A5000 Gone for good? :0

[nicf82]

Ah ok, that would explain it, I was using the contact cleaner to clean the board after soldering the jumper wires and kept getting a greasy residue which i thought was a byproduct of the solder. I do also have IPA to clean things with but I am scared to touch it now

[philpem]

Ah ok, that would explain it, I was using the contact cleaner to clean the board after soldering the jumper wires and kept getting a greasy residue which i thought was a byproduct of the solder. I do also have IPA to clean things with but I am scared to touch it now

Scared to touch it, why?

IPA is one of the most common PCB cleaning solvents - for removing flux and oily residues without damaging (most) components, it's indispensable for removing oily dirt. The most you need to do for safety is wear gloves and keep it away from sources of ignition.

[nicf82]

Scared to touch it, why?

Well I am only half joking but since I covered it in vinegar and contact cleaner unnecessarily it seems like I am just destined to break something!

I will give it a gentle clean down with IPA in a few days though

When you say it wont damage most components - anything I should be particularly careful with?

Cheers!
Nic

[nicf82]

Just posting the POSTbox results for this machine here

Code: Select all

SELFTEST R1.47
ROM :
M Size :
M Size 1000.20
Data :
Addrs :
Byte :
Exp? :
Exp? @ 2400000
Exp? FFFFFFFF
IOC :
IOC FFFC0281
IOEB :
IOEB exists
SRAM :
SRAM Err D9
IOinit :
Speed :
Speed 2EE2.1.1
RAM :
CAMs :
PPLs :
VIDC :
ARM ID :
ARM ID 41560300
PASS : 0000015A
No output for 5 seconds; exiting

[DutchAcorn]

… Also never had had any video output. I’ve not bothered to try and check the VGA pins for any output yet but since there is not even a startup beep did not think it was worth checking! …

The coloured screens output during POST are in a 15KHz video mode so your VGA monitor may not be able to display the output.

[nicf82]

Ah yes I need to try it with a CRT monitor I think?

[nicf82]

After relacing the clock chip, I am now getting a slightly different SRAM error!

Code: Select all

SELFTEST R1.47
ROM :
M Size :
M Size 1000.20
Data :
Addrs :
Byte :
Exp? :
Exp? @ 2400000
Exp? FFFFFFFF
IOC :
IOC FFFCC281
IOEB :
IOEB exists
SRAM :
SRAM Err 32
IOinit :
Speed :
Speed 2EDA.1.1
RAM :
CAMs :
PPLs :
VIDC :
ARM ID :
ARM ID 41560300
PASS : 0000015A

so it is

Code: Select all

SRAM Err 32

now rather than

Code: Select all

SRAM Err D9

Still no beep, and no response on the keyboard LEDs either. I am now wondering, could the keyboard be the problem, maybe it is not registering that I am pressing DEL and its not resetting the CMOS?

I have plugged in a CRT, although it is a bad picture - widescreen scrolling vertically, I am getting RED, BLUE, blank screens on boot. But when I use the POSTBox to trigger a test, then I get all the way to green, I also get the the floppy flashes. I am able to use show_self_test.py to draw boxes on the screen.

[nicf82]

Aha

I sat running the POSTbox tests over and over and finally it failed with this IOC fault, so I will scope the La and Bd lines and latches see if anything looks weird in that area.

Code: Select all

SELFTEST R1.47
ROM :
M Size :
M Size 1000.20
Data :
Addrs :
Byte :
Exp? :
Exp? @ 2400000
Exp? FFFFFFFF
IOC :
IOC Flt w0FFw1FF
IOEB :
IOEB exists
SRAM :
SRAM Err 0F
IOinit :
Speed :
Speed 2EDA.1.1
RAM :
CAMs :
PPLs :
VIDC :
ARM ID :
ARM ID 41560300
FAIL : 0000115A

Cheers
Nic

[nicf82]

I am just having another go at working out what is wrong with this machine, and I do keep getting the "SRAM Err 0F" or similar when I run the POSTBox on it.

I have checked over the clock chip circuit and noticed that R281 is reading 0 ohm. I cant really work out its function from the circuit diagram, but I cant find anything else wrong there, so think it might be the problem? I am tempted to try replacing it, but wondering if there is any problem using a normal resistor instead of one of the SMD kind? As my soldering is not good at that level!

Cheers!
Nic

[IanS]

I have checked over the clock chip circuit and noticed that R281 is reading 0 ohm. I cant really work out its function from the circuit diagram, but I cant find anything else wrong there, so think it might be the problem? I am tempted to try replacing it, but wondering if there is any problem using a normal resistor instead of one of the SMD kind? As my soldering is not good at that level!

With the power on, what voltage do you measure across pins 8 & 4 of the RTC chip?

If R281 is zero ohms, it is unlikely to cause an error. But if you replace it, 47R is the same in SMD or leaded form, just be careful to not lift any pads.

[nicf82]

I am getting 1.3v across 8 and 4 with power off. OK, maybe I will have a bit more of an investigate before removing anything, I could not really see how R281 might affect anything, but struggling to find anything wrong in that area

Cheers!
Nic

[nicf82]

Urgh I just switched back on to have another look at this and I have started to get a RAM error now on top of the SRAM error

It's happening pretty consistently, only thing I have done is power on the board out of the case using another power supply and I forgot to connect the -5v initially, that couldn't have damaged anything surely though??

Code: Select all

SELFTEST R1.47
ROM :
M Size :
M Size 1000.20
Data :
Addrs :
Byte :
Exp? :
Exp? @ 2400000
Exp? FFFFFFFF
IOC :
IOC FFFCC281
IOEB :
IOEB exists
SRAM :
SRAM Err 0F
IOinit :
Speed :
Speed 2EE2.1.1
RAM :
RAM Bad 2002800
RAM-0 00008000
CAMs :
skipped
VIDC :
ARM ID :
skipped
FAIL : 0004014A

[IanS]

It's happening pretty consistently, only thing I have done is power on the board out of the case using another power supply and I forgot to connect the -5v initially, that couldn't have damaged anything surely though??

No, running without -5V is fine. I regularly run an A5000 board on +5V only, no issues. (almost all acorn boards will run happily on 5V only, exception is the RISC PC which needs +12V for the Video VCO)

[nicf82]

OK thanks Ian! Good to know for future. I wonder if this RAM chip has been a bit of a problem all along then and only just fully failed.

Am I right in thinking that...

Code: Select all

RAM Bad 2002800
RAM-0 00008000

...means that RAM chip 0 has been identified as the bad chip and it will probably need replaced? I think the earlier checks should have check that the actual ram lines are ok?

Going by the A500 TRM it seems to indicate this is the case:

Large memory test
The earlier memory tests performed brief checks on the memory control and data lines to ensure that the memory components were present and to assist in finding short or open circuits in the interconnections. Ideally, a large

If that is the case, is there a way on the A5000 to bypass the on-board ram completely and use a ram expansion card in its place? (I have a 4mb atomwide expansion here to try)

Cheers!
Nic

[IanS]

If that is the case, is there a way on the A5000 to bypass the on-board ram completely and use a ram expansion card in its place? (I have a 4mb atomwide expansion here to try)

Yes, though you will need to find a way of putting 5v on LK23 pin 2 (with no other jumpers on LK23). See attachment.

The first and last rows may also be useful to identify which half of the 2MB on-board memory is bad.

You may still get issues with these configurations if the bad ram is still connected and loading the bus.

[nicf82]

Great! I am sure I can run 5v over from somewhere, but it does say use only a 2MB expansion card, does that mean that my 4mb card is no good? Or will it just ignore the extra 2MB?

Up to now I had thought the machine had 4MB installed, because the test output was saying...

Code: Select all

SELFTEST R1.47
ROM :
M Size :
M Size 1000.20

...which means 4MB IIRC.

But I do only have 1 row of chips, and if the max is 4MB it stands to reason that there is only 2MB installed? So is it somehow mis-detecting the RAM size?

Cheers!
Nic

[IanS]

The 1 row of chips could 1MB or 4MB (i think I could work it out from the chips and position, but I haven't).

From your other photos is looks like it is a 4MB "Alpha" board with a socketted MEMC.

The "4MB" card you have will actually only have 2MB on it. It will take a 2MB machine up to 4MB.

4MB is the maximum possible on a single MEMC system.

You can still try running with the "4MB" card with the jumper settings shown.

[nicf82]

Thanks for your help Ian, much appreciated, ill do some experimentation and see if I can work out which chips are bad or at least get it to behave a bit better!

[baz4096]

The 1 row of chips could 1MB or 4MB (i think I could work it out from the chips and position, but I haven't).

Those are 4mbit ICs, so 4 megabytes on board.

[nicf82]

Those are 4mbit ICs, so 4 megabytes on board.

Thanks for confirming that baz4096

I have run with only the external 2MB and seems that has gotten me past the RAM problem

Code: Select all

SELFTEST R1.47
ROM :
M Size :
M Size 0800.10
Data :
Addrs :
Byte :
Exp? :
Exp? @ 2200000
Exp? 00000000
IOC :
IOC FFFC0281
IOEB :
IOEB exists
SRAM :
SRAM Err 0F
IOinit :
Speed :
Speed 2EDA.1.1
RAM :
CAMs :
PPLs :
VIDC :
ARM ID :
ARM ID 41560300
PASS : 0000015A

I will get back to trying to solve the Clock Chip problem and deal with the RAM later

Thanks again for the help!

[nicf82]

I have replaced the bad 47R resistor, and even changed the clock chip, in case I damaged the first one putting it in, still getting the same random "SRAM Err XX"

I put the scope on the I2C pins and both are just held HIGH, no data to be seen.

I am beginning to think maybe the keyboard is not registering DEL being pressed, is that feasible? It flashes the LEDs when powering on but it does not respond to scroll/caps/num lock at all.

Is there maybe another way to get the CMOS to reset without needing the keyboard?

Cheers!
Nic

[nicf82]

I have checked the keyboard fuse and it seems ok, so I am going to try to trace the keyboard back to the IOC.

[nicf82]

I wasn’t able to find any problems with the keyboard’s circuit, so I turned to looking at the IOC itself.

I see in the A500 TRM that the POST does not actually check the function of the IOC, but I do think is shows the contents of the registers, although I am not sure of their significance, they are returning something consistent at least.

I checked the address LA2-6 pins during reset and they look good, I can see data on D0-7 after a reset, POR looks good, also I can see the I2C pins activity after a reset. I see a pulse of activity on IRQ after a reset.

I think that the POST results and the fact that there is some activity at least on the IRQ pin, point to the IOC working. I don't know much about the IOEB but I will start to have a read up on that chip next.

[IanS]

How long are you pressing DEL? with POST errors the DEL is only checked at the end of the flashes. You will have to hold DEL for a long time.

[nicf82]

I was holding for approx 20 seconds, just held for about 2 minutes though and unfortunatley no luck still no reponse on the keyboard LEDS and the same "SRAM Err 46". Will try a few more times though!

[baz4096]

What's the full Postbox output please? Just seen it above.

Check your RAM links. In another post with similar postbox output it's suggested that the ram isn't being seen at all.

https://www.stardot.org.uk/forums/viewt ... 99#p381899

[nicf82]

Thanks Baz I will check all the RAM circuitry!

Do you happen to know if working RAM is needed to get a successful SRAM test? I’m not sure of what actually happens when it checks the CMOS chip and which subsystems are involved. My best guess is that if Del is pressed, the image is loaded directly from ROM to the CMOS?

[baz4096]

I'm absolutely no expert but I suspect you need some ram for the POST code to run properly. When holding DEL, from what I remember when I looked at how the defaults were determined, there's a whole series of instructions that are conditionally executed, depending on hardware configuration. These default values are then sent individually across the I2C bus to the CMOS SRAM (I think) as address/value pairs.

What ram link positions do you have?

[nicf82]

I am currently using external RAM only because the on-board 4MB developed a fault (the next think I will have to fix). So it's the hilighted row on IanS's spreadshhed which he posted earlier.

[baz4096]

My apologies Nic, I think I'm barking up the wrong tree. Looks like your ram is fine. Your CMOS is the issue. Are you able to get any floppy flashes out of it without the postbox attached?