old PC hardware.

New 486dlc build problem.

Postby balthazor4ever » 2018-7-17 @ 06:03

I just recently decided to upgrade my 386. i bought 128kb of cache to reach 256kb, I changed the tag ram to address the bigger cache and configured the jumpers. i added 16mbs of ram. everything worked fine. Then i decided to put a 486dlc on the secondary socket. I turned on the pc and both cpus seem warm but the screen shows nothing and there is no sound from the pc speaker to indicate what's wrong. any ideas?
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Re: New 486dlc build problem.

Postby Phido » 2018-7-17 @ 06:26

I would remove the ram and put in the smallest amount that you knows works.

Is the CPU inserted correctly? Do you need to configure any jumpers to disable the on board cpu.
Try disabling your cache or reseting the cmos.

Also in your pictures there is no power going to the motherboard, I assume you have connected the power when you tried it.
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Re: New 486dlc build problem.

Postby balthazor4ever » 2018-7-17 @ 06:39

The ram works correctly and is identified. 4+16mb=20. the cache is reported correctly. and without the 486dlc the board works as intended. there is no battery on it. i removed it because it was starting to show signs of leaking. i can't find any jumpers except the one to configure the cache and and one to configure the monitor type. :-( i inserted the 486dlc putting the gold mark towards the pin 1 of the socket
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Re: New 486dlc build problem.

Postby Anonymous Coward » 2018-7-17 @ 08:02

The problem is that you already have a 386DX-40 soldered to the board. There may be a jumper to disable it. If not, the only option is to cut off the CPU. You have to be really careful doing that so that you don't damage traces. I had a similar problem with my old ALi 386 board.
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Re: New 486dlc build problem.

Postby balthazor4ever » 2018-7-17 @ 08:07

really? OMG. then why does it have the socket for? thank you i'll consider it as i'm a bit afraid of doing it. is there any chance the factory preconfigured jumpers have something to do with it?
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Re: New 486dlc build problem.

Postby Phido » 2018-7-17 @ 08:31

Isn't there a pin you can short out which will disable the cpu?
viewtopic.php?f=46&t=49376&start=140
"Depending on the revision of your AMD 386DX, you can completely disable the CPU by setting the FLT# pin to ground. Luckily, the FLT# is next to a GND pin, and you can desolder the FLT# pin and bend it over such that it is touching the GND pin. Turn on your soldering iron and reflow the solder of the GND. Once you float the AMD 386DX, you can solder on a PGA-132 socket and run any CPU. You may not have to do the FLT# to GND solder procedure if your motherboard has a jumper to float the onboard CPU."
You might get away with some foil on some scotch tape if you can cut it fine enough and have steady enough hands and are confident with what you are doing.

I would have thought there would be a bios option or a jumper.

Do you have a mobo manual or the make and model of the mobo or any identifying parts.
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Re: New 486dlc build problem.

Postby jesolo » 2018-7-17 @ 08:46

I would first try and identify your motherboard to see what the function of each jumper is.
Try this site: http://arvutimuuseum.ee/th99/#1
Based on your first picture, there are jumpers at JP5 & JP6 (close to the cache) and below your memory. Next to that appears to be a JP2 that doesn't have any pins and also JP7 & JP8 (next to the CPU's).
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Re: New 486dlc build problem.

Postby balthazor4ever » 2018-7-17 @ 08:55

the 2 jumper sets close to the cache chips are for configuring the cache size. the board was bought some time ago from ebay so i don't have any documentation. but based on a sticker on it and some googling it should be an abit fa3.
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Re: New 486dlc build problem.

Postby balthazor4ever » 2018-7-17 @ 13:26

after some searching i found a motherboard that looks like mine. http://arvutimuuseum.ee/th99/m/C-D/32319.htm
it has three jumpers for the 486dlc jp9 jp10 and jp11. there are contacts on my motherboard but no soldered jumpers. could they be the ones I need to close? how could i test them?
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Re: New 486dlc build problem.

Postby Anonymous Coward » 2018-7-17 @ 13:31

It's worth a try, but in my opinion those jumpers don't disable the onboard CPU, they just enable/disable the Cyrix cache control lines.
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Re: New 486dlc build problem.

Postby jesolo » 2018-7-17 @ 13:37

Anonymous Coward wrote:It's worth a try, but in my opinion those jumpers don't disable the onboard CPU, they just enable/disable the Cyrix cache control lines.

I agree with that.
Isn't there perhaps an option in the BIOS to enable or disable the soldered CPU?
However, if you do manage to get the Cyrix CPU working, then you will probably still have to "solder" in jumpers at those locations in order for the Cyrix CPU to function properly.

Based on the BIOS ID string, you should be able to identify the manufacturer. Sometimes, the model number is also displayed on the POST screen
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Re: New 486dlc build problem.

Postby balthazor4ever » 2018-7-17 @ 15:07

i checked the bios. there are options for the l1 cache, for normal or weitek fpu but nothing for the second socket. could i try a conductive pen for a start?
Last edited by balthazor4ever on 2018-7-17 @ 16:12, edited 1 time in total.
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Re: New 486dlc build problem.

Postby keropi » 2018-7-17 @ 15:18

Phido wrote:Isn't there a pin you can short out which will disable the cpu?
viewtopic.php?f=46&t=49376&start=140
"Depending on the revision of your AMD 386DX, you can completely disable the CPU by setting the FLT# pin to ground. Luckily, the FLT# is next to a GND pin, and you can desolder the FLT# pin and bend it over such that it is touching the GND pin. Turn on your soldering iron and reflow the solder of the GND. Once you float the AMD 386DX, you can solder on a PGA-132 socket and run any CPU. You may not have to do the FLT# to GND solder procedure if your motherboard has a jumper to float the onboard CPU."
[...]


this is interesting as I want to add a PGA132 socket to a motherboard that has an onboard AM386DX40 - is there a place that has the 386 pinout so I can try this pin?
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Re: New 486dlc build problem.

Postby balthazor4ever » 2018-7-17 @ 15:55

viewtopic.php?f=46&t=53533 i found this here on vogons. in the last image i see it doesn't have the 386dx soldered but also has jp7 pins 1-2 closed and jp9 jp10 and jp11 closed with some solder.
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Re: New 486dlc build problem.

Postby feipoa » 2018-7-17 @ 19:27

Wait, I haven't read this thread yet, but wanted to stop you from cutting off the Am386DX. You only need to set FLT# to GND on the Am386DX to disable it. I've done this on 4 motherboards and will send you a photo of how to do it.
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Re: New 486dlc build problem.

Postby keropi » 2018-7-17 @ 19:33

^ excellent thanks feipoa
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Re: New 486dlc build problem.

Postby feipoa » 2018-7-17 @ 19:44

In the photos below, I am connecting FLT# to GND. This sets floating all the pins of the Am386DX, but it is only for certain model numbers of the Am386DX. I'll have to check my previous post - this is where I mentioned which revision of the Am386DX can do this. I think it was C or later.

What I have done in these photos is to desolder the FLT# lead and solder it onto a connected GND lead.

Am386DX_all_pins_set_floating_1.jpg

Am386DX_all_pins_set_floating_2.jpg
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Re: New 486dlc build problem.

Postby feipoa » 2018-7-17 @ 20:07

This FLT# mod trick first appeared in one of my posts on another forum, namely, https://www.eevblog.com/forum/repair/ho ... illoscope/

Looking at the Am386 spec sheet, it mentions that FLT# is only found on the PQFP format for the chips (which is what you have) and is for rev C0 or later. If you have a better photo of your Am386DX, we can determine if it is C0 or later.

I do not understand why your board contains a a PGA132 socket, yet no jumper to set FLT# to GND. My board was similar.
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Re: New 486dlc build problem.

Postby balthazor4ever » 2018-7-17 @ 21:07

Here are some more photos. the only difference i found with a motherboard with the exact layout are jp7 jp9 jp10 and jp11. maybe jp7 is the flt jumper.
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Re: New 486dlc build problem.

Postby feipoa » 2018-7-17 @ 21:22

Looks like you have rev D, so it contains FLT#.

Does your motherboard contain JP7? If so, use a multi-meter to see if it goes to the Am386DX pins that I'm using in my photos.
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