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  1. Old Steve

    Help identifying IC

    Yep - Electrically Erasable Programmable Read Only Memory. They called them non-volatile static RAM, (NOVRAM or NVRAM), back then. I still have an Xicor X22C12P chip here, brand new, from 30+ years ago. 128 x 4-bit storage. Pretty useless nowadays, but big in their day. I've been using the above...
  2. Old Steve

    Help identifying IC

    Yeah, that's what I meant by "They appear to be 2 different 9410 ICs" It MUST be an early EEPROM, but I can't find data anywhere. A bit of reading tells me that EEPROMS were invented in the late '70s, so it's possible.
  3. Old Steve

    System reset circuit help please

    Thanks Danno - here in OZ they're mainly called slot machines, but sometimes one-arm bandits.
  4. Old Steve

    System reset circuit help please

    Thanks for that. Very interesting. So, I must ask - what is it?
  5. Old Steve

    Help identifying IC

    They appear to be 2 different 9410 ICs I've searched high and low, but can't find a matching IC. You would expect it to be a 64 x 4-bit EEPROM, (Non-volatile static RAM), going by the address and data pins and the 'ST' (Store) pin, but did EEPROMs even exist back then? Xicor used to make some...
  6. Old Steve

    DT9205A multimeter fault in voltages measurements

    I hope it helps. I even considered buying one from here in Australia and sending it to you, but postage from here to Uganda is AUD$25, almost twice as much as the DMM itself. (USD$8.99 = AUD$12.59)
  7. Old Steve

    System reset circuit help please

    Obviously there's more going on there than I thought. Anyway, sorry to go off-topic. :rolleyes:
  8. Old Steve

    System reset circuit help please

    It's interesting, (to me at least), that an SCR is used to discharge the capacitor on a 555 to reset the circuit, rather than simply pulling the Reset pin low. Edit: I can answer my own question - the 555 operates as a high-current-output inverter. When the cap is discharged, the output goes...
  9. Old Steve

    DT9205A multimeter fault in voltages measurements

    Tonny, I see part of your problem - almost nobody on eBay will ship to Uganda. I did, however, find one US seller with a DT9205A for sale for USD$8.99 with free postage who will ship to Uganda, according to the listing. This one:-...
  10. Old Steve

    DT9205A multimeter fault in voltages measurements

    I didn't mean to sound rude, but since you didn't mention if it was new or previously used, I thought I'd better ask about the battery. The B+ voltage itself on a CRT TV isn't usually a particularly high voltage and the DMM should have been able to handle it, I would think. Most likely, it got a...
  11. Old Steve

    zener diode

    Yes. Keep in mind, though, that a Zener is only a crude regulator, and it's voltage will vary slightly with changes in supply voltage or with changes in load. Check out Harald's link. It has good info on the subject.
  12. Old Steve

    zener diode

    Thanks Dave.
  13. Old Steve

    System reset circuit help please

    No problem Harald. This is a good illustration that a positive logic AND is also a negative logic OR. I just did a quick drawing for Danno's benefit:-
  14. Old Steve

    zener diode

    A Zener can be used a a low current shunt regulator as shown or it can provide a reference voltage that remains reasonably constant when the supply voltage changes, or it can be used as protection to keep a point in a circuit from going higher than a given voltage. If your 10V supply was not...
  15. Old Steve

    zener diode

    The Zener diode will have a voltage rating. Let's assume it's a 4.7V Zener. The output of the first circuit will be 4.7V The output of the second circuit will be 6V. ie (10V / (300 +200)) x 300
  16. Old Steve

    System reset circuit help please

    Thanks for clarifying that point, Steve. I thought that Danno was correct, but didn't want to step on Harald's toes (again). :)
  17. Old Steve

    LED Circuit not behaving as it should

    Sorry if I confused things. And I'll be interested to see where the ground connection and regulated 12V from the negative leg of the diode bridge comes into play.
  18. Old Steve

    LED Circuit not behaving as it should

    Sorry, I should have said "there are no negative voltages in the output". With respect to ground, that's true, but not in the actual output. I was really referring only to the DC 'output' in my comments - I should have made it clearer. And isn't the DC output actually (26V x 1.414)-1.2V...
  19. Old Steve

    LED Circuit not behaving as it should

    No, they're just normal, everyday diodes, across the LEDs as mentioned to protect them from high reverse-voltage. (A LED can only handle a max of about 5V reverse-voltage.)
  20. Old Steve

    LED Circuit not behaving as it should

    There are no 'negative' voltages in the circuit shown, and the ground connection is not used in the output. As shown, the output is effectively 0V and +V. Edit: It must serve a purpose, but it's a very unusual circuit configuration, unless the ground connection also comes into play somewhere...
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