Linear Power 952

[clayton]

I am in need of schematics for this amp. The thermal protection has been disconectedand don't know where it goes It is still mounted to the bottom of the board. When power is applied I get 12v on the power supply transistors center leg, but only 5v on the output transistors center legs. I think that there is poss something wrong with the turn on section. Which might have something to do with the thermal protection not being connected. All power & output transistors test good.

[jol50]

Does it have a driver IC for the PS? If so look up data sheet for pinout that might help you.

[clayton]

No, the only IC is on the output side.

[1moreamp]

I have some temp switches that you can simply add to the 12 volt turn on line to solve this issue LP is out of business and the people that have any info are cashing in on that fact. They are simple amps to work on been in them plenty over the years. Plus I have a few locals out here running LP is SPL competitions so I can check them for you if time is not a issue..

[I Am An Idiot]

Linear Power amplifiers in SPL Competition


WOW

[1moreamp]

yeah the guy has custom 18's built for the high ohm loads and like 6 LP 4.4HV's and several 8002's also 6 battery's in the back behind where the second seat would be in his Burb. Big old copper straps connecting the battery's like 2 inches wide. Its a piece of work.. Nice guy though, and very serious about competing...

[clayton]

The temp switch is still on the board just the wires have been disconnected. What is the best way to check if its still good. The way I have always checked these is to ohm it out and apply heat to it. If the ohms increase it is still good. Would this be the correct way?

[Perry Babin]

In their old amps (maybe all of their amps) Linear uses a switch (thermostat), not a thermistor. It should show either open or closed. You can heat it with your iron to make it toggle. I know some of the thermostats were normally closed but I don't know if all were.

If the switch is still on the board, you should be able to see where they go. There should be open solder pads just at the end of the wires.

[clayton]

Yes it is a themostat like you said Perry. This one has continuity till heat is applied. The wires have been cut to about 3" and I can not see any spots where it looks like they would go. Some of the turn on transistors look like they have been changed. They also test good.

[1moreamp]

If its a closed temp switch until heated, just run the 12 volt turn on lead through the switch. When the amp overheats it will open and the amp will shutdown.
The turn on lead on has about 1 milliamp of current on it so the switch contacts should last a lifetime.
If your worried about switch noise just apply a ceramic cap 0.1 ufd or there about across the switch contacts.
I have done this several times before to Orion and PPI amp many years ago for some of my more troublesome clients to warranty.

One of the local shops here liked to move and isolate temp sensors trying to defeat the temp controls on amps to give their clients a amp that would not temp cycle. The end results was a blown amp on my bench

If you can wait a bit I will contact one of my 4 local LP clients and take a look see about the temp switch connection. I am sure its all the same for each LP model as these were just scaled amps of a single design....