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Phase Linear 3500 with a missing channel.

ClemualB

ClemualB

Member
I've got a really nice clean 3500 preamp that is only putting out 1 channel. I brought it to my friend who is a solid state repair guy and he has isolated the problem to the headphone jack. Stereo goes in but only one channel comes out.

He has tried everything he can think of and no luck. Does anyone out there have a wiring diagram or service manual for this preamp? Or have you seen this problem and solved it? Your help is greatly appreciated.
 
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Good thing I looked at this thread. I also own the 3500 preamp and I am still using it on a daily basis.

When I got mine back in 1997, I contacted a guy named (can't remember first name) Nissen who worked for Phase Linear and he told me that a lot of solder joints in those things don't seem to hold up over time.

Unlike your 3500, mine had no sound output from both channels.

He recommended that I reflow and resolder every solder connection in my 3500. It only took me about an hour and that brought it back to life.

Since everything works on mine, I cannot tell you if you have a bad part but more often than not, a good cleaning of the pots and switches plus a solder touch up will cure a lot of channel dropouts and brings things back to life.

Your friend should probably know these things also.
 
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Thanks. He is well versed in Phase Linear's poor soldering. This one doesn't seem to be caused by that though.
 
Hit post too soon.

Cademan, how did you contact Mr. Nissin? Is he a member? He sounds like the man to talk to about my problem.
 
I have some contact info in a box somewhere out in my pole barn but I think it is kinda buried. I'll see if I can dig around and find it.

:yes: Now I remember the guys name: Dean Nissen. Not sure if he's a member here but a quick search will tell you. I am going to do a search also.

Have you cleaned the switches and pots?
 
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First thing I did was clean everything. Then I applied pressure to all the solder points on the boards to see if anything was loose. Got rid of all the static in the knobs and switches but still only one channel. So I gave it to my friend/repairman to look at. He played with it for awhile and has tracked the output in stereo into the headphone jack and then only one channel coming out from the headphone jack. Can't find anything wrong or anything to fix in there. Thus my post.
 
This unit has its own built in headphone amplifier so if a stereo signal is getting all the way to the headphone jack and then you are only hearing one channel with the headphones, then I have to assume the headphone jack is bad or a solder joint in association with it.

I know this might sound sound dumb, and it has happened before, but make sure the mono/stereo switch isn't pushed in. :D

Recently, I had a channel drop and had to pull it apart and do some troubleshooting. It has 4 op amp chips which are identical so I started swapping them around and my channel came back then went out again. I discovered I had a dirty IC socket so tell your tech friend so he can check that also.

I just repaired it about five months ago and as you can see where it sits, I don't want to pull it again anytime soon!
 

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Thanks all. My friend is checking it out again following your suggestions. I will update the results and post a picture when it is done and working!
 
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