Author Topic: Boss CS-2 schematic interpreting help  (Read 722 times)

somnif

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Boss CS-2 schematic interpreting help
« on: December 17, 2017, 12:56:43 AM »
Howdy folks,

I'm working on a CS-2 build. Finished populating the board, tossed the pots in, added some flying wires, hooked it up...

And not but silence out the tap. Boo.

So I am now trying to diagnose it. The voltages I'm getting of the OTA match what are listed in the build doc (with one exception, more on that later). Unfortunately I gave away my audio probe (buddy needed a portable guitar amp, and my probe rig was basically that stuffed in an altoids tin), so that will have to wait till I can assemble another one.

However, I noticed something on the schematic, and my limited electrical engineering skills may be failing me slightly.


(since its a bit hard to read: Pin 1 is at the bottom near R8, pin 5 is ground, pin 9 is VA)

So, my question is: Should I get continuity between pins 6 and 7? Because, I am not.

I get 4.4k between pins 2&3. I get 150k between pins 6&4. I get no reading between pins 7&4.

Am I reading the schematic wrong, or is there a fault on the board? Pin 7 is the only pin on the OTA that has a voltage somewhat off from the build doc, so I am wondering.

For reference here is the schematic of the OTA itself: http://wiki.openmusiclabs.com/wiki/BA662?action=AttachFile&do=view&target=ba662_sch.png
No connection between pins 6 and 7 there. 




somnif

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Re: Boss CS-2 schematic interpreting help
« Reply #1 on: December 17, 2017, 01:23:14 AM »
Small update: On the official Boss overlay image it definitely looks like 6 and 7 are linked. I think? The "B" of BA662 obscures it a bit but I think I see shading behind it? Can't find any clear pics of the solder side of the board, so I can't tell for sure

https://i.imgur.com/ZaQuqyd.jpg

EBK

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Re: Boss CS-2 schematic interpreting help
« Reply #2 on: December 17, 2017, 09:00:27 AM »
There's definitely a connection there.  A questionable solder joint could be ruining your continuity, perhaps.
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reddesert

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Re: Boss CS-2 schematic interpreting help
« Reply #3 on: December 17, 2017, 11:41:39 PM »
I have no direct experience with the CS-2, but it sure seems like those should be connected - perhaps a cold solder? To muddy the waters a little, some people say that the CS-2 doesn't use that buffer part of the chip (even though it's on the schematic), so I guess pin 6 would go to the resistor and then the transistor. In this thread on FSB http://freestompboxes.org/viewtopic.php?f=1&t=4405&start=20 you can see gut shots of a pedal where pins 7 and 8, in and out of the buffer, are not used.

somnif

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Re: Boss CS-2 schematic interpreting help
« Reply #4 on: December 18, 2017, 12:58:20 AM »
Well I jumpered 6 and 7, just to see what happened. Still no guitar sound through, but at least the power supply hum goes up and down with the level knob, so thats something.

I am 90% sure my OTA is the problem (no faith at all in my construction abilities there) but I'd rather rule out easy to fix things first. Really need to build a new audio probe, grumble grumble.

drog_trog

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Re: Boss CS-2 schematic interpreting help
« Reply #5 on: February 23, 2018, 07:27:11 AM »
Boss schem does show Pin 6 and 7 are connected however they only connect when the chip is in and powered up.

bsoncini

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Re: Boss CS-2 schematic interpreting help
« Reply #6 on: February 24, 2018, 01:10:30 AM »
Why not just make a cheapo audiobprobe? If you have a female jack you can use pretty much any kind of wire. Then you can use any cable you want to the amp. I have one with some scrap wire from a cat6 cable. Or just alligator clipped to the jack

somnif

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Re: Boss CS-2 schematic interpreting help
« Reply #7 on: February 24, 2018, 01:11:57 AM »
Why not just make a cheapo audiobprobe? If you have a female jack you can use pretty much any kind of wire. Then you can use any cable you want to the amp. I have one with some scrap wire from a cat6 cable. Or just alligator clipped to the jack

I ended up doing just that (this thread is a couple months old). My homemade OTA was indeed the culprit, and unfortunately I have yet to successfully de-solder the thing. So its sitting in my misc. projects box until I get bored enough to play with it again.