Troubleshooting a Pearl phono, anyone up for it? - diyAudio
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Old 29th January 2010, 06:10 PM   #1
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Default Troubleshooting a Pearl phono, anyone up for it?

A little background first --

I got the boards and Q pack from Pass DIY eight or nine years ago and I finally got around to building the Pearl in 2006. It's been an excellent phono stage and I love listening wo my old vinyl through it. I use a little Creek 4330 integrated amp with a MM phono stage and the difference between the Creek board and the Pearl is pretty stunning really.

A few months ago I was getting crackling in one channel. I didn't use the Pearl much after that but recently I decided to see if I could fix it.

So I fired it up and wasn't getting anything from the channel that had been crackling. I started checking voltages and when I got to Q4 it looked like it had overheated and fried. That looked like the problem and would certainly explain the crackle so I ordered some new ZTX450s from DigiKey.

I replaced the original Q4, powered it up and started checking voltages again. The voltages were off (significantly) around Q4 and there was still no sound from the channel.

After reading quite a few threads here it seems like the problem may be the 2SK389 but I don't really know how to be sure. Anyone want to help direct me through the troubleshooting process to narrow it down?

Also, if it is the 2SK389 that looks like it's a problem since that part isn't in production any longer. If that's the problem what are my options for fixing the Pearl?

Thanks in advance for any help you all can lend, it's appreciated.
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Old 29th January 2010, 06:54 PM   #2
moe29 is offline moe29  United States
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Just build the new Pearl coming out soon

it's said the boards will be the same size, you you can just drop them
in to the chassis that you already have been using. viola! better Pearl.


(maybe check to make sure you don't have a problem with the power supply,
something caused a problem to take out that part.)

(double check all solder points - crackling equals cold joints?)
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Old 29th January 2010, 07:07 PM   #3
uli is offline uli  Austria
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theres a group by goin on by spencer from HK. He sells matched quads of 2SK170BL which fit perfectly. Just swap BOTH 2SK389 to 2 pcs 2SK170 each!

cheers Uli

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Old 29th January 2010, 08:00 PM   #4
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I don't know much about this, so forgive me but is that all there is to it? Just drop a pair of 2SK170BL in where the 2SK389 was? Seems like there are seven leads from the 389.

Quote:
Originally Posted by uli View Post
theres a group by goin on by spencer from HK. He sells matched quads of 2SK170BL which fit perfectly. Just swap BOTH 2SK389 to 2 pcs 2SK170 each!

cheers Uli

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Old 29th January 2010, 08:01 PM   #5
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Seriously considering the Pearl 2 and I probably will do that. But I hate to leave the original one if it can be fixed easily, it's been a really nice piece of gear.

Quote:
Originally Posted by moe29 View Post
Just build the new Pearl coming out soon

it's said the boards will be the same size, you you can just drop them
in to the chassis that you already have been using. viola! better Pearl.


(maybe check to make sure you don't have a problem with the power supply,
something caused a problem to take out that part.)

(double check all solder points - crackling equals cold joints?)
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Old 29th January 2010, 08:20 PM   #6
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The LSK389 is a direct replacement for the 2sk389. There are also a couple of vendors who sell these parts at a premium. I think I found some of the 2sk at $15 each. After that I jumped in on the LSK389 group buy and picked up some spares.

The only way I could figure out how to troubleshoot my pearl (with this same problem) was to replace the 389. And then it started making magic again.
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Old 29th January 2010, 09:40 PM   #7
mlloyd1 is offline mlloyd1  United States
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your options are a matched pair of 2SK170 singles (or the physically smaller replacement) or this from linear systems: http://www.linearsystems.com/datasheets/LSK389.pdf

mlloyd1

Quote:
Originally Posted by WindChill View Post
... Also, if it is the 2SK389 that looks like it's a problem since that part isn't in production any longer. If that's the problem what are my options for fixing the Pearl?...
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Old 29th January 2010, 10:29 PM   #8
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I'm beginning to see how this works now. I think I see how the pins on the 2SK170s would line up from the 2SK389 datasheet and I'm willing to replace those parts anyway.

Does the grade need to be the same as the 2SK389?
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Old 30th January 2010, 02:10 PM   #9
mach.88 is offline mach.88  Germany
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Hey Windchill,

the 2SK389 is nothing but a pair of matched 2SK170. The seventh pin on the 389 is a so called substrate pin and not at all needed.

If the problem is the 389, consider the exchange an implement 2 2SK170 instead. Most propably the matched 2SK170 will even turn out to be closer in IDSS as the two parts of the 2SK389 were.

But now I remember a friend once telling me about problems with the Pearl. I donīt know if this is the case here but he told me about issues related to the 2SK389 being solved by simply using individual source resistors (R25 (value of 10R) for each half of the diff amp).

So you might want to check the 2SK389 first for integrity. In case you have to change it, there is a guy from Sweden I believe. He is here in the forum as well and he had a bunch of 2SK389 a while ago. Otherwise, take 2 matched 2SK170...

Cheers

Chris
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Old 31st January 2010, 01:21 PM   #10
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Thanks everyone. I decided to just replace the 2SK389s in both boards and ordered the 2SK170s from Spencer here on the forums. Once I get those in we'll take another look and see how it is.

Chris, how would I check the integrity of the 2SK389?

Thanks again guys, I learned a lot and I appreciate your time and help.
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