In a previous post, I went through some troubleshooting suggestions for the divMMC future, including a bit of a diversion into a repair of one of those issues, a Z80 with a bad M1 line.
In the original Patreon post, I have a further diversion from that initial diversion, with some thoughts on "refurbished" computers.
I thought that was a diversion too far for that post, so I decided to make it a post of it's own.
The Spectrum in question is one that the owner bought from ebay as "refurbished", and then bought a divMMC future and found it wasn't recognised, so I was called in to fix it for them.
This one is nicely done with an original box.
I don't want to criticise the "refurbisher", but I would have thought these days that testing with a divMMC or similar device would be an important step, as I think many users will be going for that.
There are different approaches to "refurbishing" a Spectrum, some people do less, some do more. I tend to do a few things as a given
- 7805 replacement switching regulator
- TR4 and TR5 replacement
- Capacitor or transistor buffer composite mod (depending on model)
- Replacement membrane (unless the original is pretty good)
- RAM repairs as required
- Heatsink on the ULA if there is space or possibly ULA replacement if they plan to use this a lot
Some people also go a step further and replace all the electrolytic capacitors. I don't normally do that unless specifically asked to, or unless they look or test bad.
The presentation was good on this one, all neat in the original poly's. Power supply, cables, manual (just missing a Horizons tape).
There is a new keyboard membrane.
This one is from Tesla (not that one).
The main board looks OK, not pristine original, but not overworked refurb.
There is a transistor composite video mod. There are quire a few different ways to do a composite mod, but it works.
Not the best picture I have seen from a Spectrum, but not the worst.
There is one odd looking 74HCT00 chip, but it seems to be original, just a little unusual alternative to the 74LS00 that is normally there. I don't think it is part of a later 48K upgrade as all four 74LS157s look identical, and only IC3 and IC4 would have been fitted to a factory 16K model.
There are the usual assortment of RAM repairs, one 4116 in a socket, that seems a good match.
Although there are some serious solder blobs on those legs.
The upper RAM has also been repaired, with several 4164's that don't really match the 4532s they replace.
It is not clear from the soldering how recent those RAM repairs were, they could have been from the same time as the Z80 and ROM replacements that look to have been done in the 80s. Ah, the evocative smell of 80s flux.
RAM repairs on machines like these are always a compromise between reliability and originality (and to an extent, cost).
I have made various boards which can replace 8 of those DRAM chips at a time, fixing faults and reducing the likelihood of future ones.
But that will never look original, if that is important to you.
Unless the owner wanted to retain as much originality as possible, I would have replaced the 7805 with a switching regulators and fitted new TR4/TR5 in the switching power circuitry. (another benefit of the RAM replacement boards are they run on 5V only, so are not susceptible to issues with the rubbish Spectrum 12V and -5V rails that have lead to the early demise of countless 4116 chips)
It's not my place to do extra work here, I'm just fixing the bad M1 line problem to get the divMMC working.
I am not even going to fix this crystal that is very much on the wonk, but I guess all the electrons must be having fun sliding down the slope 4.4336 million times a second.
See the original post for more information on the Z80 replacement.
With the heatsink refitted, the repaired board doesn't look much different.
But it is now working well with the divMMC.
That seems a good level for light use.
If you need a machine to use a lot, then replacing the voltage regulator and maybe the ULA and the RAM would be a good idea.
At which point, maybe you should consider a complete replacement board, like a Harlequin. Get rid of all the vintage components, but still running with "real hardware".
Or do you go even further and go to emulation with a Raspberry Pi or even a smart phone app.
"The Recreated ZX Spectrum" turned out to basically be a nice looking bluetooth keyboard.
Which is why mine wasn't even opened until 5 minutes ago. (yes, I know, I destroyed the value, it's no longer worth $1M).
I guess it's good to have all these options.
Which one would you prefer?
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DivMMC Future
The DivMMC Future is available from The Future Was 8 bit, with grey and white options available again. Don't worry if it shows as "backorder", more are currently being built.
There are various kits, upgrades and repair parts available in my store.
The SellMyRetro store is on it's last days, everything is still listed there if you need more information, but best to use the contact me link about, tell me what you want and where you are and I will send a PayPal invoice. Sorry I have to keep saying that. The new store should be here in the next week or so.
All the links can be found here:
Patreon
You can support me via Patreon, and get access to advance previews of posts like this and behind the scenes updates. These are often in more detail than I can fit in here, and some of these posts contain bits from several Patreon posts. This also includes access to my Patreon only Discord server for even more regular updates.
