Dunlop TS-1 - short circuit?

[Swampy]

Hey everyone,

I'm relatively new to the inner workings of effect pedals and need some help on a Dunlop TS-1 tremelo that I am debugging currently.

Firstly, if anyone has/knows about the location of a schematic for her that would be much help. I've tried drawing one up from the PCB myself but there are a few NAND chips in this thing which kinda make the whole process a little unwieldy.

This pedal was mistakenly given a dose of 12v ac when it was accidentally used with an incorrect adapter. Now there is no output in either bypassed or effect state, the LED indicator for the bypass/effect switch is not working BUT the mono/stereo LED is.
I've measured 0v across the power terminals of it with a known working 9vdc adapter connected, which must mean there is a short to ground somewhere huh?

Anyway, until I get some more food for thought I'm gonna put this thing aside and get some sunlight into me.
Thanks in advance for any help.
Matt

[MikeH]

Must be nice to have sunlight available to you!

First off, welcome! 

As far as the pedal goes- could be a couple things.  First check for the power protection diode.  If the power supply was also the wrong polarity this diode can fry and cause a short to ground.  Secondly check voltage ratings on the caps.  If there's a lot of surface mount components in there (and I suspect there are) it will be difficult or impossible to do this.  But you should be able to see the rating on any electrolytics in there.  Also I'm not sure what the voltage rating/reverse voltage tolerance is for the NAND chips in that thing.  They could toast.

[Swampy]

I'm drowning in it over here (Melbourne). Fresh off the boat from NZ, first time I've been exposed to a week of 40 degree+ days in my life!

Choice, thanks for your suggestions Mike. Fortunately there are no sm components on this board so I've had a bit more of a poke around and made the following analysis.

I've checked all the diodes on the board, no continuity through any of them - apologies for my ignorance but is the sure fire way to test whether they have have been fried?

Electrolytics are rated 16v and a couple @ 25v.

I've tried searching for the reverse voltage rating on the NAND chips (MC14011s) but can't find the specifications on the datasheet I have. max DC supply voltage is 18.0 V however.

Also, here is what I am 99% sure is a correct schematic of the part of the circuit the problem is possibly (am I too confident to say probably?) in - transcribed from the PCB.
Sketchy.
I've not seen a transistor used in this configuration before...I presume it's some sort of current limiting/stabilizing device? Something doesn't seem right to me about this though...



Swede,
Matt

[Mike Burgundy]

That schem doesn't make sense to me unfortunately. There are schemes in which transistors are used for polarity protection, Clean Vref, but this looks like none I know. If the values are 0.1u, the cap values is strange in that application as well, aren't they?
Are there markings on the transistor? Could it be a 7809 regulator?

If it *is* hooked up like this or close, the most likely culprits are tranny and diodes.

[Swampy]

Sorry, that was terribly rushed and as a result error ridden and utterly heinous to the eye.



Ok, here's a better idea of what's going on. Also, here's some anomolies I've noticed made from messing about - I'm sure all you seasoned folk can spot the problem straight away.

a) Once I give the circuit power (12v) the node between the diode and zener diode has continuity to ground.
b) The same goes for the emitter of the transistor. FYI the transistor markings are ZTX109 - it's a general purpose NPN.
c) Again, once the circuit has power there is no continuity between the transistor collector and the diode.

It'd be good to get some suggestions before I go swapping out any of these parts. Also, have I got my diode polarities around the correct way?

[Mike Burgundy]

That does look like polarity protection. When it's hooked up correctly, the base gets voltage through the 1k5 and turns the transistor on, so voltage applied on collector appears on emitter.
The cap locations (values, too) and the diode don't make too much sense to me, hopefully somebody else will shed some light.
The voltages are measured in-circuit?
If so, they make no sense at all - battery voltage 0V, but the base still sits at 9.5V? That can't be right. At all, even with faulty components. Must be a measuring mistake, or the schem still isn't right, or something.
Continuity testing with power applied - keep in mind continuity testing is done by applying a small voltage by the meter. If a voltage is present *in circuit*(such as when you're applying power) you're fooling the meter but not testing anything, at least not reliably.

Even without certainty about the schem, it's a good bet to take out the transistor and test it, or just replace it. I'd say the c is hooked up to +, e to Vs.
Same goes for the diodes if they test wrong. Use the diode test on your DMM for that - a lot of them nowadays measure resistance/continuity with a voltage so low it doesn't turn on semiconductors.

[Swampy]

Sweet.

Thanks for the advice (to all parties that is). I replaced the transistor and one of the diodes and am happy to report she is back in the game.

Stoked.
Matt