It's probably worth about $20 in good condition, so perhaps I overpaid, but they're a good cause. I also got some clear fir trim for $2.50 so it balances out.
More info after the break!
Sometimes you need a tiny wrench.
Saturday, October 18, 2014
Millers Falls 9C Smooth Plane
Today I lucked out at the Re-Store (Habitat for Humanity's thrift store for home supplies) and got this little gem:
It's probably worth about $20 in good condition, so perhaps I overpaid, but they're a good cause. I also got some clear fir trim for $2.50 so it balances out.
More info after the break!
It's probably worth about $20 in good condition, so perhaps I overpaid, but they're a good cause. I also got some clear fir trim for $2.50 so it balances out.
More info after the break!
Tuesday, October 7, 2014
High Scores, thanks to Logic Probotype
Solar Ride now saves high scores!
I don't need to use a post-it note on the glass any more.
I first got it going a month ago, by replacing the 5101 memory chip with a new one. Things went fine until two weeks ago, when it reverted to its previous behavior of only accepting one credit and not remembering high scores at all.
I futzed around with the power supply, replacing capacitors in a shotgun approach to hope to luck out and find the problem, but that wasn't working out.
So I made a logic probe;
And I probed.
The answer became clear shortly thereafter - the 5101 chip wasn't being enabled by the MPU. The enable circuitry is an oscillator (multivibrator) which, combined with a signal from the CPU, sets one of the wires on the RAM chip to logic high when the chip should be used.
The process went thus:
Pin 17 on Z22 was logic low. That means the Z22 (5101 RAM) isn't enabling.
Examine Z1, a quad-input AND gate (4081).
Z1 pin 6 is high. That's the CPU signal. So, the CPU is telling us to enable the RAM.
Z1 pin 5 is low. It's coming from pin 3 on itself
So, logically, either pin 1 or 2 is also low. It's pin 2.
Pin 2 is wired to Z2 Pin 9, Q2.
The C2/R2 wire is fired by the CR timing from R158 and C32. Oddly enough, when I measured the voltage drop across R158, the signal from my multimeter was enough to trigger C2/R2 and cause pin 9 to go high, enabling the RAM.
I replaced C31, C32 and Z2 and now we're getting high scores every time!
I don't need to use a post-it note on the glass any more.
I first got it going a month ago, by replacing the 5101 memory chip with a new one. Things went fine until two weeks ago, when it reverted to its previous behavior of only accepting one credit and not remembering high scores at all.
I futzed around with the power supply, replacing capacitors in a shotgun approach to hope to luck out and find the problem, but that wasn't working out.
So I made a logic probe;
And I probed.
The answer became clear shortly thereafter - the 5101 chip wasn't being enabled by the MPU. The enable circuitry is an oscillator (multivibrator) which, combined with a signal from the CPU, sets one of the wires on the RAM chip to logic high when the chip should be used.
The process went thus:
Pin 17 on Z22 was logic low. That means the Z22 (5101 RAM) isn't enabling.
Examine Z1, a quad-input AND gate (4081).
Z1 pin 6 is high. That's the CPU signal. So, the CPU is telling us to enable the RAM.
Z1 pin 5 is low. It's coming from pin 3 on itself
So, logically, either pin 1 or 2 is also low. It's pin 2.
Pin 2 is wired to Z2 Pin 9, Q2.
The C2/R2 wire is fired by the CR timing from R158 and C32. Oddly enough, when I measured the voltage drop across R158, the signal from my multimeter was enough to trigger C2/R2 and cause pin 9 to go high, enabling the RAM.
I replaced C31, C32 and Z2 and now we're getting high scores every time!
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