| Author |
 Topic  |
|
|
pawnshop_trash
Gold Member
USA
603 Posts |
 Posted - 05/01/2008 : 22:09:44
|
hello, does anyone know how to diagnose a bad electrolytic cap (specifically, the biggest one, which regulates the power supply IIRC) vs. a bad chip (e.g., BBD chips like the MN3007)?
for example, if a delay pedal works in bypass mode and lights up when switched on, but does not produce any sound with the 'blend' knob set 100% wet, is that likely a bad BBD chip? (the 'dry' signal can be heard in bypass or when switched on.)
similarly, what about a distortion pedal that is always 'on' (even after you replace the footswitch) but produces no sound; is that likely a bad electrolytic cap? (what are the symptoms of a bad electrolytic cap?)
any suggestions would be appreciated. thanks!
|
|
|
bossFan
Bronze Member
Portugal
97 Posts |
Posted - 05/01/2008 : 22:34:35
|
These things dont work that way..
If you have a delay pedal that does not produce the delay signal,it does not mean that a BBD is bad.
The same in the case of the distortion pedal.It could be something else than an electrolytic cap.
In both cases, you must analyze the correspondig circuits logically and with the proper instruments(voltmeter, ohmmeter, capacitance meter)to check for non functioning components.
Any questions, feel free to ask... 
|
Edited by - bossFan on 05/01/2008 22:36:26 |
 |
|
|
zentropa
Gold Member
USA
837 Posts |
Posted - 05/01/2008 : 22:59:41
|
bossfan is correct on the right way to troubleshoot.
first glance should be investigating the circuit board for possible bad solders/connections.
second glance should be at any components that appear bad. e.g. scorched diode, blown cap, etc.
if you prefer to do things the difficult way you can always systematically replace every component minus the chip which would be time consuming and a PITA but probably still cheaper than buying the necessary tools/gauges for doing thorough troubleshooting.
a blown cylindrical cap will usually have a slightly expanded top (this is often very very subtle).
bad caps usually surface in the form of tonal/effect degredation but i'm guessing it can go beyond that.
the delay pedal sounds like something may be shorting when the blend is @100%?
the behavior of the distortion pedal behavior sounds a little like reverse polarity current that used to happen w/ my old DOD pedals if a power supply had a negative tip instead of a positive one.
|
|
|
|
pawnshop_trash
Gold Member
USA
603 Posts |
Posted - 05/02/2008 : 01:09:05
|
thanks for the replies, BossFan and Zentropa. given my limited electronics skills and resources/equipment (a DMM and just enough knowledge to re-wire guitar electronics), I was looking for (potentially) easy solutions to try first... soldering a cap should be easy, as should replacing a chip (esp. if it's socket-mounted). from what I've read chips and electrolytic caps seem to be the usual suspects to go bad first on old (20+ year old) pedals, which is why I focused on them.
additional details, if you like:
- these pedals were tested with fresh batteries;
- the delay pedal gives 100% dry sound, regardless of where the blend pot is turned (which could indeed be a short somewhere, but I can't figure out where);
- the main electrolytic cap in the dist pedal does have a small mark on its side, but hasn't obviously blown (I have also read that electrolytic caps can go bad if the pedal was not used for a long time);
- there do not appear to be any obvious breaks in the circuit.
thanks again!  |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 05/02/2008 : 05:34:03
|
Delay:
- works in bypass mode and lights up when switched on, but does not produce any sound with the 'blend' knob set 100% wet (the 'dry' signal can be heard in bypass or when switched on.)
- the delay pedal gives 100% dry sound, regardless of where the blend pot is turned
- tested with fresh batteries;
- there do not appear to be any obvious breaks in the circuit.
What is the pedal? How did it fail? When working on it? Or it just didn�t work one day?
Distortion pedal:- is always 'on' (even after you replace the footswitch) but produces no sound
- tested with fresh batteries;
- the main electrolytic cap in the dist pedal does have a small mark on its side, but hasn't obviously blown (I have also read that electrolytic caps can go bad if the pedal was not used for a long time);
- there do not appear to be any obvious breaks in the circuit.
What is the pedal? How did it fail? When working on it? Or it just didn�t work one day? |
|
|
|
pawnshop_trash
Gold Member
USA
603 Posts |
Posted - 05/02/2008 : 21:00:17
|
| Laurie, the pedals are generic brands from the 1980s. like Boss pedals, they have FET footswitches instead of stomp switches. both pedals were bought used, and have not worked since I've owned them.... |
|
|
|
Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 05/03/2008 : 04:30:31
|
quote:
Originally posted by pawnshop_trash
Laurie, the pedals are generic brands from the 1980s. like Boss pedals, they have FET footswitches instead of stomp switches. both pedals were bought used, and have not worked since I've owned them....
Hi pawnshop_trash
Please take some internal pics, & we'll all see if we can help that way.
Regards Dr. Bob |
|
|
| |
Topic |
|
diagnose a bad electrolytic cap vs. a bad chip?
