elmegil wrote: ↑
Fri Jan 08, 2021 7:03 pm
The TP4 thing is "normal". I have a note in my copy of the service manual that it has about 7 / 7.5V offset from what is shown and the one I have in front of me shows the same behavior but works 100%. Kind of wonder if It's not a mistake in the manual. The thing about the quantizer though, that's weird. The one I have complete on my bench right now works fine in both modes (16x1, 8x2) with the sliders low, and I can see all the voltages varying.
.... I wonder if the fact that it's "some sliders" and intermittent might mean there's a solder joint issue?
Did you build from the synthcube parts kit or did you get the BOM yourself? If yourself, what are the exact part numbers and manufacturers for those chips? I don't *know* this to be a problem, but some CMOS chips from different manufacturers behave differently, and we can compare notes. Of course if it's the Synthcube kit, which is what I'm building from, odds are very low that mine is different from yours, but it might still be worth checking.
I have a working model here in front of me, so if you want to take measurements at different places besides just the test points I can tell you what they look like on my working one.
I got my kit from Synth Cube - PCB revision V6a - and all IC's are matched with part numbers on the Synthcube BOM 1.6.1.
Good to see I'm not crazy about TP4 - So you verified that the sawtooth wave is clipped at the top and offset by around +7V
Solder joints look good on all faders and the mode switch (I have a lot of experience soldering these faders and soldered, OA'd and QC'd professionally for about 6 years).
I've replaced Z21, Z24, Z25, and Z27 and checked for continutity as per Kipling's suggestion.
Reflowed anything that looks even remotely suspicious.
The unit is fully calibrated.
To sum up:
1. In 16/1 mode, every slider drops to 0V between every chromatic half step. The slider's can't decide what voltage to be set to, so when the sequencer loops around, sometimes its the value I set and other times it's 0V (as if the slider is fully down).
2. Every slider is intermittent up until around 50% when in 8/2 mode, but there is not a 0V drop in between chromatic half steps. Sometimes this mode works perfectly in terms of pitch.
3. I can only calibrate the maximum clock rate to 86Hz (the service manual specifies 100Hz) with the multi turn trimmer provided with the Rev 6A BOM. That's the end of of the trim pot's range.
4. When calibrating the Mod Adjust for Quantizer A and B, the sequencer output peaks at +4.235V when the service manual says it "should be near +5V". Is that near enough?
5. When in 8/2 mode and neither Reset or Skip is set, the Gate Bus switches of either 8 step sequencer control the gate patterns of both 8 step sequencers. I am unable to have different gate patterns per 8 step sequencer. Couldn't find anything about this bevahior in the manual or service manual so I'm unsure if this is normal or not. Seemed curious.
Thanks for reply!