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5150 motherboard ram

B

Boblogik

New Member
Joined
Jun 25, 2020
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5
Location
OH, USA
Hello everyone! I just discovered this place in my search for help with my new-to-me 5150, and while I have searched this forum, I haven't found the answer to my issue. I'm in the process of bringing it up to snuff and one of my concerns if that it's a 64-256 motherboard and all the banks are populated but when I stick my dos 3.3 startup in and boot it up, it only shows somewhere around 62kb in the ram check with no errors. I made sure all the switches in both motherboard banks are set correctly as per what I was reading on minuszerodegrees.

I'm posting this while I'm at work, so I can't test things until I get home, but I wanted to make this post to get the ball rolling!

Thank you!

Bob
 
The POST doesn't show a RAM check on a 5150. You just get a blinking cursor.

If the 5150 fails to boot from disk, it'll jump in to IBM Personal Computer BASIC which is loaded from ROM.
BASIC can only access the first 64KB of RAM and uses a little for itself, so will say something like "62940 bytes free" on any system with 64KB or more of memory.

So I suspect your DOS 3.3 boot disk isn't working. Usually (not always) this is because of a bad disk or dirty drive heads. That's where I'd start.
 
Gotcha. I know the post doesn't show the ram but the dos disk did but if it's not reading correctly, that makes more sense. Since I'm learning all this for the first time, I wouldn't know by looking if it's fully working, I had assumed it was because I could view the directory and it acted like it was normal, it isn't in IBM BASIC (I've booted without the disk, so I know what the BASIC screen looks like)

What can I do to isolate where the problem lies?

More details, I only have one working floppy right now (the other is missing pieces and not functioning, I'm working on getting it replaced), and at this moment, I only have the dos 3.3 start up floppy to test things with (getting a full copy of dos 3.3 soon)
 
If you're getting no 201 errors than the RAM test has passed so if you have 256KB and have set 256KB fitted then the system has tested for that amount and found it to be in order. As per the previous post, I would suggest your machine hasn't booted DOS but has actually fallen back to the built in ROM BASIC...does it look like the below (shameless excuse to show off my newly acquired EGA card)?

20200608_171722.jpg

Does the floppy drive light come on after the beep at the end of the RAM test, and if so can you definitely hear the disk spinning round inside the drive? If it's doing that can you hear the head moving inside the drive to drive and trying to boot DOS? I would say you're looking at bad boot disk, bad drive belt, dirty head, otherwise bad drive, or bad controller (or some combination thereof). Don't forget the obvious though - did you check the drive was connected to the controller when you had the cover off?

I'd start by trying a different boot disk. If that doesn't work then try cleaning the heads and possibly replacing the drive belt (although these don't commonly go). If it still doesn't work I would try connecting your IBM drive to another PC and seeing if it then works (it should work on any PC up to the mid-2000's even though it won't physically fit inside the case). If it then works in a different machine you have a problem with the controller (or cable but that is very unlikely to be the case).
 
Boblogik said:
Gotcha. I know the post doesn't show the ram but the dos disk did but if it's not reading correctly, that makes more sense. Since I'm learning all this for the first time, I wouldn't know by looking if it's fully working, I had assumed it was because I could view the directory and it acted like it was normal, it isn't in IBM BASIC (I've booted without the disk, so I know what the BASIC screen looks like)

What can I do to isolate where the problem lies?

More details, I only have one working floppy right now (the other is missing pieces and not functioning, I'm working on getting it replaced), and at this moment, I only have the dos 3.3 start up floppy to test things with (getting a full copy of dos 3.3 soon)
Click to expand...
Ignore my previous post - for some reason I didn't see your last post confirming you are in DOS. Where are you getting this 'RAM Check' from? If it's the bytes free at the end of a DIR command, then that is the space free on the disk, not in RAM. The only way to get a free RAM check from DOS 3.3 (without 3rd party utilities) is to run CHKDSK, which will test the disk then at the end display the amount of fitted and free RAM (later versions of DOS included a more useful MEM command just for checking on RAM without also doing a disk check and was also more comprehensive in showing how the RAM was allocated in systems with > 640KB).
 
No worries, you probably didn't see it because while I submitted it, it hadn't been approved yet (new member rule). I'll have to set the 5150 back up and give you an answer to specifically where I saw the numbers. I also came across a 5160 that I couldn't pass up so I snagged it and set it up in the 5150's spot. It may all be a moot point because the drive on the 5160 isn't reading the floppies and so I'll probably try swapping drives. But before I do, I'll boot the 5150 back up and test the new 3.3 dos startup disk I got with the 5160 in that drive as well.

I may have just misread the 62,000ish kb as some kind of diskette capacity but it was part of the dos 3.3 startup I thought. I'll give an answer later tonight when my room cools down so I can start experimenting.
 
So an update. The 5150 is sitting because I had to rob its floppy controller card for the 5160 (screwdriver slipped and hit a cap, breaking it halfway off, really upset with myself about it). Right now, I'm having trouble getting the 5160 to post again, so the 5150 is going on the back burner. Figures that the poo hits the fan when you try to fix stuff...

I'll have to revisit this when everything is happy with the 5160 again... I'm hoping it is only the power supply. I just can't test it tonight because my multimeter is 45min away at my shop because I was using it on my cars
 
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