InterM PA Amp PAM-360 Protection Problem

[DjKrish]

As stated, i have this PA system amplifier that im trying to fix for sometime. It is having a clip and protection light on. When i disassemble the entire unit, i manage to find that a lot of components thats burned on the amp pcb. Power amplifier transistors, resistors, normal transistors etc. I manage to check all the components and replace all the faulty ones. Now the clip light no longer lit but the protection light is still on after turning on. I even replaced the protection IC. But im still having the protection light on. Any guru's may kindly help me with this? I have attached the necessary SM and amp SD. I have replaced all the faulty components already. I just dont know where else to look at. Any help will be highly appreciated. Hoping to fix this a.s.a.p

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

PS: The relay on the Amp PCB doesn't click either when turned on

[redwire]

Re: InterM PA Amp PAM-360 Protection Problem

The protection circuit can trip for a few reasons:
1. DC voltage at either channel amp's output (measure at L201, L301) - (most likely, as one channel was blown)
2. Overtemp circuit (thermistor PO301)

I would guess your power amp still has a problem, resulting in too much DC at one channel's output. Measure the voltages at the inductors or output relays.

[audiobrad]

Re: InterM PA Amp PAM-360 Protection Problem

Hey tech's

Check the resistors around the sub driver transistors if i remember correct its a 22 ohm and 47kilo-ohm resistor on both side of the board . make sure that your output transistors are idling correct if not the protection stage will kick in even if there is no dc on output .

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

The protection circuit can trip for a few reasons:
1. DC voltage at either channel amp's output (measure at L201, L301) - (most likely, as one channel was blown)
2. Overtemp circuit (thermistor PO301)

I would guess your power amp still has a problem, resulting in too much DC at one channel's output. Measure the voltages at the inductors or output relays.

How do i check the thermistor? Theres 2 and both also showing different reading in cold temperature with no power plugged in. One is high reading and another is low reading

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

Hey tech's

Check the resistors around the sub driver transistors if i remember correct its a 22 ohm and 47kilo-ohm resistor on both side of the board . make sure that your output transistors are idling correct if not the protection stage will kick in even if there is no dc on output .

The resistor was blown before and i have replaced with same value. Now the resistors u mentioned is perfectly fine.

[redwire]

Re: InterM PA Amp PAM-360 Protection Problem

On the protection IC TA7317P, if there is any DC on pin 2 or pin 3, above around +/-1V it will trip the protect latch. You should measure close to 0V on those pins.

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

My bad assuming one row of the transistor are heating up thinking one channel will work, i plugged in a small speaker and a loud humming sound came out from the speaker assuming its blown already, resistor blown again and the power fuse blown too. I guess some of the power transistors burned again. Big mistake.

Could the transformer be faulty too since the power fuse blowing up? How can i measure the transformer based on the schematic diagram? I have multimeter and digital multimeter too. How can i measure the transformer just to make sure its working fine? How do i measure those wires from the transformer?

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

Pictures of the unit

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

Ok, replaced all the caps, output transistors, bias transistors and resistors. Amp board is as good as new now. Luckily i plugged it via the light bulb limiter, turned on, its dim but not very and not bright either. The protection light is still ON. The relay on the amp pcb is not working either. Only the relay on the power pcb and the relay on the main pcb is working when turn on. Amp pcb relay seems to be off. Checked the relay with 30v power supply, its working fine and clicking. Where else should i be checking? Please help meeeeeeeeeeeeeeeeeeeeeeeeeeeee ............................

[redwire]

Re: InterM PA Amp PAM-360 Protection Problem

Like I said, measure the protection IC TA7317P, pin 2 and pin 3...

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

Like I said, measure the protection IC TA7317P, pin 2 and pin 3...

Yes there's DC voltages present on pin 2 and 3 upon turning on with the light bulb limiter. Around 5 to 7 volts.

[redwire]

Re: InterM PA Amp PAM-360 Protection Problem

Check your light-bulb limiter is not interfering with things too much. Measure the amp power supply voltage (I use multimeter on the collector/tab of the output transistors), and the +/-26V rail voltages.
DC voltage on TA7317P pins 2 and 3 means there is DC at the power amp's output in both channels, and the protection circuit has tripped. Did you have both channels blown? I am guessing there is still a problem with the power amp section but it could be elsewhere, as it is odd to have both channels doing the same thing.
What you are troubleshooting is very hard to do. Power amps are difficult to fix with power on. Patience....

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

Check your light-bulb limiter is not interfering with things too much. Measure the amp power supply voltage (I use multimeter on the collector/tab of the output transistors), and the +/-26V rail voltages.
DC voltage on TA7317P pins 2 and 3 means there is DC at the power amp's output in both channels, and the protection circuit has tripped. Did you have both channels blown? I am guessing there is still a problem with the power amp section but it could be elsewhere, as it is odd to have both channels doing the same thing.
What you are troubleshooting is very hard to do. Power amps are difficult to fix with power on. Patience....

If u noticed, there's 2 sections of output transistors. Current drive one side and voltage drive one side as u see in the block diagram.

[redwire]

Re: InterM PA Amp PAM-360 Protection Problem

"Current drive" refers to the power amp output stage i.e Q217/218, Q219/220, Q221/222 and "Voltage drive" refers the voltage gain stage before.
The protection circuit is doing the right thing because it is seeing DC voltage on the amp's output, which should be 0V.
Did you check the eight 0.47R emitter resistors for open circuit.
Measure your power supply rails and the output voltage.

[budm]

Re: InterM PA Amp PAM-360 Protection Problem

Something is not making sense here:
https://www.badcaps.net/forum/showthread.php?t=36954

You have indicated that you see 0V at the output.

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

New progress : Now i know why the relay didn't click on the amp pcb. I popped it out, short with 24vdc psu, it still didnt click either. Opened up the relay, noticed its burned. And also c4001 transistor is short. Gonna change this both today and see how it goes and make more measurement and update in here.

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

Something is not making sense here:
https://www.badcaps.net/forum/showthread.php?t=36954

You have indicated that you see 0V at the output.

That is after i replaced all the output transistors, before that had some dc voltages

"Current drive" refers to the power amp output stage i.e Q217/218, Q219/220, Q221/222 and "Voltage drive" refers the voltage gain stage before.
The protection circuit is doing the right thing because it is seeing DC voltage on the amp's output, which should be 0V.
Did you check the eight 0.47R emitter resistors for open circuit.
Measure your power supply rails and the output voltage.

Now the voltage is absolutely zero on all the speaker outputs. The relay is working perfectly fine on the amp board. It clicks after turning on the power immediately. No DC voltages on pin 2 and 3 on the protection IC TA7317P. So i guess im getting closer to solving the issue. Where else should i be checking now? I appreciate everyone's help in here. Very informative and helpful.

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

Edit : I see 0V on pin 3 but i see -0.02V on pin 2 of TA7317P Protection IC. Is that bad?

[DjKrish]

Re: InterM PA Amp PAM-360 Protection Problem

There is 2 piece of 260 Ohms resistors near both variable resistors. One resistor shows around 74ohms and another shows near 98ohms. I find this too low for the original value.

R233 and R333 on the amp circuit.