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Vtech Laser Turbo XT - POST problem

3

3pcedev

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Jun 8, 2014
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Hi all,

Just new to these forums and I am hoping that someone can help me out. I've got a Laser Turbo XT which I have kept for nostalgia. When it went into the cupboard about 12 years ago it was working fine.

Today I decided to power it up; however I was greeted with a POST beep code. I have done quite a bit of searching but I can't seem to find any reference to what the beep code means.

The beep code is short-long-short. Also the pitch of the beep changes from low-high-low respectively. The screen also goes solid white on power up.

Could someone with a laser manual (or some knowledge of Laser XT's) identify this code?

Thanks! Matt.
 
Welcome to these forums.

I do not know what the beep codes correspond to on a Laser XT, but something basic to try is to reseat the cards. With power off, pull out the cards and then put them back in. Doing that a few times should resolve any poor electrical connection that may have developed between a card and its socket.

The Laser XT documentation at [here] indicates the presence of a NiCad battery to maintain the computer's date and time when the compuer is powered off.
Old NiCad batteries leak (a blue/green substance), and the leakage can destroy electronics. You should inspect the NiCad battery to see if it has started leaking.

3pcedev said:
The screen also goes solid white on power up.
Click to expand...
A lot of CGA and EGA monitors do that when they receive no video signal.
 
The closest thing in the manual is one long and two short which means the video card mono/VGA switch is set wrong
 
I've re-seated the cards a few times to check that it wasn't the problem. No change.

The NiCd battery is located on an expansion board (I think it's the COM/LPT board & FDD controller combo). It has started to leak (will replace it) but the tracks around it seem intact. Also could a failure of this board cause a POST problem? I thought it would at least initialise the screen and then display an error?

The bios chip only has a VTI sticker on it (along with a quality check sticker). Not much there to go on I am afraid. Can't seem to match up the beep code with anything either; seems to be a one-off Vtech thing.

The video card is an EGA only card; there are no switches on it. From memory these early cards do not interrogate the monitor (so if the monitor is bad it will still boot). I've listened out for the characteristic 'ticks' of the memory test but they do not happen; so its definitely stuck in POST.
 
Just found a YouTube clip of someone booting up their Turbo XT - the bios (on the screen) displays as: "Central Point Software Inc".

Didn't help me googling it - hopefully this is useful though!
 
Wow Tom, that's a pretty awesome collection for this machine. OP will be stoked!

From what I found in it:

1 long 1 short = base 64KB RAM failure.
1 long + 2 short = video card selection incorrect
1 long + 5 short = BIOS ROM checksum failure.

I found that youtube video, and couldn't help but notice the thing beeps immediately when he flicks the switch. So I wondered if the first short beep isn't part of the code.
 
3pcedev said:
The NiCd battery is located on an expansion board (I think it's the COM/LPT board & FDD controller combo). It has started to leak (will replace it) but the tracks around it seem intact.
Click to expand...
As shown in the photo [here], as the leakage continues, the blue/green substance starts appearing in places ever more distant from the battery. I have certainly encountered it up to 6 inches from the battery. Your battery overhangs the motherboard, and so you should inspect the motherboard as well.
 
Thanks Tom! That's exactly what I was after! The motherboard layout / tech manual are invaluable; I can now troubleshoot this without massive reverse engineering (and/or guessing!) Luckily enough I am an electrical engineer; so I have a CRO etc which I can use to check signals around the board.

I also think SpidersWeb might just be onto something. I actually watched the video with the sound off so I didn't notice that first beep. I have a feeling that it might not be part of the code too; so that indicates some of the 64K base ram might be faulty. I have an old XT clone motherboard laying around; I will have to check if the RAM is the same and if so I will begin switching some out.

Also I too have seen the dreaded NiCd battery leakage. I once had to replace a battery on a very expensive instrument that did exactly as you described. Luckily I caught it before it damaged anything. I chose to replace it with a battery on flying leads; just in case it decided to happen again!

One last question; what would people suggest to use for cleaning the motherboard? I used an air duster to get the majority of dust off of it; however there is still a 'residue' of dust everywhere. I am thinking plastic safe contact cleaner (which I have used in the past); however since this board is rare I don't want to chance destroying it!

Thanks again all; I will keep you posted with progress.
 
Quick update - I looked at swapping the bank 0 ram around. Unfortunately Laser decided to use a mix of 4464 and 4164 in bank 0 and then used 41256 in everything else. I've ordered some new RAM from eBay so fingers crossed that is the fault....
 
Mild dish soap and water will be good to clean the board. Dry it with an air gun, or, carefully with a hair dryer. You will likely lose any stickers if you're not careful though.
 
Good news! I burnt myself a Supersoft diagnostic ROM and gave it a try in the machine. As suspected it came up with a RAM error in the first 16K of memory.

For those who don't know the ROM replaces the BIOS chip and performs a number of low level system tests. It brings up video very early in the initialization so you can actually see what is going on. Plus if the video fails it has some very comprehensive beep codes. I found the instructions HERE based on a suggestion I got about another problem I have with an IBM 5160.

I bought myself a $40 EPROM programmer which I highly recommend. It is a TL866 made by autoelectric.cn. When it first arrived I was a bit skeptical; but it worked perfectly with Win8 x64. I also purchased an EPROM from the local electronics store for about $6. It can program just about every EPROM/EEPROM/microcontroller imaginable; plus it comes with handy adapters.

Also for those interested I also saved the contents of the BIOS EPROM to a file. I thought this would be prudent just in case the original is damaged at some point. (The bios EPROM is a 27C64 for reference). Let me know if you would like me to attach it or send via email.

Just waiting for the RAM to arrive now!
 
Even better news!

The RAM fixed up the no-boot issues. I ended up replacing the first 128k of RAM (as it was all the same type). All working as it should now!
 
3pcedev said:
The RAM fixed up the no-boot issues. I ended up replacing the first 128k of RAM (as it was all the same type). All working as it should now!
Click to expand...
Another patient saved.

3pcedev said:
Also for those interested I also saved the contents of the BIOS EPROM to a file. I thought this would be prudent just in case the original is damaged at some point. (The bios EPROM is a 27C64 for reference). Let me know if you would like me to attach it or send via email.
Click to expand...
Thank you. I will add it those at [here]. Check your PMs for my email address.
 
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