Sunday 20 October 2024

A Change of Plan...

The end of life of the Z80 in it's original 40 pin form back in April was a bit of a blow, as that was the heart of a lot of projects in production, and even more that were still in development.

At the time, I tried to buy in enough Z80s to keep me going for a short while, but it was a bit of a thin time for me, so I was only able to get enough to cover a final batch or two of Minstrel kits.

That was further frustrated when I finally did get a bit of money in and went looking for Z80s only to find my usually suppliers had already sold out. I knew it would happen, but was hoping I might scrape through.

One site was actually showing several hundred in stock, but it wouldn't let me order any, and when I checked with their customer support there was apparently an order already in the system and the stock hadn't been updated.

When it was updated, it was updated to 0. Obsolete, no longer manufactured.

Missed them by a day.

Another supplier did look promising as it was showing them as available to backorder.

But when I did order, I got an email the next days saying they were unable to fulfill the order and it had been cancelled.

(They are still showing as available for backorder)

I was resigned to the fact that all those projects were dead, and I put fresh effort into reviving some old 6502 projects that had stalled in the past.

Including one which now has a very yellow PCB.

And another with at least one deliberate mistake.....

(missing the slot in the datasette connector)

More on those later.... (or now if you are on my Patreon)

What to do?

I was still upset about missing out on the last of the Z80s.

I would occasionally check around to see if anyone had magically found some stock behind the fridge (or rather when their last time buy allocations would appear).

The problem is the Z80 CPU was always listed in strange places, and in strange ways.

It often appeared as "ROMless microcontroller" or things like that, not immediately obvious that it was the right thing. The part number was never anything simple like "Z80 CPU", it was Z84C00xx with xx being 04 06 08 10 or 20 depending on the speed grade. I normally bough the 10MHz version as they were the same price as the slower speeds and only the 20Hz was more expensive.

Even in those days it seemed like Zilog (or LittleDiode I think the parent company) didn't care about the Z80, with the confusing descriptions, obfuscated part numbers and listings with badly photocopied 90s product catalogues.

And then one day last week (this was originally on Patreon last month), I found some in stock.

They are the 8MHz version, which is fine. The ZX80 and ZX81 (and the Minstrel 2 and 3) run at 3.25MHz, so any of those would do. The Minstrel 4th runs at 6.5MHz, and the RC2014 in general runs at 7.372MHz, so the 8MHz covers all of those.

I did a silly thing.

I decided to do what may turn out to be a silly thing, or maybe it will turn out to have been a good decision. Time will tell.

I didn't think I would get the chance again, and I know I had been disappointed when I missed out before.

So I bought a lifetime supply of Z80 chips.

That may be optimistic in both the number of Z80 based kits I would sell, and also how long my lifetime may be, but either way, it will cover me for the foreseeable future.

Lots and lots of Z80s.

2024 date code, 27th week, that would make it July 1 to July 7 2024, some of the last Z80s ever made.

A Change of Plan

All Z80 developments are back on the table. All systems go!

The Minstrel 2 and 3 are back then, and I have respun both in the "+ keyboard" versions that were previously TFW8b exclusives.

It is a bit of a gamble, I have invested a lot of time and money into parts to relaunch these kits, so I hope they will sell.

In order to give them the best change, I have reopened by Tindie store and listed them on there.

All kits will be supplied with one of those 2427 date coded Z80s.

I currently have four listings:

Minstrel 2 For ZX81 Case

Minstrel 2 With Keyboard

Minstrel 3 For ZX81 Case

Minstrel 3 With Keyboard

Minstrel 3 Full With Keyboard and ZXpand Micro

(should be live shortly)

I plan to move all the listings over to Tindie, so let me know if there is anything I haven't listed yet and I will get that added.

Shipping should be worldwide, and hopefully won't have all the issues with European shipping I had at SellMyRetro. As ever, international orders may be subject to additional charges at customs.

Anything else?

It also means other things can continue to be developed.

Some of the other project may also still see the light of day.

I have a a couple of other 8-bit computer compatible kits in the works, and another big project that has been on and off several times.

The Mini Micro Professor would also need a Z80-CTC and a Z80-PIO, and I think everyone has sold out of those, but again, Zilog part numbers make them a pain to search for.

Conclusion

I may never sell another Minstrel kit and could be left with a big box full of Z80s but I hope this wasn't the absurdly silly thing it might seem.

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I am slowly going through everything and adding them to Tindie, if there is anything you specifically want, let me know and I will get that added.

Shipping should be worldwide, and hopefully won't have all the issues with European shipping I had at SellMyRetro. As ever, international orders may be subject to additional charges at customs.

I sell on Tindie

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.

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Sunday 13 October 2024

Sony TCM-818 Cassette Recorder Part 1 - Overview

This is a Sony TCM-818. A very simple mono cassette recorder, ideal for use with 1980s computers that load programs from tape like the ZX81 or ZX Spectrum etc., or modern recreations like the Minstrel 2 or 3 etc.

It was introduced into Sony's range in 1989.

It was replaced by the face-lifted TCM-919 in 1993

A common sight in Argos catalogues of the time, they still had versions of these into the 2000s. See the important note - you can't plug one of these into your Commodore or Atari computer.

Argos no longer sell these, but you can pick them up for £20-£30 on ebay, and they generally just work with nothing more than a wipe over with a damp cloth.

These are usually the model I recommend if anyone wants a decent cassette recorder to use with a Minstrel kit. I also can't resist picking them up if I see them cheap on ebay. Always handy to have a few spares.......

Here is one I have just received, a boxed one, which is nice. (credit to the seller for packing this very well)

Must remember to fill in the warranty card.....

No instructions in this one, but give me a minute, I think I have another boxed one somewhere.

Ah yes, and it even has the Argos catalogue number seen above.

That one does have the instructions. For some reason, it's a giant fold out sheet like a road map.

I had been looking for another boxed one to see if it might include the handle. I don't need the handle, I wouldn't use it, but none of mine have handles. I might have removed all the handles years ago, but apparently all the UK models should have included one?

Features

The Sony TCM-818 is a very simple old fashioned design that suits this application perfectly. The amplifier that is used to drive the internal speaker also drives the earphone. That means you get a good strong drive signal which works well with the simple input circuits of those computers, and a nice volume wheel to twist.

It also has the standard arrangement of two 3.5mm jacks for Mic and Ear, and a 2.5mm jack for motor control, which means you can use these with a BBC, MSX or an Oric.

And yes, although most of the ones you see are black, they did make a white version to match for BBC and Oric users.

The easiest way to test one of these is with a music cassette, preferably something appropriately 80s.

It is usually very easy to tell if it is fast or slow or if there is significant wow and flutter or noise. (but maybe try a rubbish tape first in case it chews it up, before getting the Dire Straits out)

If you want to get a bit more scientific, you can use a test tone tape.

This one has a 3KHz tone recorded on it, so you can do various tests. The first one is signal level. At the maximum volume it has just started to clip.

Turning it down a touch and it's fine.

You can see why I like these, that's a solid nearly 7V peak to peak, not the 1V line level you get these days.

The 'scope also confirms the frequency is fairly close to the expected 3KHz.

Maintenance

Any cassette player usually benefits from an occasional head clean, particularly if it is new to you, and it might never have been cleaned before.

You can use a tape such as this one

Or just some IPA and a cotton bud / Q-tip as it describes in the manual.

Does it make a difference? Well, as I had this setup, I went through a few of these, and one of them was showing about 4.5V at maximum volume. I ran through the head cleaner tape and tried again. And there you go, up to 6V. So yes, it does make a difference.

The azimuth does not need adjusting. Please don't adjust the azimuth. The only time I ever need to adjust azimuth is if someone has previously moved it out of adjustment.

You can use the test tone tapes with a frequency counter, an oscilloscope, or you could use a PC sound card to record a sample and use various tools to analyse the signal.

Audacity has a Spectrum analyser, and here you can see the central tone, alongside the harmonics.

That all looks good.

Here I was running from mains, I was interested to see if there was a peak at 50Hz from mains noise, but it seems fine.

These things used to be everywhere, but I never seem to be able to find one when I need it.

They used to just be called "cassette recorder mains leads", but now you would need to search for "figure of 8" or type C7.

The standard TCM-818 can be powered from mains or using four seashells.

Sorry, four C cells.

I generally use battery power as that should give a cleaner signal and should remove any potential issues with mains noise or ground loops etc. (although this design is isolated using a transformer).

The only problem is that C cells are not very convenient these days.

I don't like using non-rechargeable batteries these days, so I normally use these adapters for rechargeable AA cells.

That means I can just recharge the AA cells as required.

However, they are quite a faff to fit in as they keep jumping out.

Next week, in the part 2, I will look at updating my tattiest work horse TCM-818 with a more convenient power source.

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There are various kits, upgrades and repair parts available in my store.

SellMyRetro seems to be broken at the moment. 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 info 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.

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Sunday 6 October 2024

Thoughts on "Refurbished" Spectrums

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.

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