+2 crashes upon pressing some keys

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Alessandro
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+2 crashes upon pressing some keys

Post by Alessandro »

Years ago I purchased off ebay a mint condition, Dixons special offer boxed UK-made issue 1 +2. I did not use so much until recently however, focusing my hardware tests on the 48K, 128K and +2A. In the last few months, I tested my later games on it as well.

Since a couple of days, I discovered a strange issue. After about 20-30 minutes of continuous usage, the machine crashes when a game is loaded (i.e. not under the BASIC prompt) if I press keys N, M or Space. Crashes take the form of usual screen corruption (random flashing squares, lines, pixels etc.) and/or reset.

I downloaded and ran a couple of test programs for the ULA and RAM, first this one, then this, but the computer passed them all without problems.

I tried two different PSUs, the one which came with the machine and an identical, new one I purchased from Dataserve Retro. The issue did not change. Neither it would whether I loaded software from tape or from my DivMMC EnJoy.

Here is the link to a photo of the +2's motherboard; I hope that it could help someone more knowledgeable than me in finding the fault. I don't know how to test voltages etc. myself, but maybe I could get some help down here for that.

https://drive.google.com/open?id=1WjyAi ... 7FMlI35xeb
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Re: +2 crashes upon pressing some keys

Post by RMartins »

Since it takes a while to fail, it is probably related with some component heating, which then starts to malfunction.

I would first check, when it is already failing, if any of the components, in particular is hotter then the others or similar components.

I would then check the capacitors if they were not yet replaced.

I would also check the voltage levels in the power rails of the RAM chips.

I would also check the transistors involved in the power circuit and the thermal coupling of the linear regulator.

Finally, it could be a bad solder joint that stops making contact when the board or the component heats up, due to expansion of the metal of the contact.

A simple way to confirm that is heat related is to run an app with the machine open, with a fan blowing on the entire board.
If it does not fail or takes a lot longer to fail, then it is safe to assume it is heat related.

You should also measue the power rails values from cool state and then re-check every minute to see if the value is changing with time.

Note: During testing you have the machine open, hence it is probable that it takes longer to heat up.

I would also recomend you keep a RAM test running for an hour, after you checked power voltage is stable.
Last edited by RMartins on Mon Apr 09, 2018 11:59 pm, edited 1 time in total.
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Re: +2 crashes upon pressing some keys

Post by RMartins »

From the image I see a thermal dissipator on top of the ULA.

If there is no thermal paste between it and the ULA, it can make it worse by blocking the chip natural dissipation by convection.

Note: The thermal paste is usually a white creamy substance.
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Re: +2 crashes upon pressing some keys

Post by Alessandro »

RMartins wrote: Mon Apr 09, 2018 11:58 pm From the image I see a thermal dissipator on top of the ULA.

If there is no thermal paste between it and the ULA, it can make it worse by blocking the chip natural dissipation by convection.

Note: The thermal paste is usually a white creamy substance.
I know this, I have been assembling PCs for more than 20 years :lol: From other pictures on the Web, I understood the heatsink is glued to the ULA with a layer of thermal adhesive paste. I already thought about buying a thermal adhesive tube, removing the heatsink, cleaning it and the chip, putting a new strip of paste and refitting the heatsink. But I wished to hear some more advice first.

On the other hand, I don''t know how to test voltages and am not skilled at soldering and desoldering, therefore the capacitors are still the original ones. I think I could be able to substitute the voltage regulator however, should the necessity for it arise, because it's not soldered to the mainboard and would not require much effort.

Finally, I cannot test the +2 by leaving it opened as in the picture. The keyboard would be disconnected since the strip cables connecting it to the motherboard are too short.
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Re: +2 crashes upon pressing some keys

Post by Nomad »

From the photo (very high quality!) you can see many of the capacitors are bulging. Re-capping the whole board would be a good idea. It is more tedious than complex. Just practice on some junk you have laying around the house before you start on the spectrum. When you are confident de-soldering, soldering have a crack at the spectrum.

It might not be the cause of your problem - but with intermittent faults they are hard to troubleshoot anyway. However like H said if its heat related there are only so many things it can be. Get the low hanging fruit first. Re-capping the board is something that needs to be done anyway - if it fixes the problem so much the better, if not then carry on looking at other potential culprits.

Those capacitors are a time bomb in that machine, its just a matter of time before one of them fails catastrophically and you will have lost the magic smoke and a cascade failure.
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Re: +2 crashes upon pressing some keys

Post by RMartins »

Alessandro wrote: Tue Apr 10, 2018 7:39 am ... From other pictures on the Web, I understood the heatsink is glued to the ULA with a layer of thermal adhesive paste. I already thought about buying a thermal adhesive tube, removing the heatsink, cleaning it and the chip, putting a new strip of paste and refitting the heatsink. But I wished to hear some more advice first.
Removing the heat sync shouldn't present a problem, since the machine always worked without one from the beginning.
It's also the part you seem to be most comfortable with.

Thermal adhesive tape is known to work bad, if not from one of the major brands (3M, for example), so I would not count on it doing a good job.
Alessandro wrote: Tue Apr 10, 2018 7:39 am On the other hand, I don''t know how to test voltages and am not skilled at soldering and desoldering, therefore the capacitors are still the original ones. I think I could be able to substitute the voltage regulator however, should the necessity for it arise, because it's not soldered to the mainboard and would not require much effort.
Some of the capacitors, seem a bit "fat" on the edges, since the plastic seems to be curling.
If you can't replace them, you probably have a friend who can, if not you can always get it into an electronics service repair shop, to be on the safe side.

I would not replace the voltage regulator, if not proven that it's faulty, since its' working at least for 30 minutes, so it's very unlikely to be the cause of the problem, specially with such a large heat sync attached.
Alessandro wrote: Tue Apr 10, 2018 7:39 am Finally, I cannot test the +2 by leaving it opened as in the picture. The keyboard would be disconnected since the strip cables connecting it to the motherboard are too short.
If you have an interface, that allows you to test the machine automatically, like the Retroleuam Smar Card, or any other that allows the same, you can boot it without keyboard, after you set the correct deep switch, to enter test mode on boot.

The other option is either have another membrane that is longer, or just use a piece of wire, to fake key presses between the 2 sockets, by making a connection with the wire, which is what the keyboard does.
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Re: +2 crashes upon pressing some keys

Post by Alessandro »

Nomad wrote: Tue Apr 10, 2018 9:44 am From the photo (very high quality!) you can see many of the capacitors are bulging. Re-capping the whole board would be a good idea. It is more tedious than complex.
Thanks :) it was just a quick snap I took with my cell phone. I did some soldering in the past but it was limited to cable and connector repairing, nothing near as precise as substituting a component. I am afraid I would make a mess, and definitely must do more practice before attempting to do that myself.

I think I will start with the thermal paste anyway, and see if the problem disappears.
Nomad wrote: Tue Apr 10, 2018 9:44 amThose capacitors are a time bomb in that machine, its just a matter of time before one of them fails catastrophically and you will have lost the magic smoke and a cascade failure.
I have got 11 Spectrums, ranging all the way from the 16K to the +3 and +2A. Are you implying I should substitute every single capacitor for each one of them? :shock: That would require an awful lot of time and skill; to make matters worse, I should know what goes where - i.e., which kind of capacitor I would need for each board and how many of them, and where should they be placed. For example,the +2 parts list found on the +2 service manual available on WOS lists 3 different types of capacitors for a total of 59 pieces. Am I supposed to substitute all of them? :o Or just the electrolytic ones, which are 21 anyway?

I downloaded from the WOS archive and from other sources some schemes and part lists in the past, but with so many issue variations, I am afraid , even if I should be able to actually perform a decent soldering, to make a mess due to incomplete/wrong/outdated lists.

It would take me ages to do that :cry:
RMartins wrote: Tue Apr 10, 2018 10:26 am Thermal adhesive tape is known to work bad, if not from one of the major brands (3M, for example), so I would not count on it doing a good job.
I considered an adhesive paste in fact. I am thinking about something like this.
RMartins wrote: Tue Apr 10, 2018 10:26 am Some of the capacitors, seem a bit "fat" on the edges, since the plastic seems to be curling.
If you can't replace them, you probably have a friend who can, if not you can always get it into an electronics service repair shop, to be on the safe side.
I am not comfortable giving my Spectrums to a repair shop. I think I should learn to do it myself, even if it will take me ages due to my lack of spare time. My Dad is an expert at this sort of thing but at his age (he will be 80 this year!) I cannot certainly ask him to do all of the work for me. Moreover, there is the problem of the component list (see above).
RMartins wrote: Tue Apr 10, 2018 10:26 am If you have an interface, that allows you to test the machine automatically, like the Retroleuam Smar Card, or any other that allows the same, you can boot it without keyboard, after you set the correct deep switch, to enter test mode on boot.
I have a DivMMC EnJoy but I am not sure if I can select the memory test file from the menu by mimicking the cursor movement with a joystick in the Sinclair ports. I could try though, because the other solution (wires etc.) seem less viable to me.
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Re: +2 crashes upon pressing some keys

Post by Ast A. Moore »

Alessandro wrote: Tue Apr 10, 2018 10:53 am I have got 11 Spectrums, ranging all the way from the 16K to the +3 and +2A. Are you implying I should substitute every single capacitor for each one of them?
Definitely the 16K/48K machines, especially the earlier issues. The +2A/+3 can be left alone for the most part. There are newer, and there are fewer capacitors in them.

Incidentally, some 128K machines (Sinclair originals), have high-quality Philips electorlytics in them. Unless you’re planning to run these machines for extended periods, they can be left un-recapped (with luck).

I generally don’t condone the “recap everything you can get your hands on” craze, but in some cases it can prove very effective and prevent damage to certain components.
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Re: +2 crashes upon pressing some keys

Post by Nomad »

With the 11 systems, do a visual inspection of all of them. Check for obvious faults/potential failing parts. You have a lot of machines so its a big job. But it is worth checking them all to see what state they are in.

First off - commendable you want to do it yourself. Once you get the hang of it its easy. Like learning to tie shoe laces. You can then start looking at every electronic widget in your house as something you can hack/repair. Every dumpster/trash bin becomes a potential goldmine (among the used syringes, broken glass and animal products :lol: )

The score's you can make from suff other people thought was junk are great, especially in a first world situation. (in the third world, nothing gets left on the sidewalk like in UK or US, it is collected by scavengers immediately or repaired by the orignal owner. :lol: )

I can remember in the UK finding TVs that needed a few traces bridged and the power block replaced. Another time I got a typewriter that needed a new motor. :lol:

Once you have looked through the 11 machines. There should be a spread from systems that look perfect to ones that have very worrying issues and probably most are somewhere in between - Just like your machine that you posted. It's a blessing you have a noticeable fault this early with a system like that. If you had had silent errors like most boards - its only when you get a catastrophic event that you notice there was ever a problem.

After you graded your machines, checked for stuff like bulging, leaking caps. That is one of the obvious tells of a sick board. But like Rmartins said cold solders/stress fracture on the board are another common thing you will find. With a bit of practice you can fix this with bridges.

If its the ICS, the thing might fail completely, or behave very strangely under load (it will get hot, exceed its operation range and start to behave in unpredictable ways.)

Now you have your graded list of 11 machines, fix the one at the top of the list first, and just go down as you have time.

Tackle the re-capping first. Then repair traces, then ICs. IT would be very unlucky for you to get all 3 problems on the same machine. At that point unless it has a lot of value its probably not worth repairing the widget just the amount of time it would take. :lol:

Re-capping boards that are 30+ years old is probably a good idea as the components are way outside of there expected lifespan. The boards might work fine for years to come yet but its a situation the manufactures never planned for. Components are cheap, these machines are getting more and more scares as time goes on/harder to replace. I know its a pain and boring replacing the caps but think of it another way you are ensuring that your collection can be enjoyed by someone else for another 30+ years. (Kids ect).
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Re: +2 crashes upon pressing some keys

Post by RMartins »

Alessandro wrote: Tue Apr 10, 2018 10:53 am ...
Nomad wrote: Tue Apr 10, 2018 9:44 amThose capacitors are a time bomb in that machine, its just a matter of time before one of them fails catastrophically and you will have lost the magic smoke and a cascade failure.
I have got 11 Spectrums, ranging all the way from the 16K to the +3 and +2A. Are you implying I should substitute every single capacitor for each one of them? :shock: That would require an awful lot of time and skill; to make matters worse, I should know what goes where - i.e., which kind of capacitor I would need for each board and how many of them, and where should they be placed. For example,the +2 parts list found on the +2 service manual available on WOS lists 3 different types of capacitors for a total of 59 pieces. Am I supposed to substitute all of them? :o Or just the electrolytic ones, which are 21 anyway?

I downloaded from the WOS archive and from other sources some schemes and part lists in the past, but with so many issue variations, I am afraid , even if I should be able to actually perform a decent soldering, to make a mess due to incomplete/wrong/outdated lists.

It would take me ages to do that :cry:
It's actually simpler than you think.
First, take photos of every component before desoldering, so that you have a reference :)

Second, each component, has values written on it, so each time you take one out of the board, mark it's place and orientation on a drawing and the value it has written. This minimizes potencial for mistakes.
TIP: Use your reference photos if needed or if you forget to mark the orientation.

Third, you only need to replaced the Electrolytic capacitors, which are the ones that use liquid/gel inside, which is what dries after a few years or when over exposed to high temperatures, which makes them get out of spec.

Why do you need to replace them ?
1 - it improves picture quality
2 - improves output power voltages
3 - prevents, burning your RAM chips

That last two reasons are the critical ones, since replacement capacitors are easy to find and source, but the RAM chips are more and more harder to source even in NOS (New Old Stock) state.
Capacitors are really cheap when compared to RAM chip prices.
Alessandro wrote: Tue Apr 10, 2018 10:53 am ...
RMartins wrote: Tue Apr 10, 2018 10:26 am Thermal adhesive tape is known to work bad, if not from one of the major brands (3M, for example), so I would not count on it doing a good job.
I considered an adhesive paste in fact. I am thinking about something like this.
In these cases, going for the cheaper unbranded product, might cost you more and be extra trouble in the long run.
It's up to you, but I only use proven/good thermal paste.

Alessandro wrote: Tue Apr 10, 2018 10:53 am ...
RMartins wrote: Tue Apr 10, 2018 10:26 am Some of the capacitors, seem a bit "fat" on the edges, since the plastic seems to be curling.
If you can't replace them, you probably have a friend who can, if not you can always get it into an electronics service repair shop, to be on the safe side.
I am not comfortable giving my Spectrums to a repair shop. I think I should learn to do it myself, even if it will take me ages due to my lack of spare time. My Dad is an expert at this sort of thing but at his age (he will be 80 this year!) I cannot certainly ask him to do all of the work for me. Moreover, there is the problem of the component list (see above).
That's great!!!

You have the best solution in the world.

Someone that knows the subject that can teach you, and better yet, it can work as a father/son "bonding" moment, and it will surely be something that you and him will appreciate, by sharing that extra time.
Alessandro wrote: Tue Apr 10, 2018 10:53 am ...
RMartins wrote: Tue Apr 10, 2018 10:26 am If you have an interface, that allows you to test the machine automatically, like the Retroleuam Smar Card, or any other that allows the same, you can boot it without keyboard, after you set the correct deep switch, to enter test mode on boot.
I have a DivMMC EnJoy but I am not sure if I can select the memory test file from the menu by mimicking the cursor movement with a joystick in the Sinclair ports. I could try though, because the other solution (wires etc.) seem less viable to me.
It only uses the numeric keys (no need for CAPS-SHIFT), so it should be doable.
I'm not sure the DivMMC menu supports navigation using Kempston. It should, but I have a vague idea of trying it, and of it not working.
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Re: +2 crashes upon pressing some keys

Post by 1024MAK »

Some suggestions and hints and tips:

Only the electrolytic capacitors normally need to be changed.

Don't try to desolder the capacitors unless you are an expert and have suitable tools. Instead cut the leads. Then you can heat the solder pad, and use a pair of long noise pliers to gently pull the old wire out. Then clear the hole of solder using a solder sucker / desolder pump or good quality desolder braid. Don't even think about trying to use cheap stuff.

The advice about taking photos of each capacitor before starting work is an excellent tip that I recommend.

Polarity is very important with electrolytic capacitors. The negative lead is next to the side of the capacitor marked with - signs (radial types). But most circuit board markings use + signs to indicate where the positive lead goes.

Silicon heatsink paste is recommended. The adhesive type was not used when they were manufactured.

It's always a good idea to clean the old heatsink paste off and then apply a thin smear over the surface of the chip and the heatsink before reassembling. You only need a thin smear, as the idea is to fill in any unevenness in the surface, NOT to form a sandwich filling!

With the ULA, the metal heatsink parts fit together in such a way, that they are supposed to securely stay in place. You may however have to adjust the parts, or in some cases, bend the clip very slightly.

Have you ran a simple BASIC program (that shows that it is running, say by printing a counter on screen) for one or two hours?

A dry solder joint can also appear to be a heat related fault. Especially if physical disturbance of the PCB effects the operation.

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Re: +2 crashes upon pressing some keys

Post by Alessandro »

Thanks everyone for the answers. Now, I'll try to summarize my answer as much as I can :lol:

Actually I have 10 Spectrums. Maybe I unconsciously included the Next in them! :mrgreen:

Further examinations of the ULA showed that the heatsink is firmly kept in place by a clip; I prefer not to take it apart, at least for now because I would not want to break it or damage the circuit board by applying strength to it. I still suspect the cause of the strange behavior could be a cold or dry soldering of the largest keyboard ribbon connector, as Mark suggested in fact. Therefore, no need to apply thermal paste, adhesive or not, at least for the time being.

After some advice from Dad, I purchased a soldering station like this one and a soldering pump. However it will take a very long time before I feel confident enough to even try to substitute the capacitors. I am starting from zero and am afraid I could butcher my Spectrum beyond repair.

Brendan Alford's test can be run continuously, but it won't demonstrate anything by itself, apart from the fact that the ULA and RAM seem to be in good order when the problem arises. The only way to invoke the strange behavior is to press the N, M and Space keys in fact, which which occurs after about 20-25 minutes of continuous operation.

Again, due to my complete lack of skill in soldering, it's going to take a long time before I attempt to check the keyboard connector and maybe resold it. I will make some practice with old cards when I have time to spare, then re-solder the largest ribbon cable connector, and see if the problem has been resolved. Then I plan to take note of all electrolytic capacitors on the +2's board and buy the new ones, then try to substitute them one by one. It will take me ages, but at least I have no hurry. I am doing this for my own personal enjoyment - like my other retrocomputing/retrogaming activities actually. I have no kids and my niece is not interested in present day computers, let alone 30-35 year old ones. This means I'll most probably leave them in my will to a computer museum or some other academic institution :lol:
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Re: +2 crashes upon pressing some keys

Post by DanHero »

Hi, have you solved the issue? I've got the very same problem and I was looking for a solution, then I read your topic and I see I'm not alone!
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Re: +2 crashes upon pressing some keys

Post by Alessandro »

Hi [mention]DanHero[/mention], welcome on this forum :) Unfortunately I lost interest in the question, then I had more important things to look after, and the +2 has been left in its box and in a drawer since then.

Now that you mention this, I remember a fellow Italian Spectrum aficionado I have been in contact with for years once briefly talked me about another one who could possibly be able to repair it. I am sure that in the UK there can be someone able to do it, maybe even on this forum, but the postage costs would be too scary to mention :o
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Re: +2 crashes upon pressing some keys

Post by DanHero »

Ah, I hope they were not too serious problems. I'm Italian too, apparently this problem was particularly widespread here :D
Thank you very much in any case!
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