Phase Linear 700 series 2 questions

OZ of da trap

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#1
Hi, I was given a Phase Linear power amp 700 series 2 from a cousin who passed away. I found the unit has issues. I may just sell it since I have other amps if the cost of repair tends to be high.
Heres the scoop:
The amp has been put away since 2004. Preliminary checked the amp and found the following. With no preamp connected or speaker loads, the L speaker fuses were blown. I found the left power switch as you face the front of the amp turns on the left meter/red indicator light on. But the right power switch when pushed in blows the amp speaker fuses to the left channel. As I view the rear of the unit tb inputs and outputs are labeled right and left. The left speaker fuses are the ones connected to that front right panel power switch. That power switch movement is not as crisp and firm as the other power switch to the left of it. I removed the left blown fuses and placed new AGX 5a fuses in the left speaker fuse holder and they blew.
So looking at the movement of the power switch that controls the left speaker fuse it does not move as crisp in and out when pushed as the other switch. Mounted onto the switch are two small resistors that leads up to the meter board. Will check them for value and if they are open. Would the switch be the obvious here and remove and replace the switch.

I did not want to go any further now before I download a manual etc.

Question. I thought about leaving the left channel speaker blown fuse out and turn the right power switch on and see if the right channel sensitivity control works on the sensitivity meter. Can this amp right channel be played and connected to a load / fused 8 ohm speaker to see if the channel actually works or is the the left channel associated with it that may cause further problems.

This 700 two has the following info sticker on the inside chassis side panel behind the fuse tb:

700 series Two 1100
Part 300-0053-0
7096
quant 150
unit 71

Facing front panel:
front panel has two vu meters l&R of center.
In center of front panel area two push button power switches.
Control /knob below each vu meter
Transformer to left side
8 heat sink fins at rear, column of resistors at rear between fins
on transformer - Phase Linear , Model 700, Serial 7A10886

Thanks in advance ...replies are appreciated
OZ
 

AngrySailor

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---not quite right
#2
Those aren’t speaker fuses. They are rail fuses. You have shorted outputs by the sounds of things. I’m no expert but pull all the outputs except the bottom drivers and plug it in through a dim bulb... The experts will be along, probably stuffing themselves with ham and turkey!

btw Welcome aboard.
 

OZ of da trap

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#3
Thanks for the "input" of the outputs. Yeah but they are associated with that side of the channels. I'ii keep a lookout for the ham and turkey experts. Sure they will shed some "light" on the PL700 network. I will look see for the wiring schematic/diagrams for the 700....
 

laatsch55

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#4
There are 2push buttons on the front of a Ser II. The left is power, the right is a meter sensitivity switch. There are 5 fuse holders on back. The one on the bottom is the mains (in) fuse. The 4 in a box arrangement are the plus/minus DC tail fuses for each channel.
If you are blowing rail fuses on power up, you have a direct short, usually an output transistor.
 

laatsch55

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#5
If the switch arrangement I described doesnt jive with what you are seeing, post a pic of the front panel.
 

OZ of da trap

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#6
There are 2push buttons on the front of a Ser II. The left is power, the right is a meter sensitivity switch. There are 5 fuse holders on back. The one on the bottom is the mains (in) fuse. The 4 in a box arrangement are the plus/minus DC tail fuses for each channel.
If you are blowing rail fuses on power up, you have a direct short, usually an output transistor.
Thanks. Ok The main fuse of course is not blown. Only 2 of the rail fuses are blown. These 2 are directly located below the left channel speaker binding knobs. These 2 would then be the negative side of the rails correct. So the front switch on the left of the front cover is power on/off while the right switch is meter sensitivity. So go looking for and test resistors on that side of rail?
 

OZ of da trap

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#7
If the switch arrangement I described doesnt jive with what you are seeing, post a pic of the front panel.
Yes it is as you described. So being the unit powers up but the rails have or may have shorts some where do not install a pre amp and of course speakers.
 

laatsch55

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#9
We're not testing anything yet. Do you have a multimeter? Or any other test equipment?
 

laatsch55

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#11
Hookay, download the 700 service manual from hi fi engine and study the troubleshooting section. Then we can talk some more..
 

OZ of da trap

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#12
We're not testing anything yet. Do you have a multimeter? Or any other test equipment?
I looked briefly at the 4 out put boards inside the unit that are mounted at inside back panel ....each board / rails has 5 resistors that are 2 orange bands followed by 2 silver bands 33 ohm? The second board from the fuse / speaker tb has on of these resistor that is cracked. Not measuring anything just over viewing the inside of the unit....no power connected .
 

laatsch55

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#14
Those are emitter resistors. .33 ohm. If they are blown that is also an indication of an old blown output!!
 

laatsch55

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#16
No, the transistors bolted to the outside of the heatsinks. If an output is blown, often q7, q10on the driver board are also blown.
 

mlucitt

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#18
Sounds to me like this particular PL700 Series II would benefit from the White Oak Audio upgrade process. You have two options:
1. Sell the amplifier as is, for parts. Whomever buys it can do a complete rebuild and bring it back to life.
2. Rebuild the amplifier yourself, with help from the rebuild technicians on this forum.

If you decide on #2, you will need to purchase the following parts from https://www.whiteoakaudio.com/estore.aspx
PL700 Capacitor Assembly - Pair
PL14_20 RevG1 Dual Mono Control Board Kit w/Phoenix Connector Option
PL700 Backplane Kit
PL400-700 Backplane Wire Kit
Output Transistors (12) ON Semi MJ21195G
Output Transistors (12) ON Semi MJ21196G
SIL400 Bergquist SIL-PADs (24)

Good luck whichever way you decide to go.
 

MarkWComer

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#19
Sounds to me like this particular PL700 Series II would benefit from the White Oak Audio upgrade process. You have two options:
1. Sell the amplifier as is, for parts. Whomever buys it can do a complete rebuild and bring it back to life.
2. Rebuild the amplifier yourself, with help from the rebuild technicians on this forum.

If you decide on #2, you will need to purchase the following parts from https://www.whiteoakaudio.com/estore.aspx
PL700 Capacitor Assembly - Pair
PL14_20 RevG1 Dual Mono Control Board Kit w/Phoenix Connector Option
PL700 Backplane Kit
PL400-700 Backplane Wire Kit
Output Transistors (12) ON Semi MJ21195G
Output Transistors (12) ON Semi MJ21196G
SIL400 Bergquist SIL-PADs (24)

Good luck whichever way you decide to go.
Well worth the money...
 

wattsabundant

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#20
The series II amps are about the easiest amp to troubleshoot because they are so simple. The service manual tells you how to test all of the outputs in circuit. No need to pull them. Then you test all of the transistors and diodes on the board. Keep in mind the manual was written when all we had were analog meters such as the Simpson 260. Today everybody uses a digital meter. Regardless, a shorted transistor junction or shorted diode reads zero ohms.

For some reason , R101, 7.5K/2W likes to fail. They never show signs of heat stress. They drift then open.

There is no question doing all of the W/O mods is the long term solution. However it's nice to know the amp was working before starting the rebuild.
 
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