Laney dp100 bass amp disaster

[nosaj]

Was given a laney dp100 bass amp yesterday. It had tin foil on all the fuses which I removed and put in proper fuses. R28 and r29 would get really hot to the touch. So I pulled the output transistors TS8 and TS10 and tested them they test good. left them out for now. Pulled TS3(tip31c) tested good. But R10 and R13 are burnt to a crisp . With these transistors pulled I am not getting heat. And realize I'm aimlessly wandering. And would like some assistance. Off the Bridge rectifier I'm getting 45.6 and -45.6v . I've contacted Laney for official schematic for power and pre, but have found this schem of the power section which doesn't list voltages. amplifiers head combo drawings/LANEY/DP100-DP150[pict] - schemes drawings schematics | GuitarElectric.eu
Thanks, nosaj

[Jazz P Bass]

Was given a laney dp100 bass amp yesterday. It had tin foil on all the fuses which I removed and put in proper fuses.

Give it back!

[nosaj]

I can't it was given to me.

[drewl]

Does the amp work?

Without looking at the schematic (what language is that?)

If the output drivers are okay, it's possible the burnt resistors are from the out put section drawing too much current.
Possibly from an incorrect speaker load or the output transistors being biased too hot.

Are they power supply dropping resistors?
Output transistor emitter resistors?

[g1]

I can't even read the numbers on that schem, and there's no "magnifier" tool.

[MarkusBass]

Without looking at the schematic (what language is that?)

I'm affraid it's Polish . The website is not of the best quality. But with few clicks you can can get this picture:
http://www.tremolo.pl//Firmowe/LANEY/DP100-DP150.jpg
Preamp is here: http://www.tremolo.pl//Firmowe/LANEY/DP-BassPreamp2.pdf

Mark

[DrGonz78]

I can't even read the numbers on that schem, and there's no "magnifier" tool.

Just right click that schematic and save image file as. Then you can look at it correctly. That site does the whole preview function horribly, but has good high contrast files. Personally I do not like these types of sites that embed pdf or image files into the page in a preview fashion. It slows my computer down way too much. The file that MarkusBass included is a better way to do it...

[nosaj]

Here is a link from my google drive
https://drive.google.com/file/d/0B6x...ew?usp=sharing


No the amp is not currently working.
Thanks, nosaj

Attached is a notated schematic pic of what's burnt and tested so far.

[J M Fahey]

Sorry but I don't trust your health report.
What are the measurements which tell you TS3/7/8/9/10 are fine?

Not being shorted CE is not enough, sorry.

Each of them needs to pass 6 diode tests:
on diode scale:
* with black probe on base, Vcb and Vce
* same with red probe on base
* base open, Vce with black on emitter
* base open, Vce with red on emitter

The only way that R17/18 are burnt, is that a lot of current went through them, which shouldn't.

For tht to happen, either BE junctions in parallel are open (so they must pass all current required by load) , or BC junctions leadin g to them or driver transistors in series are shorted.
Either way, 46V across a 100 ohms resistor is a mini nuke detonating nearby for them.

Possible culprits may be:
* TS8/10 open BE
* TS8/10 shorted BC
^^^ notice these failures can happen and yet CE not be shorted
* shorted TS7/9

to which we might add:
* open R21 (R22 is not in position to do that)

TS3 might be fine, protected by R13 , which would be toasted otherwise.

The amp itself is a classic and quite repairable, although it might be one of those where Laney needlessly used SMT parts.

[nosaj]

Sorry but I don't trust your health report.
What are the measurements which tell you TS3/7/8/9/10 are fine?

Not being shorted CE is not enough, sorry.

Each of them needs to pass 6 diode tests:
on diode scale:
* with black probe on base, Vcb and Vce
* same with red probe on base
* base open, Vce with black on emitter
* base open, Vce with red on emitter

The only way that R17/18 are burnt, is that a lot of current went through them, which shouldn't.

For tht to happen, either BE junctions in parallel are open (so they must pass all current required by load) , or BC junctions leadin g to them or driver transistors in series are shorted.
Either way, 46V across a 100 ohms resistor is a mini nuke detonating nearby for them.

Possible culprits may be:
* TS8/10 open BE
* TS8/10 shorted BC
^^^ notice these failures can happen and yet CE not be shorted
* shorted TS7/9

to which we might add:
* open R21 (R22 is not in position to do that)

TS3 might be fine, protected by R13 , which would be toasted otherwise.

The amp itself is a classic and quite repairable, although it might be one of those where Laney needlessly used SMT parts.

I will do the recommended diode tests on the the transistors and note measurements tomorrow. Not a single SMT in here at all. Touch base tomorrow with results. Thanks,
Jason

[g1]

Agree with JM that if those resistors are fried, some of those transistors should also be bad.
However, it sounds like this unit was given to you of unknown origin. So perhaps it is in a state of partial repair? Maybe someone replaced some of the transistors already but didn't finish the repair?

[nosaj]

Agree with JM that if those resistors are fried, some of those transistors should also be bad.
However, it sounds like this unit was given to you of unknown origin. So perhaps it is in a state of partial repair? Maybe someone replaced some of the transistors already but didn't finish the repair?

Well after reading fahey description I may have caused those resistors to fry. Here is what i did. I pulled the output transistors and the 2 tip31c to test. When i founf them good I wanted to check voltages. My thinking was like when you pull output tubes but I guess this is different than tubes. I restested the transistors per Faheys notes and will post shortly.

Thanks a bunch,
nosaj

Here's the measurements i took. I'm ready to solder them backin and replace the burnt resistors. And move to the next step whatever that should be.

2n3442
Black lead Vcb Vce nothing
Red Lead Vcb 616 Vce 621
base open, Vce with black on emitter nothing
base open, Vce with red on emitter nothing

2n3442
Black lead Vcb Vce nothing
Red Lead Vcb 615 Vce 619
base open, Vce with black on emitter nothing
base open, Vce with red on emitter nothing

tip31c

Black lead Vcb Vce nothing
Red lead Vcb 661 Vce 674
base open, Vce with black on emitter nothing
base open, Vce with red on emitter nothing

tip31c

Black lead Vcb Vce nothing
Red lead Vcb 671 Vce 683
base open, Vce with black on emitter nothing
base open, Vce with red on emitter nothing

[g1]

Ok, there is a bit of a problem here, I think it started as a typo:

Each of them needs to pass 6 diode tests:
on diode scale:
* with black probe on base, Vcb and Vce
* same with red probe on base
* base open, Vce with black on emitter
* base open, Vce with red on emitter

Where he said "black probe on base, Vcb and Vce" (same with red probe on base), I think it should be Vcb and Vbe.

But looking at your results, it appears you may have been measuring from base to each of the other legs anyway.
Of note is that BtoE will almost always measure a bit higher than BtoC.
Just to be 100% sure, can you verify that your higher numbers where BtoE (not CtoE).

[g1]

Also, you mentioned 2 Tip31C's, there should be different parts for upper and lower, one NPN, one PNP, shown as Tip31 & Tip32 on schem.

[nosaj]

I did not pull the tip32 for fear of pulling too many parts to measure out of circuit and putting one back wrong.. There are 3 tip31c I believe.

"black probe on base, Vcb and Vce" (same with red probe on base), I think it should be Vcb and Vbe.

This means clip black lead on C(Base TO-3) then with red prob measure B then measure E? I'm trying to clarify cause this is how I understood it.

On a side note I've soldered and replaced the resistors. Powered up with preamp disconnected. Dim bulb lights up then quickly dims. On full power nothing is getting warm and ammeter barely showing a current pulled.

On the header pins +v1 +v2 correct voltage there -v1 -v2 correct voltage there.

On clarification of the above I'll pull those results.

Thanks a bunch,
nosaj