Phase Linear 700B Series II -Right channel out- - diyAudio
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Old 19th March 2007, 03:31 AM   #1
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Default Phase Linear 700B Series II -Right channel out-

$U?"4igned up and do not have electronic repair skills. I thought by searching and reviewing some posts I might be able to figure out what's wrong with my amp. What I found is just way over my head.

Here is what I have and what is wrong:
Phase Linear Model 700B Series II-
The right side channel gets very low sound, but does produce some and goes up and down when I turn the sensitivity knob. The sound is extremely low (light bar never moves). The left side seams to work ok except that while turning up the sensitivity knob the sound cracks and goes in and out. Playing with it I can get great sound out of the left side.

I don't think I have the skills to fix this on my own and was hoping it is worth fixing.

I live just outside of Philadelphia, Pa maybe someone here lives close by that knows how to fix this or knows a good shop that won't rape me for repairs.

Thanks for any help.
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Old 19th March 2007, 08:02 AM   #2
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Before you take heavy measures, you will want to look at your interconnects and the input sockets of the amp. The latter are prone to fail, at least in the units I serviced. Next, tighten all output transistor screws mildly and check if your speaker cables are well attached.

/Hugo
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Old 19th March 2007, 04:16 PM   #3
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Default the mighty leviathan!

First check the B+ fuses (rail fuses) that are on the back rear top of the amp... If one or more is blown, that indicates a blown fuse, and possibly a blown output transistor(s).

If you replace the fuse - take the fuse from the other channel's fuse holder. It needs to be the proper TYPE (physical size) which is slightly off the beaten track for fuses and rating (amperage).

So, once you have replaced the fried fuse and turn it on, and it turns the good fuse into vapor, you know the outputs are blown - at least in part.

PM me if you want to unload the beast.

The repair is on the order of $200 from a tech who is being nice - since it takes time and the power transistors need to be tested and replaced as a "unit" per rail, per channel. So if ONE was bad, unless you had the matching OLD devices, you'd have to swap in an entire row of new devices on that side (preferably on both sides...)

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Old 20th March 2007, 02:48 AM   #4
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Guys, thanks for quick responses. I checked the fuses they are not blown. I will check the input sockets next. I've tried switching the cables and I get the same issue.
I'm pretty good with an ohm meter, but I don't have a good schematic or testing instructions to go much further.

Again thanks for your input.
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Old 20th March 2007, 02:48 AM   #5
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Netlist, you are the man. I played with the input connections and the channel came up. What great feeling hearing this thing again. There are still two things I wish I could get fixed.

1. The right channel light bar does not move at all. Just stays all the way to the letf.

2. The sensitivity knobs crack while being adjusted.

Thanks again!
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Old 20th March 2007, 08:19 AM   #6
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Don't forget to tighten the big transistors on the back of the amp. There are 24 of them. Make sure you unplug the mains and leave the amp for at least half an hour before proceeding.
As for the schematic, it's here

You could use a tiny bit of contact cleaner on the sensitivity knobs - inside the amp of course - and see if the light bar comes up when playing with the meter range switch. If it does a bit of cleaner might fix that as well.

/Hugo
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Old 20th March 2007, 05:51 PM   #7
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Hugo, I'll try that tonight. Do you think I should replace the input sockets? If so where could I find a replacement?

Thanks
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Old 20th March 2007, 06:00 PM   #8
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I like the Neutrik gear a lot and something like this is cheap and widely available. Of course any other good quality socket will do.
Together with these plugs I make nice interconnects.
Note that I'm not affiliated with Neutrik in any way.

/Hugo
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Old 21st March 2007, 12:52 AM   #9
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I used a little contact cleaner on the sensitivity knobs and meter switch. Wow what a difference that made. Absolutely clean sound while turning the knobs. Very sweet! Thanks Hugo you have probably saved me a few hundred bucks here if just dropped this off at a local shop.

Although the right side meter still doesn't get any movement, would you have any suggestions?

Paul
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Old 21st March 2007, 05:15 AM   #10
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C6 goes open with age and the amp will work, but have no gain.

http://www.diyaudio.com/forums/attac...amp=1162602599

C11 on this schema:

http://members.aol.com/phasetek2/pl36.jpg
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