PL700B Damage due to multiple fast on/off cycles - Where to start ?

MusicJunky

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Jul 22, 2019
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#1
I have been using a Phase Linear 700B for about 10 years (most every day) for the rear channels of my audio setup.
The front channels were powered by a pair of 400's the center was powered by my receiver.

Somehow I managed to get over-zealous and accidentally hit the power toggle on the Isobar that controlled the 700B.
I don't know did it, but I know I hit the power on and off and again on (I must have been having a bad day and If I wasn't, I sure was now !!!). . .

The 700B made a small thump and the fuses blew, 5AGX. Short story long, I could not find any 5A fuses that would fit, so I put the 700B away.
Now that I have more time and a little cash at times, I would like to recover my 700B. I have replaced the fuses, but they blow the moment you power-up.
I know the outputs did not fail as I only blew the speaker fuses. I have had outputs fail and take speaker fuses and usually at least the tweeters. The speakers were fine after replacing the fuses.

I have a schematic for the 700B, but I is very poor, and can't really read the numbers. I believe I may have blown the drivers that drive the outputs (RCA-410's)
I have some knowledge of and was originally interested in becoming an electronic technician, but had an opportunity to get into machining and making precision parts. I went with the latter, as the pay was much better and was offered an apprenticeship.

I recently discovered WOPL and figured I could maybe order the 4 driver transistors and if that does not solve the issue, I would invest in replacing the PCB with a new assembled one with the Phoenix connector. I will be able to check each output to be sure they are not shorted (I have some basic equipment). Maybe part of the circuit died as designed, to save damage to the outputs ?? Could the problem be on the circuit board?

If all goes well, I will then replace the power capacitors with the updated set from WOPL. Just need a little help/advice. I even have the purchased service manuals from Phase Linear. I just haven't found them as we recently moved. I bought them way back in the day (just in case). If I get on a lucky streak, I will upgrade the 400's power capacitors as they are from the 70's..
I would like to pass this stuff onto my sons when the time comes, and it would be nice if I left them with some equipment that still works.. This will be a hobby project as time and funds permit (I am now retired with limited income). I can't afford to have a service person do the work.

Any thoughts or helpful advice appreciated.
Thank You in advance - MusicJunky
 
Last edited:

mlucitt

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#2
You are in the right place. One on the contributors on this board, Joe, is a gifted engineer that understands the Phase Linear amplifiers very well. Others on the board have years of experience rebuilding, restoring, and upgrading the PL 700B.

Likely, you will be asked to conduct a few basic tests on the amplifier with a multimeter to diagnose the issue. It happens. We like to get the amplifier to working condition before upgrading, if possible. Good luck.

Oh, and some pictures, description, S/N, and how you obtained your amp will spark greater interest. There are folks here that will want to know your speaker arrangement and maybe even a picture of your listening room.

Mark
 

Northwinds

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#3
I am sure you 700B will be a relatively easy fix once problem is diagnosed. Welcome to Phoenix
 

MarkWComer

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#4
Look for blown emitter resistors- this can lead you to faulty transistors. You'll have to open the case, pull out the control board, and have a look at the big brown resistors on the back. If they're blown up, the associated transistor is likely to blame.
 

MarkWComer

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#5
I have four RCA 410s pulled from my 700. If you can’t find new ones and are willing to take the chance on my used ones let me know.
 

Gepetto

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#6
I have been using a Phase Linear 700B for about 10 years (most every day) for the rear channels of my audio setup.
The front channels were powered by a pair of 400's the center was powered by my receiver.

Somehow I managed to get over-zealous and accidentally hit the power toggle on the Isobar that controlled the 700B.
I don't know did it, but I know I hit the power on and off and again on (I must have been having a bad day and If I wasn't, I sure was now !!!). . .

The 700B made a small thump and the fuses blew, 5AGX. Short story long, I could not find any 5A fuses that would fit, so I put the 700B away.
Now that I have more time and a little cash at times, I would like to recover my 700B. I have replaced the fuses, but they blow the moment you power-up.
I know the outputs did not fail as I only blew the speaker fuses. I have had outputs fail and take speaker fuses and usually at least the tweeters. The speakers were fine after replacing the fuses.

I have a schematic for the 700B, but I is very poor, and can't really read the numbers. I believe I may have blown the drivers that drive the outputs (RCA-410's)
I have some knowledge of and was originally interested in becoming an electronic technician, but had an opportunity to get into machining and making precision parts. I went with the latter, as the pay was much better and was offered an apprenticeship.

I recently discovered WOPL and figured I could maybe order the 4 driver transistors and if that does not solve the issue, I would invest in replacing the PCB with a new assembled one with the Phoenix connector. I will be able to check each output to be sure they are not shorted (I have some basic equipment). Maybe part of the circuit died as designed, to save damage to the outputs ?? Could the problem be on the circuit board?

If all goes well, I will then replace the power capacitors with the updated set from WOPL. Just need a little help/advice. I even have the purchased service manuals from Phase Linear. I just haven't found them as we recently moved. I bought them way back in the day (just in case). If I get on a lucky streak, I will upgrade the 400's power capacitors as they are from the 70's..
I would like to pass this stuff onto my sons when the time comes, and it would be nice if I left them with some equipment that still works.. This will be a hobby project as time and funds permit (I am now retired with limited income). I can't afford to have a service person do the work.

Any thoughts or helpful advice appreciated.
Thank You in advance - MusicJunky
I would start with checking each one of the outputs on the back wall. 95% of PL problems are on the back wall. Rail fuse blowing like you describe is usually associated with blown upper and lower output transistors.
 

oldphaser

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#7
I would start with checking each one of the outputs on the back wall. 95% of PL problems are on the back wall. Rail fuse blowing like you describe is usually associated with blown upper and lower output transistors.
I would agree with Joe. Most failures of Phase Linear amplifiers include blown output transistors.

Ed
 

orange

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#8
That and I would still make sure that power switch isn't shorted or in dire need of cleaning. As I recall from many old stereo receivers there was often a large ceramic resistor or flat circular capacitor on the line and while an open cap wouldn't let it turn on at all I believe, a resistor might intermittently fail after a certain threshold was reached or then just fail to resist, and when, of course, resistance is futile...failure is not an option.
 

MusicJunky

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Jul 22, 2019
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#9
Hello and Thank You all for your replies.
I am new to this type of forum, so don't get angry if I screw up posting.
Looks like I have to reply to everyone with one general message only. I tried to reply to each message via the [Post Reply] button
but for some reason it quotes my original message rather than quoting the user I am replying to . . . So here goes !:)!

Thank You to all that replied,

mlucitt - I just recently moved into a larger house, so I have a lot of things that require attention, plus painting, yard rework, and general
stuff you miss when going on the walk thru. Thankful we hired an Inspector.. Well worth the $$$. Now with all the work I have to do, I hope I
can find some quiet time and a place where I can attempt to work on the 700B. Funny how things can get lost. We are still living out
of boxes. . . haven't been able to find the PL Service Manuals and I lost track of a bunch of AGX5 fuses. I had a major problem locating a replacement, as a regular 5A will not fit (if I remember correctly, the 5AGX fuses are shorter in length). Heck I might even have to buy a new
soldering iron etc. if they don't show up soon. Talk about being organized huh!

When the 700B went bad, I purchased a Crown class D to replace it. I eventually removed the two PL400's from the front channels and replaced
with a pair of Crowns. At least they now all match and run much cooler and don't require as much space. I did prefer the old school meters and
fat-chunky looks of Phase Linear vs the slim new Crowns. But I gained some room and the new ones run much cooler. That's a big plus in Arizona.

So as time permits, I will attempt to figure out what became defective. I will respond to any replies or questions (as soon as I can) and take it slowly.

MarkWComer - Will follow your suggestion when time permits. I am retired now but still don't seem to have any more time.
Everything now takes longer to finish. Hopefully when it cools down I will have more time & energy.
Thank you for the offer, not sure on what I will need yet. I live about 50 miles outside of the Phoenix metro area and haven't
found a place to purchase electronic parts locally. I will probably purchase online. But if you are willing to sell the RCA410's reasonably and would be willing to ship them to me, I could have the spouse get a money order made and send to you. Can never have too many spare parts, right? LoL No hurry tho !!

Gepetto - I will take all the ideas offered and follow-up as time permits.. I hope it's not outputs as they are mostly expensive.

oldphaser - I will check the outputs on the rear case & will take all the ideas offered and follow-up as time permits.. BTW I like your user name.

orange - I was not using the built-in power switch when I damaged the unit. I was using an IsoBar power conditioner/surge protector.
It has a rocker switch which makes it very easy and quick to flip-on and flip-off. Too quick !! (for sure). I have assigned it to a different task.
I would not have thought of the capacitor being shorted. Thanks for the idea tho.


Thanks to all again. I somehow feel better that I have some experts available for consultation...
Maybe this can still be a good year!
MusicJunky
 

MarkWComer

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#10
¿Get angry if you screw up posting?

It’s a competitive sport here to find out how far a post can be hijacked!

It’s all in fun, and it’s all good-spirited mutual support here.
 

FredR

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---
#11
And the hijacks are extreme. More than any other board out there. By far. Particularly by a group of common perpetrators. :)


"It’s a competitive sport here to find out how far a post can be hijacked!"
 

MusicJunky

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Jul 22, 2019
Messages
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#14
Hello,
Thanks for the link. I purchased 100 fuses (AGX5) from Allied Electronics about 2-3 years ago. As I mentioned we just moved and we are still living out of boxes and haven't had a chance to mess around with the 700B. The wife says that can wait. She wants the paint on the walls first, plus we have to rework our rear yard irrigation system. Sometime soon I hope to find all my electronic parts and schematics and make a permanent work area where I can safely leave the amplifier opened and on a work bench. I still appreciate any input or ideas tho.
Thanks again,
MusicJunky
 

MusicJunky

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Joined
Jul 22, 2019
Messages
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#15
PM your mailing address to me. I have 20 MJ21196G (used) from the same amp if you want them, too.

Free...
Hello again,
I will send you my email and address, but I don't know how to send a private message.
If you could give me a hint, I don't spend much time in forums, and this one seems advanced. LoL
Nothing like looking stoopid in front of the world !! I can always delete this message after you reply!

Thanks,
MusicJunky
 

oldphaser

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Messages
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#16
If in the long run you need some drivers......

I might suggest you getting some RCA66546's instead of RCA410's from some forum member who has some spares.

It has been my experience that the RCA66546's are a little better than the RCA410's.

Ed
 

VSAT88

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#17
No damn way you can screw up too much here. Believe me I have tried. Welcome ! One more thing. I am also willing to send you spare parts that I have without charge. These guys ponied up big time on my projects so its about time I helped out too. Click on the image all the way to the left (In my case the picture of the jackass) and in the drop down box click "start conversation". That should allow you to send a private message. Someone correct me if I am wrong...Oh, that wont be a problem :whdat:...
 
Last edited:

MusicJunky

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Joined
Jul 22, 2019
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#18
00 fuses (AGX5) from Allied Electronics about 2-3 years ago. As I mentioned we just moved and we are still living out of boxes and haven't had a chance to mess around with the 700B. The wife says that can wait. She wants the p
If in the long run you need some drivers......

I might suggest you getting some RCA66546's instead of RCA410's from some forum member who has some spares.

It has been my experience that the RCA66546's are a little better than the RCA410's.

Ed
Hello,
If in the long run you need some drivers......

I might suggest you getting some RCA66546's instead of RCA410's from some forum member who has some spares.

It has been my experience that the RCA66546's are a little better than the RCA410's.

Ed
Hello, and Thanks for the reply.
I will eventually purchase parts and build a collection of spares for both the PL700B plus the I have a pair of 400's..
If I can get the 700B up and running I will slowly update it with WOPL control board and power capacitors. And the 400's
were purchased new back in the 70's when they just hit the market. They are working and packed away after I blew the 700B,
and replaced all with Crown amplifiers. They all need to have their components updated especially capacitors.

If anyone cares to send me parts, I don't expect them for free. I don't want to be a mooch, I have never been and don't want to start now.
I am willing to send a money order via mail if anyone has some extra parts that they have too many of, lying around. (LoL)
I am no way near being an electronic technician, but had some basic classes and have been messing around with components for some time,
at times I have been lucky and there have been a tine or two that I have smoked a few components. (Oops..)
I really feel blessed that many here are willing to help out and answer questions. I only wish I have waited till I was ready and had the 700B opened and ready to work on it. I figured I would get some clues as to where to start and build a list of what to check, and what to replace.

So I am Thanking you (and all who reply in advance).
MusicJunky
 

MusicJunky

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Joined
Jul 22, 2019
Messages
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#19
No damn way you can screw up too much here. Believe me I have tried. Welcome ! One more thing. I am also willing to send you spare parts that I have without charge. These guys ponied up big time on my projects so its about time I helped out too. Click on the image all the way to the left (In my case the picture of the jackass) and in the drop down box click "start conversation". That should allow you to send a private message. Someone correct me if I am wrong...Oh, that wont be a problem :whdat:...
Hello, Thanks for the reply...
As I mentioned on a couple of my messages, I appreciate the offer of spare parts. I do not have any at the moment except for some spare 5AGX fuses. MarkWComer offered to send some parts, which I am thankful for. I am, not wanting anything for free. I am willing to send a money order via mail. As of now I don't know what will need to be replaced. I assume the drivers that drive the outputs, and with my luck probably all the outputs. I am not sure.
Eventually I will order parts, like spare outputs and I will need to replace all the capacitors in both the 700B and the pair of 400's that
are packed away in their cartons. If I get the 700B up and running, I will be more encouraged to work on the 400's too. I hope to update the control boards and replace all the component parts in all of the amps and the replace the jumbo power capacitors too. Gets pretty expensive when you are talking about 3 amplifiers, but that is my goal.. After that, I will have some experience and might be able to offer up some help to someone on this forum too !!!
BTW, I did manage to send a private reply - at least I think I did.

Thanks again,
MusicJunky

 

MusicJunky

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Joined
Jul 22, 2019
Messages
13
#20
PM your mailing address to me. I have 20 MJ21196G (used) from the same amp if you want them, too.

Free...
Hello again!
I sent you a private message, I believe it worked at it did not show up in the regular forum.
Please let me know that you did receive it. I saw the [Start Conversation] button in the drop-down as you hover over the users name/icon
but I figured it would post a new message to the regular Forum for everyone to see. They should change that to [Send Private Message]
as it would be less confusing.

Thanks again,
MusicJunky
 
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