Laney bass amp blows output transistors!

[spy]

So, they're not "house" numbered transistors!

Any equivalents?

Otherwise, I'll leave the originals. They don't seem faulty.

[Jazz P Bass]

I do not see anything that will "directly" replace those drivers.
What I cannot figure is why they picked that one.
That B/C 240 volts makes no sense.
Makes it seem like they wanted a bulletproof driver.
Do they test o/k?
TIP 102/107 pair should work.(sans B/C 240V)
MJE13030/31 pair as well.

[J M Fahey]

Use very common MJE15030/31 http://www.datasheetcatalog.org/data...rtgucl9jwy.pdf
Of course, first pull the originals and measure them outside.
Anyway, when you ask for your output transistors, also order a couple of these.
Worst case, you already have them for your next repair.
Watch pinout and polarity , just in case.
They *should* match as is, but Murphy's Law lurks everywhere.

[spy]

I measured the drivers, outside, and they're fine!

Around 530mV at B-C and B-E at both of them (with the correct polarity on each) and infinite backwards. C-E is infinite at both ways. Keep them?

[J M Fahey]

Yes, they are fine and you can keep them.
Anyway, if you have not ordered the output ones yet, add a couple drivers, just to have them in your parts box; they are pretty much universal drivers, good to have around.
If too late, fine, do it the next time you order something.
Good luck and remember to always start through a series lamp, until you are 100% sure about everything else.

[Enzo]

The MJE types would be perfect.

TIP102/107 are Darlingtons, and would not be appropriate subs here.

[bajaman]

use genuine ON semiconductors MJ15003 and 004 types (not generic fakes), AND replace the bias transistor Motorola MPSA42.
Avoid generic KPS42 etc types.

[spy]

ok folks! I'll let you know about the results! (fingers crossed)

[spy]

By the way, ON is Motorola? I found some locally at 3.5euro/each. Are these expensive?

[Steve Conner]

Yes, ON is what used to be Motorola's linear and discrete semiconductor division. Watch out for fakes if buying these transistors from Ebay etc.

[spy]

Cool!

Is it possible to have the label ON on them and be fakes?

[Steve Conner]

Maybe. Best bet is to buy from a larger distributor.

[Stewen]

Laney DB300H bassamp

Hallo ! I have the same problem . One pair of the outputtransistors out . And C3 exploded when I the first time replaced the 5A fuse , FS1 . C3 is 10uF/100V . IŽll choose a higher voltage. But the drivertransistors seems OK , but further back on the board the PNP TS 13 , surfacemounted on the backside had also given up . TS 10 (BC847B) is OK . IŽll follow your advice to change several transistors ...... You , who started this tread ....... Have you managed to repair your amp today ????
Thanks for an answer . Regards Stewen
A friendly guy at Laney sent me the schematics ......

[spy]

Hi and welcome to the forum!
I haven't fixed it yet. I didn't have all the parts but now I have them! So maybe I'll continue with it today.

Weird that we have the same pairs fried. C3 exploded in mine too. What's the problem with this amp. The first time I replaced the fried pair and after a few gigs fried again. Now I'm planning to replace all of them plus some parts at the output section. Hope now it'll be fine.

[spy]

Ok, now I have a serious problem!

I replaced all MJs with genuine ON, all the .22 transistors, both C3 & C19 plus some other parts that I have spare like D3-D7, C9-C13, R20-R21, etc. I didn't replace the drivers as they measure ok.

I have the amp plugged on a Variac and I'm giving the primary voltage slowly so I can check it safely. After a few volts the amp shows dc at the output! I tried to check everything and I found a broken smd resistor, R15. I replaced it with another one. Everything else measure just fine. But I have the same dc at the output! I measure a negative dc voltage at the output that it follows the mains voltage.