PL-400 series ii issue

[Michael F]

Hi All,
I just picked up one of these hopefully to mate with my 700s2. Its in really nice original, unmolested condition.
No issues with the left channel but the right channel will intermitantly flat line, under an 8 ohm load. It will run up to 49 volts before clipping but then go dead.
An interesting observation I made was when flat lined, if the load is removed it will swing back to 49 volts. Load it down and it will work ok for while and then go dead.
What would cause such a condition?

 

[WOPL Sniffer]

What will cause that???? 40 year old junk components. WOPL it and set yourself free.

 

[Gepetto]

Possible causes:

1. One of the control board semiconductor devices in the affected channel heating up as you load it and having a bond wire open up...you remove the load, it cools down and reconnects. Rinse and repeat.
2. A bad wire solder joint on the back wall or control board that opens when the amp heats up.
3. What Perry said...

 

[MarkWComer]

Hi All,
. Its in really nice original, unmolested condition.

It’s time to molest it! Crack it open and get the WOPL kits!

 

[e30m3mon]

It’s time to molest it! Crack it open and get the WOPL kits!

Yup ... this ^^^

 

[Michael F]

It’s time to molest it! Crack it open and get the WOPL kits!

How I`d love to but money is extremely tight these days
I think Ill start with Joe`s first two suggestions, they make sense and wont cost me anything but time.

 

[MarkWComer]

How I`d love to but money is extremely tight these days
I think Ill start with Joe`s first two suggestions, they make sense and wont cost me anything but time.

Right- nobody has money for anything right now- buy gas or buy food?
Bit by bit, one step at a time, and don’t forget the protection relays!

 

[WOPL Sniffer]

How I`d love to but money is extremely tight these days
I think Ill start with Joe`s first two suggestions, they make sense and wont cost me anything but time.

Stereo is a bad hobby if you are broke. If you can't fix it properly, you are asking for more problems than you bargained for. A $1.00 transistor can take out $500 in speakers....... Save your money AND your system. Park it until you CAN afford it. Half assing will cause you big issues.

 

[Michael F]

Stereo is a bad hobby if you are broke. If you can't fix it properly, you are asking for more problems than you bargained for. A $1.00 transistor can take out $500 in speakers....... Save your money AND your system. Park it until you CAN afford it. Half assing will cause you big issues.

Its more a matter of discretionary spending than being broke.
Im not one to half ass anything least of which my sound system. This amp wont get within 20 feet of my $5000 speakers in its present state.
If all that is needed to rectify the issue is a $1.00 transitor, Im all for it.

 

[WOPL Sniffer]

$1 won't do it. Every time you turn it on it will cost you. Phase Linear was junk when it was built and after 40 years, it's really junk. You'll see.....

To do a rebuild on them will cost you. Blowing money on temp fixes is NOT discretionary spending.

 

[WOPL Sniffer]

The first 2 items in Joes list is CHEAP and not going to get you amp running for long. He engineered the WOPL do-dads so we wouldn't have to cheap-ass it.

 

[gene french]

dont be discouraged...i have two stock pl400s that have the white oak led upgrades, the ps cap upgrade and the dc protection board from watts abundant...and of course a recap of the control boards...
it took a bit of time and patience...and some help from members here...but, they are performing well....for several months now...without issues...
i did take a junk 4 finner i bought in a package deal and converted it to wopl...it is a great dependable amp...best way to describe how i feel when i listen to it....it speaks with authority....it sure dont tip toe into the room....lol
i turn it on with confidence knowing what it is..and fully confident it will be around for a while a few decades at the very least...
however, the other pl400s ran nearly 50 years as designed...i disagree it was total junk...
maybe not up to todays standards...however, 50 years ago it was quite the amp...and plenty of them were sold...a dollar a watt...what a bargain for the day....making bob carver a household word in the audio world...
the old boards and wiring are low quality, brittle, and easily damaged...a lot of these amps were abused....and overheated...overdriven, etc...
care must be exercised when repairing...
when the stock repair adds up....it maybe be more economically realistic to upgrade to modern electronics...
the originals were worthy of a lot of design and production work by white oak to keep the amps going...and prevelant in the audio world...
the wopls are designed to emulate the pl14 specs according to joe....so they sound like the pl400s we all know and love...
so...there is value there in my opinion....(which i must admit...dont amount to much ....)
as long as my stock ones are performing i will stay with the status quo...but, would not hesitate one minute to upgrade to white oak when it is necessary because of scarce parts, extensive costs or complexity of repairing, or i just want to upgrade.....
and eventually i know i will upgrade ....another project for another day...
as sniff said...this is not a cheap hobby....
as well, it does not need to become a money pit either...
that one requires finess...lol
there are a lot of very nice setups on this forums...and a lot of wisdom...
good luck ...

 

[J!m]

Half assing will cause you big issues.

I ALWAYS at least 3/4-ass stuff myself...

 

[MusicSteve]

Hi All,
I just picked up one of these hopefully to mate with my 700s2. Its in really nice original, unmolested condition.
No issues with the left channel but the right channel will intermitantly flat line, under an 8 ohm load. It will run up to 49 volts before clipping but then go dead.
An interesting observation I made was when flat lined, if the load is removed it will swing back to 49 volts. Load it down and it will work ok for while and then go dead.
What would cause such a condition?

That's new to me, might be that the caps are reforming , might want to bring it up slowly w a bulb tester or low voltage. And that Joe said ***** , I like the 400 ll and 700 ll the boards work ok until you open them up . I check all wires and solder joints and traces than all the wires to the board . when this happens what's the rail voltage and the 15v on the diodes? Good luck

 

[gene french]

Possible causes:

1. One of the control board semiconductor devices in the affected channel heating up as you load it and having a bond wire open up...you remove the load, it cools down and reconnects. Rinse and repeat.
2. A bad wire solder joint on the back wall or control board that opens when the amp heats up.
3. What Perry said...

a can of freeze spray may come in handy for overheating parts...

 

[Michael F]

I check all wires and solder joints and traces than all the wires to the board . when this happens what's the rail voltage and the 15v on the diodes?

Good points

 

[Michael F]

That's new to me, might be that the caps are reforming , might want to bring it up slowly w a bulb tester or low voltage. And that Joe said ***** , I like the 400 ll and 700 ll the boards work ok until you open them up . I check all wires and solder joints and traces than all the wires to the board . when this happens what's the rail voltage and the 15v on the diodes? Good luck

I re-flowed every component on the drive board and inspected the back plane for anything obvious. I did notice that the transformer secondary wires were only being held to the bridge rectifier through the holes in the tabs, they werent properly soldered and both worked themselves loose. Resoldering them surely prevented a future problem but unfortunately was not related to my issue.
The voltages at the opamp are a steady + and - 15 while the amp is functioning or when it goes flat line and B+ and B- voltages are at 85.
Would freeze spraying the semiconductors be adviseable?

 

[laatsch55]

Does it do it everytime it warms up? Freeze spray is exactly what you need if is what Joe thinks it is..

 

[Michael F]

Does it do it everytime it warms up? Freeze spray is exactly what you need if is what Joe thinks it is..

Yes Lee, the amp will work just fine from a cold start and then go dead depending on how much its putting out. With lower output (20vrms@8R) the amp functions for longer periods.

 

[MusicSteve]

I re-flowed every component on the drive board and inspected the back plane for anything obvious. I did notice that the transformer secondary wires were only being held to the bridge rectifier through the holes in the tabs, they werent properly soldered and both worked themselves loose. Resoldering them surely prevented a future problem but unfortunately was not related to my issue.
The voltages at the opamp are a steady + and - 15 while the amp is functioning or when it goes flat line and B+ and B- voltages are at 85.
Would freeze spraying the semiconductors be adviseable?

Well, the good news is your transformer appears to be good.

laatsch55 said:
Does it do it everytime it warms up? Freeze spray is exactly what you need if is what Joe thinks it is..

(can use OfficeMax compress air might be cheaper) and
buy a Harbor Freight Infrared Laser Thermometer and check between the left and right channel and they also sell BLOW OFF DUSTER 10 Oz. Compressed Air (never seems to last very long)

https://www.harborfreight.com/121-infrared-laser-thermometer-63985.html

Only thing I can think of is maybe the protection circuit is faulting out.. is that possible Joe?
maybe post some pics? (Note the transistors w the sq-heat sink, they got pretty hot)

when the channel goes dead, will it stay that way?