+2B with a non responsive keyboard

[1024MAK]

Yeah, take with a pinch of salt all the ‘recap’ everything that you find on the internet and YouTube. It’s not always necessary.

Yes, electrolytic capacitors do have a limited lifespan. So they may well need replacing eventually. Generally they only need renewing when symptoms of failure or degradation are noticed.

However, in critical applications, or where they are subjected to heat (either internal heating or external heating), then it’s wise to replace before failure, or as part of servicing.

However, in the 1990s, a new water-based electrolyte was being developed. An incomplete formula made it into the wilds. Some capacitor manufacturers produced capacitors based on this (incomplete) information. This resulted in the so called ‘capacitor plague". These ‘bad caps’ fail far sooner than they should. And they often leak electrolyte over the board which corrodes the PCB tracks. They often deform or burst. Unfortunately a wide range of equipment was affected between about 1999 to 2010.

The good news is that unless a Sinclair computer was recapped using these ‘bad’ capacitors, then they don’t normally suffer from leaking electrolytic capacitors. As they were made before the ‘bad’ caps were available.

However, the 16k/48k/+ machines do run rather warm. And they use a discrete DC-DC converter circuit based on transistors TR4, TR5, the ‘coil’ and various electrolytic capacitors. This DC-DC circuitry generates the +12V and -5V supplies that the ‘lower’ (4116 or equivalent) DRAM chips need. Loss of the +12V stops this memory from working. But worst, the loss of the -5V supply (while the positive supply voltages are still present) can result in one or more of these memory chips self destructing.

And as all these Sinclair computers are now over 35 years old, it’s wise to replace at least the critical electrolytic capacitors and the ones next to or under the heatsink for the 7805. Especially on issue one and issue two boards. But you may as well replace all of them while the board is out for servicing.

It’s less of a problem on the 128K machines (including the +2 and later models), because they use a different type of DRAM chip, that only need a single +5V supply. And these machines don’t get so hot inside and have better ventilation.

Later computers (some Amigas for example, and various PCs and laptops) and various other devices that may have been manufactured using ‘bad’ capacitors should have any affected or suspected capacitors replaced if you want them to continue to work and before the damage to the PCB becomes too bad.

Since then, modern good quality products should be okay, as no manufacturer should be using electrolytic capacitors made with the bad electrolyte.

However, the quality of the electrolytic capacitors available from some sellers on trading sites like eBay, is a bit of a gamble.

Mark

[JollyRoger]

Cheers Mark, I'll take that all onboard. You'd also advised me in the "Dead Spectrum Plus?" thread to replace the critical electrolytic capacitors and I'll carry that out on both machines. Phil is still closed for a few more days and I'll wait for him to reopen to be certain that I'm buying the correct components instead of taking a gamble elsewhere.

On a side note, it's interesting that you mentioned Amigas - it sounds like I need to examine my 1992 A600: I've not used it in decades and by now the PCB has probably been irrevocably damaged!

[MrClump]

Cheers Mark, I'll take that all onboard. You'd also advised me in the "Dead Spectrum Plus?" thread to replace the critical electrolytic capacitors and I'll carry that out on both machines. Phil is still closed for a few more days and I'll wait for him to reopen to be certain that I'm buying the correct components instead of taking a gamble elsewhere.

On a side note, it's interesting that you mentioned Amigas - it sounds like I need to examine my 1992 A600: I've not used it in decades and by now the PCB has probably been irrevocably damaged!

The caps on A600s, A1200s and CD32s are pretty much ticking time bombs. My A1200 had the early signs of leaking caps but was caught in time before any major damage was caused. It’s not always obvious they are leaking as it can be underneath the cap out of sight. A telltale early sign is discolouration of the visible solder, below is a picture from my A1200 before it was recapped. It’s also worth taking a look on the English Amiga Board forums.



If you want to get it done professionally then I can recommend Steve at Retropassion, he did a bang up job of mine, never leak polymer caps and an ultrasonic clean of the PCB so that it now looks brand new.

[JollyRoger]

The caps on A600s, A1200s and CD32s are pretty much ticking time bombs. My A1200 had the early signs of leaking caps but was caught in time before any major damage was caused. It’s not always obvious they are leaking as it can be underneath the cap out of sight. A telltale early sign is discolouration of the visible solder, below is a picture from my A1200 before it was recapped. It’s also worth taking a look on the English Amiga Board forums.



If you want to get it done professionally then I can recommend Steve at Retropassion, he did a bang up job of mine, never leak polymer caps and an ultrasonic clean of the PCB so that it now looks brand new.

Thanks, I'll keep that in mind. It's packed away here somewhere - still in its box, along with tons of Amiga stuff. I'd better dig it out. Commodore were such an incompetent organisation that I'm surprised they managed to survive as long as 1994/95.

[JollyRoger]

On the theme of the Amstrad Spectrum's that were bundled with light gun packs, would they have been predominantly +2B's (like mine) or a mixture of +2A's and B's?

[1024MAK]

It’s impossible to say for certain (unless an Amstrad employee steps forward with information), but I suspect that they would all have been +2B machines.

The vast majority of +2A machines have exactly the same circuit board as the +2B machines.

Mark

[Guesser]

It’s impossible to say for certain (unless an Amstrad employee steps forward with information), but I suspect that they would all have been +2B machines.

The vast majority of +2A machines have exactly the same circuit board as the +2B machines.

Mark

Well, the same part number, different circuit revisions. I gather the change happened after switching to Issue 2 boards and before Issue 4.

[JollyRoger]

Cheers - I knew you guys would have the answers.

[JollyRoger]

A little update: I raised the issue of the keyboard with the seller - considering that they had assured me prior to bidding that the computer was in full working order and I received a partial refund of £20, so I got the +2B for £21. I'm more than satisfied with that outcome.

[MrClump]

A little update: I raised the issue of the keyboard with the seller - considering that they had assured me prior to bidding that the computer was in full working order and I received a partial refund of £20, so I got the +2B for £21. I'm more than satisfied with that outcome.

That's an absolute steal.

[speccypsh]

hi guys
have a similar problem with a black plus 2 hope you can help with started when i replaced power connector certain keys now dont work 1/2 and enter among others) have taken keyboard apart and completely and cleaned reseated connectors with no joy strange thing when using keyboard check on
retroleum v2 all keys work but while checking through the keys when pressing certain keys 2 keys lights up ie 1 and 2 . also when selecting games from the sd card the enter key works but in the game .do you think the membrane is at fault thanks in advance

[1024MAK]

With faults, I much prefer members to start a new topic. This saves confusion. However, I'm not an admin or moderator here.

Mark

[JollyRoger]

However, I'm not an admin or moderator here.
Mark

You should be!