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Any help with TimexSinclair 1000

I have a lightly used 16K RAM module for the Timex Sinclair 1000 including the box and all.. if he'd like to sidestep the issue, I'd be happy to sell it as I could use the money and my Sinclair (as mentioned above) is quite useless to me.
 
Nathan, The outside or main power supply is stable, also few minutes ago I was connected another source of 9VDC external power supply and have same problem.
Thanks for your inputs and all inputs are welcome.

I'm very agree with Dwight that the problem is with the power supply inside the Memory pack, I will buy some capacitor tomorrow and let to know my finding.
Dwight in first reply said "something is shorted" and found the transistor shorted.
Thanks

Raven thanks for the offer, But I would like to know what is wrong in the memory pack, Let me know how much including the shipping.
Thanks
 
Last edited:
Hi,
Sorry but yesterday was unable to connect to the internet due the Hurricane Earl, So I have no internet connection, I'm connected right now in the public hot spot.
Here is my findings:
1. Was replace all capacitors in the circuit with brand new and same value, also replace the transistor, but the problem persist, the transistor become very hot.
2. The voltage in the emitter is about 8.95V and same in the base, and 12V Output source = 8.69V
3. Cut the trace that supply 12V to the RAMs and the 12V Output source fix, but the transistor become very hot.
4. Take out the Transistor and measure is: 10.02V in emitter place and 0V in Base and collector place.

I very confuse right now.
Any help.
Thanks
 
Junior Ramos said:
Hi,
Sorry but yesterday was unable to connect to the internet due the Hurricane Earl, So I have no internet connection, I'm connected right now in the public hot spot.
Here is my findings:
1. Was replace all capacitors in the circuit with brand new and same value, also replace the transistor, but the problem persist, the transistor become very hot.
2. The voltage in the emitter is about 8.95V and same in the base, and 12V Output source = 8.69V
3. Cut the trace that supply 12V to the RAMs and the 12V Output source fix, but the transistor become very hot.
4. Take out the Transistor and measure is: 10.02V in emitter place and 0V in Base and collector place.

I very confuse right now.

Any help.
Thanks
Click to expand...


How about the -5v line, with the RAM connected and disconnected from the 12v line?
The fact that it goes to 12v leads me to think that the 12V zener is working, at least not
shorted. It is a feedback to shut down the transistor when the line reaches the working
level.
I'm begining to think the problem could be something in the -5v circuit.
Dwight
 
Hi Dwight,
The RAMs was disconnected from 12V line and the 12V remain but the -5V off after 5 seconds of power on the computer.
Check this 5 times and has same results.
Thanks
 
Hi
There isn't much to that circuit.
First measure on both sides of the 2.2K resistor.
If zero on the zener side, and some positive on the
other, it must be a shorted zener.
If on the other side, it can only be diodes
or caps. Something is shorted.
Dwight
 
The measure in both side of the resistor is -5.02 and -7.1 V but in some seconds the voltage drop to 0 in both side.
I measure all diodes and all are ok.
Why the other member has different transistor? 2N6727 bigger transistor
Thanks
 
Last edited:
Junior Ramos said:
The measure in both side of the resistor is -5.02 and -7.1 V but in some seconds the voltage drop to 0 in both side.
I measure all diodes and all are ok.
Why the other member has different transistor? 2N6727 bigger transistor
Thanks
Click to expand...
The 12V is probably just the output of the nominal 9V supply so it doesn't really tell you much about the switcher; what's the actual measured voltage of the 9V supply? DC or AC?

Sounds like it works for a while but something heats up and the transistor stops oscillating; after that it will probably be toast after a few seconds. You could try removing the 1uf cap between the coil and the two 1N4148s and see if it keeps oscillating without overheating, just in case it is one of the voltage doubler components, but unlikely.

I'd sure try a more substantial transistor, say a PNP with around a 1W power rating; don't know about the -22, but most of the MPSA series was pretty low power stuff. Sounds like the original may have been a little underrated to start with, especially if the 9V power supply were a little on the high side.

Or just replace the whole shamozzle with a 32K RAM chip and a decoder IC ;-)
 
Junior Ramos said:
The measure in both side of the resistor is -5.02 and -7.1 V but in some seconds the voltage drop to 0 in both side.
I measure all diodes and all are ok.
Why the other member has different transistor? 2N6727 bigger transistor
Thanks
Click to expand...

Hi
The fact that is dropped to zero may be that the oscillator stopped because of the
transistor over heating or it might be because there is no load on the +12V line and
the voltage on the output capacitor has exceeded the zener value enough to
shut down the oscillation.
Assuming the replacement transistor is good, there is only about one thing that
is left and that is the coil. It may be one of two things. One is that there is a
shorted turn and the other is that the core has been magnetized.
Both could have been caused by the original shorted transistor. Checking for
magnetized is easy but a shorted turn is a little more difficult.
If the core was magnetized it should be corrected by removing and reversing
the leads and putting a momentary short on your 9V line. The flyback current
will most likely then be able to bring it back to the normal operating range.
If one knows what one is looking for, one can tell with an oscilloscope by looking
at the signal ring on the coil.
As for the different transistor, it was most likely to avoid the failure your currently
seeing.
Dwight
 
If it were mine, I'd cut out the +12 and -5 volt power supply lines to the DRAM, add 1 jumper to put the +5v on the proper pin, and replace all the 4116 DRAMs with 4516 (5v only 16k chips) or with 4164 (5v only 64k chips)...

Those RAMs will draw less power and you won't have to mess with the power supply problems. ;)

RJ
 
Rather than doing such an intrusive modification to the T/S 1016, a 1.5x2.5 inch board with the edge connector on a short ribbon cable and a point to point wired 32K SRAM pulled from a 486 cache would use only 5V, draw little power, and provide twice as much RAM. In fact, 32K is the max you can add to a T/S 1000 if I'm remembering correctly.
 
saundby said:
Rather than doing such an intrusive modification to the T/S 1016, a 1.5x2.5 inch board with the edge connector on a short ribbon cable and a point to point wired 32K SRAM pulled from a 486 cache would use only 5V, draw little power, and provide twice as much RAM. In fact, 32K is the max you can add to a T/S 1000 if I'm remembering correctly.
Click to expand...
Yeah, that's what I suggested, assuming he can't sort out the power supply problems and especially if the RAM chips have been damaged in the process, but I think you might need an additional IC or two to decode chip select; isn't there a schematic for that on the web somewhere?

Replacing all the RAM chips with single-supply versions sounds like a lot more work (and expense?)...

But first I'd still try a beefier switching transistor...
 
Hi to all,
Here my findings:
1. Today arrive one module buy in ebay for $5.00.
2. Tested and work fine.
3. Opened the module to check the transistor it's a MPS6727, NTE replacement 129P without tab.
4. I solder a 129 small transistor and the module work perfect without heat.

The problem was a transistor I used. As per schematic, should be NTE 159, this transistor work but heat and burn after 1 minute.
The transistor in the module of Saundby senior member is perfect is more big but not problem heating.

So Thanks for every people that help me with this issue.
 
Hurray!

I'm glad you've got a working 16k expansion.

Now you need to make a jumper cable so it doesn't lose power while attached to the back of the T/S1000. Some ribbon cable and a piece of card edge with the right fingers on it is easy to come by (fried PC expansion card.) The cinch connector is an oddball. It's 46 pin. If you find a non-bulky 50 pin connector and block out the extra pins you can use that. Otherwise, cut down a larger connector.

I use an old ISA connector. I count out 23 leaves, then pull the next few. I then drill through and put a screw where the new edge will be and fill inside with hot glue. Then I cut it off at the right length. I'll see if I can pull one out for pics and post them sometime in the next few days.
 
I was happy to stumble across this forum and thread, as I am trying to fix no less than 3 Sinclair RAM packs with bad power supply voltages. In particular, thank-you Dwight E. for the explanation of how the power section of these little animals work. (My electronics knowledge is not sufficient to figure that out from the schematic.) I am waiting for replacement transistors to come from eBay, having replaced other parts more easily available in that section of the modules, with no success.

Some observations I'd like to contribute to your discussion:

- Schematic for the RAM module can be found here: http://www.myprius.co.za/ZX81.htm

- Excellent replacements keyboards can be found here: http://www.sellmyretro.com/index.php

- Crafting an edge connector to stand-off the module sounds like work. I simply tin the edge connector on the motherboard with a thin coat of solder. The thicker softer metal increases grip and eliminates 99% of wobble crashes.

- An easy 16 or 32K internal RAM mod (no decoder) can be found here: http://www.zx81.de/english/_frame_e.htm under Hardware Projects, Internal RAM Expansion.

- The 4116 RAM chips of these packs are notorious for burning out, especially when their finicky palate is offended by bad voltages. Expect secondary problems in some cases. I have managed to repair a module (which had no voltage issues) by socketing and replacing 4116s one-by-one until I found the offender. A working pack with any sockets also becomes a good chip tester.

Cheers,
Ian
 
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