Repairing a DOD 680 Analog Delay

[ppatchmods]

I bought this thing broken on ebay. It is the one with the single r5101 chip and the toggle normal/PA switch. I noticed in the pic before I bought it that the BBD was in backwards and the on/off toggle was broken. I received it and flipped the BBD around, and jimmied the switch with a screw driver. It powered up and nothing is overheating or anything, but the transformer is making a buzzing sound and it has a blue wire that is clipped and tied in a knot. Is the transformer suppose to buzz with my cables hooked to it?

[Govmnt_Lacky]

Found this after a quick search. Hope it helps:

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

Good Luck 

[ppatchmods]

Thanks. That is actually not the version I have, but maybe it will be helpful. After playing with it a minute, both volume controls work but no delayed signal. The bypass sound the exact same as the effected signal. The switch has to work because the volumes work when engaged. I'm at the office right now, but when I get home I'm gonna change out the regulator first thing, and then check the diodes. Probably get an audio probe after it.

[ppatchmods]

i see that the blue wire is for 220-240v, so European power.  It seems to me that the sound would at least be a little different when effect is engaged because of filtering? It doesn't make a snap, crackle, pop, or any other discernible difference when engaged. 

[rustypinto]

Sounds like the BBD. The internal filtering will have no effect on the un-delayed signal, since the filters are only applied before and after the BBD. The delayed signal is blended with the buffered input, so you're probably only hearing this buffered input sent right back out of the box. I would expect the signal you're hearing to get slightly quieter if you dial in "Local" and "Remote" to be mixed to 100% delayed signal, but you will always hear the buffered input no matter what.

Audio probe sounds like a good idea. Do the usual stepping through all the output pins of: input buffer > compressor > filter > up to the BBD input pin, and if nothing wiggles at the BBD output, either the BBD is dead or the input bias is off. Also ensure proper voltage regulation (+15VDC supply, ~7.5V at the op-amp virtual grounds, etc) and check ~7.5V at the clock pins or check clock with a scope. If the BBD is really dead, then get ready to make an MN3XXX adapter if you want to get it working.

[Rodgre]

My old DOD Flanger and Chorus (same box) have buzzy transformers. I shimmed some cardboard underneath them to stop the vibration. You could probably put a new transformer in pretty easily, if it bothers you.

Roger

[ppatchmods]

The 7815 regulator seems to checkout. The BBD was in, what I thought was the wrong way, but it has the same effect no matter which way it's turned. It seems to be getting voltage to the chip, but I need to audioprobe it. Can I replace the 3 lug switch with a dpdt 125v switch and just solder to one side? If the R5101 is bad, is there a 3205 or different conversion? I think the 5101 has a internal clock so it might be pretty extensive. maybe a 2399 would be easier...

[rustypinto]

The R5101 only has one clock on pin 21, but not complimentary clocks like BBD's require. BUT, if your heart is set on reviving this pedal, it can still be adapted for use with a BBD if the R5101 is in fact bad. This version of the 680 *probably* (don't know for sure) uses the same clocking scheme as it's SAD4096 variant, so it would be easy to grab Qnot from the 4013 for the clock's compliment. When i do BBD retrofit adapters, i use the "tall" DIP sockets to bring up signals/ resources to the target BBD. Here is an example i did on a Deluxe Memory Man that used 4x SAD1024's:





Other variants i've done have two sockets where the tall one is left empty and only used to bring out signals to another socket with the BBD. It all depends on the BBD you go with, if it can use everything you bring up from the socket (eg. MN3205 could not use the 15VDC supply), etc. Also keep the mechanicals in mind by making sure any adapter that you install will actually fit before you do it!

[ppatchmods]

wasn't there a retrofit for the 5101 that was in the MXR 118? i think it used a pt2399. would it work the same in this circuit?

[rustypinto]

I don't know for sure if there was a mod to use a PT2399, but i have no doubt it would work. There are two significant drawbacks to this method (among others): providing 5V to the PT2399, and then you have to modify the delay time control/ circuit on the 680. If you use a BBD, you can use the clock circuit already in place, and then all you have to worry about is the proper supply voltage (Vdd), gate voltge (Vgg), and input bias voltage.

[ppatchmods]

sounds easy enough...   
when i turn the chip around, i get the exact same sound. the trimmers have no effect. this, imo, sounds like a different problem than a delay chip. i know these chip are very unreliable, so it is possible that it's dead...i'm just holding out hope. any thoughts?

[rustypinto]

IMHO, you dont' want to keep flipping the R5101 around hoping for the best. This could potentially kill it.

Like i said before, you should be getting clock to pin 21 of the socket/ R5101. Verify that the clock comes from pins 1, 2, 12, or 13 of the 4013 chip, you will have to do some tracing to figure it out. I can't say for sure because i don't have the specific DOD680 schematic with the R5101. Once you figure that part out, you can certainly install the R5101 with more confidence.

Then its as simple as verifying that you do get a signal to the input pin (you can probe the current limiting resistor coming from the bias trim) and then see if you get output for any range of the bias trim. You don't necessarily need the pinout of the R5101 because the surrounding circuit can give you just as strong evidence of this device's operation.

BTW, here is a similar MXR design using the R5101:
http://www.experimentalistsanonymous.com/diy/Schematics/Delay%20Echo%20and%20Samplers/MXR%20Analog%20Delay%203.png

[ppatchmods]

thanks again. yeah, i flipped it once because of a gutshot i found on the interweb... i'll start audio probing soon. i've been doing some research on CCD's and there actually may be a replacement with a little modification in the TCD102

[ppatchmods]

Well, i'm pretty sure the CCD is DOA...code blue...
Now on to retrofits. I have no info on the 5101 pinouts or anything. The BBDementia file at Mark Hammer's site had very little in it about the 5101.

I have a 3205 so i might shoot for that one. Is there any info on retrofitting BBD's? I've googled and bing'd but can't seem to find any details. Any help getting this beast back up will be very much appreciated! Thanks