SOLVED Arachnid V2 - No Reverb / No Delay, everything else works

andrewsrea

andrewsrea

Well-known member
To @Robert or any other FV-1 experts:

My first 'DSP' build is almost alive:
An Arachnid V2, with a Module 8 and a custom EPROM 24LC32A (both from Pedal PCB). Additional info: FV-1 and 32.768HZ crystal from Amplified Parts. I used static protection, which includes a Spidel ground wrist strap, grounded soldering iron receiver and an unfinished wood bench.

What works in effect mode: modulation, oscillation, phase and pitch shift. Decade selector appears to be changing the programs. Bypass works and the effects signal sounds great (no artifacts, the tone is musical and mostly transparent).

What doesn't work: no reverbs, no delays. On the reverb and delay selections, it goes silent when I place the 'mix' on 100%. This condition is present on both EPROMS.

What I have tried so far:
- Total circuit component value & function check - passed. Exception was the FV1 and 24LC32, as I do not know what to check for.
- Total circuit continuity check (I originally had about 5 poor solders on the FV1 - next time I am getting the PCB with this installed!) - passed.
- +3.3VDC power supply. Dead on, with zero ripple on the scope.

I am hoping a knowledgeable person in DSP can weigh in here with some suggestions!

20251015_110919.jpg 20251015_110900.jpg
 
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jwin615 said:
Is it certain program numbers that don't work. I.e. programs 5-8?
If so, it's probably related to the diode logic and/or their connection to the fv-1
Click to expand...

No, the problem affects any selection which is supposed to have delay or reverb. I just re-performed the continuity check thru each stage of the diode array, from the +3.3V common pin of the decade selector, to the diodes for that selection and to the pins. I performed the same check reading the voltages in each selection. The selector and diodes are functioning as drawn.

I noticed I am getting +3.3V on pins 5 & 6 of IC2 (the EPROM), which comes from the FV-1 via pins 14 & 15 and not pin 8 of IC2 or the EPROM itself (which would be an indication of an internal short). I am not sure if that is typical or a fault.
 
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chongmagic said:
That FV-1 chip has some suspicious looking solder at some of the pads. I will try to clean it up, could possibly be legs shorting out together.
Click to expand...

I appreciate your recommendation!

I performed a pin-to-pin short test and there were no sequential pin short circuits, except as designed (pins 11 & 12, pins 24 & 25). I also performed a comprehensive continuity check (gently) from the top of the pins (not the pads) to the prior / next component. Everything checked out. Last, I performed a pin voltage check, which all were fine for those which should have +3.3V and 0V (ground).

The only thing I am not sure on with that test, is +3.3 volts on pins 14 and pins 15. Those are the EPROM Clock and EPROM Data, respectively I am not sure if that is normal. I pulled the socketed EPROM to verify that the +3.3V is coming from the FV-1 IC and not the EPROM. I am wondering if that is not normal and was caused by a defective IC or static damage.

I am hoping to come across an FV-1 expert.

This pedal is presenting a strange condition, where the effect pots function with oscillation, speed, and modulation - just no reverb or delay.
 
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The clock and data signals between the processor and EEPROM will measure 3.3v - they are digital signals alternating between 3.3v and 0v. With a multimeter they read 3.3v. You will need an oscilloscope to determine more detail about these signals, but it sounds as if they are present. I have the modul8 EEPROM and have made up a few custom EEPROMs. The delays and reverb all work for me. The select pins on the FV-1 are 16 to 18. Measure the voltages on those pins in each of the selection positions and see if the voltages are correct in each position.
 
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PJS said:
The clock and data signals between the processor and EEPROM will measure 3.3v - they are digital signals alternating between 3.3v and 0v. With a multimeter they read 3.3v. You will need an oscilloscope to determine more detail about these signals, but it sounds as if they are present. I have the modul8 EEPROM and have made up a few custom EEPROMs. The delays and reverb all work for me. The select pins on the FV-1 are 16 to 18. Measure the voltages on those pins in each of the selection positions and see if the voltages are correct in each position.
Click to expand...

Thanks for the recommendation and info. I'll check again, but I am sure I had +3.3V to the common of the decade switch and checked all continuity. I don't recall checking all the combinations, so I will check that.
 
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Do all the patches on the module8 chip work as expected? (I don’t see any day or reverb on that one so from the description it seems like all the patch numbers 1-8 work.

I can’t think of any reasons for the reverb and delays only wouldn’t work, unless you got a bad chip? That’d be surprising. The pitch shift and chorus use delay memory as well
 
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phi1 said:
Do all the patches on the module8 chip work as expected? (I don’t see any day or reverb on that one so from the description it seems like all the patch numbers 1-8 work.

I can’t think of any reasons for the reverb and delays only wouldn’t work, unless you got a bad chip? That’d be surprising. The pitch shift and chorus use delay memory as well
Click to expand...

Bingo! Thought I bought the Octagon EPROM and I actually ordered the Module8 (as written above, but it didn't dawn on me until your post!

Yes all the programs of the Module8 function as described.

The problem must be the custom EPROM I ordered from PedalPCB, which should have had 'Blackface Reverb,' Spatialist (Room Reverb), Spatialist (Hall Reverb) Harmonic Tremolo, Modulated Delay, Tape Delay, Unison (Dual Detune) and Dual Pitch Shifter. The only program which seems to work is the Unison.
 
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Ok if reach out to Robert in a DM or email, seems like there’s pretty good evidence that your build is functional (since all Module8 patches work well), and that you have a bad chip (only the Unison patch was loaded).
 
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I wanted to follow up to let everyone know that PedalPCB replaced my defective Custom EEPROM and it works great! I really appreciate their help!

Here are all the effects I chose:
Program 0: REV004 - Blackface Reverb
Program 1: REV006 - Spatialist (Room Reverb)
Program 2: REV007 - Spatialist (Hall Reverb)
Program 3: MOD005 - Harmonic Tremolo
Program 4: DLY002 - Modulated Delay
Program 5: DLY003 - Tape Delay
Program 6: UNI001 - Unison (Dual Detune)
Program 7: PIT001 - Dual Pitch Shifter
 
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