Computer won't even boot to bios!

[RetroB1977]

3 hours ago, wierd_w said:

Re-reading the opening post, the OP has already disconnected all drives.

 

The image is pretty grainy, but it looks like there are yellow tantalum caps near the AT power connector.  Those should be inspected for any signs of scorching or cracks, and should be touched gently while power is on to see if any of them feel hot or warm.

 

If the OP has (and knows how to use) an LCR meter, they should check them. 

FYI This machine was stored in a barn for who knows how long so I wouldn't be surprised if the caps are going.

[RetroB1977]

6 hours ago, RodLightning said:

Could be a confused BIOS.  If everything suggested previously doesn't work, also try pulling that daughter card and boot without it.  Is it a modem board on the riser?  Network card or something else?  I remember sometimes having lockup on boot with 90s pcs after swapping hardware around.  After a few cmos resets and tinkering, the problem would go away.   I would definitely replace the battery.   I would also probably try to get it back to a bootable state with the original drive and stock configuration before going any further.

 

my two cents

All I had in there was a Adlib and some other sound card but I removed them.

[wierd_w]

Those look like ceramic caps now that I have a better look. It is very rare for a ceramic cap to fail, and not ... explode..  so I doubt that is the issue. Wouldnt hurt to check to make sure none of them have full continuity across them, but they are probably fine.

 

Does the problem persist with the backplane removed?

 

also, those 72pin simms are miss-matched.

[RetroB1977]

2 minutes ago, wierd_w said:

Those look like ceramic caps now that I have a better look. It is very rare for a ceramic cap to fail, and not ... explode..  so I doubt that is the issue. Wouldnt hurt to check to make sure none of them have full continuity across them, but they are probably fine.

 

Does the problem persist with the backplane removed?

 

also, those 72pin simms are miss-matched.

Ok. You mean the ISA backplane? Yes. 

 

The RAM is the exact same way I found it but with only one stick it doesn't work either.

Edited March 27, 2022 by RetroB1977

[RetroB1977]

Hmm... I can't find that clear CMOS jumper.

[wierd_w]

No, it needs 2 simms for the full 32bits wide data bus. (30 pin simms are 8bit wide, 72pin are 16bit wide, DIMM is 32bit wide)

If this was a 286, you could run it with just one, but this is a 486, and it needs 2.

 

However, mismatched simms can cause all manner of problems. Do you have a matched set to try in it?

[RetroB1977]

1 minute ago, wierd_w said:

No, it needs 2 simms for the full 32bits wide data bus. (30 pin simms are 8bit wide, 72pin are 16bit wide, DIMM is 32bit wide)

If this was a 286, you could run it with just one, but this is a 486, and it needs 2.

 

However, mismatched simms can cause all manner of problems. Do you have a matched set to try in it?

Nope.

[wierd_w]

That sucks.

 

(but has made me have a very silly idea, and then immediately wonder if anyone has ever done it yet...)

 

(silly idea spoilered because it really doesnt belong here.)

Spoiler

A SIMM module is actually rather simple electronically. A module that uses SRAM and just ignores the strobe signals-- or uses the strobe signals as a timing signal-- and which has 4 2pin jumpers for the sense detect configuration, which is totally empty except for some DIP sockets to accept DIP SRAM modules, should be totally doable.  Making them in pairs with one taller than the other (so that the stickout of the socket isnt an issue), would be very useful in keeping these old machines alive, as a bad chip would be easily replaced.

 

[RetroB1977]

2 minutes ago, wierd_w said:

That sucks.

 

(but has made me have a very silly idea, and then immediately wonder if anyone has ever done it yet...)

 

(silly idea spoilered because it really doesnt belong here.)

  Reveal hidden contents

A SIMM module is actually rather simple electronically. A module that uses SRAM and just ignores the strobe signals-- or uses the strobe signals as a timing signal-- and which has 4 2pin jumpers for the sense detect configuration, which is totally empty except for some DIP sockets to accept DIP SRAM modules, should be totally doable.  Making them in pairs with one taller than the other (so that the stickout of the socket isnt an issue), would be very useful in keeping these old machines alive, as a bad chip would be easily replaced.

 

I could buy some if you think it would work.

[wierd_w]

Do you have other systems that could benefit from the RAM if this is a bust?  If you are willing to take that risk/can still use the RAM, go ahead-- otherwise.. *shrug*

[RetroB1977]

28 minutes ago, wierd_w said:

Do you have other systems that could benefit from the RAM if this is a bust?  If you are willing to take that risk/can still use the RAM, go ahead-- otherwise.. *shrug*

Nope.

[DragonGrafx-16]

7 hours ago, RetroB1977 said:

 

 

Yuck... I don't like that the CPU is soldered to the board. 

[RetroB1977]

Just now, DragonGrafx-16 said:

Yuck... I don't like that the CPU is soldered to the board. 

I don't like that "486SX-33" written on it. I like that OverDrive slot though.

[Keatah]

6 hours ago, RetroB1977 said:

Hmm... I can't find that clear CMOS jumper.

That's ok. The small Quad Flat Pack 100-pin chip labeled OPTI F82C206 is going to be the clock chip and CMOS memory (along with other PC/XT/AT functions). Just say'n what it does.

 

Disconnecting the external battery for 15 minutes should ensure a wiped CMOS. My board (not like yours) clears itself within 3-10 minutes of no power. My board is totally different model, and is a less integrated. In fact mine has design cues of having been a 386 design updated to be a 486! 1992. Just commenting.

 

I see that your board has some empty sockets for video memory and cache AND an OverDrive socket. There ARE some expansion possibilities! But the first goal is to get it running reliably.

 

[Keatah]

9 minutes ago, RetroB1977 said:

I don't like that "486SX-33" written on it. I like that OverDrive slot though.

 

You can use this..

 

 

To fix it like so..

 

[eightbit]

If a controller card is not connected at all to my machine it will sit there like this on the POST boot screen for an EXTENDED period of time before it reports hard disk fail and no floppy. Why don't you try plugging the riser board and controller card back in but no cables (no hdd, no floppy) and turn it on and wait to see if it reports the failure.

[RetroB1977]

19 minutes ago, eightbit said:

If a controller card is not connected at all to my machine it will sit there like this on the POST boot screen for an EXTENDED period of time before it reports hard disk fail and no floppy. Why don't you try plugging the riser board and controller card back in but no cables (no hdd, no floppy) and turn it on and wait to see if it reports the failure.

Controller card?

[eightbit]

Just now, RetroB1977 said:

Controller card?

 

Ahh, nevermind. I see your board has an IDE connection on the board now that I look closer. I am used to 486's utilizing I/O cards. Are you powering this on without the riser card installed? Maybe this motherboard needs it in place in order to POST.

 

 

[RetroB1977]

Just now, eightbit said:

 

Ahh, nevermind. I see your board has an IDE connection on the board now that I look closer. I am used to 486's utilizing I/O cards. Are you powering this on without the riser card installed? Maybe this motherboard needs it in place in order to POST.

 

 

I've tried it both ways.

[RetroB1977]

34 minutes ago, Keatah said:

That's ok. The small Quad Flat Pack 100-pin chip labeled OPTI F82C206 is going to be the clock chip and CMOS memory (along with other PC/XT/AT functions). Just say'n what it does.

 

Disconnecting the external battery for 15 minutes should ensure a wiped CMOS. My board (not like yours) clears itself within 3-10 minutes of no power. My board is totally different model, and is a less integrated. In fact mine has design cues of having been a 386 design updated to be a 486! 1992. Just commenting.

 

I see that your board has some empty sockets for video memory and cache AND an OverDrive socket. There ARE some expansion possibilities! But the first goal is to get it running reliably.

 

Well the battery hasn't been in the thing for a forever so yeah...

[eightbit]

I think this protect/enable jumper may be the CMOS clear jumper. Try moving it from the first two pins to the second two (enable) and power on. Then power off and bring it back to protect.

 

 

[RetroB1977]

3 minutes ago, eightbit said:

I think this protect/enable jumper may be the CMOS clear jumper. Try moving it from the first two pins to the second two (enable) and power on. Then power off and bring it back to protect.

 

 

Nothing... Could this be it?

 

[eightbit]

That is just the primary IDE enable jumper....secondary missing of course since they didn't add it to this board. You can pull that jumper off and see if you at least get something else. Maybe the IDE controller on this board is toast.

 

I will mention that there appears to be some corrosion around that battery header. Looks like some acid leakage residue there.

Edited March 27, 2022 by eightbit

[RetroB1977]

25 minutes ago, eightbit said:

That is just the primary IDE enable jumper....secondary missing of course since they didn't add it to this board. You can pull that jumper off and see if you at least get something else. Maybe the IDE controller on this board is toast.

 

I will mention that there appears to be some corrosion around that battery header. Looks like some acid leakage residue there.

Yeah, the battery started to leak.

[eightbit]

You should clean that area and neutralize the acid with some vinegar or lemon juice. Follow up with a good scrub with a toothbrush and 91% or better alcohol. The leakage was very close to the IDE channel. You just never know what was actually damaged if anything. Maybe while you thought you caught it in time you really didn't and some components or traces were severed.