DOD680 Strange Circuit and Troubleshooting

[mth5044]

Hello,

I was going to start this thread to ask for help in trouble shooting a DOD680. As I was collecting voltages, I pulled up the schematic I had to see if I could get some resolution on where each device was in the circuit, when I noticed mine was significantly different from the schematic. I know there's a version with SAD4096, which is the chip mine has, and a R5101. I can't find the schematic for the R5101, but in pictures I saw, it does have the NE571 or other compander. Mine is void of companders, isn't that odd?

http://www.dirk-hendrik.com/temp/dod680.gif

The active components in my DOD680 are:
SAD4096
15V regulator
4013BPC
2N2124
2x LM385
2x R4558

I took readings of all the active components besides the BBD, which I took out for poking around. Unfortunately the socket has too much plastic around the legs to be able to get readings on without the chip in.

The first thing I'd like to do is convert it to run on an 18V power supply, cause why not I guess. But I'd also like to see an alternate schematic, if anyone has one. I can see on the bottom right side of the board, there's copper for the compander and components, but no holes were drilled for it, so I suspect this version came later in life, and they had reason to remove that part of the circuit? Cost cuts?

As far as what's going wrong, I am getting one delay, and it sounds alright, until the repeat knob is turned up about half way, then the single repeat gets real farty, and and further turning the knob up causes no delay. The delay time knob has effect on the delay time, depending on where the repeat knob is. If the repeat knob is all the way down, I can get a delay from very short to longish. With the repeat knob at 11 o'clock, the delay time pot reaches it's minimum delay at noon.

Voltages are below, but I don't know what any of it means without a schematic.

Regulator   
1   24.1
2   SPARK (oops)
3   15.02
   
Trim   
1   0
2   4.95
3   8.14
   
4013BPC   
1   15.01
2   4.38
3   15.01
4   6.49
5   15.01
6   15.01
7   0
8   0
9   7.5
10   0
11   4.38
12   7.5
13   7.5
14   15.01
   
2N2124   
E   0
B   0.23
C   6.48
   
LM385P 1   
1   6.99
2   7.44
3   7.44
4   0
5   7.18
6   7.45
7   7.45
8   15.01
   
LM385P 2   
1   7.59
2   0
3   7.37
4   0
5   7.24
6   7.46
7   7.46
8   15.01
   
RC4558P 1   
1   7.44
2   7.44
3   7.44
4   0
5   7.58
6   7.58
7   7.58
8   14.89
   
RC4558P 2   
1   7.58
2   7.58
3   6.87
4   0
5   7.58
6   7.58
7   7.58
8   14.89

That's a lot to unload here, but thanks for any help!

[mth5044]

I am... out of my league. The stuff around output 2 doesn't seem right at all, and the wiring of the delay chip seems quite different from the other schematic. Could be I have the pinout rotated 180 degrees, but still, I don't think it would make any sense.

https://imgur.com/a/0rqaKjr

EDIT: Butts, the delay chip is flipped 180 degrees and now the pinouts make a bit more sense with the other schematic... Not completely, but it seems to be a bit better.


I think some of the confusion is getting all of the caps and resistors in order to form their whatever-pole filters, as I'm not too familiar with that topography. The circuitry around output two still has me thrown. Why is the output of the chip running directly to the output? Can't be the feedback can it?

And why are IC4_A and _B facing that direction? ?

[mth5044]

Now we're cookin with gas, friends. A companderless analog delay with an unobtainable chip haha

https://i.imgur.com/a/RM4LfyM

Just need to figure out why it don't work no more. 

[mth5044]

And here with are with component values!

https://imgur.com/a/uXWtFjT

The caps labeled C12+C13 and C14+C15 seem to be a repair at some point. They are two greenie caps wired in series and in place of where a single cap used to go. The 12/13 are two 100n in series, and the 14/15 are two 10n in series.

Is there a way to imbed imgur images? The regular [img ] [/ img] isn't workin

[Scruffie]

LM385-2, assuming it matches up to your new schematic, pin 2 should definitely not be ground.

[duck_arse]

And here with are with component values!

https://imgur.com/a/uXWtFjT

The caps labeled C12+C13 and C14+C15 seem to be a repair at some point. They are two greenie caps wired in series and in place of where a single cap used to go. The 12/13 are two 100n in series, and the 14/15 are two 10n in series.

Is there a way to imbed imgur images? The regular [img ]http://[/ img] isn't workin

if you hover over the image and right klik/copy image address, then past it here:
https://i.imgur.com/e5uD8cu.png
then highlight that addy and clikk ^ "mona", you get this:


when you post at imgur, there should be a little "three dots" from memory appear in the upper right of the image. go on that and it gives you various coded codes for various uses.

well, I would have left it, but then I saw the image size, so now I've added " height=400" between [img and ], thus <img height=400>. I seem to recall seeing sized link options somewhere at imgur, but I never use them.

[reddesert]

FWIW, I think it's likely that this uses an LM358 (dual opamp), not an LM385 (voltage reference diode).

[Govmnt_Lacky]

Kinda odd. The only 4096-based boards I see have the 571 in the loop. Only the R5101 boards do not have it. I'm thinking someone got "creative" in that pedal.

Anyways, here is a schematic for the DOD680 with the 4096 (which shows the 571 in the loop)

[Govmnt_Lacky]

I know there's a version with SAD4096, which is the chip mine has, and a R5101. I can't find the schematic for the R5101, but in pictures I saw, it does have the NE571 or other compander. Mine is void of companders, isn't that odd?

Ok.. lets analyze this.

The only 680s that I see DO NOT have a compander are the 5101 versions. They have a clock chip (MC14013) and 2 quad op amp chips (RC4316??)

Does your box have the older script writing or the newer block lettering?

The fact that your circuit has several dual op amps instead of 2 quad op amps tells me that it should be the 4096 version BUT, that means it should also have the 571 and associated circuitry.

Would be VERY interested in seeing some pics

[mth5044]

LM385-2, assuming it matches up to your new schematic, pin 2 should definitely not be ground.

Good catch - I have to rewire this for the 18V adapter, then I'll head to pin 2 first and see if that was a mistake when I was taking measurements.

if you hover over the image and right klik/copy image address, then past it here:
https://i.imgur.com/e5uD8cu.png
then highlight that addy and clikk ^ "mona", you get this:


when you post at imgur, there should be a little "three dots" from memory appear in the upper right of the image. go on that and it gives you various coded codes for various uses.

well, I would have left it, but then I saw the image size, so now I've added " height=400" between [img and ], thus <img height=400>. I seem to recall seeing sized link options somewhere at imgur, but I never use them.

Thanks Duck!

FWIW, I think it's likely that this uses an LM358 (dual opamp), not an LM385 (voltage reference diode).

You are correct! I mistyped, they are 358. Good catch!

I know there's a version with SAD4096, which is the chip mine has, and a R5101. I can't find the schematic for the R5101, but in pictures I saw, it does have the NE571 or other compander. Mine is void of companders, isn't that odd?

Ok.. lets analyze this.

The only 680s that I see DO NOT have a compander are the 5101 versions. They have a clock chip (MC14013) and 2 quad op amp chips (RC4316??)

Does your box have the older script writing or the newer block lettering?

The fact that your circuit has several dual op amps instead of 2 quad op amps tells me that it should be the 4096 version BUT, that means it should also have the 571 and associated circuitry.

Would be VERY interested in seeing some pics

Yep, that's why I clipped the thing out and traced it, seemed like an odd bird. It has the copper traces for the compander part, based on some of the online gut shots I've seen, but no holes drilled for them, which at least let's me know this PCB never had the compander to begin with and that it wasn't modded to remove it. The only mods I can plainly see are the replacement of some of the original cap's with greenie's in series.

The writing is block, not script.

I'll take some photo's now and report back!

[mth5044]

Top of enclosure


Inside enclosure


PCB - Note the traces for another IC and supporting components can be seen through the board on the bottom right. There's only one copper path back to the circuit, which seems dubious. Also, dead center, one spot for a cap-sized component, one pad connecting to ground.


Trace side


Some close ups

[Govmnt_Lacky]

Very perplexing! The more I look at it the more I see... wrong 

Even if you wanted to incorporate the 571, half the traces are missing! It makes me wonder if this is someone's pcb design that they installed themselves.

[mth5044]

No idea. If I read you right, the block style came after the script. What came first, the SAD or the R5101 versions? Is this some sort of transition? Seems like a lot of work to DIY a circuit, with the circuit and layout be so close to the original, but make a bunch of mods.

Do you have a schematic for the R5101 version?

[Govmnt_Lacky]

No idea. If I read you right, the block style came after the script. What came first, the SAD or the R5101 versions? Is this some sort of transition? Seems like a lot of work to DIY a circuit, with the circuit and layout be so close to the original, but make a bunch of mods.

Do you have a schematic for the R5101 version?

I believe the 5101 was in the script versions and were the first offerings. The 4096 came later in the block versions. The only explanation I can see is that this is an early version of the block logo. Perhaps even an early prototype of the block version.

The 5101 is a slightly 'wider' chip than the 4096 so I doubt it is just a 5101 circuit with the 4096 chip installed.

My only advise is to contact DOD for the 5101 schematic. It has been out of production for a while and, if you explain your circumstances, they may offer it to you.

[mth5044]

I emailed DOD a few weeks ago asking if they had schematics available. Eric emailed me back saying he looked everywhere, but the product is super old and records weren't kept well - all the people at the old Utah office who might have had a copy are long gone now!

Bummer.

[Govmnt_Lacky]

Based on the pics I have seen, none of the trace patterns match your pedal. Might have to do some deep digging and reverse engineering on it.
If I were you, I would draw up a schematic and pass it to Scruffie. He is as wise on BBD effects than others I have seen. I'm sure he could offer you some insight.

[mth5044]

Based on the pics I have seen, none of the trace patterns match your pedal. Might have to do some deep digging and reverse engineering on it.
If I were you, I would draw up a schematic and pass it to Scruffie. He is as wise on BBD effects than others I have seen. I'm sure he could offer you some insight.

Schematic posted in reply #3 and Scruffie posted in this thread already 

[duck_arse]

erm, just on the empty copper - without following the circuit diagram against pin numbers, the pad layout on the blank looks vrr similar to the layout around the LM358 pair. perhaps the empty was for a SIP pack, maybe moved away from a noise source?