Help with DOD DFX9 Delay Problem - something fried

[effectsbay]

Hello All

Continuing my learning on pedals and repair I thought I'd dig out an old DOD pedal that I had, that wasn't working. Simple battery strap issue, but I thought I would see if I can update the power supply to a standard Boss style 9V plug. Normally, I would figure this would be a no-brainer. After drilling the enclosure to accept the wider plug (had the original 1/8" plug before), I connected the positive lead, connected positive from the battery, and connected a ground to the input jack. That we were all good, then I plugged the effect in to test.. wow.

Pure distortion sound. Effect level obviously increased the distortion with dry signal. No delay effect at all. Delay and Repeat controls.. do nothing. LED lights up, and bypassed signal works fine. Range control appears to select and lights second LED when set to infinite.

My only guess is that something is wrong with the power, since that's all I touched. Battery causes the same problem. I went back and restored the original power plug, and the problem persists.

I'm suspecting the NEC D41256C-10 RAM might be the culprit, since it appears to come right after the power diode/cap in line, and it's in a socket. I figured it's in a socket for easy replacing. Can any of you recognize what might be happening?

I put together a little video. I started doing an audio trace, to see where things get bad, but not super familiar with some of these chips and ICs. Doing some research. I've also started confirming some of the component values.

Thanks!
hank

[effectsbay]

Still digging in on this one and running into a wall. I'm really thinking there is something really stupid/easy that happened. I keep coming back that I don't think adding that PS was the problem, but something while I adding the component (loose component or broken solder joint). I'm still looking closely at everything, but judging by the sound, can any of you recommend where to focus on? It's continuous which makes me think it's one of the ICs. The first IC looks to be for the buffer (and that is working ok), but trying to think what's in the effects portion that could be doing this.

I'm still digging for a schematic too. Found a couple of leads from years ago, and PM'd them since at the time, they did have a zip file of the schematic.

Thanks!
hank

[Govmnt_Lacky]

DOD is pretty liberal with the schematics. I bet if you email them they will send it to you. Unless, of course, this is still a production pedal.

[mcknib]

I'm not 100% but are these DOD pedals not centre positive DC jacks rather than centre negative as with the Boss type jacks would that not have some bearing on it working correctly

[effectsbay]

DOD is pretty liberal with the schematics. I bet if you email them they will send it to you. Unless, of course, this is still a production pedal.

I'll shoot 'em a message. I would say the chances are pretty low. This pedal hasn't been in production in a long, long time.

UPDATE. Just sent a request.. we'll see.

Thanks!
hank

[effectsbay]

I'm not 100% but are these DOD pedals not centre positive DC jacks rather than centre negative as with the Boss type jacks would that not have some bearing on it working correctly

mcknib.. thanks. But wouldn't it all be correct on the other side? Meaning, I put in a modern Boss style plug, and wiring + lead to board, + lead to battery and ground to ground? Also, like I mentioned earlier, I wired it all back to it's original state to see if that improved.. and that (or with battery) still has the badness.

Thanks!
hank

[effectsbay]

I've identified all the ICs and RAM on board. I'll try an audio probe trace at the in/out to see if that yields anything (I have the pin outs marked down) I'll put what I found so far.

RC4558P / OpAmp (first one is good, directly after the input). Probably buffer?
LM311N / Voltage Comparator x 2
LF353N / OpAmp
CD4066BE / CMOS Quad Bilateral Switch
NE570N / Comparator
KA4558 / Dual OpAmp
RC4558P / OpAmp
D41526C-10 / NEC RAM 16 PIN DIP (socket)
SCX6218WEW/V4 / micro CMOS gate array chip (socket)

UPDATE.. here is what my probes found.
RC4558P first one.. good on in/out
LM311N Weird solid signal tone (like keyboard) on in+ nothing on in- and same solid tone on out
LM311N (another IC) Bad distortion sound on in+ or in-
LF353N band distortion on in and out

The LM311N LM311N and LF353N are very close together.

CD4066BE I get good guitar signal on Sig D in/out and Sig D out/in
KA4558 Good signal on in and out
344ASM Good signal on in and out
NE570N Good signal for the most part on multiple pins. Slightly distorted signal on primary out

Note.. no delay effect (repeats, etc) while I'm probing anything.

Thanks!
hank

[mcknib]

mcknib.. thanks. But wouldn't it all be correct on the other side? Meaning, I put in a modern Boss style plug, and wiring + lead to board, + lead to battery and ground to ground? Also, like I mentioned earlier, I wired it all back to it's original state to see if that improved.. and that (or with battery) still has the badness.

Thanks!
hank

Yeah that'd work! Hank I mentioned it because I had a bit of a headache with a Rat until I realised it was centre positive but that was working with the original DC jack I had a hard time getting the battery snap wired correctly.

Anyway I found this link
http://doktorsewage.com/operating-theater-dod-dfx9-digital-delay/

Not that it'll solve your problem but it gives some useful little snippets about the pedal

[effectsbay]

mcknib.. thanks. But wouldn't it all be correct on the other side? Meaning, I put in a modern Boss style plug, and wiring + lead to board, + lead to battery and ground to ground? Also, like I mentioned earlier, I wired it all back to it's original state to see if that improved.. and that (or with battery) still has the badness.

Thanks!
hank

Yeah that'd work! Hank I mentioned it because I had a bit of a headache with a Rat until I realised it was centre positive but that was working with the original DC jack I had a hard time getting the battery snap wired correctly.

Anyway I found this link
http://doktorsewage.com/operating-theater-dod-dfx9-digital-delay/

Not that it'll solve your problem but it gives some useful little snippets about the pedal

No worries!

Thanks for the link, but unfortunately, I've already read it several times hoping for some clues.

Thanks for the help and replies!
hank

[effectsbay]

Ok.. I'm getting somewhere. DOD did get back to me with schematics

http://www.effectsbay.com/files/DFX9Schem.zip

With the combination of the audio probe, I'm starting to think I have it isolated.  It appears the 4558 ICs (U11, U10, U9) are in good shape. The 311N (U5 / U6) and 353N (U4) interact with the big chip, and I can't tell if things are fine there, but I think things go bad before this.  I things are getting weird at U12 (NE570N) and/or U6 (CD4066BE). I was able to find these on eBay and they're in route.

If anyone can take a look at the schematic and let me know your opinions.. that would be great!

Thanks!
hank

[Tony Forestiere]

Great that the sent you the schematic, and so quickly! I'm going to go by gut here. Since you were modifying the power supply area, I would use the first board schematic to check your voltages out of the supply. 9V into the 78L05 regulator, and 5V out. 5V powers the delay thingie chip. It seems the Dual Op Amps are powered by 7v, and biased by Vbias (probably around 3.5V). The schematic is going to be a BIG help.
Hopefully everybody smarter than me, (meaning Everybody) will be along shortly.

[effectsbay]

Great that the sent you the schematic, and so quickly! I'm going to go by gut here. Since you were modifying the power supply area, I would use the first board schematic to check your voltages out of the supply. 9V into the 78L05 regulator, and 5V out. 5V powers the delay thingie chip. It seems the Dual Op Amps are powered by 7v, and biased by Vbias (probably around 3.5V). The schematic is going to be a BIG help.
Hopefully everybody smarter than me, (meaning Everybody) will be along shortly.

I like your thinking. I measured the 78L05 (U13). It's definitely showing 5v out and 9v in. I think it might be okay.

Thanks!
hank

[Tony Forestiere]

V Bias and 7V?

[effectsbay]

V Bias and 7V?

I hope I'm following your question.

I measured the cap before V Bias (C8) and it was reading 3.5v. I measured pin 8 on U9B [pin 8] and it was reading 6.27v. I did an audio trace probe on that IC, and it was passing signal great. But.. now I'm wondering if you meant the 7V after C6. That is also reading around 6.26v.

Thanks!
hank

[zedsnotdead]

Hello!

Sorry to resurrect this topic, but does anyone have the schematic that could share?
Link doesn't work any more. I have a faulty DFX91, pretty similar do this one, maybe I could find something...

Much appreciated!

Ok.. I'm getting somewhere. DOD did get back to me with schematics

http://www.effectsbay.com/files/DFX9Schem.zip

With the combination of the audio probe, I'm starting to think I have it isolated.  It appears the 4558 ICs (U11, U10, U9) are in good shape. The 311N (U5 / U6) and 353N (U4) interact with the big chip, and I can't tell if things are fine there, but I think things go bad before this.  I things are getting weird at U12 (NE570N) and/or U6 (CD4066BE). I was able to find these on eBay and they're in route.

If anyone can take a look at the schematic and let me know your opinions.. that would be great!

Thanks!
hank