Timex 2048 only 16k

landex
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Re: Timex 2048 only 16k

Post by landex »

sP1d3r wrote: Wed Jun 29, 2022 10:28 am
landex wrote: Mon Jun 27, 2022 6:27 pm I bought it, and it works very good! :lol:
Do you mean that your TC2048 now has 48K of ram?
YES!:)
But there is an another issue that I found: I used an normal Zx Spectrum power supply who has 15V output. After the TC2048 running about 4, 5 min the screen begins to flash the colours and changing colours.
Then try it with another PU who has exactly 9V, and it works really fine.

So, there must be a difference between the original TC2048 and Spectrum.
I must say, 15V is a little too much, but it was normal for the ZX back in those days. Wasn't it?
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1024MAK
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Re: Timex 2048 only 16k

Post by 1024MAK »

McKlaud wrote: Sun Jul 03, 2022 6:34 pm The latest and most accurate schematic of Timex Computer 2048, PCB rev 5 attached.
Is this different to the version here?

If yes, can you please put the image file in a ZIP file, then attach the ZIP file. Also if possible please use PNG rather than JPEG.
The forum software automatically reduces the resolution of attached photo/picture image files (to save space when members attach high resolution photos), which unfortunately makes large detailed schematic diagrams hard to read.

Mark
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Re: Timex 2048 only 16k

Post by 1024MAK »

landex wrote: Mon Jul 04, 2022 12:10 am But there is an another issue that I found: I used an normal Zx Spectrum power supply who has 15V output. After the TC2048 running about 4, 5 min the screen begins to flash the colours and changing colours.
Then try it with another PU who has exactly 9V, and it works really fine.

So, there must be a difference between the original TC2048 and Spectrum.
I must say, 15V is a little too much, but it was normal for the ZX back in those days. Wasn't it?
The ZX Spectrum (and indeed all the 9V power supply units (PSU) for the Sinclair computers) are of the unregulated type. So despite them all being rated at 9V DC, they will only output 9V when fully loaded and supplying their maximum rated current.

With no load (the computer not connected), the output voltage will be between about 14V to 16V.

When a UK1400 (ZX Spectrum) PSU is used with a 48K ZX Spectrum, the actual voltage will be between approximately 10.5V and 11.5V.

Note that a 48K ZX Spectrum uses between about 500mA (0.5A) to 700mA (0.7A) so is using half (or less) of the capacity of the UK1400 PSU.

The design of the internal power supply circuitry in the TC2048 is different to that of a ZX Spectrum. Because of this, connecting a PSU that produces more than 11.9V may well lead to problems . As it is a more modern design, it likely requires less current than a 48K ZX Spectrum, so the on load voltage from a UK1400 PSU could well be higher than 12V. So a ZX Spectrum UK1400 PSU may not be suitable.

Mark
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Re: Timex 2048 only 16k

Post by McKlaud »

1024MAK wrote: Mon Jul 04, 2022 12:01 pm
McKlaud wrote: Sun Jul 03, 2022 6:34 pm The latest and most accurate schematic of Timex Computer 2048, PCB rev 5 attached.
Is this different to the version here?
Yes, It is. The version (1.3) in the linked tread had a few errors, that been corrected in the latest rev 1.8.

I will zip the latest schematic and attach here when I am back home later today.
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landex
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Re: Timex 2048 only 16k

Post by landex »

1024MAK wrote: Mon Jul 04, 2022 12:23 pm
landex wrote: Mon Jul 04, 2022 12:10 am But there is an another issue that I found: I used an normal Zx Spectrum power supply who has 15V output. After the TC2048 running about 4, 5 min the screen begins to flash the colours and changing colours.
Then try it with another PU who has exactly 9V, and it works really fine.

So, there must be a difference between the original TC2048 and Spectrum.
I must say, 15V is a little too much, but it was normal for the ZX back in those days. Wasn't it?
The ZX Spectrum (and indeed all the 9V power supply units (PSU) for the Sinclair computers) are of the unregulated type. So despite them all being rated at 9V DC, they will only output 9V when fully loaded and supplying their maximum rated current.

With no load (the computer not connected), the output voltage will be between about 14V to 16V.

When a UK1400 (ZX Spectrum) PSU is used with a 48K ZX Spectrum, the actual voltage will be between approximately 10.5V and 11.5V.

Note that a 48K ZX Spectrum uses between about 500mA (0.5A) to 700mA (0.7A) so is using half (or less) of the capacity of the UK1400 PSU.

The design of the internal power supply circuitry in the TC2048 is different to that of a ZX Spectrum. Because of this, connecting a PSU that produces more than 11.9V may well lead to problems . As it is a more modern design, it likely requires less current than a 48K ZX Spectrum, so the on load voltage from a UK1400 PSU could well be higher than 12V. So a ZX Spectrum UK1400 PSU may not be suitable.

Mark
Thanks Mark.
Iam using now a modern PSU, and it works fine with TC2048 48k.
If you say that the Spectrum uses 0.5A, a battery of 9V could do it:p. But I think it has only 0.3A.
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Re: Timex 2048 only 16k

Post by McKlaud »

All DRAM used in any TC2048 or TC2068 is a single voltage and 4-bit type.

TC2048 with PCB rev 5 can have the upper RAM built in two variants:
1. 4416 DRAM x 4 chips = 2 x 16K
2. 4464/41464 DRAM x 2 chips = 1 x 64K

On the rev 5 board there are places for additional two diodes and resistor forming OR gate that combines /CAS1 & /CAS2 (Column Address Strobe) signals for 64K DRAM. If the upper RAM is fitted with 64K it is a reasonably easy make a modification to 80K with the upper RAM banked in two 32K chunks.

In any lover PCB version Timex installed 4 x 4416 DRAM in the upper RAM.

Regarding supplies, TC2048 and TC2068 can be fed off the ZX Spectrum PSU (the power supply polarity is the same). An internal DC converter makes 12V that is used by PAL encoder. All logic requires 5V only. So, no 12V means no colours on the screen and that's it.

The latest schematic diagram zipped and attached.

BTW I cloned TC2048 a while ago, have a look there: Timmy
Attachments
TC2048 rev. 5 v1_8.zip
Timex Computer 2048 ver 5 schematic diagram by trojacek
(296.86 KiB) Downloaded 11 times
Claudius
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sP1d3r
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Re: Timex 2048 only 16k

Post by sP1d3r »

This is the Timex 2068 'homebrew' ic kit I saw, but it doesn't bear any resemblance to the Timmy project and I couldn't find out any details about which PCB it uses;

https://www.ebay.com/itm/114968713354?h ... OSwjZ9hMif~
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Re: Timex 2048 only 16k

Post by 1024MAK »

McKlaud wrote: Thu Jul 14, 2022 6:38 am The latest schematic diagram zipped and attached.
:D Thank you :D
sP1d3r wrote: Thu Jul 14, 2022 11:48 am This is the Timex 2068 'homebrew' ic kit I saw, but it doesn't bear any resemblance to the Timmy project and I couldn't find out any details about which PCB it uses;

https://www.ebay.com/itm/114968713354?h ... OSwjZ9hMif~
Like the sellers other items, it’s just a collection of chips that may be useful if you want to have a go at creating your own computer design based roughly on an existing architecture. There is no schematic diagram, no PCB design, and no other documentation. Also the chips you get may not be the same as in another similar sale earlier or later than the current listing.

A couple of the Chinese sellers caught on to this idea some years ago after a U.K. guy did the same.

Mark
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Re: Timex 2048 only 16k

Post by McKlaud »

sP1d3r wrote: Thu Jul 14, 2022 11:48 am This is the Timex 2068 'homebrew' ic kit I saw, but it doesn't bear any resemblance to the Timmy project and I couldn't find out any details about which PCB it uses;

https://www.ebay.com/itm/114968713354?h ... OSwjZ9hMif~
The seller offers in the kit:

Z80 CPU .....DIP40....2pcs - one might be used in any Z80 based computer
8255/82C55 PIO..... DIP40 - no use with any Timex machine
32K SRAM (HM62256 or Similar) DIP28 - as above
UM61256 32K Fast SRAM SDIP28 - as above
UM61512-xx Fast SRAM SDIP32 0 - as above
IDT7006 16kx8bit Dual Port SRAM PLCC68 - as above
27C128 or Similar 16K UV EPROM DIP28 - might be used for ROM
EPM7512AETC144-12N or similar CPLD TQFP144 - just a random CPLD and no use with any Timex computer
GAL16V8 DIP20....2pcs - as above
DS12885 RTC DIP24 - as above
AM9511 Maths CPU DIP24 - as above
VT82C42 PS/2/Mouse Controller Chip DIP40 - as above
YM2149 PSG DIP40 - well, might be used for any AY-3-8910 based interface, but no direct application with Timex machines

So, in my mind this is a random set that might used for building your own Z80 based microcomputer.

Timmy was designed around Timex SCLD (ULA) chip. and dynamic RAMs. I did the board because one of my TC2048 had badly damaged PCB. So I salvaged a lot of components from the broken unit and re-sued in my design.
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sP1d3r
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Re: Timex 2048 only 16k

Post by sP1d3r »

McKlaud wrote: Thu Jul 14, 2022 3:47 pm So, in my mind this is a random set that might used for building your own Z80 based microcomputer.
This particular seller sells a lot of 'homebrew' kits also kits for ZX Harlequin 48K and 128K, the chips are shipped in plastic anti-static tubes.
Seems like good value, especially if all the chips work.

I'd never seen your clone of the TC2048, I'm more than likely to have a go at one now.
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