Author Topic: MIJ TS-9 Drive not functioning  (Read 1843 times)

BDuguay

MIJ TS-9 Drive not functioning
« on: February 01, 2009, 11:10:17 AM »
I was asked to change the chip in this TS-9 as the owner wanted more gain from it. I checked  it out first and discovered there is practically no gain at all. This pedal looks like it's rarely been used and certainly never been altered electronically. It's virtually brand new. I went ahead and removed the original chip, installed a socket, and tried another chip but it remained the same; no gain.
When engaged, the tone control and level work fine but the drive does not do what I know it should. I've checked out the drive pot and it's fine. I've also checked all active components on the board and they all seem to be functioning properly. Nothing on the board looks blown, damaged, or non-orignal. When examined under a magnifying glass, all solder joints look sound.
Unless someone has another suggestion, I'm at the point now where I think I need to check and be sure the components were put in they're proper locations on the PCB. I have the TS schematic from R.G.Keen to verify.
Anyone? Please?
Thanks,
B.

Mark Hammer

Re: MIJ TS-9 Drive not functioning
« Reply #1 on: February 01, 2009, 07:35:18 PM »
Well the simplest thing to do is to check that the resistance between the two pins where the Gain pot is connected demonstrate the appropriate variation in resistance.

Note that in the noninverting configuration used for the TS, the resistance to ground from the inverting pin has to be small in order to produce gain.  If, for example, the lead on the .047uf cap had separated from the body of the cap, the ground leg would be open and the gain of that stage would be x1.  Indeed, anything that makes the 4k7/47nf path larger than 4k7 (crack in a resistor or copper trace) will rob the thing of gain.

Sound like a possibility?

BDuguay

Re: MIJ TS-9 Drive not functioning
« Reply #2 on: February 02, 2009, 07:29:22 AM »
Yes, that does sound like a possibility for sure. It would only make sense for something like that because, like I said, everything else seems to check out.
I will investigate that whole section tonight and report my findings.
Thanks Mark, it's that sort of insight I needed and believe me, I'm learning from it too!
B.

BDuguay

Re: MIJ TS-9 Drive not functioning
« Reply #3 on: February 02, 2009, 05:27:32 PM »
Okay, I have a couple of TS-9 schematics and they seem different. This pedal has the 4k7 resistor in question going to 4.5vdc vref, which jives with one of the schematics. The other ones I have show that resistor going to ground.
Now what?
B.

slacker

Re: MIJ TS-9 Drive not functioning
« Reply #4 on: February 02, 2009, 05:40:13 PM »
For practical purposes it doesn't matter whether the resistor goes to ground or vref. I'm pretty sure that it is supposed to go to vref though.

BDuguay

Re: MIJ TS-9 Drive not functioning
« Reply #5 on: February 03, 2009, 07:07:31 AM »
Yeah, I realized after my post that it probably didn't matter. This pedal is really starting to melt my cheese....
B.

BDuguay

Re: MIJ TS-9 Drive not functioning
« Reply #6 on: February 03, 2009, 09:52:25 AM »
Does anyone have other suggestions I can ponder while at work here?
B.

R.G.

Re: MIJ TS-9 Drive not functioning
« Reply #7 on: February 03, 2009, 10:15:49 AM »
There are a few off-the-wall possibilities. I hate to even say these in public, because they are so rare, but the "I've built it, why doesn't it just work?" guys will decide these are their problems instead of the big three (pinout/polarity, soldering and wiring).

It is possible that one of the clipping stage components is shorted. Could be the small ceramic cap, could be one of the diodes.

It is also possible that there is a hair-fine copper thread that is shorting the output. I've seen these too fine to notice without magnification.

Test the components for shorted as Mark suggested. If you get low resistance, test the parts and also test the copper for shorts.
R.G.

Quick IQ Test: If anyone in a governmental position suspected that YOU had top-secret information on YOUR computer, how many minutes would you remain outside a jail cell?

Gus

Re: MIJ TS-9 Drive not functioning
« Reply #8 on: February 03, 2009, 11:55:01 AM »
I see BYOC at the bottom of the first post.  Use a scope an signal gen to trace the signal.

If I was to make a guess for a real TS9 if DC voltages at the chip and circuit were OK and I had a low output measure the .22tant in the low pass.  If that is shorted or going bad it can "drag" the signal to ground.  Easy test lift one end of it or just remove it as a test.

Did the TS9 ever work correctly was it bad out of the box?

Mark Hammer

Re: MIJ TS-9 Drive not functioning
« Reply #9 on: February 03, 2009, 12:15:43 PM »
This is also one of those instances where I think removing flux from the copper side can be useful in troubleshooting.  The glare of light off the flux can sometimes make it difficult to see a fracture.

BDuguay

Re: MIJ TS-9 Drive not functioning
« Reply #10 on: February 03, 2009, 12:44:59 PM »
As suggested by Gus, I'm not sure but I'm begining to wonder if it ever worked properly. And although my sig makes mention of BYOC, I do not have a scope, but I do have a signal probe/tester that, honestly, I'm not sure how to utilize for further troubleshooting in a situation like this.
This pedal was bought second hand at Capsule Muisc in Toronto and returned because of a lack of gain, surprise surprise. My brother in law, who works there, popped it open and, thanks to the world wide innerweb, discovered it had one of those 'less diserable' chips and asked if I would sawp it out. Like i said, I checked the pedal pre chip swap and discovered the gain issue which remained even afterwards. I've cleaned all the flux residue and examined the board with a magnifying glass for solder bridges, trace cracks, and any other suspect goings on. Nuthin.
As R.G. suggested, I've already checked the clipping diodes and they're fine too. If the 51pf ceramic cap were shorted, that would have unvailed itself while checking the diodes right?
For sanity sake, I'll try another chip in it tonight and see what happens.
I sincerely appreciate all of your help and suggestions.
B.

Mark Hammer

Re: MIJ TS-9 Drive not functioning
« Reply #11 on: February 03, 2009, 12:59:30 PM »
The thing with chip substitutions is that sometimes the people pushing them into place push hard.  Those types of stress-based fractures can be a bugger to track down sometimes, because the continuity can be easily re-established when testing/measuring, and lost the moment you aren't pressing meter probes to the board.

My first personal computer in 1982 had a heat-based (don't ask :icon_rolleyes: ) fracture on the motherboard.  Each day when I booted up, I had to expedite the process by warming up the motherboard with a hair dryer.  The small amount of local warming was enough to expand the copper traces and re-establish continuity that permitted the thing to complete its boot-up.  I mention that to bear witness to how twitchy board fractures can be and how ephemeral they can seem.

Just out of curiosity, is there a socket on the board now, and do we know that the chip is establishing continuity with the socket pins?

BDuguay

Re: MIJ TS-9 Drive not functioning
« Reply #12 on: February 03, 2009, 02:28:07 PM »
I put in an 8 pin socket right after I removed the original chip, yes. If need be, I'll bring the board into work here and examine it under my microscope.
I'm going to look into the .22mf tantalum cap that Gus  suggested earlier too.
B.

BDuguay

Re: MIJ TS-9 Drive not functioning
« Reply #13 on: February 05, 2009, 07:34:28 AM »
Okay, as per Gus' suggestion, I checked both tantalum caps and they're okay. As per Mark's suggestion, I examined the socket closely and checked that none of the pins were shorting to one another. All good. I removed both clipping diodes, the 51pf cap, the .047mf cap, and the drive pot from the board and tested them separately and everything checks out. I was hoping that after re-installing all the parts, the problem would've fixed itself. Nope.
Although the drive pot does not add the gain that it should, it does increase the output of the pedal a tiny bit. Beyond that, I'm and both stumped and P.O.'d!
B.

BDuguay

Re: MIJ TS-9 Drive not functioning
« Reply #14 on: February 05, 2009, 08:43:21 PM »
Fixed!
After trying every possibility I could think of and all that were suggested here, I started to remove the caps and check them. When I removed the 47mf cap I noticed the PCB was discoloured where that cap was placed. The cap itself did not look like it was burned out. I changed that one and the 100mf cap and it works fine now.
I'm not sure if these 2 caps are bad and I won't find out untill I have a chance to test them at work but for now, it seems okay.
B.