power acoustik TS-620-2

[scampo77]

I have this amp here and it is powering up and the LED is coming on green.

there is no sound coming out of it. i even tried playing with the gains and controls and i cant even get scratching.

also there is a light that is certainly part of the appeal of this amp. i dont have any voltage at the bulb is it AC or DC?

 

[I Am An Idiot]

I thought I knew which amp you had, but you said that the light thing was appealing. If it is an amp with the Plasma Sphere on the top, It needs audio to make the light work. There are also problems with the power supply board of the Light. There are a couple parts that suffer from bad solder joints. But you really need to get the amp producing sound before you assume the light is not working.

 

[Perry Babin]

Does it have rail voltage on the outputs?

Does it have regulated ±15v on the op-amps?

The plasma display has a weak power supply and they often fail. Generally, the power transistor(s) inside the metal enclosure fail. Be careful when working with it, it produces at least several hundred volts. There will be no display unless there is audio output.

 

[jol50]

I had one of those, the light is cool but I don't ride in the trunk of my car Anyway, IIRC it had blown outputs and not recalling what LED it showed. Make sure someone has not broken off the RCA and in some the gain control.

 

[scampo77]

all the legs of all the op amps are reading zero (i measured 4 op amps).

i beleive i found the outputs but the markings are strange,

F25
F0P
50N06

all i can tell is that they are made by fairchild they have that "F" on them, and there is 6 of them. all of them have +15v DC on the center legs.

i had the ground lead on the NEG power terminals on the amp.

how do i find out the rail voltage?

 

[Perry Babin]

Could it be FQP50N06?

Did you have 0v DC on the first leg of the power supply FETs?

To measure the rail voltage, place the black probe on one of the non-bridging speaker terminals and the red probe on the center leg of the output transistors.

 

[I Am An Idiot]

The output transistors are the larger devices. They are on the end of the amp away from the Power input terminals.

 

[scampo77]

yes it is a Q in FQP50N06

if the out puts are in fact the 6x FQP50N06. then i am getting 15v DC on all 3 legs. i get the same measurments weather the black lead is on the speaker output or the ground terminal.

also i noticed that a IC marked TL494CN is geting really hot.

i also have 4x TIP36C 0 , 1x mur1620cta and 1x uf16202ct

 

[Perry Babin]

The FQP50N06s are the power supply FETs. The outputs are likely TIP35Cs and TIP36Cs.

If you have 15v on all 3 terminals of each of the power supply FETs, you have several problems. With the black probe on the chassis ground terminal, you should have 0-5v on pin1, B+ voltage on pin 2 and 0v on pin 3.

Recheck this.

If you have 15v on leg 3, you have an open ground trace or solder connection in the ground circuit path.

 

[scampo77]

how do i chase something like that down? is there a place i should be looking at more than others? i pulled the board from the heat sink and the underside lookes like an assmbly line workers first day with a solder gun.

i have about 1000 ohms resistance between the + and the - chasis terminals which seems to support your diagnoses.

 

[Perry Babin]

How much resistance do you have between leg 3 of the power supply FETs and the chassis ground terminal? It should be 0 ohms.

 

[scampo77]

ok i found it!!!! can i just bridge these gaps with solder?

 

[scampo77]

yes i have 0 ohms

is the 3rd leg the collector leg?

 

[Perry Babin]

You can't use solder only to jump the trace. Use a piece of wire or desoldering braid.

I think you'll find that those FETs are shorted.

FETs don't have a collector. The pin-out for those is:
1. Gate
2. Drain
3. Source

 

[scampo77]

i pulled all 6 and from the gate to the other 2 legs on diode check i am getting 1.5. im getting this on all but 1 of them

is this enough to be replaced ?

how do i know if they are p-channel? because i had the leads in the meter normally

should i pull the TIP35Cs and TIP36Cs?

 

[scampo77]

is it common for them to fail and not explode and burn? because these look perfectly fine

 

[jol50]

I usually do ohms check and if it is high and near the same as others I figure they are ok. If one is toast the others may be damaged that were in parallel with it, is good practice to put them all in. Some puke and others do not. They are pretty cheap to buy as both are common parts. For the 35/36C also check for shorts.

My fluke never shows 1.5 on diode so I don't know about that. For any of these parts go a store or google and find a datasheet on them, most mosfets are pretty similar in function but the BJT are not. When in question always follow the datasheets.

For example here is datasheet at mouser
http://www.fairchildsemi.com/ds/FQ/FQP50N06.pdf
found from this page
http://www.mouser.com/Search/Refine.aspx?Keyword=512-FQP50N06

Or you can google things a store does not have or if its easier. Also have a way to fire it up on limited power so you don't smoke good parts when you get it done.

Amps with really huge fusing tend to burn more stuff inside, but you never know. IRFZ44 seem to smoke often when they go.

 

[Perry Babin]

The only way you should have a 1 displayed is if your meter displays a 1 when there is an open circuit. There should be absolutely no DC continuity between the first leg and the other legs of the power supply FETs. The following page (and the links on it) will help you to learn to test transistors.

http://www.bcae1.com/repairbasicsforbcae1/images/transistortestpage02.html

 

[scampo77]

on 5 of the 6 power supplies are reading about 1 ohm between the gate and the other 2 legs. i tried using the meter on diode check and i am getting what i think is .001. it is certainly not open. it reads OL when i turn it on and when i put the leads on it jumps straight to 001. im pretty sure they are bad because the one that is ok seems to pass all the tests.

can i test the TIP36(5)C the same way? according to the data sheets these seems to have collectors and emitters. does this signify something?


please bear with me im just doing this repair till i wait for the fluke meter to arrive in the mail

 

[I Am An Idiot]

The 35s and 36s are known as a Bi-Polar transistor. They are different than the MOSFET transistors. The procedure for testing them is a bit different, but you can check for shorts between the collector and emitter of each transistor. That is the most common failure.