Sunday 27 October 2024

Sony TCM-818 Cassette Recorder Part 2 - Battery Upgrade

In the last post I look at the Sony TCM-818, a great cassette recorders for use with 1980s computers.

One of the things I didn't like was the battery power option, since I would rather not use C cells, and using AA rechargeables in adapters is not ideal.

Battery Upgrade

My plan is to take a bit of a tatty TCM-818, I picked up recently and make it my daily driver work horse. I could use power it from the mains, but I would rather keep it battery, so I plan to replace the four C cells with something better.

The C cell voltage is between 1.2V and 1.5V, so 4.8V-6.0V for a set of four.

Checking the schematic, the main IC is an LA4162.

(I was slightly disappointed to note the erase head on the bottom left there is a magnet rather than being a proper one, but I guess it works fine and I rarely record on these)

There isn't much information on that IC, but it appears to be rated for 3-10V, so this is well in the range.

In a previous post, I harvested some 18650 cells from a laptop battery.

My plan is to use two of these in place of four C cells.

The 18650s are nominally 3.7V, but that can range from about 3.6V to 4.2V depending on the charge level. A pair of those should give me between 7.2V to 8.4V.

That is maybe a little high, so I was thinking of various ways to reduce the voltage a bit. My first thought was a couple of 1N4001 diodes, these have approximately 0.6V drop, to should reduce the nominal 7.4V to 6.2V.

The other option was a 7806 linear voltage regulator. That should fix the voltage at 6.0V, and turn the rest into heat.

Players like these do not have a power switch, they only activate when one of the buttons has been pressed. The regulator would need to be placed after those switches, so it was only be active when the device was in use, and I am sure I could find a bit of metalwork to bolt it to. I wouldn't use one of those switching buck / boost regulators, as they will introduce high frequency noise.

I couldn't find a two inline 18650 holder, so I have used two individual 18650 cell holders, test fitting those it looks good.

Wiring two of those in series is one of the odd occasions where you connect black to red. Still seems wrong.

I left a bit of length to those two wires, and covered the join with a bit of heatshrink.

I was hoping I might be able to make the connections without opening it up, but it didn't look like I could. (if I was one of those people who have made the time to setup a 3D printer properly, I might have designed 3D printed C cell shaped end caps that would have held the cells and made contact at both ends, but I am not, so I didn't)

Disassembly

I looked around and found there was only one screw. None hidden under labels or in the battery compartment.

Other than this one screw, it is held together with a series of clips. To disassemble, you start with the one on the back left of the battery compartment, and work around to the one on the right.

Not ideal, but I have been running a variety of these for decades and I think this is the first time I have actually had to open one up.

It looks like the replacement TCM-919 has screws around the side rather than those clips, so I might have a look for one of those. But I still prefer the styling of these.

Now I had it open, I thought it was worth checking what voltage the mains power supply was putting out.

It is a very simple transformer / bridge rectifier / capacitor circuit.

Measuring that shows it is outputting about 8.4V, which dropped to about 7.6V when playing.

Given that, I think I could just go for the easiest option and wire two 18650s holders directly in place of the four C cells. That would give a similar voltage range to the one it is already getting from the mains power supply.

The positive side of the battery connection is on a PCB on the side, so I soldered the red wire to the back of that.

The negative side is the usual battery spring.

The spring wire continues all the way to the main PCB. So I just soldered onto that at a convenient point. (bottom left)

You can see the LA4162 IC in the centre. No Sony branding on the IC itself? No branding of any kind?

This should give me a nice convenient way of powering one of these drives, and should last for ages. I was going to use hot glue or foam pads, but they seem to fit in place quite nicely, keeping the mods minimal and easily reversible.

Two of those recovered Samsung 18650 will do nicely. They were effectively free, recovered from an old laptop battery.  Ideally you would use ones with the built in protection chips. You should probably add one of those small boards with DW01 protection chips on. I didn't have any to hand, but should probably get some.

Whilst I had the unit apart, I thought I would do the usual maintenance, clean all the grot from the mechanism and add a little white lithium grease to the moving plastic parts.

Belt up

I bought a belt kit a while ago, but have never had a reason to fit it, they have all just worked fine.

I thought since I had this one apart, I would swap them out, see if it made a noticeable difference.

There are three belts, the smallest goes under the flywheel.

The largest goes from the top of that to the motor

There is a third thin belt that drives the tape counter.

With the new belts and 18650 based power supply, I went through the tape speed test again.

3.002 KHz, I'll take that.

That was about half volume. No clipping at the top, 7.5V.

Testing

Let's run this through a few tests, this is ideal to test out the new Minstrel 2 and 3 kits.

I'll start with a Minstrel 3, and 3D Monster Maze.

Carefully following the instructions on the back of the case.

Nice loading bars.

There were several sections where the tape is clearly worn out and the signal dropped to almost nothing. I tried both sides of the tape, but the B side was worse. No 3D Monster Maze for me today unfortunately.

Most of the other things I tried did load.

Paul Farrow's games are good tests as they have a checksum test before launching the game.

As does Psion's Flight Simulator.

Of course, you can use a real ZX81 if you have one of those.

I just had a new Spectrum cassette turn up, so I'll give that a go as well.

The Spectrum has nicer loading screens.

Ooh.. Nasty!

That has all worked out quite nicely. I was pleased to find a better solution to those fiddly C cell adapters.

The TCM-818 was clearly built to a price. I was a little disappointed to find a magnet erase head and the case being held together with clips, but I guess they spent the money on a decent cassette mechanism. Neither but neither of those caused me any problems over the years, these have been solid and reliable cassette recorders, and I hope they will continue to be for many years to come.


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As I announced last week, I have reopened my Tindie store and have new batches of Minstrel 2 and 3 kits, for ZX81 case or standalone with keyboard, and ZXpand microSD card interface.

From there I can ship worldwide.

I will slowly be moving things over there from my SellMyRetro store, so if there is anything that you want, let me know and I'll add it.

More 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.

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 five listings:

Minstrel 2 For ZX81 Case

Minstrel 2 With Keyboard

Minstrel 3 For ZX81 Case

Minstrel 3 With Keyboard

Minstrel 3 With Keyboard and Micro ZXpand 

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.