TS Problem

[mnordbye]

I have a problem with my recently "finished" 808 tubescreamer built from the GGG PCB and project files.. When the effects is on, there is light in the LED, but no guitar sound. It's a buzz sound which sounds like a earth short, but i'm not sure if it is. I have checked for shorts, but maybe not good enough?

Anyway, heres the voltages, which also look crazy to me.. Measured with a new battery by the way.
IC1:
1: 4,60
2: 4,75
3: 4,40
4: 0
5: 4,40
6: 4,40
7: 4,40
8: 9,20

Q1:
E: 8,20
B: 8,20
C: 8,90

Q2:
E: 8,10
B: 8,10
C: 8,80

Anyone who can make me happy? 

Magnus N

[GibsonGM]

Hi Magnus...

Your IC voltages look fine, within normal ranges.  The transistor voltages are OFF, man! ;o)
Q1 and Q2 should have around  3.5v on E and B, and battery voltage at collectors.
This makes me think the transistors could be shorted together (check your soldering for bridges!), or they are not installed in the right direction - so check your pinout.  Another reason for the voltages being so high...check that Vr is actually about 3.5v!  Could be an error there...check at the junction of the 10k resistors/47uF cap for proper reference voltage.  You might be putting full batt. voltage to the Q's bases....

Next:
There's a chance they got fried....soldering on them too long can do that (I grab mine with small needlenose pliers above the board, solder below, to make a heat sink).  If they were in backwards too long they could also have fried, happens once in a while.

A test for a short circuit...hook up the battery and measure voltage across it.  If there's a short, it should warm up and voltage will be dropping fairly rapidly! 

This should get you started...

~Mike )

[mnordbye]

Tried to change transistors (which sits in sockets by the way), no change. When i changed the transistors around the other way, i got that "noise" sound one get from overdrive pedals, but still no guitar. I forgot to mention i didn't have the noise sound at all in the first post, sorry about that. 

The voltages whit the transistors the other way:
Q1:
E: 0,20
B: 2, something
C: 9, something

Q2 is about the same.

By the way, when i measured the voltage near the 10k resistors and the 47µF cap, i got 4,2V.. Is this too high? Yo mentioned 3,5V

Magnus N

[QSQCaito]

Could you tell exactly which transistors are you using?
Because in GGG PCB the pinout is for 2SC1815, if you use C1815 you would actually need to swap E and B legs.


Bye bye

[mnordbye]

Could you tell exactly which transistors are you using?
Because in GGG PCB the pinout is for 2SC1815, if you use C1815 you would actually need to swap E and B legs.

Well well, would you know. The 2SC1815 transistors i got from Banzai are actually marked C1815 on themselves! I'm gona try this the first thing in the morning. Well, actually i just sold my practice amp, so i'm stuck with waiting for the moment of truth. Talk about bad timing.

But thanks QSQ! You might be my savior.

Magnus N

[GibsonGM]

The 4.2v is correct, at the Vref point.  My #'s are smaller because my battery was lower ;o)   So, why is your base sitting at 8.~ volts after going thru that resistor there??  Either you connected the collector of the transistors to 9V, or there is a solder bridge somewhere....

Those new readings are really off!!  If your soldering and wiring is ok.... Resistor values maybe? Double check the resistors on the transistors, be sure they are REALLY the right values (read the bands)...you should read something like 3.2, 3.5, 9.0 at E, B, C of your Q's.    Double check the pinout for your transistors, too (look up a data sheet and check EBC). But that is probably not what's giving these voltages.

Caito is right - what transistors are you using?

You can't even audio probe unless the transistors are doing something, which they don't seem to be.   Also check any electrolytic caps, make sure they are oriented with "-" to ground or lowest potential, but again that likely wouldn't cause those high voltages.  And triple check your soldering again, ok? ;o)  Any shorts around those transistors will cause the symptoms you report...usually it's the simple thing, and even tho I've checked 10 times, I've had the same thing happen - solder bridges!!

[mnordbye]

Okay, i think i found the problem, and yes, it was the pinout who i believe was wrong.
I first tried to switch E and B legs, but that was completely wrong. All voltages was between 8 and 9V.
Then, i searched for the pinout on the C1815, found a toshiba datasheet or something, and it actually suggested to switch not E and B, but B and C legs. I think the voltages are okay now, aren't able to listen to it an actually try it now, but can someone confirm that these newest voltages should work?

Q1:
E: 3,00
B: 1,80
C: 8,80

Q2:
E: 3,00
B: 1,95
C: 8,80

Magnus N

[GibsonGM]

The base voltages look low to me...remember, they are tied to Vref, so should have about 3.xx to 4.xx volts on them along with your input signal for biasing.  When you try to play through it, it will probably go "Splatttt".   

The E and C voltages look fine, so there's probably another error between the bases and Vref...should be easy to find, though!  Check the value of the biasing resistors (the 510K at base of Q1 & Q2, and all other Vr connections).  Should be around 1/2 battery value. 

[mnordbye]

I see.. the base is low..
I checked those 510K resistors, they're okay, and the right value. Since it's the only problem now, the Base voltage, i guess it ould be something wrong with the power supply then?
What should i check? Except more solder bridges and stuff.. 

Magnus N

[GibsonGM]

Of course, bridges would be suspect.....check your voltages at the power supply...9v at one end, ground (0V) at the other.  Check the 47uF cap for correct orientation....1/2 supply at Vref....same 1/2 supply at one end of the 510K resistor, and the trouble is somewhere around there, I think...

[yeeshkul]

I have completely the same trouble . I thought i fried my trannies while soldering, but no, they are ok. Voltages on IO are perfect. Vr is 4.75 (a new batters 9.7V). The voltages on my trannies are same as those mentioned above - all around 9V. Oh well. I was testing the trannies (in sockets now) in my tester and they seem to have normal pinout EBC, NPN.