Boss DF-2 Distortion/feedbacker switching problem

GorillaHuman · Post by **GorillaHuman** » 29 Jan 2016, 13:43

My Japanese Boss DF-2 is acting up. It stopped going into distortion when engaged, and goes straight into feedback modus, with the LED blinking. So basically, it passes signal, but when engaging there's only feedback going on.
Schematic/service notes: http://www.synfo.nl/servicemanuals/Boss ... _NOTES.pdf
(synfo.nl/servicemanuals is great by the way, many thanks to the owner, who hopefully reads this)

Anyways, the "SW LOGIC"-part isn't quite as obvious to me as I hoped. I understand the Ibanez JFET switching, but this seems different, with the chip in place and all.
Any ideas why it wouldnt go into normal distortion modus?

Thanks in advance!

Pruttelherrie · Post by **Pruttelherrie** » 29 Jan 2016, 17:59

GorillaHuman wrote:Anyways, the "SW LOGIC"-part isn't quite as obvious to me as I hoped. I understand the Ibanez JFET switching, but this seems different, with the chip in place and all.

That's because of the added Feedbacker functionality, which kickes in if you hold the footswitch depressed. This requires some extra logic and cap/resistor.

Any ideas why it wouldnt go into normal distortion modus?

Nope, sorry

GorillaHuman · Post by **GorillaHuman** » 30 Jan 2016, 16:50

OK on closer inspection it is as follows:
LED blinks by default, and there's an increase in gain
If the switch is pressed (held down), the LED goes off, but goes back upon release. The sound is not really distorted but does respond to the volume knob a bit. The rest is not affected. I am really puzzled.... Anyone? A pointer?

nr372 · Post by **nr372** » 31 Jan 2016, 05:43

Just so I have this straight: the pedal works fine in bypass? If so, then we at least know the buffer amps (Q1 and Q7) are working. This probably rules out major power supply problems, but it wouldn't hurt to check the 9V and 5V power rails along with the 4.5V reference. The 5V rail may be a little more interesting to check simply because it feeds IC5 and IC7, both of which are involved in the feedback mode.

If the feedback state functions correctly and there's no other odd behavior, then something in the "SW LOGIC" section seems like the culprit. One suspicion I have is C55 and C56; both are electrolytic capacitors which may have gone bad as they've aged. That could cause strange switching behavior. There's also the chance of a bad footswitch or connection, including bad solder joints.

GorillaHuman · Post by **GorillaHuman** » 01 Feb 2016, 17:40

The behavior is odd:
The pedal starts in "LED blinking mode". This should give feedback modus, but does not, it gives clean bypass.
The pedal goes into "no LED mode", it should give bypass, but gives feedback.
The pedal does NOT go into "normal distortion mode".

I replaced the C55/C56, to no avail. The caps looked in alright condition (replaced them anyways).

New suspect: The SW LOGIC chip?

GorillaHuman · Post by **GorillaHuman** » 10 Feb 2016, 10:12

Any thoughts on how to assess the chip?

Pruttelherrie · Post by **Pruttelherrie** » 11 Feb 2016, 22:39

It shouldn't start in "LED blinking mode", it should only blink if the footswitch is pressed. Are you sure the switch is ok? Desolder one wire and power the pedal: it should not be blinking. If it doesn't blink, touch the wire to the other FS wire for switching.
Also, measure pins 10 and 11 of IC9.

GorillaHuman · Post by **GorillaHuman** » 06 Mar 2016, 12:45

Yes I am positive the switch is working correctly.
What should I measure on pins 10 and 11? Use my trusty audioprobe?