(Topic ID: 254399)

Hollywood Heat - Stopped booting after NVRAM

By MaxAsh

8 months ago

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  • 107 posts
  • 18 Pinsiders participating
  • Latest reply 7 months ago by pincity
  • Topic is favorited by 1 Pinsider


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#17 8 months ago

OK -- 5V at the board input but need to know what the voltage is at the 5101 socket.
Probably difficult to measure at Z5. Z4 uses the same power - measure voltages between pins 14 and 7.

If that is ok -- what is voltage at pin 4 of Z4?

#19 8 months ago

So you have a 1/2 volt drop across CR34 -- that's normal.

Plenty high enough for the FRAM. There is a second IC on that board. It *might* not like lower voltages.
It might be a 74HC type part which is OK with lower operating voltage but is pickier with the input logic levels.
Could also be a 74HCTxx type part - doesn't like low operating voltage levels but is less picky with input logic levels.

As long as you *do not* plan on going back to using batteries, you can short out CR34 to bring voltage levels up a bit. Might try temporarily shorting CR34 to see if it helps.

#40 8 months ago
Quoted from barakandl:

The CE combining chip is a 74HCT00D. I haven't run into any situations where the v drop from the battery block diode causes issues.

74HCT00 parts are rated for 4.5 to 5.5V operation. At his 4.5V, he's at the very bottom edge of the parts rated VCC range. I would think shorting CR34 would bring the VCC back into proper operating voltage range. Running at the voltage extremes (either high or low) is never a good idea.

74HC00 parts will run at the lower voltage range (2V to 6V) with no problems. And since the two CE inputs are driven by 4000 series CMOS operating from the same Vbat voltage - the 74HC00 would be a much better choice. Food for thought - two FET's and a pullup resistor would have been a good choice as well.

As to the mention of not running without the reset board. Some boards refuse to operate properly without the DIP plug installed regardless of whether or not the reset board is connected. This is due to the addition of a pullup resistor that Gottlieb added during 80A days.
When this resistor is added - some of the boards come back to life.

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#44 8 months ago
Quoted from GRUMPY:

Tell me more, as I have a unresponsive Raven taking up space in my basement. Which pins, how many ohms, any service bulletin to read?

Don't know when this took effect. But my Ice Fever came with this mod. And there was a slip-in page in the manual describing a 3K resistor -- pulling the read/write* signal (pin 11) to Vcc (pin 7). Of course - I cannot find this page now.

#45 8 months ago

Might be worth investigating why the 74HC00 didn't work. One bad thing is the timing for the Gottlieb circuitry was horribly s-l-o-w. 4000 series parts aren't exactly known for speed. The 74HC00s would add to this so you need to factor that into the timing calculations. I'd hang a scope on there to capture any glitches to see where they would be coming from, that enable must be disabled when power down/up is occuring. Would be better than running the HCT part at the minimum VCC rating.

Or easiest --> just tell people to jumper over CR34 if using this module. Not that this helped the O.P., though.

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