I’ve been spending the last few weeks troubleshooting a non-working Cadet Sync Generator I built, and it seems like the ATMEGA88A I received from LZX either wasn’t programmed or got corrupted somehow. I’ve confirmed that the ATMEGA88A is getting supplied with the correct voltage, but the outputs seem messed up. If someone with a multimeter could measure the pins on their ATMEGA88A, it would be an enormous help in confirming the problem.
if you look at the ATMEGA88A with the notch at the top, the top left pin is #1, and the numbers run counter-clockwise until you reach #28 at the top right. Pin # 8 is the ground. If you don’t have time to read all the pins, if you could just measure the voltages on pins #12, #13, and #15–that would still help a lot. Thanks!
I don’t think measuring the voltages are going to be very helpful, except to check that it’s getting power on the right pin (which you already did). It’s outputs are only digital, so they’ll either be a high (~5V) signal or a low signal (~0V), but since this should be generating sync signals, they’ll be switching between high and low really fast (too fast for most general multimeters to keep up). Now, if you have access to a decent oscilloscope (so probably not one of the $20-ish ones from ebay/aliexpress - but maybe one of those will show a signal enough to know if it’s doing anything?), you could use that to see the signals that are output. Or you could probably use a logic analyzer for the same thing, again as long as it’s fast enough.
I’m trying to think of an easy way you can check to see if any signals are being generated without a scope/analyzer, but I’m not coming up with anything good. Some of the outputs should be audio range, so maybe hook an amp and speaker up to an output and see if you hear a tone? (And for the ones that are faster, see if your dog can hear it? )
Thanks @csboling and @joem! I was wondering about the usefulness of a multimeter, but i’m getting some different numbers. Pins #12, #13, and #15, are ATMEGA88_ODDEVEN, ATMEGA88_VSYNC_INV, and ATMEGA88_HSYNC_INV, respectively. I don’t get any signal off those pins, so I don’t think they’re outputting any voltage at all. Those are the pins that feed the LM6172’s, and output to the front panel H-sync, V-sync, and Frame sync outputs–which are all dead, in my case.
It’s possible your multimeter just isn’t seeing anything there due to the frequencies.
For fun and reference, here are the types of signals on the different pins of the atmega88a in this particular circuit:
Pin #
Pin Name
Function in the Cadet I
1
PC6
programming header
2
PD0
+5V
3
PD1
no connection
4
PD2
input from LM1881
5
PD3
output
6
PD4
input from LM1881
7
Vcc
+5V
8
GND
ground
9
PB6
input from crystal
10
PB7
no connection
11
PD5
output
12
PD6
output
13
PD7
output
14
PB0
output
15
PB1
output
16
PB2
output
17
PB3
programming header
18
PB4
programming header
19
PB5
programming header
20
AVcc
+5V
21
AREF
no connection
22
GND
ground
23
PC0
either +5V or ground depending on the NTSC/PAL switch
24
PC1
no connection
25
PC2
no connection
26
PC3
no connection
27
PC4
no connection
28
PC5
no connection
All the outputs should have some sort of video rate sync output, all the programming headers don’t do much (or anything?) when you’re not actually programming it, and the inputs from the LM1881 I think will only have signal if you’ve got something connected to the sync input (and the LM1881 is working).
I would expect the voltage reading to be roughly the average voltage, so when measuring a pulse wave output it should be more or less linearly related to the duty cycle. This seems consistent with ODDEVEN and ODDEVEN_INV reading as 2.5V for instance, but this is certainly a rough ballpark. In case the issue is that your firmware hasn’t been flashed, there were some tips on doing that in this thread a little while back.
Thanks for posting that link. Flashing the ATMEGA looks like a headache, but I guess it’s my next step. It seems like the ATMEGA only needs a few inputs to function:
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