My trimpot won't trim....

[Buzz]

Still going through my unfinished project box....

Another fuzz face.

When I made my first Ge Fuzz I breadboarded it before stuffing the board. I had three fuzz face tranny sets and tested them on the same breadboard layout, all good.

I populated two boards and two charge pumps, boxed one up with a pump and left the other in the to do box.

I boxed the second one up today and oh poops it doesn't work.

The bypass worked fine.

The indicator LED does not function.

When the effect was on, no noise unless at full volume and full fuzz. Then I get a very quiet spluttery fuzz when I hit a string.

So first things first, I went to the bias trimpot. The collector at Q2 remains at -8.9v no matter where the trimpot is moved to.

I removed the trimpot and found no error with the trimpot.

So the things I have tested so far are as follows:

The charge pump is functioning normally. ~+9v in, roughly -9v out. Tested against all available ground points. all good.



I'm getting -8.99v at A.

Here's where some funny business starts, between B and C, with the trimpot removed, I'm getting a resistance of around 40k. Shouldn't that be an open line?

Is this an indication of transistor failure?

I know the standard gig is to provide a photo, but it's sticking halfway of of the box and I can't get a good one.

[Buzz]

This is my power setup for the charge pump. It's worked so far in a tonebender and a FF.


And a link to the schematic...http://www.generalguitargadgets.com/pdf/ggg_ff5_sc_pnp.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

[duck_arse]

try reversing yr probes across B and C, see if yr 40k changes. and did you point your led the correct way, seeing as you ground voltage has been "reversed"?

[Buzz]

Yeah, I may have reversed the LED, haven't checked but not a big issue atm.

I tried reversing the probes and did get different results With the black ( com ) probe on Point B i get 37.6k

With the red probe on point B I get 42.7k.

Did it a few times, same result.

But it doesn't give the full reading straight away, takes a few seconds to creep up to the reading before steadying out on the final number, starting out on just a couple of ohms to the 42.7k, starts out at about 16k the other way 'round.

[Uriziel]

try measuring resistance on your transistors... i'm not sure but the measurement you're getting sounds a lot like R2, R5, what ever is dialed on your trimmer and what is left of the transistor resistance in series. I'm worried about Q2 and that C and B are shorted. you can find out by measuring resistance between B and C leads and then reverse your probes. Because there is a diode inside you will get a very low resistance one way and a very high resistance the other way, because a diode conducts only in one direction... if your transistor is blown you will get very low resistance both ways meaning the signal will go freely through no matter what and that part of the transistor is reduced to a simple jumper with maybe some small resistance.

also try measuring B and E the same way on Q2... and just in case measure Q1 too. If your multimeter has a diode measurement function, use that. Probes one way you will get a forward voltage of the germanium diode inside... it should be around 0.7 V, probes the other way should read infinity. If you get reading that is much less than 0.7 V and a reading both ways, the diode inside is fried... sometimes it is easier to use continuity mode and not concentrate on readings too much... the multimeter will beep if it finds a short. but diodes sometimes can short to a state that still has enough resistance that the continuity mode on the multimeter will not recognize as a short, because in reality continuity mode is just measuring resistance and if the resistance is low enough, usually lower than 5-10 Ohm it will beep.

Also the fact that you wont get the reading right away means that there is a capacitance somewhere that starts charging when you measure, but nothing seems to be between the path you use to measure.

Also check really hard if you maybe left some pins unconnected or connected to the wrong place etc, verify you build and the double and triple check.

Hope it helps.

[Uriziel]

also you need to take the transistors out to measure them, i forgot to mention that

[Buzz]

Thanks Uriziel.

Unfortunately the transistors are soldered in.

They are AC125s ( if memory serves me correctly ) and are in those really tall tins ( TO-1? ). So in a 1590BB there's not much room, so I soldered them to save the extra height added by a socket.

I'm pretty quick on the iron and use little gator clips as heat sinks so it's usually not a problem, but maybe I cooked one this time.

I think my next move will be to take the board back out of the box, and test it minus DC input jack and charge pump. Like I should have before I put it in the box.

If I still can't get function then, I'll desolder the trannies and test them.

And lesson learned.... sockets.

I did see a good thread on here about making sockets by drilling out the holes in the board to fit IC pins. Nice and low profile too. Going to have to make that a habit, especially with Ge trannies.


Edit: And yes to Duckarse. I did have the negative lead of the LED connected to ground. Knew I had to reverse it but somehow habit must have taken over

[PRR]

> collector at Q2 remains at -8.9v no matter where the trimpot

No-connection at Q2 Emitter is a strong bet.

Voltages throughout (not just hilights) might be clue-ful.

[Buzz]

Hi Paul.

I'll pop the trimpot back in and come back with a full set of voltages for both trannies.

Avoiding the soldering iron tonight though.... my latest homebrew ale has turned out to be a particularly tasty batch.

[deadastronaut]

my latest homebrew ale has turned out to be a particularly tasty batch.

yay, another real ale brewer...that first taste of a new batch  ..nice, enjoy....

[Buzz]

my latest homebrew ale has turned out to be a particularly tasty batch.

yay, another real ale brewer...that first taste of a new batch  ..nice, enjoy....

Greetings brew brother! Real Ale is a beautiful thing!

[Buzz]

Some more voltages....

Battery 8.86v

Board in -8.84v.

Q1   

E: 0v
B -105mV
C -356mV

Q2

E -367mV
B -358mV
C -8.75v.

?

[PRR]

?

Indeed. Multiple wrongnesses and I'm not seeing a clear pattern.

40K leakage on Q2(?) is not for-sure wrong in Ge, but I'd start chewing there. Get another Q2. It can even be Silicon, but must be PNP. (If that works better, Q2 will force Q1 to adapt to the higher Vbe of Silicon Q2.)

But the large drop in the 100K makes me wonder if Q1 also has a problem. (Sadly we can't drop-in a Silicon at Q1 without multiple other changes.)

As always: get it out in the open, bright light, sharp eyes (or magnifier). Shorts, opens, bad joints.

How sure are you of your pinouts?

Can you get the previous build open and compare voltages and parts?

[Buzz]

Thanks Paul.

To simplify I'm going to pull the board out of the box, disconnect the DC in, charge pump and stompswitch. I'll just run it off a reversed 9v battery.

To hard to get a good eye on the back of the board while it's in the box.

I've just ordered some IC socket strips so I'll wait for them to arrive to proceed, then follow your advice.

By then I'll be looking at it with fresh eyes. That's always an advantage too.

[duck_arse]

homebrew you say, buzz? and in australia, you say? and a problem w/ a trimpot, I think you mentioned. I'm certainly now interested, if of no use ....

and sharpening, you mentioned?

[Buzz]

Mr Duck!

I see you are in Sydney too.

I've ( come close to ) perfecting a beautiful British Real Ale, All easy to find ingredients, super easy recipe. So yep.... homebrew.

Sharpening? you can shave with my kitchen knives. I was great with chisels too... until my 3yo combined my whetstone and my fretsaw, he was *fixing* it.

It is certainly fixed now. Can't be angry, the little bugger wanted to help, and wanted to be like dad. Awwww...

But hey, chuck us a PM. We can meet up in an appropriate boozer and share our common interests.

At least you know my eyes won't glaze over when you discuss the comparative tonal differences between using 1N34a Ge vs 1N4148 Si diodes as clipper pairs... lol.

[duck_arse]

I'm busting to talk chisel sharpening with someone. I've just found how much damage I can do to a piece of wood with a chisel, especially if I've just managed to put a good sharp on it. trouble is, I seem to take the sharp off as much when I try to sharpen, and this just adze to my problems.

do you only beer, or do you cider as well?

diode clippers? mmmmm, well.

[Kipper4]

Have fun boys.

[Buzz]

OK, it's not the trannies.

I desoldered them and gave them the diode test as Uriziel suggested, and they worked.

Then I realised I hadn't marked them before taking them out. Derp.

So I hooked them up on the breadboard with RG's transistor tester. 

The first came out at 82 hFE with 172ua leakage. The second with 109 hFE and 260ua.

( Note to self.... I marked the 82 hFE! it's Q1! )

Well, double tested and shown to be working.

I've just started etching my own boards and have a nice FF board ready to go.

I think I'll build it in that and do a post mortem on the other board. I'm interested in where I stuffed up. I bet it's something real stupid....

[chromesphere]

Hey Buzz,
I wonder if increasing that collector trimmer would help you bring down that 8.9v?  40k "should" be fine but maybe it needs more?  Or test it with another, 20-40k resistor in series wit it, save ordering / waiting for a new one.
Paul