Read-only archive snapshot (as of 2026-06-03). The live forum is closed. For current support, see https://lzxindustries.net/.

LZX Community Archive

All topics · Categories

Can someone with a working Cadet Sync Generator please do me a favor?

Category: Unknown · Tags: — · Posts: 8

#1 — Resonant_Space · 2019-04-15

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!

#2 — csboling · 2019-04-16

On my sync generator (rev 1.1) the voltages read roughly as follows (nothing plugged into the front panel, switch set to NTSC).

Left voltageLeft pinRight pinRight voltage5V1282.0V5V2272.1VToggling 0-5V3261.95V0V4250.1V0V5240.1V0V6235V5V7220VGND8210V2.5V9205V0V10190V1.2V11180V2.5V12170V0.1V13160.44V2.5V14150.44V

#3 — joem · 2019-04-16

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?

:grin:

)

#4 — Resonant_Space · 2019-04-16

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.

#5 — joem · 2019-04-16

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 NameFunction in the Cadet I1PC6programming header2PD0+5V3PD1no connection4PD2input from LM18815PD3output6PD4input from LM18817Vcc+5V8GNDground9PB6input from crystal10PB7no connection11PD5output12PD6output13PD7output14PB0output15PB1output16PB2output17PB3programming header18PB4programming header19PB5programming header20AVcc+5V21AREFno connection22GNDground23PC0either +5V or ground depending on the NTSC/PAL switch24PC1no connection25PC2no connection26PC3no connection27PC4no connection28PC5no connectionAll 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).

#6 — Resonant_Space · 2019-04-16

joem wrote:

It’s possible your multimeter just isn’t seeing anything there due to the frequencies.

Good point—so the measurement differences may just be artifacts of the different multimeters.

#7 — csboling · 2019-04-16

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.

#8 — Resonant_Space · 2019-04-16

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: