Problem with Pearl. Please Help

[Lucas_G]

Hi guys,

I am afraid I need a little help.

I have finished my Pearl phonoamp a few days ago.

The left channel is working, the right does not (very low sound, hardly any level).

I checked the voltages:

Q2 & Q12 = both channels 8.5 Volt
Q3 = both channels 24 Volt

Q4: Left = 13.3 Volt Right = 1.0 Volt
Q5: Left = 12.5 Volt Right = 10.6 Volt
Q6: Left = 13.3 Volt Right = 1.0 Volt

Q8-Q11: Left = 12,5 Volt Right = 10.6 Volt

I checked the ground connections, but sofar I could not find any faults...

Can anyone offer some advice where to look now?

Much appreciated. The one working channel sounds very good!

Regards,

Lucas

 

[Lucas_G]

I include this here.

 

[Lucas_G]

Here are the measured voltages. Problems are situated around Q6.

Any advice is highly appreciated!

 

[Lucas_G]

I just measured the impedance on various resistors (mounted), in order to find descrepancies between the workin left-channel and the broken right channel.

I found one major difference: the resistance over R24 (100k) is indeed 100k on the working channel, but it is only 40k on the broken channel. Is this another sign that the 2SK389 (Q6) is rotten?

 

[Lucas_G]

I immediately add another question:

Where can I order a new 2SK389
?

 

[vinylkid58]

I immediately add another question:

Where can I order a new 2SK389
?

Digikey has them. Sorry to hear you're having trouble.
Love my Pearl BTW.

Jeff

 

[Lucas_G]

Digikey has them. Sorry to hear you're having trouble.
Love my Pearl BTW.

Jeff

Digikey will be a bit probelmatic for me, I guess. Shipment to Europe and minimal order...

Yes, the one working channel does sound promising....

 

[promitheus]

It looks like it is shorted.
I have contacted you per Email about the 2SK389 BL.

 

[RoboMan]

I don't have a Pearl, but according to the voltages of Q6, it seems that Q6 is not biased properly and caused it to conduct. The gate voltage should be 0 and source should be 0.05V so that the gate is negative to the source.

I think either C11 or C12 may be leaking and supplies a positive voltage to the gate of Q6. Try disconnect both C11 and C12 from Q6. If the voltage of Q6 becomes normal, then find out which cap is bad.

If voltage of Q6 are the same after disconnecting both caps, then may be Q6 is bad. I have bought a few 2SK389 from a shop in Toronto a few months ago. I think they may be able to ship small quantity. Let me know if you find that your Q6 is bad.

 

[Lucas_G]

I don't have a Pearl, but according to the voltages of Q6, it seems that Q6 is not biased properly and caused it to conduct. The gate voltage should be 0 and source should be 0.05V so that the gate is negative to the source.

I think either C11 or C12 may be leaking and supplies a positive voltage to the gate of Q6. Try disconnect both C11 and C12 from Q6. If the voltage of Q6 becomes normal, then find out which cap is bad.

If voltage of Q6 are the same after disconnecting both caps, then may be Q6 is bad. I have bought a few 2SK389 from a shop in Toronto a few months ago. I think they may be able to ship small quantity. Let me know if you find that your Q6 is bad.

Hi Roboman,

Thanks for your help. A clever thought concerning C11 and C12.

I have just desoldered them but the poblem remains, so I guess we can be pretty sure now that Q6 is rotten...

Thanks too for the address to order 2SK389 from.

Fortunately Promitheus has also offered to send me these from Germany, which will be faster and cheaper (customs...).

Thank you both! I will report back here when I have a new 2SK389 fitted, and when it works, I will also post some pictures here.

Regards,

Lucas

 

[Cobra2]

2SK389 fakes???

It must be the weather?
It just happened to me...again. First fet died a couple of months ago, for no reason...
OK, maybe just one bad, I thought.
But now, this one, on the other board.
They both were 2SK389, BL, code: 4c

Arne K

 

[Lucas_G]

Re: 2SK389 fakes???

It must be the weather?
It just happened to me...again. First fet died a couple of months ago, for no reason...
OK, maybe just one bad, I thought.
But now, this one, on the other board.
They both were 2SK389, BL, code: 4c

Arne K

Yes, it is a bit suspect indeed!
I always take care with antistatics and also with the heat when soldering... For me, this is a first time

Regards,

Lucas

 

[icewall]

Just one simpe question, where did you get the PBC:s? passdiy.com are sold out and I'm wondering if someone out there has a couple of extra boards for sale???

 

[steenoe]

where did you get the PBC:s?

Promitheus that tuned in on this thread, had some made a while back as far as I can recall. Try and ask him if there is a pair left
That Pearl sounds really nice indeed.

Steen

 

[icewall]

Thanks! I'll send him an email as soon as I'm no longer under moderation
Beginner you know....

 

[steenoe]

Beginner you know....

Okay, I will ping-pong you, untill you can send emails Your turn, by the way

Steen

 

[icewall]

Thanks, everything has to be hard in the beginning

 

[icewall]

By the way, sorry for "kidnapping" tihs tread

 

[Cobra2]

and now did the third 2SK389 decide to retire...
Of a different lot/date.
I have triple-checked all voltages, they are within 0,5V of Mr. Pass specs. All other parts are matched, exept zeners & electrolytic caps...

Any hint of what is killing them?
My stock of 2SK389 is running low...

Arne K

 

[d to the g]

Thanks! I'll send him an email as soon as I'm no longer under moderation
Beginner you know....

i'd like to do the same thing, for the same reason.