Boss DD-2 problem solved

[geertjacobs]

My friend has a Boss DD-2 delay that is not working as it should.

When I opened it, i noticed that it has already seen some service before:
- the pcb has been broken on the output side and has been jumpered to compensate for the broken pcb traces.
- the Zener diode on the input had been replaced quite brutally (with a diode that had thicker leads which ruined the pcb pads).

I have removed the D6 to eliminate this as a possible cause, but there still is another problem.
- i'm operating on a battery ( just to be safe)
- the normal output (labeled "mono", on the opposite side of the input) always gives a straight signal.
- when switching on either of the three delay modes, the led lights up very dimly and then fades after 20 secs. If I retry immediately, the led lights up and already fades out after a few seconds.
- the good news is that the straight output (on the same side as the input) gives out the hold signal when the hold mode is used, so the delay circuitry is all still working.

Any ideas?

DD-2 schematic

[geertjacobs]

Update:
Apparently I switched the output jacks when reassembling the box  :oops:
So the hold mode is working normally, all knobs working.
The error is still in: I set the rotary switch to get one of the delay modes and when I stomp the switch to activate it, it doesn't "latch"(i.e. stay in the delay mode). If I keep it pressed down, I see the led flickering a bit.
The "mono" output always gives a straight signal.

Any suggestions are greatly appreciated.

G.

[geertjacobs]

So I continued my bug hunting. Found a nice logic table on the schematic and checked that. Was almost alright, i probably have a short between the S and M position.
But the real problem appears to be the BA634 flipflop.
I'm guessing it should flip or flop when the switch is pushed and it doesn't. When I short the input and output very briefly (just testing...) the led comes on, so I think the flipflop is the guilty party.  My guess is that it has been burned by desoldering an soldering the zener diode ("fuse") a few times too many.
Problem is that I can't even find a datasheet on the BA634! Is it for sale somewhere?

G.

[Paul Perry (Frostwave)]

Well, here's one source:
http://www.donberg.ie/descript/b/ba634.htm

[geertjacobs]

Believe it or not, but in the meantime I found a BA634.
The Benelux Service Center for Roland happens to be in my home town, so I figured i had nothing to loose and called them. They were kind enough to give me one of the two last BA634's they had for just 2.18 euro's.  

Unfortunately, replacing the BA634 that didn't solve my problem.  :oops:

I just isolated measured the output of the BA634 (pin 2).
- I set the delay mode switch to one of the delay modes.
- I plug in the input and switch the pedal and the led goes on. Pin2 gives me 6.70 Volts.
- after about 40 secs the led goes off. Pin 2 suddenly drops to 0.

My guess now is that the muting circuit that controls the flipflop when the pedal is "booting" is acting funny. A friend gave me a hint that i should look form elcaps that are wrong and now i suspect the cap in the muting circuit.
But the parts are so close together that it's very hard to figure out where the guilty part exactly is. Does anyone happen to have a layout for a dd-2?

[TheBigMan]

Sounds to me like there's an unstable voltage somewhere.  One of the most common faults I've heard with Boss delays (DD-2/3/5) is in the regulator chip.  If that chip (IC10 on the schematic) is not producing a stable Vref then the switching FET (2SK30A-Y, Q8) won't be stable.  I'd check that the reference points on the pedal actually are at +5V E.g. R37 and R38 (both 1M on either side of Q8) and  R2 (1M input buffer resistor)

Also I'd get a replacement for D6 so that you can test the pedal with an adapter rather than a battery.  The DD-2 draws a rather hefty 55mA in use, which will drain batteries quite quickly.

[geertjacobs]

So the pedal is switching happily on and off again.
Only I'm not sure what exactly was the solution.
I did replace the BA634, but in the end I think the rewiring the switch was the solution (almost broken wires).
The protection diode still has to go back in.
This was a tough nut to to crack though...

[Zero the hero]

Man where did you find a BA634?
I planned to build an OC-2 which uses this flip-flop in dividing, but I coulnd't find it elsewhere!!!!

[slideman82]

Hi! This is my first post or participation on the forum. Well, a friend of mine gave me an old DD-2 to fix it. As many around the world, it had had a burnt 5V regulator problem that someone, I think some beast or a non smooth-soldering guy, repaired it, breaking up many pcb tracks around this regulator (replaced by resistors leads), making a hole where D6 used to be. The fact is this delay still works, but just the dry signal. Sometimes I can hear some type of noise, like endless repeats beating quite fast... so, if this is the syntom, which is the diagnostic? I hope some user could help me a bit.
I think the BA634 is working fine, I compared some voltages and resistance with other DD-2 (I've got 2 of them at home... from the same guy!!!!!!), mint condition (looks like new!), and noticed they were the same.

I have a lot of great experiences with stompboxes and some tips someday I'll post here, or contribute on others.

[Dirk_Hendrik]

The fact is this delay still works, but just the dry signal. Sometimes I can hear some type of noise, like endless repeats beating quite fast... so, if this is the syntom, which is the diagnostic? I hope some user could

The usual cause of the 7805 regultator to burn in a Boss DD is a reversed power supply. There's some 3 of 4 (out of the head 10uF) elco's in a DD2/3 that start to leak after a voltage reverse.Therefore check the copper side of the board for a "black-isc" colorization of the green, usually under electrolytics. Those are the ones to replace. Another telltale sign is corrosion of the soldering due to the acid in the elco's.

hope this helps

[Processaurus]

slideman, my vague notion would be to check around the HOLD line to the main chip, and see what happens to the DC voltage on that pin in and out of the hold mode, switching the footswitch.  Maybe the hold pin is stuck on somehow...

[Processaurus]

Man where did you find a BA634?
I planned to build an OC-2 which uses this flip-flop in dividing, but I coulnd't find it elsewhere!!!!

2x 4013 flip flops will work just fine for the OC2, its funny they could have used 2, and avoided their complex discrete flip flop circuit for the switching.  Old habits...