Hello,
I'm French, so please escuse my bad english.
I've got a phase linear 700B that have been rebuild by a pro t( done by the old owner ).
After a bad manipulation with the "normal/direct coupled" switch, one side has broken down.
two trans are in short circuit.
I've test all the power transistors and the drivers.
The preamp board seems to be good ( good trans, and other components ).
First i've replaced the two broken transistors.
I've try the amp without charge ( speakers ).
the fuses have not burned.
Then i've tryed the amp with the speakers.
First nothing.
unplugged preamp and repluged: then just one side OK.
two transistors have burned
Many questions:
Have you an idea, why the transistors burn?
Is there a problem with the bias? ( why now? )
i've got 8 other trans and i would like to find a solution to repair this amp.
Do you have a technique?
Can i plug just two transistors ( with the drivers ), to limit the problem possibility?
Many many thanks for your help
I'm French, so please escuse my bad english.
I've got a phase linear 700B that have been rebuild by a pro t( done by the old owner ).
After a bad manipulation with the "normal/direct coupled" switch, one side has broken down.
two trans are in short circuit.
I've test all the power transistors and the drivers.
The preamp board seems to be good ( good trans, and other components ).
First i've replaced the two broken transistors.
I've try the amp without charge ( speakers ).
the fuses have not burned.
Then i've tryed the amp with the speakers.
First nothing.
unplugged preamp and repluged: then just one side OK.
two transistors have burned
Many questions:
Have you an idea, why the transistors burn?
Is there a problem with the bias? ( why now? )
i've got 8 other trans and i would like to find a solution to repair this amp.
Do you have a technique?
Can i plug just two transistors ( with the drivers ), to limit the problem possibility?
Many many thanks for your help
So which transistors are failing?
http://hometown.aol.com/phasetek2/pl20.jpg
If you only replaced two of the 30 year old transistors (out of ten per channel) you were asking for problems.
http://hometown.aol.com/phasetek2/pl20.jpg
If you only replaced two of the 30 year old transistors (out of ten per channel) you were asking for problems.
Hello,
Thank you for your help.
The last owner have sell me the amplifier after having done a bad manipulation (with the direct-normal switch ).
This manipulation has damaged the amp.
but before this, he has give this amplifier to a pro who has rebuild the amp with new transistors. ( MJ 15024 motorola ).
In order to repair this amp, i've buyed 10 transistors ( MJ15024 from ON semi ex motorola ).
It's the reason of my questions in the first post.
DO YOU THINK THAT IF I REPLACED ALL THE TRANSISTORS THERE ARE MORE CHANCE THE AMP WILL BE OK?
IS THERE PROBABILITY THE PREAMP BOARD OR THE BIAS COULD BE RESPONSABLE?
Many many thanks
PS:
The many questions in the first post are more for me to understand the amplifier principes...
One more time excuse me for my "bad english" and thanks you for your help.
In trying to repair this amp, it's because i love this vintage model and more because i love learn how to do.
Thank you for your help.
The last owner have sell me the amplifier after having done a bad manipulation (with the direct-normal switch ).
This manipulation has damaged the amp.
but before this, he has give this amplifier to a pro who has rebuild the amp with new transistors. ( MJ 15024 motorola ).
In order to repair this amp, i've buyed 10 transistors ( MJ15024 from ON semi ex motorola ).
It's the reason of my questions in the first post.
DO YOU THINK THAT IF I REPLACED ALL THE TRANSISTORS THERE ARE MORE CHANCE THE AMP WILL BE OK?
IS THERE PROBABILITY THE PREAMP BOARD OR THE BIAS COULD BE RESPONSABLE?
Many many thanks
PS:
The many questions in the first post are more for me to understand the amplifier principes...
One more time excuse me for my "bad english" and thanks you for your help.
In trying to repair this amp, it's because i love this vintage model and more because i love learn how to do.
I posted the schematic.
I asked which transistors failed.
I still need to know.
Did the previous rebuild replace all the outputs?
What about the drivers?
Are the protection transistors still germanium (won't protect with silicon)?
Do you have the proper AGX series fuses (I see a lot of AGC fuses forced into the fuseholders)?
I asked which transistors failed.
I still need to know.
Did the previous rebuild replace all the outputs?
What about the drivers?
Are the protection transistors still germanium (won't protect with silicon)?
Do you have the proper AGX series fuses (I see a lot of AGC fuses forced into the fuseholders)?
Hello,
Many thanks djk
I've already had the schematics
Yes the previous rebuild replace all the outputs
i think the drivers to but i'm not sure ( now, they are model 15020 motorola )
I don't know if the protection transistors are still germanium ( do you want a photo of the preamp board ? )
The fuses are 6*32mm 4A 250V quick blow glass fuses
Do you think that if i replace all the outputs transistors with the new ones and the
( just two of the new have been used when i first tryed to repair it ) it will be OK.
Perhaps i have to do something with the bias ( maxi resistor? )
many thanks
Many thanks djk
I've already had the schematics
Yes the previous rebuild replace all the outputs
i think the drivers to but i'm not sure ( now, they are model 15020 motorola )
I don't know if the protection transistors are still germanium ( do you want a photo of the preamp board ? )
The fuses are 6*32mm 4A 250V quick blow glass fuses
Do you think that if i replace all the outputs transistors with the new ones and the
( just two of the new have been used when i first tryed to repair it ) it will be OK.
Perhaps i have to do something with the bias ( maxi resistor? )
many thanks
I also had the problem that you describe but on the original model 700. I had replaced all output transistors in a rebuild/refurb operation (used OnSemi 21196, but did not replace the drivers) and at some point after I replaced them (amp worked fine for a period) I blew a couple of output transistors. Now when I replaced the bad transistors the amp continues to attempt to fry the outputs (I put a lightbulb in series with the power in to prevent frying). Anyhow, my assumption was that the problem was on the main board somwhere, and I began to get out of my league in electronic problem solving, so I sent it out for repair. I have not received it back so I cannot tell you what the source problem is, but our problems do indeed sound about the same. I would be interested to know what the source of your amp problem is - when the tech finishes mine I will report to you what the root cause was for mine.
I learned the hard way many years ago that replacing the drivers and bias transistor needed to be done along with the outputs as a common practice. This is the minimum step that I take. To go thru an amplifier and relpace ALL the transistors/semiconductors is the way to go. In addition one should take a hard look at the caps and resistors.
Typical shop repair thinking is to replace only what is bad and hope that the amplifier will make it thru the 30 day warranty.
Typical shop repair thinking is to replace only what is bad and hope that the amplifier will make it thru the 30 day warranty.
phased smoke
yeah IMHO burnedfingers is right replace all semis in this amp
back in the 80s I repaired a PL 700 for the rock band Foghat.
their drummer thought it was cool to do some banging on one of his microphones with his sticks , which flammed the 700b and then set the woofer in the klipsch lascala stage monitor on fire!
needless to say it was a basket case.
yeah IMHO burnedfingers is right replace all semis in this amp
back in the 80s I repaired a PL 700 for the rock band Foghat.
their drummer thought it was cool to do some banging on one of his microphones with his sticks , which flammed the 700b and then set the woofer in the klipsch lascala stage monitor on fire!
needless to say it was a basket case.
burnedfingers said:
In my PL amp, I replaced all the resistors in the output as well as the semiconductors.
The R' were cracked through stress.
Andy
"The fuses are 6*32mm 4A 250V quick blow glass fuses"
Wrong type of fuse, too slow.
The AGX-5A is the correct fuse, 6mmX25mm.
Hard to say what is wrong at this point.
PNP outputs from ON Semiconductor are like peas in a pod, but the NPNs are all over the place, consider matching them.
burnedfingers has a good idea with replacing the bias transistor.
I would also replace C19 at the output. Use as high of a voltage cap as will fit.
Wrong type of fuse, too slow.
The AGX-5A is the correct fuse, 6mmX25mm.
Hard to say what is wrong at this point.
PNP outputs from ON Semiconductor are like peas in a pod, but the NPNs are all over the place, consider matching them.
burnedfingers has a good idea with replacing the bias transistor.
I would also replace C19 at the output. Use as high of a voltage cap as will fit.
At this point in time I would be willing to guess that some steps were skipped when the Phase Linear had its outputs replaced.
Its time to bite the bullet and do it the correct way now. Start from the input of the amplifier and replace ALL, yes all semiconductors because everything has been stressed several times. Yes, it will cost a few dollars but the result will be a working functional amplifier.
When you have completed this and the amplifier has the correct fuses then and only then will you think about turning the amplifier on. At this point you need a variac or a light bulb as a safety factor. Plug the amplifier into the variac and slowly start turning the voltage up while monitoring the current draw. If you cannot borrow a variac then put a light bulb in series with the power cord.
NEVER NEVER NEVER just plug the amplifier into the power outlet and give her a turn on.
Its time to bite the bullet and do it the correct way now. Start from the input of the amplifier and replace ALL, yes all semiconductors because everything has been stressed several times. Yes, it will cost a few dollars but the result will be a working functional amplifier.
When you have completed this and the amplifier has the correct fuses then and only then will you think about turning the amplifier on. At this point you need a variac or a light bulb as a safety factor. Plug the amplifier into the variac and slowly start turning the voltage up while monitoring the current draw. If you cannot borrow a variac then put a light bulb in series with the power cord.
NEVER NEVER NEVER just plug the amplifier into the power outlet and give her a turn on.
Ok
Many thanks for your help!
i know that i'm not a pro 🙄
I will do what you say
( i've got ten MJ15024 with the 2 i've used to replace the burned one, do you think i can use this two transistors or i have to replace them to ).
When i will turn the amplifier on , after having replace the transistors, and using a bulb in series with the power cord, what sould i do?
many thanks
Many thanks for your help!
i know that i'm not a pro 🙄
I will do what you say
( i've got ten MJ15024 with the 2 i've used to replace the burned one, do you think i can use this two transistors or i have to replace them to ).
When i will turn the amplifier on , after having replace the transistors, and using a bulb in series with the power cord, what sould i do?
many thanks
Do you have a schematic of the amplifier? If not then find one before you go further.
Check all resistors both for value and physical condition. You might as well replace the electrolytics on the driver board also
because of their age. Do not forget C19 as Mr. DJK suggested.
Replace the semiconductors as suggested with ALL new ones.
Also replace the bias pot because these can go bad and all of
your work would have been in vain.
After replacing the parts, the bias and DC offset need to be checked/adjusted.
After everything is satisfactory then and only then will you consider trying to pass a sine wave and test the amplifier.
Upon completion of this step a satisfactory completion that is..
then you can consider passing music and hooking up your speakers.
If it seems that I am making this out to be a major undertaking then I guess I am. It is always easier to repair something the first time than to repair it 5 times and still have it be non-functional.
If you follow the advice of Mr. DJK, anatech, and others in the know you will have rebuilt the amplifier the correct way and it will
provide many years of service. If you fail to follow the simple suggestions then the almightly speaker god will strike the amplifier down and allow the magic smoke to be released.
The choice is yours
Check all resistors both for value and physical condition. You might as well replace the electrolytics on the driver board also
because of their age. Do not forget C19 as Mr. DJK suggested.
Replace the semiconductors as suggested with ALL new ones.
Also replace the bias pot because these can go bad and all of
your work would have been in vain.
After replacing the parts, the bias and DC offset need to be checked/adjusted.
After everything is satisfactory then and only then will you consider trying to pass a sine wave and test the amplifier.
Upon completion of this step a satisfactory completion that is..
then you can consider passing music and hooking up your speakers.
If it seems that I am making this out to be a major undertaking then I guess I am. It is always easier to repair something the first time than to repair it 5 times and still have it be non-functional.
If you follow the advice of Mr. DJK, anatech, and others in the know you will have rebuilt the amplifier the correct way and it will
provide many years of service. If you fail to follow the simple suggestions then the almightly speaker god will strike the amplifier down and allow the magic smoke to be released.
The choice is yours
There has been given terrific info in this thread.
PL700's are though guys and need careful and thorough repair. Not an easy task.
May I add that you definitely check all diodes (1N4148) as well.
Also, when replacing outputs, make sure to measure between collector and chassis for short circuits before applying power.
Bad mica insulation can cause this but also the way the outputs are tightened to the heat sinks are prone to failures/shorts. Eventually renew the mica or kapton or whatever is used if the previous tech hasn’t done so.
This could be a very rewarding job but as said by many people above, you need to work meticulously.
And yes, a picture would be nice, as always. 🙂
Good luck.
/Hugo
PL700's are though guys and need careful and thorough repair. Not an easy task.
May I add that you definitely check all diodes (1N4148) as well.
Also, when replacing outputs, make sure to measure between collector and chassis for short circuits before applying power.
Bad mica insulation can cause this but also the way the outputs are tightened to the heat sinks are prone to failures/shorts. Eventually renew the mica or kapton or whatever is used if the previous tech hasn’t done so.
This could be a very rewarding job but as said by many people above, you need to work meticulously.
And yes, a picture would be nice, as always. 🙂
Good luck.
/Hugo
Hi Joe, Hugo,
Your summaries are things that should be pounded into every technician's head. All our lives would be so much easier then.
-Chris
Your summaries are things that should be pounded into every technician's head. All our lives would be so much easier then.
-Chris
Netlist,
Very good point about the diodes and mica insulators. Some of us
tend to forget to mention some of these things we do as part of
normal repair. I can remember having not replaced the insulators
in the past and having an amplifier fail. It is important when
repairing an amplifier not to scrimp on the small details.
Very good point about the diodes and mica insulators. Some of us
tend to forget to mention some of these things we do as part of
normal repair. I can remember having not replaced the insulators
in the past and having an amplifier fail. It is important when
repairing an amplifier not to scrimp on the small details.
🙂 🙂
Many many thanks for all your help.
I'm waiting for an oscilloscope that i've buyed to repair this amp and for the rest of my passion after ( there is a long time i 'd like to have own, and now it's easier to found one in the net ).
Do you think it's possible ( after i'll have done all the things you said to me ), to use a preamplifier with a sine wave coming from a computer ( adjust with the oscillo ), to test the amp.
many thanks one more time.
PS: i'll send you photos of the amp as soon as possible
Many many thanks for all your help.
I'm waiting for an oscilloscope that i've buyed to repair this amp and for the rest of my passion after ( there is a long time i 'd like to have own, and now it's easier to found one in the net ).
Do you think it's possible ( after i'll have done all the things you said to me ), to use a preamplifier with a sine wave coming from a computer ( adjust with the oscillo ), to test the amp.
many thanks one more time.
PS: i'll send you photos of the amp as soon as possible
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