TS1016 16K RAM expansion - Repair

[Nibby99]

I snagged a Timex Sinclair TS1000 locally (Here in Nova Scotia, Canada) and after discovering that the keyboard didn't all work I was able to do the trick of cutting back the ribbon cable which worked great. I was on a roll and the printer that was included worked too after 30+ years of sitting around. Included was a TS1016 expansion back that when plugged in simply shows a white screen with no [K] cursor.

I am probably going to open it up tomorrow and post some pictures to see if someone can help. From what I've read of the ZX carts on here they were particularly dodgy with 3 voltages being made internally (+ & - 5v and +12v?). Also I read that you couldn't use a regulated supply that it needed a noisy supply to generate all 3 voltages, I am wondering if this is using an original supply (I will photo that too).

Does anyone think they can walk me through diagnosing this? I'm handy with a multimeter and originally my training was in electronics (albiet 20+ years ago I did know how to use a scope fairly well). Maybe first off is replacing the caps after checking for proper voltages.

I guess also is the TS1016 expansion identical internally to the ZX81 cart?

This machine was my first ever machine that I owned in my youth, I have many retro machines but this one is of particular nostalgia for me.

[TMAOne]

Welcome to the forum, from a fellow Canadian. (Waterloo Ontario)

I once took a stab at a tutorial for repairing these packs. viewtopic.php?f=7&t=1613 You could start there.

And yes, the ZX81 branded packs and the TS1016 differ only in the shell decoration. They are interchangeable.

[Nibby99]

Greetings fellow Canadian! Bookmarked the same link last night . PM'd the guy that posted it because he mentioned that a bad ULA in one case caused one machine to not work with any expansion. I'm hoping that isn't the case in mine. What makes my situation rather annoying is I don't have another machine to test it in, nor do I have another rampack to try in it.

PS: It is far too early in the morning, I just realised you ARE the guy that wrote the tutorial initially! doh!

[1024MAK]

Included was a TS1016 expansion back that when plugged in simply shows a white screen with no [K] cursor.

Keep in mind that it takes the ROM code rather longer to work out how much RAM is present when a 16k byte RAM pack is connected. So the K cursor will take longer to appear.

I am probably going to open it up tomorrow and post some pictures to see if someone can help. From what I've read of the ZX carts on here they were particularly dodgy with 3 voltages being made internally (+ & - 5v and +12v?). Also I read that you couldn't use a regulated supply that it needed a noisy supply to generate all 3 voltages, I am wondering if this is using an original supply (I will photo that too).

There are a number of versions of the Sinclair 16k byte RAM pack. It will be interesting to see your TS1016 pack innards.

The type of DRAM chips used (4116 or equivalent) actually need a +12V DC supply to operate, a -5V DC supply to bias the internal circuits, and a +5V supply so they can interface to all the other digital circuitry (which all runs from a single +5V supply).

So Sinclair included a crude and simple DC to DC inverter/converter in the RAM pack. It requires a nominal +9V DC input (from the "mains adapter" / PSU and routed via the computers main board to the edge-connector). This supply is an unregulated DC supply because the Sinclair / Timex mains adapter / PSU is an unregulated type.

The DC to DC inverter/converter in the RAM pack generates the +12V and -5V supplies. The +5V rail comes from the computer.
Note that the DC to DC inverter/converter in the RAM pack will not function correctly if the input is too low, and it will not work correctly if the input "on-load" voltage is 12V or greater.

By "on-load", I mean with the PSU connected to the computer and the RAM pack plugged into the computer. If you test the PSU output voltage with the output not connected, the voltage will be around 12V to 16V. This is normal.

Mark

[TMAOne]

There are a number of versions of the Sinclair 16k byte RAM pack. It will be interesting to see your TS1016 pack innards.

I don't think the medley of versions made it to this side of The Pond, Mark. I got into my ZX81 early in the game, for Canada anyway, when it first arrived as a $150 kit. The RAM pack I bought a couple of months later is the same as the end of the TS1016 run. Subtle variations in board color or component suppliers aside, every pack I've seen over here is essentially the same. I'd be happy to be corrected by something different though.

As for that flaky ULA I had, I wouldn't worry about that Nibby99. It was a bizarre situation, the ULA had other issues, and has since died completely. No doubt the universe is still unfolding as it should. If computer works naked, and you're waiting long enough for the 16K to boot up as Mark wisely points out, you can be all but certain it's the RAM pack which has failed.

Good luck fixing it.
Ian

[1024MAK]

Included was a TS1016 expansion back that when plugged in simply shows a white screen with no [K] cursor.

Keep in mind that it takes the ROM code rather longer to work out how much RAM is present when a 16k byte RAM pack is connected. So the K cursor will take longer to appear.

I've just timed this on one of mine, it takes about 3 seconds. Which does not sound very long, but when you are expecting an "instant start", it does appear longer...!

Mark

[Nibby99]

I let it set for about 1-2mins (didn't want to wait too long and really risk toasting something from overheating or something). I will attempt to open it tonight and get some pics.

[Nibby99]

So here is what mine looks like opened up. Might start by checking those voltages indicated in the post, replace the electrolytic caps and see what happens...

[1024MAK]

That's a two board (issue 2 PCBs) type. I have a single board version.

Mark