Boss DS-1 troubleshooting

[mds]

Hey guys!

I've been a tinkerer for awhile and modded some amps, built some pedals, etc. etc...I just got my hands on a broken DS-1 and I'm trying to fix it. The power LED lights, and signal passes when the pedal is bypassed, but when the circuit is on no signal goes through. I popped the hood and noticed the D1 recifier was broken in half, so I replaced it with an 1n4004. Pedal still didn't work...C23 was bulging a lot on top, so I replaced it with a 100uF 35v (16v was there, but this should be a fine replacement). The pedal still doesn't pass signal when engaged. I don't see any other components that look damaged and all of my continuity testing of various lines and paths hasn't revealed any problems. Do you guys have any ideas what I could look for or other approaches to diagnosing problems on this pedal?

Thanks!

Mike

[gulliver]

Make sure you go over it with a magnifying glass. My distortion level wasn't working after tonight's mod, and I found a problem I couldn't see with my eyes alone.

[wampcat1]

does it work in bypass mode?
What are your readings? See here:
http://www.elixant.com/~stompbox/smfforum/index.php?topic=29816.0

(Sticky thread: What to do when it doesn't work )

Take care,
Brian

[mds]

Started measuring and I think my IC my be fried. It is pretty clear someone plugged the wrong polarity adapter into this and fried it do to the damage to D1 and C23. Someone in another thread had the same damage and their IC died. Here's some info:

1.What does it do, not do, and sound like?

No signal is passed when the effect is on. Signal passes when the unit is off/in bypass. Power LED works when plugged in and with a battery.

2.Name of the circuit = BOSS DS-1

3.Source of the circuit (URL of schematic or project) = Branded BOSS Pedal

4.Any modifications to the circuit? Not yet!

5.Any parts substitutions? 35v 100uF capacitor on C23 instead of 16v 100uF

6.Positive ground to negative ground conversion? Nope

7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => 9.31v

Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead =  9.3v
Voltage at the circuit board end of the black battery lead = 0


IC1 (or U1)
P1= starts near 0 then climbs up....after a minute or so it is at 40mV
P2= starts near 0 then climbs up....after a minute or so it is at 40mV
P3= 4.55V
P4= .2mV
P5= cycles from 0 up to about 400mV repeatedly
P6= cycles from 0 up to about 400mV repeatedly
P7= cycles from 0 up to about 400mV repeatedly
P8= 9.29V

I'm measureing the rest of the stuff now, but all that weird cycling doesn't look right to me...I'll post more later. Any chance I can get a BA728N at radio shack or fry's? Anyone know a good parts place in Los Angeles? The Mar Vac near me closed. :-(

Thanks!

[mds]

Here is the rest...some of the stuff cycles a bit...I'm not sure what that means...and I couldn't find D3 on the board. 

Q1
C= 7.99V
B= 3.472V
E= 2.992V

Q2
C= 4.06V
B= .6V
E= 13.5mV

Q3
C= 7.93V 
B= 2.791V
E= 2.382V

Q4
C= 62.6mV
B= 2.4mV
E= 2.3mV 

Q5
C= 5.24V
B= 24mV
E= 2.3mV

Q6
C= cycles from 0-4V
B= 3.86V
E= 3.87V

Q7
C= cycles from 0-4V 
B= 3.87V
E= 3.87V

Q8
C= 60.6mV
B= 3.9V
E= 3.85V


IC1 (or U1)
P1= starts near 0 then climbs up....after a minute or so it is at 40mV
P2= starts near 0 then climbs up....after a minute or so it is at 40mV
P3= 4.55V
P4= .2mV
P5= cycles from 0 up to about 400mV repeatedly
P6= cycles from 0 up to about 400mV repeatedly
P7= cycles from 0 up to about 400mV repeatedly
P8= 9.29V

D1
A= 1.9mv
K= 7.76V

D2
A = 3.31V
K = 7.75V

D3 - Am I an idiot? I can't find D3 anywhere!!
A=
K=

D4
A= 3.82V
K= 3.83V

D5
A= 3.8V
K= 3.8V

D6
A= jumps around 0
K= 61mv

D7
A= 0-4V cycle
K= 4.55V

D8
A= 5.1mv
K= 3.75V

[mds]

If I do need to replace the IC, is there a replacement better than what is in there now? Can I use an equivalent without problems? What are my options?

Thanks!

Mike

[johngreene]

I would say that the IC is blown. With Pin 3 at 4.55V, pins 1 and 2 should be at 4.55V as well. The BA728N is a dual opamp in a SIP package which may be rather hard to find (even at Mar Vacs!) Mouser has NJM4558L's in stock which would work. Or you could always make your own DIP to SIP board as the two are pin-for-pin.

--john

[mds]

Got the chip and fixed it...works great now...does the JCR chip affect the tone much compared to the stock BA728n? I've never owned a DS-1, so I'm not sure if what I'm hearing is the stock sound or not...sounds pretty good...kinda harsh, though...

SO! What mods should I do? I've got LEDs handy, so I'm thinking of swapping at least on of the clipping diodes with an LED...what else are must have mods?

Thanks for your help guys!!

Mike

[johngreene]

I don't know how much the IC would affect the tone. Since the DS-1 uses diodes to ground after the IC I would think that the only real difference it would have would be in noise. FWIW the DS-1 I had with the BA728 sounded really harsh to me as well. At least through a Fender amp.

--john

[mds]

The BA728 is in the garbage,now. I'm using a JCR 4558 chip per your suggestion.   I ordered 4 of them, so if anyone needs a chip for their DS-1, let me know!