Problem Beeb MotherBoard

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KarateEd
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Problem Beeb MotherBoard

Postby KarateEd » Sat Nov 11, 2017 5:27 am

Hi Folks,

Time to reach out to the knowledgeable among you.

My motherboard on Issue7 seems to have gone awol. I'm getting the Beeeeeeeeeep issue but I think it's more than memory.

When I am able to bring up a screen it's intermittent. I took out the 6522, IC 73, IC 7 and the BASIC ROM and was once in about 4 tries able to get the BASIC, no language? screen to pop up. Good, it's not fully dead yet.

I replaced those chips as I doubt they are the problem and the following test suggests that.

I've managed about once in 10 tries since replacing the chips to get a screen. I get various types of beeps, mostly long though and garbage on the screen as the video will show. Once in a while the whole screen is a big white square.

I've done some more CTL BRKs and once in a while a blinking cursor appears but no keystrokes work. Also once in a while the middle LED light comes on but often blinks off as does the right most light. They seem inconsistent.

I have to up load that to YouTube and will put the link on here once that's happened.

https://youtu.be/CJf2-3SQ5u8

Anyway, curious as to what my next step should be.

Thanks,

Ed...... :-)

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danielj
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Re: Problem Beeb MotherBoard

Postby danielj » Sat Nov 11, 2017 6:13 am

Swap the 6522s and check the keyboard cable in the first instance. :)

d.

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KarateEd
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Re: Problem Beeb MotherBoard

Postby KarateEd » Sat Nov 11, 2017 6:48 am

Ok, I've done that. It would seem I have a somewhat faulty keyboard cable even though it's only around 1 year old. I'll do some continuity tests on it. In the meantime I think I have a memory fault so I'll do the drill on that. I moved S25 to south and after a couple CTL BRKs It came up with 16k.

Well, something new and interesting. Rebooted and after the same several CTL BRKs, it says 32k. I'm sure that's a phantom as the S25 jumper is south.

Another reboot and 16k again. I'm going to assume that's what should be correct.

Next test - no jumper on S25 - It also comes up BBC Computer 16k...............BASIC

ok, I'm pretty sure this has to be a RAM issue as with the S25 on north I get the gobbledy gook screens.

So...... next step would be to find the program for checking which RAM chip is bad and running it and deducing it.

I do have a question here though. Why does it take several CTL BRKs for the 16k to show up. Shouldn't that happen on one reboot?

At any rate, right now I have a perfectly good BBC A....LOL

Ed...... :-)

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danielj
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Re: Problem Beeb MotherBoard

Postby danielj » Sat Nov 11, 2017 6:58 am

It won't boot properly with a dodgy keyboard cable connected so in the first instance I'd assume that's why it's needing a few ctrls before you catch it right... Once that's ruled out then it's time to look further :)

d.

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KarateEd
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Re: Problem Beeb MotherBoard

Postby KarateEd » Sat Nov 11, 2017 7:05 am

danielj wrote:It won't boot properly with a dodgy keyboard cable connected so in the first instance I'd assume that's why it's needing a few ctrls before you catch it right... Once that's ruled out then it's time to look further :)

d.


The cable I'm using now seems to be good. It's off another working keyboard. I still need to CTL BRK a few times to get the 16k to come up but at least I know it's a bad RAM somewhere.

Daniel, what it seems to be doing is completing it's POST after a few CTL BRKs. It usually comes up with a line of block, letter size, of 25 characters before one or two more keystrokes. It then gives one beep and 16k Beeb appears.

Ed...... :-)

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danielj
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Re: Problem Beeb MotherBoard

Postby danielj » Sat Nov 11, 2017 7:41 am

I'm going to have to defer on this one - personally I'd try and clear up the RAM fault first and make sure my 6522s were good, but there are any number of other things that could be arguing a bit - I'd probably scope the reset/clock lines to see what they were doing on boot. However, until you've ironed out the things you know for sure are a problem, like the RAM, then you might actually just be chasing a symptom that you've identified the cause of already...

d.

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KarateEd
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Re: Problem Beeb MotherBoard

Postby KarateEd » Sat Nov 11, 2017 8:28 am

Thanks Daniel,

That's going to be my next step - remove one problem to find if there is another.

Ed...... :-)

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DutchAcorn
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Re: Problem Beeb MotherBoard

Postby DutchAcorn » Sat Nov 11, 2017 10:02 am

The principle behind finding bad ram from software is that you have bootable BBC with partly bad ram. So either the lower RAM is good enough to start her up or you create a small logic circuit to swap lower and higher RAM and use that to create a bootable computer. You can then look for the faulty chips using a program. See here.

The symptoms on your computer are a bit odd in that apparently it does it does boot with only lower (S25 removed) ram but not with lower ram + higher ram. It could also be caused by different part of the memory circuit, looking at the behaviour the different settings of S25 is causing.

But bad memory can give all kinds of symptoms. Do you have the facilities to burn Tricky's test rom? That can help diagnosis.
Paul

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KarateEd
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Re: Problem Beeb MotherBoard

Postby KarateEd » Sat Nov 11, 2017 4:10 pm

Hi Paul,

I do have the facility and ability to burn the ROM. I'll do that later today and see what turns up. I'll also finish building my inverter. I have the chip around here somewhere to do that as well.

Thanks Paul,

Ed...... :-)

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Re: Problem Beeb MotherBoard

Postby KarateEd » Tue Dec 05, 2017 12:13 am

Ok, for these 2 ROMs, I have M27C256B windowed EPROMs.

I understand that these hold 2 ROM images possibly. I see after exporting the Test ROMs that there are 2 ROMs.

Do I need both ROMs? If so, what might be the best way to program the EPROMs, where in the memory should these ROMs be written? (it's been quite a while since I burned a ROM)

The other thing I'm wondering about is where do the ROM(s) sit in the ROM sockets? Are they particular to any socket or any open one. Right now all I have on the board (it's somewhat minimally populated right now) is the OS and BASIC installed.

I think it's interesting that I can get 16k to show up with the S25 on the south side of the jumpers as well as when S25 is unlinked. Does this mean the RAM is good on the upper and lower side and that the problem lies elsewhere? I may be overthinking things a bit, not sure.

Thanks guys,

Ed...... :-)

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tricky
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Re: Problem Beeb MotherBoard

Postby tricky » Tue Dec 05, 2017 12:31 am

Assuming that the ROM is my "self test os", it needs to go in the os socket, as your eproms are 32kB, you could put the same image in twice, at 0 and &8000 &4000, or you could tie the highest address line. There are some videos linked here that show what should happen. If your images are the same, someone might have already created a 32KB file.

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Re: Problem Beeb MotherBoard

Postby KarateEd » Tue Dec 05, 2017 12:46 am

tricky wrote:Assuming that the ROM is my "self test os", it needs to go in the os socket, as your eproms are 32kB, you could put the same image in twice, at 0 and &8000 &4000, or you could tie the highest address line. There are some videos linked here that show what should happen. If your images are the same, someone might have already created a 32KB file.


Hi Tricky,

Thanks for the quick response. I used BeeBem to extract the ROMs. There are 2 that are named $.ROMIMAG and $.TESTROM.

There are also 2 other files, $ROMIMAG.INF with values of $.ROMIMAG 003000 003000 002000

and

$.TESTROM FF1900 FF8023 00080F

My assumption is these will run at those memory locations......

Can you tell me which ROM I should be using?

Thanks Tricky.......

Ed...... :-)

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Re: Problem Beeb MotherBoard

Postby tricky » Tue Dec 05, 2017 7:24 am

Neither of those look like mine, I think it should be 16KB to make it easier to burn.
I found the original thread here, sorry for the confusion.

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DutchAcorn
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Re: Problem Beeb MotherBoard

Postby DutchAcorn » Tue Dec 05, 2017 12:07 pm

tricky wrote:Neither of those look like mine, I think it should be 16KB to make it easier to burn.
I found the original thread here, sorry for the confusion.

I’m afraid I am the cause of the confusion. The link I provided was not for Tricky’s testrom but for the testrom from the BBC Service Manual. Sorry for the confusion I caused... :oops:
Paul

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KarateEd
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Re: Problem Beeb MotherBoard

Postby KarateEd » Tue Dec 05, 2017 6:09 pm

tricky wrote:Neither of those look like mine, I think it should be 16KB to make it easier to burn.
I found the original thread here, sorry for the confusion.


No problem Tricky, people have been pointing to the one I showed you attributing that SSD to you. Guess it wasn't so..... thanks for the link. I'll burn tha one, it is 16k so I have the right one now I suppose.

Thanks again,

Ed...... :-)

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Re: Problem Beeb MotherBoard

Postby KarateEd » Tue Dec 05, 2017 6:10 pm

DutchAcorn wrote:
tricky wrote:Neither of those look like mine, I think it should be 16KB to make it easier to burn.
I found the original thread here, sorry for the confusion.

I’m afraid I am the cause of the confusion. The link I provided was not for Tricky’s testrom but for the testrom from the BBC Service Manual. Sorry for the confusion I caused... :oops:


Saw this after seeing Tricky's note. No problem Paul, it always seems to work out so there is never a fault when trying to help people.

Thanks,

Ed...... :-)

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Re: Problem Beeb MotherBoard

Postby KarateEd » Wed Dec 06, 2017 12:52 pm

ok, so after burning the ROM from Tricky and running it, all the correct sounds are there. However, video seems absent when running the test.

Edit: Power had fallen out of my GB-8200, that's why no video.... ok, have video but not what's described in your notes.....


I do get video when I do enough CTL BRKs when powering up with the normal OS but the behaviour is very similar to memory issues.

@Tricky - does this test program only test the OS and various associated chips, can you tell me exactly what it is testing?

Thanks folks,

Maybe a step further.

Further edit: When I'm in 32k mode (S25 North) then the screen never gives me 'frogger'. When in South jumpered, I get the frogger screen. I'm suspecting memory so have to ensure my tester is correctly wired....that's next again.

ok, North - scrambled screens, south - frogger and what seem 'normal' from your descriptions on the other threads, no jumper - frogger and normal also....

Am I likely looking at a bad RAM then?

Ed...... :-)

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tricky
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Re: Problem Beeb MotherBoard

Postby tricky » Wed Dec 06, 2017 2:09 pm

RAM or the circuitry between the 6502 and the RAM.
After the mode 7 screen, you should see the mode 0 screen which goes through a few test patterns for the first 16K (leaving a bit unchanged at the bottom so that you can see which bit is supposed to be changing) then repeats for the second 16K with the bit at the top left unchanged.

http://youtu.be/ookuXJdF_AA Here the top 80% is being updated.
The test patterns in the mode 0 sections are supposed to help you identify stuck bits, cross-talk etc, but I haven't really documented them.
If you can't see from my video what is supposed to happen, you can put the ROM in beebem or b-em (I can't remember which is easiest) and run at 0.1X speed to get a better idea.

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Re: Problem Beeb MotherBoard

Postby KarateEd » Wed Dec 06, 2017 3:10 pm

Here's the first few seconds of what I get..

https://youtu.be/NS4JsXxjn4s

Ed...... :-)

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Re: Problem Beeb MotherBoard

Postby tricky » Wed Dec 06, 2017 10:20 pm

So, the mode 7 image is rubbish, and looks like the same line repeated, I don't understand how that would happen.
Once you get to mode 7, it looks like you have the palette working and some data is being written.
Did you have your hi-lo swap on as it seems to be updating the high half of memory first, but your video stops just before I would expect it to do the other half (check my video).
It does look like the only set/only unset bit is walking across the byte correctly at the bottom of the screen.
I can't read the wiring diagram to work out what might be going wrong, but I didn't see any misbehaving bits in what I can see of the high half of memory.
Hopefully someone else will jump in.

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Re: Problem Beeb MotherBoard

Postby KarateEd » Thu Dec 07, 2017 1:14 am

tricky wrote:So, the mode 7 image is rubbish, and looks like the same line repeated, I don't understand how that would happen.
Once you get to mode 7, it looks like you have the palette working and some data is being written.
Did you have your hi-lo swap on as it seems to be updating the high half of memory first, but your video stops just before I would expect it to do the other half (check my video).
It does look like the only set/only unset bit is walking across the byte correctly at the bottom of the screen.
I can't read the wiring diagram to work out what might be going wrong, but I didn't see any misbehaving bits in what I can see of the high half of memory.
Hopefully someone else will jump in.


Hi Tricky,

I had the S25 jumper normal on the North setting. I wanted to see the results when jumpered normally. I tend to think that's the most useful way to see the problem. When I put the jumper south, I got the frogger screen more or less correctly. Same when no jumper was on S25.

If nothing else it's an interesting problem but I'm suspecting memory still. I did make an inverter but out of a 74ls02. As I understand it, to make this work I need to give the chip power and ground on pin 14 (+5), pin 7 (GND), tie pin 2 & 3 together to invert the signal coming out at pin 1. Does that sound about right?

For some reason my inverter didn't seem to work in finding RAM issues (if that wiring sound correct).

Thanks,

Ed...... :-)

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Re: Problem Beeb MotherBoard

Postby KarateEd » Thu Dec 07, 2017 4:24 am

I've just created a video showing the BeebEm emulator along side what I'm getting on my Beeb.

They are definitely not the same. I see pattern similarities but they are on opposite of the street so to speak.

Any comments on this vid before what's left of my hair falls out?

Thanks folks,

Ed...... :-)

https://youtu.be/EOm6-L2Q7u8

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Re: Problem Beeb MotherBoard

Postby KarateEd » Thu Dec 07, 2017 5:01 am

Just wanted to be clearer on the wiring for my 74ls02 as an inverter.

Wiring for 74ls02.jpg

74ls02 Truth Table.jpg
(18.13 KiB) Not downloaded yet


Pin 7 goes to a ground wire, pin 14 goes to a +5V wire.

I've connected pins 8 & 9 together and they should go to the south most pin of S25.

Pin 10 should be the center pin of S25.

Would someone kindly confirm that I've got this right. I know it's simple but the simplest mistakes are easiest to make.

One more thing has come up that might be useful.... When I try to do a Mode0, i get Bad MODE. I thought from Mark's explanation on his RAM troubleshooting video that I could get to Mode0. Is this a clue to a problem?

Thanks folks,

Ed...... :-)

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tricky
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Re: Problem Beeb MotherBoard

Postby tricky » Thu Dec 07, 2017 8:19 am

Your inverter certainly seems to invest one pin to the other, what I don't know is if that is what it is supposed to do.
From your video, it looks like at least one bit is wrong in one half of the memory, which makes sense as I think there are basically two sets of 16Kx1bit memory banks.
From my limited experience, it does look like you have one broken chip, the bit that worries me is that that shouldn't give a totally corrupt mode 7 screen, nor make the 6845 display the wrong part of memory.
If this was one broken chip in the top 16k and the 6845 was stuck on the bottom half of memory, that might give what you see, basically uninitialised memory instead of Frogger's and always seeing the first 20k of memory in mode 0.

We really need someone with more beeb fixing experience now to say if this is feasible.

As half the memory works ok and the rest (what we can see) is mostly ok and the test program work, I think the address and data lines are probably good, as is the logic between the CPU and ram.

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DutchAcorn
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Re: Problem Beeb MotherBoard

Postby DutchAcorn » Thu Dec 07, 2017 9:52 pm

KarateEd wrote:I've just created a video showing the BeebEm emulator along side what I'm getting on my Beeb.

They are definitely not the same. I see pattern similarities but they are on opposite of the street so to speak.

Any comments on this vid before what's left of my hair falls out?

Thanks folks,

Ed...... :-)

https://youtu.be/EOm6-L2Q7u8

Odd. The mode 7 screen on frame 0:11 is exactly test 2 of the test rom from the service manual. See here for comparison. Are you sure the rom was burned ok?
Paul

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KarateEd
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Re: Problem Beeb MotherBoard

Postby KarateEd » Fri Dec 08, 2017 1:31 am

DutchAcorn wrote:
KarateEd wrote:I've just created a video showing the BeebEm emulator along side what I'm getting on my Beeb.

They are definitely not the same. I see pattern similarities but they are on opposite of the street so to speak.

Any comments on this vid before what's left of my hair falls out?

Thanks folks,

Ed...... :-)

https://youtu.be/EOm6-L2Q7u8

Odd. The mode 7 screen on frame 0:11 is exactly test 2 of the test rom from the service manual. See here for comparison. Are you sure the rom was burned ok?


Hi Paul,

Yes, it burned fine. When I put it in 16k mode, either jumpered South or no jumper, the tests work as expected except of course with the split showing the different patterns, it's just one screen of one pattern type.

Ed...... :-)

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DutchAcorn
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Re: Problem Beeb MotherBoard

Postby DutchAcorn » Fri Dec 08, 2017 6:49 am

KarateEd wrote:... When I put the jumper south, I got the frogger screen more or less correctly. ...

What do you mean "more or less"? Do you have a picture of the frogger screen?
Paul

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KarateEd
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Re: Problem Beeb MotherBoard

Postby KarateEd » Fri Dec 08, 2017 7:14 am

DutchAcorn wrote:
KarateEd wrote:... When I put the jumper south, I got the frogger screen more or less correctly. ...

What do you mean "more or less"? Do you have a picture of the frogger screen?


Sorry, poor terminology on my part. Here's what I get and I'll include one screen showing full screen pattern with jumper South in both cases.

Ed...... :-)

Frogger Screen.JPG

Full Screen.JPG

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Re: Problem Beeb MotherBoard

Postby KarateEd » Fri Dec 08, 2017 7:17 am

One more thing Paul.... when I first start up the machine with my normal OS ROM in it, I have to hit CTL BRK a few times to get it to boot, even to 16k. It never actually boots to completion in 32k.

That may have been lost in the other comments on this thread.

When I use Tricky's ROM, no problem booting. Is there a chance that my OS chip isn't perfect? I can burn one from my files and test I suppose.

EDIT: Created an OS 1.2 ROM. The OS chip is fine, the symptoms are the same.

Ed...... :-)

cmorley
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Re: Problem Beeb MotherBoard

Postby cmorley » Fri Dec 08, 2017 8:01 am

KarateEd wrote:One more thing Paul.... when I first start up the machine with my normal OS ROM in it, I have to hit CTL BRK a few times to get it to boot, even to 16k. It never actually boots to completion in 32k.


System VIA reset (!RSTA) problem? Perhaps try connecting the reset pin (34) on the system VIA to the reset from the user VIA and see if it will boot.


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