EM5 clone (DFX Inchindown) issue...how to test hex inverter / delay chip?

[slowpogo]

I built the Inchindown, an Ibanez EM5 clone. It passes a dry signal but I get no delay, and no frequency read at the test point.

I've done all the standard troubleshooting steps I can think of. ICs and transistors seem to be getting appropriate voltage. Diodes test fine and are properly oriented. All the transistors are correct, oriented correctly and test good, I reflowed joints, made sure ICs were situated, etc. The trimmers were centered but adjusting them makes no difference.

I've poked around with an audio probe and I'm getting output from the op amps, but the only output from the delay chip is pin 22, "LPF1 Out"

My tentative conclusion is there's an issue with either the 74HCU04N, or the M65831AP. The hex inverter comes from Mouser.

The delay chip is NOS Mitsubishi (not the Renesas remake) from Dalbani Corporation, who I've never gotten a bad or counterfeit part from before. But does it look legit in the photo below?

Maybe someone can see something obvious I'm missing. I boxed it for now but I pored over the back and saw no bridges or anything amiss. Is there a simple way to determine if one or both of these chips are indeed the issue?

[slowpogo]

I got it. I was using one of the listed transistor subs, 2N3906 in place of the 2SA1015Y...which is EBC instead of ECB. Weirdly the build doc notes pinout differences for another of the subs, but not that one for some reason.

Ultimately it was my lack of due diligence...but that build doc is misleading.

[digi2t]

Darn!

I usually always put a note in regards to this in our build docs, but this one slipped by me. I'll put a note in the document, and thanks for the heads up.

In any case... bet you won't be making that mistake again any  soon.

[slowpogo]

Darn!

I usually always put a note in regards to this in our build docs, but this one slipped by me. I'll put a note in the document, and thanks for the heads up.

In any case... bet you won't be making that mistake again any  soon.

No worries, I should have thought to check this much sooner.  Alas, I'm getting delay now, but there are still a few issues.

I'm still not able to read frequencies at the test point. Sometimes a random frequency will pop up right when I touch the test point...100.2 Hz, 16.8 kHz... then it disappears half a second later. If I retouch the test point a totally different frequency will pop up and disappear. I've tried with the trimmers in various positions. My DMM can read up to 10MHz, has new batteries etc. and this function has worked in the past so I don't think it's the DMM.

So I tried adjusting by ear. I'm able to increase the maximum delay time with TRIM3, so I set it to about a second. (The repeat seems slightly dirty and bit-crushed at max time, but cleaner at shorter times, is this normal?) I didn't bother with TRIM2 because the minimum delay seemed very short like I would expect.

BUT I'm hardly getting any repeats. The Repeats knob fully CW gives just a few repeats at shorter delays, and just one at max delay.  TRIM1 seems to have no affect whatsoever on the decay time. Any ideas?

[digi2t]

The delay chip is NOS Mitsubishi (not the Renesas remake) from Dalbani Corporation, who I've never gotten a bad or counterfeit part from before. But does it look legit in the photo below?

The problem with resellers is that they resell whatever they buy, regardless of the provenance. I occasionally buy from UT Source, and while for the most part the parts are legit, there are duds that get past along from their suppliers. It's a sad circle, but all they can do is refund you, and flag the supplier.

I'm wondering if perhaps loading the transistors in the wrong pinouts the first time around may have damaged the clock chip?

[slowpogo]

That would not be surprising, I'll add a new one to my next Mouser order.  I'm curious, would the M65831P (not AP) work in this build too? It looks identical from the datasheet.

[digi2t]

That would not be surprising, I'll add a new one to my next Mouser order.  I'm curious, would the M65831P (not AP) work in this build too? It looks identical from the datasheet.

All I see are slight differences in power consumption and thermal ratings, but the rest seems identical.

[slowpogo]

I tried a new clock chip, and nothing changed. Couldn't read frequencies, but I'm getting delay, and all the knobs and trimmers do what they should except TRIM1. It's stuck at 4 repeats maximum.

However...and maybe I'm an idiot...I've been trying to read frequencies with the positive DMM lead on the test pad, and ground lead to ground on the pedal.  I reversed the polarity, and now it works. With the positive lead to ground and the black lead on the test pad, I can read frequencies and I'm able to calibrate per the instructions. Is that normal ?

I also tried a different delay chip (the M65831P) which was a pull, not NOS. Did not affect TRIM1 or the amount of repeats.

I haven't checked continuity on the entire pedal but I checked between delay pin 23 (LPF1IN) and TRIM1, and all was good. Anywhere else I should strategically check continuity, or any other ideas?

[digi2t]

Is the trimmer you installed in the TRIM1 spot a 10K?

[slowpogo]

Yes it is. I actually swapped it for a different 10k trimmer just to be sure but it made no difference.

[digi2t]

OK. How about R26? It should be 30R. Check color bands.

[slowpogo]

Yup, orange-black-black-gold-brown. I actually checked all the resistors by color yesterday, and checked the caps as well. I had reflowed the joints on the ICs already but for good measure, I reflowed ALL the joints (using flux) yesterday.

[slowpogo]

Thanks, digi2t for the support. I know it's not obligated and feel bad bugging you so much over this one. Just one more thing before I admit I'm truly stumped and either give up or get a new board.

I removed TRIM1 and jumpered it just for giggles, and also tried various values of resistor in its place...8k, 33k, just to see. Didn't change anything.

I also removed and jumpered R26 out of curiosity...same, did not change anything. Still the same maximum of 3 repeats (which are also rather faint).

It's like some functionality is just missing from the chips, even though I've tried multiple versions of them and reflowed joints on the socket. Not sure what else to even try at this point other than complete do-over.

[anotherjim]

However...and maybe I'm an idiot...I've been trying to read frequencies with the positive DMM lead on the test pad, and ground lead to ground on the pedal.  I reversed the polarity, and now it works. With the positive lead to ground and the black lead on the test pad, I can read frequencies and I'm able to calibrate per the instructions. Is that normal ?

That's an interesting issue - I could have been fooled for months. Possibly your meter has to be reversed for that measurement or got built with a diode the wrong way around - or something!