Boss CS-3 Killed

thehallofshields · February 03, 2011, 09:44:40 PM

Swear it was an accident!
My Monte Allums Opto-Plus CS-3 (MIT 1st version) was running great until decided to experiment with IC4 in effort to adittionally quiet and boost the sustain.

When I loaded in a Dual Stacked Burr-Brown in place of IC4 my LED flashed twice and everything died.

No Lights, No Bypass, No Effect.

All I am getting is noise from the switch and a prominent 60hz hum coming through. My guess is that the current demanded by the (4 total) Opamps was too great for one of the power supplying transistors (Q4 or Q6) and one or more blew out.

I've got no idea where to start but I do have my voltometer ready and a good deal of spare parts.

Govmnt_Lacky · February 03, 2011, 09:51:25 PM

3 questions:

1) Did you install a socket for IC4 or did you desolder the old and resolder the new?
2) Are you SURE you did not put the stacked op amps in backwards?
3) With your trusty DMM, are you reading V+ and V- on the correct pins... on the board... with IC4 removed?

Good Luck

thehallofshields · February 03, 2011, 10:52:54 PM

Thanks for the quick reply.

1. I socketed IC4 and it ran fine with the original IC before loaded the stacked BurrBrown chips.
2. The stacked Opamp put in could have backwards, but I doubt it.
3. I dont know what voltages the pins should readout. Could you direct me to find out? What would ground the meter on?

askwho69 · February 04, 2011, 12:32:47 AM

We'll this my experience installing OPA2134 in IC4 ... M5223al is the best on sustain it has more compressed that burr brown:D try putting back the Original Ic on Ic4 and reply if its working?

twabelljr · February 04, 2011, 06:18:05 AM

QuoteI dont know what voltages the pins should readout. Could you direct me to find out? What would ground the meter on?

This is THE ultimate guide and will be necessary for you to do if you can't find something obvious.
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

thehallofshields · February 19, 2011, 07:10:25 PM

By God, this is bad: I bought another CS-3 off Cragslist for cheap, and killed it too. And the only modification I made was socketing IC2!

I am getting a clean bypass, and a wall of fuzz with Zero Guitar Signal when the pedal is engaged.
This is the THAT chip model MIT. The one irregularity I notices was that R35 (LED Resistor) has a Silicon Diode prior to the resistor.
No Mods except the Socket Extender in IC2. It is possible that I could have pulled some trace off the pcb when pushing the Desolder Braid against the leads.
D1 is functioning. (Tested it by removing it from the board temporarily.
No Crossed Leads, no Loose Wires, I've triple-checked the 8 solder joints for the socket extender, tried different op-amps - no change.

I'll be back with a list of Voltages soon. Maybe someone can recommend which class of parts to start with. Would pictures help? I could really use a helping hand...

thehallofshields · February 20, 2011, 12:38:32 AM

IC Readouts:
*Left to Right if Label is facing Forward.

     IC1     IC2     IC3     IC4
Pin 1   4.62   4.61   4.59   0
Pin 2   4.62   4.58   4.74   4.59
Pin 3   2.3   4.59   4.59   4.59
Pin 4   0   0   4.74   4.59
Pin 5   4.56   5.77   1.79   0.01
Pin 6   4.58   7.9   4.59   6.31
Pin 7   4.58   9.15   9.15   6.37
Pin 8   9.15   9.15   4.59   6.37

Govmnt_Lacky · February 20, 2011, 02:16:08 PM

Quote from: thehallofshields on February 19, 2011, 07:10:25 PM
It is possible that I could have pulled some trace off the pcb when pushing the Desolder Braid against the leads.[/li][/list]

Get yourself a solder-sucker. I highly recomend it and it will keep those pesky pads from lifting when you have to remove solder.

thehallofshields · February 24, 2011, 07:04:52 AM

Does anyone see anything wrong with the IC voltages?

thehallofshields · March 06, 2011, 08:23:46 PM

Transistor Voltages (Left to Right)

Pin 1 Pin2 Pin3
Q1 0 0 9.11
Q2 0 0.03 0.6
Q3 0 0.05 0.62
Q4 4.55 0 4.55
Q5 4.55 0 2.27
Q6 0 6.69 0
Q7 9.11 6.69 7
Q8 0 6.69 0

thehallofshields · March 10, 2011, 11:57:08 PM

Good News:
Using an Audio Probe, I've been testing both broken pedals and see where signal was passing. Here is what's happening in the unmodded CS-3:

IC1
I'm getting signal on Pins 1 & 2, (they are connected on the PCB) and none others. Looking at the CS-3 Schematic I was expecting to get the same result from Pins 6 & 7; but I am not.

IC2
Pins 1 and 5 sound good!

IC3
Not finding any signal! I want to socket it and try a different Opamp, but I don't know what I can use or what pinout to expect. The joints and opamp are still factory soldered. I have SIP8 to DIP8 converters, socket extenders, OPA2134PA, NE5532P and LM386 on hand. HELP?

IC4
Signal Passing through Pin1 & Pin2! Sounds great, although mildly distorted! Sustain control can take it to 0 Volume, but otherwise, it sounds as if the Level Pot is maxed out.

Q1 & Q4
Signal Passing through Pin 3 only when when effect is disengaged! Q1 is moderate volume while Q4 is particularly quiet.

ayayay! · March 11, 2011, 09:30:53 AM

I don't know which pedal you're on right now, but mabye focus on the one that had the least done to it. The newer one.

Does it light up when engaged? You can't really probe well unless you know it's engaged. You need to really make sure Q4 &Q5 and their corresponding diodes D6 and D7 are good. Check all diodes for that matter.

thehallofshields · March 19, 2011, 03:45:59 PM

Quote from: ayayay! on March 11, 2011, 09:30:53 AM
I don't know which pedal you're on right now, but mabye focus on the one that had the least done to it.

I've abandoned the older, messy, Allums modded CS-3. All of the info in the last few posts pertains to the newer one which I only added a socket extender to. Both pedals, however, are exhibiting very similar behavior.

Quote from: ayayay! on March 11, 2011, 09:30:53 AM
Does it light up when engaged? You can't really probe well unless you know it's engaged.

The LED's are now functional in both (the Blue did actually blow out in the M.A. modded Pedal.) Actually; I believe was getting the same results whether or not the pedal was engaged. Don't Boss pedals always process your signal? Well, just to be safe, I took all of the Voltage readings with the pedal engaged.

Quote from: ayayay! on March 11, 2011, 09:30:53 AM
You need to really make sure Q4 &Q5 and their corresponding diodes D6 and D7 are good. Check all diodes for that matter.

Is it possible to test them without removing them? After killing two pedals by adding socket extenders; I'd prefer to make as few changes to the PCB as possible.

thehallofshields · March 20, 2011, 05:28:49 AM

Alright.

D7 and D8 are functioning.

Q4 However, is conducting in both directions from pin1 to pin3.
Q4 Reads:
____
K30A
7 4L
-------

Looking around this seems to be a Toshiba 2sk30atm with a D-G-S Pinout.

thedefog · March 21, 2011, 09:57:31 AM

Hey Hall,

I'd check continuity from those pads to another point on the board where they run to. The Boss pedal traces are pretty easily lifted with even a low amount of heat. When I first started modding them years ago, I used to F them up all the time and I'd have to scratch up some of the laquer on the traces next to the lifted pad and bend the component leads to solder it directly onto the trace.

thehallofshields · March 22, 2011, 07:41:53 PM

Alright, I'm going to order some 2SK30A's if I can't find a substitute. Could I jury-rig another J-FET (an MPF102) in the meantime? Are these little K30a's the "tone suckers" that everyone complains about in Boss bypass?

Just to double-check; If my multimeter (on the Diode test setting) is passing current from the Source to Drain in both directions then the transistor has blown - Correct?

thedefog · March 23, 2011, 10:46:08 AM

Quote from: thehallofshields on March 22, 2011, 07:41:53 PM
Alright, I'm going to order some 2SK30A's if I can't find a substitute. Could I jury-rig another J-FET (an MPF102) in the meantime? Are these little K30a's the "tone suckers" that everyone complains about in Boss bypass?

Just to double-check; If my multimeter (on the Diode test setting) is passing current from the Source to Drain in both directions then the transistor has blown - Correct?

That is correct when it is out of the circuit. I have extra 2SK30as. I can mail you one if you're in the US.

thehallofshields · April 02, 2011, 03:42:46 PM

I borrowed two working sk30a's from another pedal and soldered them into Q4 and Q5. Didn't change anything!

thehallofshields · April 18, 2012, 09:52:23 PM

SOLVED:

After a year of additional electronics experience I opened the CS-3 back up. It turned out that I had a short between pin 7 and pin 8 of IC2. The signal was getting grounded out before it could make it to the sustain pot.

I am very sorry to have wasted so much of everyone's time, but I'm very happy to have a working compressor again. I did a Monte Allums style mod in about 30 minutes after getting this working again and it sounds great.