Atom Hardware Advice Needed

discussion of games, software, hardware & emulators relating to the Acorn Atom and Acorn System machines.
AndyGarton
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Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 9:15 am

Hi all,

Disclaimer first: I'm a programmer, and have very little electronics/hardware knowledge, so am basically fumbling around in the dark!

My Atom is having intermittent problems, in that it often won't turn on or function properly. The display will show corruption (incorrect characters), or nothing, and simple commands won't work properly. Sometimes the keyboard won't work, apart from the break key. Sometimes the Atom MMC device isn't seen. These problems seems to happen more once the system warms up, but I'm not 100% sure on that.

I took it apart and re-seated all the chips, and that actually seems to have "fixed" it for now, I've done a few restarts, and left a "print Andy, goto 10" program running for an hour, and everything has been ok. However, I suspect that won't last long, and in any case I spotted some potential issues on the board that I'd like an expert opinion on if possible.

The first photo shows the back of the board, around the power input area - the soldering looks dodgy (and corroded?) in places (I think where the power socket is mounted), plus it looks like it has overheated at some point (that metal thing (some kind of heat sink?) is running cool now though, I checked). Should I attempt to re-solder the bad parts (I'm terrible at soldering, but willing to give it a go)? Is the "burned" area something to worry about?

The second photo shows a white substance which has possibly leaked onto the metal bracket, or perhaps it's some kind of glue/sealant? I'd already attempted to wipe it away a bit when I took this photo. Is this normal? If not, what could/should I do about it?

The third photo shows some what I think is poor quality soldering where the MMC interface plugs in - I honestly can't remember if I did this myself some years ago, it's quite likely being so badly done! Could it cause problems, and should I re-do it? Is the orange stuff (flux?) a problem? I tried cleaning it (with Windolene, because I don't have any IPA, but have ordered some) without much success, but will try again if it's important.

The last photo is just a high level picture of the complete board in case it helps.

Sorry for all the questions! I really appreciate any help or advice that can be offered.

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Last edited by AndyGarton on Thu Aug 30, 2018 9:28 am, edited 2 times in total.

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Re: Atom Hardware Advice Needed

Post by 1024MAK » Thu Aug 30, 2018 10:08 am

Andy, can you please confirm what type and rating of power supply unit (PSU) you are using with your Atom.

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 10:15 am

This one Mark:

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Re: Atom Hardware Advice Needed

Post by 1024MAK » Thu Aug 30, 2018 10:30 am

AndyGarton wrote:
Thu Aug 30, 2018 9:15 am
The first photo shows the back of the board, around the power input area - the soldering looks dodgy (and corroded?) in places (I think where the power socket is mounted), plus it looks like it has overheated at some point (that metal thing (some kind of heat sink?) is running cool now though, I checked). Should I attempt to re-solder the bad parts (I'm terrible at soldering, but willing to give it a go)? Is the "burned" area something to worry about?
The orange/brown crusty stuff on and around the solder joints is flux. You can clean it off with IPA (or electrical flux remover solvent cleaner) and a toothbrush (get a cheap new one). Tin/lead solder when it degrades tends to go a very dull powdery grey. It's not really possible to say anything further until the flux has been cleaned off. Good solder joints should be shiny.

The 'metal thing' is indeed a heatsink. It's there so that the two 7805 voltage regulators can transfer heat into the air, so they don't get too hot. At some time in the past, the heatsink has got so hot, that the material that the PCB (printed circuit board) is made of has discoloured. This Atom has been converted to run from an external 5V regulated PSU. So the heatsink will no longer even get warm (as the 7805 voltage regulators are no longer in use). So I would not worry about the discolouration, as it will not get any worse.
AndyGarton wrote:
Thu Aug 30, 2018 9:15 am
The second photo shows a white substance which has possibly leaked onto the metal bracket, or perhaps it's some kind of glue/sealant? I'd already attempted to wipe it away a bit when I took this photo. Is this normal? If not, what could/should I do about it?
That white stuff is heatsink / heat transfer compound / silicon grease (many names, same function). It's meant to be between the 7805 voltage regulators and the heatsink. But a bit often gets squashed out when these are assembled.
AndyGarton wrote:
Thu Aug 30, 2018 9:15 am
The third photo shows some what I think is poor quality soldering where the MMC interface plugs in - I honestly can't remember if I did this myself some years ago, it's quite likely being so badly done! Could it cause problems, and should I re-do it? Is the orange stuff (flux?) a problem? I tried cleaning it (with Windolene, because I don't have any IPA, but have ordered some) without much success, but will try again if it's important.
I don't think Windolene will do much good. Again, the flux needs cleaning off. But although it does not look too bad, it's hard to tell. At this stage, I don't think it's worthwhile trying to resolder anything yet.

Once the flux has been cleaned off, post up some new photos.

Mark
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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 10:40 am

Ok, thanks Mark.

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Re: Atom Hardware Advice Needed

Post by CMcDougall » Thu Aug 30, 2018 10:55 am

I bet it's those ancient 2114 RAMs thats are making it flacky. & those not so good white sockets!

don't worry about the 'mess' on solder, it's 37yrs old, & always been like that anyways from BITD 8)
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Re: Atom Hardware Advice Needed

Post by roland » Thu Aug 30, 2018 11:36 am

I wonder if LK6 is closed. It looks like it is open...

If it's open, one of the 7805's is still in use and might get warm or hot. And it gets an input voltage that is too low resulting in a low output voltage and the input and output pins of the 7805 are shortened. Please check this first.
If you have a multimeter, check also the voltage on each IC.
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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 11:51 am

LK6 is closed (the link is made on the keyboard side of the board).

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Re: Atom Hardware Advice Needed

Post by bprosman » Thu Aug 30, 2018 2:15 pm

I would replace the dodgy white sockets by professional ones.
If youre not that experienced I would do it one by one, to avoid making a mistake and not knowing which socket it was.

Kind regards, Bram

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 3:59 pm

My IPA arrived, and, together with my wife's toothbrush, was very effective at cleaning up the orange sticky stuff (and indeed there was no corrosion, everything is now nice and shiny).

Back together, and my was-now-working Atom is now broken again - it seems to boot ok every time, displays the right ACORN ATOM + ATOMMC2 header, but the keyboard won't respond at all now, break key excepted.

Any ideas please? Still "replace all the white sockets"? Sadly this is way beyond my abilities with a soldering iron.

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Re: Atom Hardware Advice Needed

Post by hoglet » Thu Aug 30, 2018 4:02 pm

AndyGarton wrote:
Thu Aug 30, 2018 3:59 pm
Any ideas please? Still "replace all the white sockets"? Sadly this is way beyond my abilities with a soldering iron.
Does anything show up on the screen if you press the REPT key?

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 4:13 pm

hoglet wrote:
Thu Aug 30, 2018 4:02 pm
AndyGarton wrote:
Thu Aug 30, 2018 3:59 pm
Any ideas please? Still "replace all the white sockets"? Sadly this is way beyond my abilities with a soldering iron.
Does anything show up on the screen if you press the REPT key?
It doesn't. Although bizarrely, the first time I tried it, it seemed to "release" the rest of the keys, and the machine worked again. Every subsequent time I've tried it it has had no effect though.

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 4:15 pm

Progress! If I remove the AtomMMC, the machine works fine.

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 4:18 pm

Fixed it ... I think. I reseated all the AtomMMC chips, reconnected the cables, and reinserted the MMC card itself, and it seems fine now.

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 4:26 pm

Nah, it's intermittent, probably worse with heat ... dammit.

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Re: Atom Hardware Advice Needed

Post by hoglet » Thu Aug 30, 2018 4:36 pm

Is it always hanging at the following prompt?

ACORN ATOM

>█

(i.e. the > is there)

One reason an Atom can hang here is a keyboard fault (e.g. a stuck key) - but usually this is revealed by pressing REPT.

If it hangs earlier, then there might be a problem with AtoMMC

ACORN ATOM



(i.e. the > is missing)

But there can be lots of other causes as well.

Dave

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 4:40 pm

I always get the "greater than" cursor yes.

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Re: Atom Hardware Advice Needed

Post by hoglet » Thu Aug 30, 2018 4:53 pm

AndyGarton wrote:
Thu Aug 30, 2018 4:40 pm
I always get the "greater than" cursor yes.
So this does make me suspicious of a stuck key on the keyboard, or possibly a connection issue with one of the ICs relating to the keyboard (e.g. the 8255 or the 7445).

If pressing REPT doesn't show a key is stuck, that could mean:
- there's not a problem with a key being stuck, or
- the stuck key is one that doesn't show anything when REPT is pressed (like LOCK)

Dave
Last edited by hoglet on Thu Aug 30, 2018 4:53 pm, edited 1 time in total.

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 5:17 pm

Thanks Dave, I'll keep looking. At this point it does look "random" - I just ran for five minutes or so without an issue, trying a couple of games from the MMC card. It ended with a break press which led to a "no keyboard" incident again, repeat doing nothing. Turning off and on again gave the same thing. I suspect once it's cooled down again it will be fine. Does this indicate something like a bad solder joint perhaps?

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Re: Atom Hardware Advice Needed

Post by hoglet » Thu Aug 30, 2018 5:23 pm

AndyGarton wrote:
Thu Aug 30, 2018 5:17 pm
I suspect once it's cooled down again it will be fine. Does this indicate something like a bad solder joint perhaps?
On an Atom with white sockets, I think a bad joint between a socket and an IC is more likely. Or possibly a failing 8255.

Do you ever see random error messages? They can signify a RAM fault.

Here's another small test you can try, if it stays working for long enough to enter it:

Code: Select all

DO P."HELLO WORLD!!!"; U.0
And see how long that can stay running for.

(I'm trying to narrow down whether this is general unreliability / crashing, or whether it's specific to the keyboard).

Dave
Last edited by hoglet on Thu Aug 30, 2018 5:25 pm, edited 1 time in total.

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 5:28 pm

Thanks, I appreciate your time - I'll try that program as soon as it starts ok again!

One other (possibly) interesting thing: I noticed that when things go bad it often results in a slight screen flicker as well, and that pressing down IC25 (marked P8255/INS8255N) makes that flicker go away.

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 8:27 pm

hoglet wrote:
Thu Aug 30, 2018 5:23 pm
Here's another small test you can try, if it stays working for long enough to enter it:

Code: Select all

DO P."HELLO WORLD!!!"; U.0
And see how long that can stay running for.

(I'm trying to narrow down whether this is general unreliability / crashing, or whether it's specific to the keyboard).

Dave
I've been running the HELLO WORLD program for an hour now without an issue - I'll leave it running overnight.

(So it certainly seems heat related to me - I couldn't get the Atom to start (no keyboard input) at all when I tried it a few times after I first read your post this afternoon.)

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Re: Atom Hardware Advice Needed

Post by hoglet » Thu Aug 30, 2018 9:16 pm

AndyGarton wrote:
Thu Aug 30, 2018 8:27 pm
I've been running the HELLO WORLD program for an hour now without an issue - I'll leave it running overnight.

(So it certainly seems heat related to me - I couldn't get the Atom to start (no keyboard input) at all when I tried it a few times after I first read your post this afternoon.)
This suggests to me that the problem is either the 8255 (IC25) or the 7445 (IC26) (or possibly in the chip select logic for IC25).

Does applying pressure to either of these chips restore keyboard function?

Do you have any freezer spray?

Dave
Last edited by hoglet on Thu Aug 30, 2018 9:16 pm, edited 1 time in total.

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 9:24 pm

Applying pressure to IC25 (the one I tried earlier and noticed it affected the display) didn't affect the keyboard problem. I tried nearly all other chips, but can't remember for sure whether IC26 was one of them. I'll experiment further with this tomorrow anyway.

I don't have any freezer spray, but will get some if it can help?!?

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Re: Atom Hardware Advice Needed

Post by hoglet » Thu Aug 30, 2018 9:35 pm

AndyGarton wrote:
Thu Aug 30, 2018 9:24 pm
I don't have any freezer spray, but will get some if it can help?!?
If you think it is heat related, then in might help pinpoint a suspect chip.

There is another test program that might also shed some light on it. For example.

Code: Select all

10 @=4;P=#2800
20[
30 JSR #FE71;STY #80; RTS
40]
50 DO
60 LINK #2800
70 P. &?#80,&?#B000,&?#B001,&?#B002'
80 UNTIL 0
If you can get than running, and then the fault appears, the values printed might be useful.

Dave

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Thu Aug 30, 2018 9:40 pm

I get ERROR 94 LINE 4112 with that? EDIT - ignore, muppet error. That's running now, chucking out FF 0 FF C7/D7 etc. I'll leave it overnight.
Last edited by AndyGarton on Thu Aug 30, 2018 9:44 pm, edited 3 times in total.

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Re: Atom Hardware Advice Needed

Post by hoglet » Fri Aug 31, 2018 6:35 am

AndyGarton wrote:
Thu Aug 30, 2018 9:40 pm
I get ERROR 94 LINE 4112 with that? EDIT - ignore, muppet error. That's running now, chucking out FF 0 FF C7/D7 etc. I'll leave it overnight.
Some thigs to check in the morning....

The first hex number is the keycode of the key being pressed (FF meaning no key). If this ever shows anything other than FF (without a key being pressed) then that's interesting.

If you press shift or control, you should the third number change (BF or 7F rather than FF)

If you press rept, the fourth number should change (rept connects to bit 6)

If everything is still working in the morning, stop the program with Escape then check whether the problem has occurred.

Then press break, and see how things are.

Dave
Last edited by hoglet on Fri Aug 31, 2018 6:36 am, edited 1 time in total.

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Fri Aug 31, 2018 6:55 am

Interesting - maybe: it was still running this morning, and doing exactly as you describe (i.e. everything working as expected). But after pressing break, the keyboard was dead again. Ctrl-break and it was still dead. I could shift-break, and it attempted to load the MMC menu, but pretty much every character on the screen was corrupted.

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Re: Atom Hardware Advice Needed

Post by hoglet » Fri Aug 31, 2018 7:13 am

AndyGarton wrote:
Fri Aug 31, 2018 6:55 am
I could shift-break, and it attempted to load the MMC menu, but pretty much every character on the screen was corrupted.
That sounds like it is not correctly switching to the CLEAR 4 graphics mode. Again this is pointing to a problem with the 8255 (or with it's chip select logic).

Had any of the numbers changed prior to pressing BREAK? Especially, was the first number still FF?

If you can get the program running again, try terminating it with escape.

I'm slightly suspicious the issue seems to be triggered by pressing BREAK, and is not just happening on it's own. That's a bit unusual. Can you measure the voltage on pin 35 of the 8255 (referenced to ground) when it is hanging. It's just possible there is something weird going on with the reset circuit.

Dave

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Re: Atom Hardware Advice Needed

Post by AndyGarton » Fri Aug 31, 2018 7:35 am

I stopped it with escape the first time, and it was fine, I could list the program, re-run it etc. Only pressing break killed it.

The first number was always FF yes, and no other numbers had changed (the last number would always alternate between two different values, is that expected?).

I'll attempt the voltage measuring thing this weekend (I'm away with work today, and need to Google how to do it first also!). I'll also re-seat 8255 (although I probably did already).
Last edited by AndyGarton on Fri Aug 31, 2018 7:36 am, edited 1 time in total.

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