Problem with power supply or TS2068
3 messages · 2005-12-10 → 2005-12-12 · Yahoo Group era · View archive on archive.org
Participants: jfroco, M. Emrah Oral, Jeff Burrell
Preserved from the Timex/Sinclair 2068 Yahoo Group (2001–2019), which is no longer online. Text reproduced from the archive.org archive; email addresses masked.
Messages
1. Problem with power supply or TS2068
jfroco · Sat, 10 Dec 2005 05:19
Hi,
I just got a TS2068. I don't have a 15V power supply, so I tested
with a 9V 1A power source and it worked, but the screen was in B&W.
Later, I tested it with a 14V 850mA PS and the image was in color.
Then I changed the polarity of the PS and the 14V PS stopped working.
After that I tried with the 9V PS and the TS2068 still worked.
Did I damage the TS2068 reversing the polarity? Can I damage the PS
reversing the polarity? If I get a 15V PS will it work?
I don't understand why the 14V PS stopped working and I don't have a
volmeter to test it.
Any idea or comment?
Thank you
JF
2. Re: [ts2068] Problem with power supply or TS2068
M. Emrah Oral · Mon, 12 Dec 2005 09:54
You have done the worst thing you could do to an electronic circuit like the TS2068 by reversing the polarity and you were so lucky that the 2068 was NOT damaged. I was quite syrprised to read that. You should never reverse the polarity. If you did get a color image with the 14V adapter why did you reverse the polarity ? I know the ZX spectrum circuitry pretty well but I am very new to the 2068 so I can't really tell if you damaged any components. I would run a RAM test, an AY test and of course the color test. These chould verify that the main components RAM, ROM, CPU, AY and ULA (i think it is called something else in the timex) are in good shape. I have a feeling what saved the wole computer and probably killed the PSU was the voltage regulator inside the 2068. It is a little black component with 3 pins.
jfroco <[email]> wrote: Hi,
I just got a TS2068. I don't have a 15V power supply, so I tested
with a 9V 1A power source and it worked, but the screen was in B&W.
Later, I tested it with a 14V 850mA PS and the image was in color.
Then I changed the polarity of the PS and the 14V PS stopped working.
After that I tried with the 9V PS and the TS2068 still worked.
Did I damage the TS2068 reversing the polarity? Can I damage the PS
reversing the polarity? If I get a 15V PS will it work?
I don't understand why the 14V PS stopped working and I don't have a
volmeter to test it.
Any idea or comment?
Thank you
JF
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3. Re: [ts2068] Problem with power supply or TS2068
Jeff Burrell · Mon, 12 Dec 2005 18:15
You may have gotten lucky. The 2068 has both a linear 12V regulator and a switchmode regulator. The 12V is used for some video functions so that may explain the black and white picture. The switcher provides the main 5V rails for the logic.
From the techmanual schematic:
When you applied reverse power to the connector, U1 (the switching regulator) and U8
(the +12V regulator) probably shorted the output of the +14V power supply. Most likely a fuse internal to the +14V supply blew and so it is inoperative. C3, a 470uF
electrolytic capacitor was subjected to a reverse voltage and may be damaged. If so,
it will get hot and eventually open up. This may allow more noise on the supply rails
for the video resulting in a "swimming" display. The switching transistor and another
electrolytic capacitor may also have been damaged. I don't know the base-emitter
reverse breakdown voltage is, but it is generally much less than the 14V of the power supply.
The upshot is that several components may be degraded. The 2068 may work fine
for a while, but be prepared for something in the power supply circuit to pop later on.
I suspect that the remainder of the 2068 is probably OK since little energy would get
from the power supply section to the rest of the computer.
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