Packard bell PB450 two beeps

[ahtoh]

Hi, I have a PB450 motherboard that won't turn on.
The monitor seem to turn on but stays black and I get two beeps.
I already tried changing the memory, disabling onboard memory and also tried to connect external cmos battery but it did not help

Also flashed bios using recovery disk (J17) and it successfully flashed (got four beeps in the end) but the problem still persists.
Tried to disable on-board video using jumpers and the only difference is the monitor stays in stand-by and not turns on, and two beeps again.
Unfortunately I have no ISA graphics card to try so I can not verify if it is the graphics problem.

Anyone knows what could be the cause?

 

[Raven]

Make sure the jumpers are set properly (see here):
http://www.uktsupport.co.uk/pb/mb/450.htm

Needs to have the right settings for CPU/RAM/etc..

What type of memory have you tried? There's a lot of specifics on that page for this board, such as no EDO, has to be specific latency, certain settings for different memory types, etc..

So when you flashed the BIOS you say you did it with a recovery disk.. did you do this with this motherboard itself running the operation? If so, unless this has a separate BIOS flash routine then that means you booted to a floppy, so there's (probably) nothing wrong with the CPU/memory. If that's correct, the best thing to do would really be to test with another video card. Since it's not refusing to boot outright the chip is likely OK, so a corrupted VBIOS or VRAM issue could be to blame. There are VRAM chips on the board presently, yes? If not, that'd of course be a likely candidate.

It's also possible to flash the VBIOS on Cirrus Logic chips of this era, so if everything else gets eliminated as a possibility you could try that. This is pretty unlikely to be the problem, so really don't do this unless you try everything else. If you do end up doing that, note that running the file for one of those instantly applies it with no warning or prompt, just a few lines of output saying the new VBIOS version. It's also possible to flash the wrong version with the wrong amount of VRAM, so take care with that (I can possibly help locate the right one if you can't find it).

 

[ahtoh]

Yes I verified all jumpers and memory type is correct. I have some spare sticks from another packard bell board.
The board indeed has some built-in bios recovery procedure, that is activated with J17. It only uses beeps to indicate the progress and shows nothing on the screen.
I'm not able to boot from any drive and I have no output on the screen, so I can't update VBIOS

Here are a few shots of the VGA chip area on the motherboard

 

[Raven]

Could have sworn I'd replied to this, but maybe I never hit the button.

Those NEC chips are very likely the VRAM, and they're soldered in so not much chance of them coming unseated (lol).

I'd really recommend trying to get another video card to test with, but if you really can't then if you have electronics know-how and the tools you could check the signals on the lines of the video chip.

I've studied the 542x inside and out in my quest to bizarrely extend my Presario 425's abilities, so I happen to know that in this document http://old.vgamuseum.info/images/stories/doc/cirrus/cl-gd542x.pdf Cirrus published the pinout of the graphics chip (page 3-10 through 3-12). Since this is built into the motherboard and it's a 486 board I imagine they probably hooked it up over VLB (they'd be kinda dumb not to, since it's essentially free performance) but it could also be on the ISA bus. A quick glance at the pinouts shows that they look the same, but I didn't check every pin.

Also, just in case you didn't realize - there's space for some more VRAM to upgrade the graphics on this board model, down below the NEC chips.

 

[ahtoh]

Do you know if it is possible to replace 5428 with 5424?
I happen to have another dead board with 5424 chip

 

[Raven]

It should be entirely possible - the pinout for that line of chips seems to be identical as far as I'm aware, and I very much doubt there's a difference in the VRAM they use. If you do do that, let me know, because that'd be an interesting upgrade for my All-In-One Compaq 486 box (which has a 5420)..

That said, what's stopping you from getting your hands on an ISA card to throw in there and test with? I have dozens, so maybe I'm out of touch with how rare they are?

*checks*

They're a bit pricier than I thought, but there's definitely some affordable ones out there:
https://www.ebay.com/sch/i.html?_fr...0.H0.Xisa+vga.TRS0.TSS0&_nkw=isa+vga&_sacat=0

 

[ahtoh]

I now figured out the two beeps indicates cmos checksum error, that is expected.
So when I press F1 it allows me to boot off the floppy drive, but I'm still not able to get anything on the screen.
I also managed to run diag.exe that can generate a report and save to the disk. And I got two different BIOS checksums for two runs.
So I now suspect it is the BIOS chip that could be faulty.

 

[Raven]

Now that you can do that, you can perhaps flash the BIOS. If the BIOS was the problem I'd expect to see more issues, to be honest - it still seems like the video card to me. That said, the checksum thing is definitely weird - where'd you get this diag tool? Is it something specific for this board or PB boards?

 

[ahtoh]

The VGA was at fault.
I was able to boot with another VGA plugged in and all works fine.

Replaced 5428 chip with 5424 and it did not work.
The board will not start at all now.
Though the marking say 5424/8 on the board

It could be that I burned the 5424 chip when desoldering it from a donor board though
Will try to replace with a new 5429 chip

 

[retro-pc_user]

How's it coming along?

 

[ahtoh]

I fixed the board today
replaced the chip but it did not work,
then checked passives and found an open inductor L12
replaced it and this fiexd the board
Now I have PB450 with Cirrus logic 5429 chip