Debugging the RAMP GENERATOR

Hi guys my Ramp is not working after the build. I started by checking the Cadet I Sync (I attach some pictures underneath of its signals from the jack outputs and pins of the sync plugs). Does it look normal? Seems ok to me but I don’t know how the sync signals should be. My ramp has flat output on all jacks. Tried changing the ICs and turning the trimpots. All ICs get power (-11 +11 is it maybe too low?). Any idea what could be. Attach all pictures.

JACK OUTPUTS 3 pictures SYNC HEADER PINS 7 pictures + boards and connections

Hi Jestern. +/-11V is fine (the IN4001 diodes steal a bit of the 12V from your supply, but that’s fine and normal).

Check out the schematic for information you’ll need to work out what’s wrong. Don’t worry if you don’t understand the details of how the circuit works, just try to get an understanding of how the schematic relates to your PCB and the components you soldered to it.

First check the voltage on all the power pins on all the ICs. You can google the chips to find their datasheets or pinouts to work out which pins are which (“lm6172 datasheet” or “lm6172 pinout”). “V+” or “Vcc” means +11V, “V-” or “Vee” means -11V, ground means 0V. You should check these with the module plugged in to power, but be careful not to accidently short your test lead across two pins - while it’s usually OK sometimes doing that can damage things.

You can also check that ground pins are all connected, by using a multimeter on resistance with the module disconnected from the euro power. Check that the ground pins on the euro power connector (there are lots of them) have nearly no resistance to anywhere you see a ground signal on an IC pin in the schematic.

Next, make sure the sync signals are making it to R45 and R27 (i.e. they look the same as they do coming out of the sync module).

Then, see if there’s any ramp on the + input to U13.2 and U12.2.

There’s another thread on the forum recently where someone was having trouble with one of their two ramp outputs - you might find some other helpful debugging advice there.

When I zoom in your photos of the PCBs are a bit blurry so it’s a bit hard to comment usefully on them, sorry.

Let us know how you go, there are plenty more things to check!

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Hi Aladan thanks so much for your time in helping me. I finally found the time to check all previous points. this is what I found:
All ICs get the aforementioned power, All ground pins are connected as far as I can see from the schematics.
The TL072 gets +10 and -12 is that ok?
The 74HC14 gets +4.2 and -0.8 on the ground.
Measuring around I noticed a little disparity in the pins of the two LM6172 (few KOhm difference), something around 11k on all right pins of the H lm6172 and 17 Kohm for the ones of the V lm6172. Maybe due to the trimmer?
Anyway the sync comes to both resistors 27 and 45. I attach some pictures. on the 45, I think is H sync, is faster than the one on 27.
After that I noticed no signal input at the TL074, I’m not a schematic guru, but I thought U13.2 means the non inverting input of opamp number 2 of the TL074, eg. pin 5, same for U12.2.
So where could the signal get lost?
I attach some pictures of the sync and the boards with better resolution I hope.
Thanks a lot, this keeps me going.

I am not trying to be rude, but can you clean the burned flux between the transistor pins on the bottom of your board? Q1, Q2, Q3 and Q4. I find these footprints are harder to solder than soic chips.

Also double check the text on each transistor to make sure none of the 3906, BS170 or TL431 got switched by mistake. I keep my 3904’s and 3906’s in a drawer next to eachother, so I am always weary of them getting mixed up.

Are you using any substituted parts? A common alternative for the BS170 has a reversed pinout for example.

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completely agree on this definitely looks to be the most suspect area of soldering, but hard to tell!!!

soldering those transistors is horrible - very thin solder and plenty of flux is the answer I suspect

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Hi Alberto,
Thanks for all that. It’s a little bit surprising that you say the ground pin on the 74HC14 reads -0.8V. It should definitely read 0V, maybe 0.1V at most. Where did you put the other lead of the multimeter when you found that? But I think that just might be an issue with measuring, not with the circuit.
Based on the missing signal at U13.2 pin 5, I agree with what Fox and Agawell said which is that the transistor (Q4, BS170) might be backwards, have a short (solder across two pins) or be an incorrect part, so check that out first.
Other possibilities might be a wrong/faulty capacitor C18, or an issue with the current source (Q2/U13.1/U9). Measuring that might be a little bit tricky, but first could you see what your multimeter says is the voltage between ground (on the power header) and U13.1 pin 3?
Looking at the photo, the TL072 (U1) looks like it could be better seated (pushed down into the socket). But that’s unlikely to be causing the problem you’re seeing.
Aha! I think I just found the problem. Q2 is a 2N3904, it should be a 2N3906! You might have swapped it with another transistor…



I cannot believe you spotted that.

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I am nothing if not meticulous and detail-oriented! :slight_smile:

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Also Alberto, please accept my compliments on your Strange Attractor Sequence - it’s my favourite video of yours (although I just found you now have heaps more on your vimeo that I haven’t look through yet!)

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Alan and everyone thanks so much for spotting this!!! I’ll work on it now and hopefully it’s the only mistake. Thanks so much for the compliments. I started working with lasers but now I’m slowly transitioning towards more video work.
I find more and more this is a great community of incredibly competent and kind people. I hope to contribute back when I have all up and running. I’ll report back when all works fine. :slight_smile:

Thanks I did swap those transistors!!! :frowning: My BS170 has a WA 11 written on it before the BS170. How do I know which version is it?

Every BS170 should have the same pinout, even if it has other markings. They are batch numbers, year of manufacture codes etc.

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OK Gents, unfortunately that was not enough. But, I now get some signals :slight_smile: I see some ramps, that are very weak (around 200mV I think). The trimmer makes them bigger but that’s the max I reach. It seems they are freq modulated :frowning: I can’t stabilize them with my old scope. I show you some pictures of the six outputs ! Sorry for the quality

It would be an interesting coincidence if both signals were at the lower level, since they don’t really share any circuitry other than the power supply. Can you make sure you are connecting Ground when you’re making your readings?
Viewing video on a 10MHz bandwidth scope is pushing it near to its limit, so those images are pretty good really. Here’s the scope’s manual:
You may get more stable results connecting the source video signal (that you are inputting to the Cadet I sync gen) to the trigger input in the top right corner, and selecting TV Frame. The smaller outer knob on the V/div adjusts how many volts each division (i.e. between the lines on the scope’s screen) covers, and on most scopes I’ve used it would normally be set all the way to the right for calibrated use. I can’t be sure if that’s true for this scope since my Dutch isn’t good enough :slight_smile:
If it turns out the ramp voltages really are attenuated then start by check the U12.2/U13.2 output voltage on the scope - it should go from 0V to 1V.

What kind of probes do you have too?

Hey thanks for your help and quick answers. I just found out maybe the probes were set on attenuation 10 !!! Ok so I’ll try to get my shit together with scope and probes and come back with more reasonable results / measurements :slight_smile: I really appreciate all your help !!!

That’s great news! Nothing beats finding a simple problem. I’m sure you’re very close! :slight_smile:

Ok I’m here again now the Horizontal part seems to work fine. I had a burned IC. But the Vertical is still off. I suspect it is in the Sync Generator.
Here the horizontal:

My Sync Generator outputs these three signals from the jacks:

The Horizontal Sync signal reaching the Ramps module seems logical while the Vertical Sync is very weird having spikes that I can’t stabilise in time. Is it supposed to be the same that comes through the jacks? I’ll keep on checking. The ramps seems ok to me I checked for shorts, power for the ICs, changed the ICs checked resistors being symmetrical between horizontal and vertical.

Those ramps look great!

Vsync should be far slower and wider than Hsync, so it should be easier to capture on your scope. Intermittent spikes may be related to a floating input or no negative feedback or maybe even something else.
On to the cadet I schematic, we see that the output opamp is shared between both sync signals: U1.

For starters can you disconnect the other modules form Cadet I and probe the two signals? Please then measure the resistance and continuity points of R3 (3.92K), R6 (1K), R14(1K), R5(499R) and R20(499R).
If these seem accurate, swap U1 with another op amp and look at the signals again.

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