Phase 90 debugging

willienillie · February 25, 2020, 07:07:24 PM

Quote from: Rob Strand on February 25, 2020, 04:44:50 PM
So, are you sure you have the opamps in the right way around?

Good question! Two of the sockets are upside-down, which of course doesn't matter as long as the ICs are right.

ljudsystem · February 26, 2020, 02:10:38 AM

Hmm, hadn't noticed the sockets being upside down. I'll put the opamps back in, but I'm pretty sure they were facing the right way. They should all be facing the same way, right? With the dot and indentation to the top of the layout?

ljudsystem · February 26, 2020, 02:12:34 AM

They're all TL072s btw

Rob Strand · February 26, 2020, 02:18:34 AM

QuoteWith the dot and indentation to the top of the layout?

Yes, the layout is drawn with the indentation at the top on all chips.

ljudsystem · February 27, 2020, 02:00:58 AM

Ok, I think I've found the Culprit. I desoldered the trim pot last night and it read 200R instead of 250K.

Slowpoke101 · February 27, 2020, 02:22:43 AM

Well done. I was really wondering about this one.
But out of interest I note that across the zener (D1 ) you measured 190mV...But on IC3 (the lowest one on the layout ) you measured around 0.8V on pins 3 and 5. Odd, very odd.
Anyway, hopefully you've got it all working.

Rob Strand · February 27, 2020, 02:37:03 AM

Yes, well done.

Quote
But out of interest I note that across the zener (D1 ) you measured 190mV...But on IC3 (the lowest one on the layout ) you measured around 0.8V on pins 3 and 5. Odd, very odd.

The opamps outputs probably saturate at a higher voltage than 190mV. That makes sense.
I'm still puzzled how the reference can be low and so many opamps had 8.5V on the outputs *and* on the -ve input.
You would think the low reference would just pull everything down.

ljudsystem · February 27, 2020, 04:10:26 AM

Thanks Rob, it was your coment about a short around the trim pot that made me measure the resistance across it.

I'm gonna see if I can find a 250k pot in my stash, but I remember ordering a 250k trimmer for this project so I suspect the supplier sent me the wrong trimmer... Or maby I made a mistake and ordered a 250r.

ljudsystem · March 02, 2020, 02:37:34 AM

Did the site go down? I havn't been able to access it for a few days. Anyway, replaced the trim pot last week and now the 70s are back!

I can play Waylon songs all day long ha ha.

Thanks for all the help guys! If it wasn't for you it would still be sitting on a shelf collecting dust.

Kipper4 · March 02, 2020, 02:55:20 AM

Great job
Happy phasing

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Phase 90 debugging