Infinity 475a car amplifier 75Wx4Ohm

[budm]

Re: Infinity 475a car amplifier 75Wx4Ohm

When that pin2 of the SMPS IC is less positive than pin1, that is when the SMPS goes into shutdown. Pin2 can be pulled down toward ground if Q3 is turned on due to error signals from output detection circuits, or if the thermal sensor RT1 resistance goes low to cause pin 2 to be lower than pin 1 which will cause pin3 output to swing HIGH (it is normally LO).
Q7 (2SC1815) symbol is drawn wrong, it is NPN not PNP as shown in the diagram page 28.
You can defeat output detection by lifting D4, but you have to be careful because if there is problem in the output section in one or more of the amplifiers you can have damaged circuits.

[tibimakai]

Re: Infinity 475a car amplifier 75Wx4Ohm

I'm getting frustrated with this amp.
The schematic doesn't match 100% with my amp. It seems like they were two versions out there judging by the top cover differences.
There is no variable resistor and I can't find that RT1 either.
I have cut the power(after the two main capacitors) to the finals(VCc+/-) and protection mode is still on.
I don't know how to do measurements and the FETs to be installed on the heatsink, it's almost impossible. This is a single layer board and the layer is at the bottom, can't reach it. I guess, I will end up removing the board and re-installing it a few(20x) times.
I have to be sure that the power supply delivers what it should deliver first, no?
I can't find the 7815 section either.
Another thing is, how to discharge the amp, because it takes forever to drop the voltage? I have sparked a couple of times the FEts, while trying to remove the PCB.

[tibimakai]

Re: Infinity 475a car amplifier 75Wx4Ohm

It seems like the VH+/- is missing.
I'm measuring +/-0.2V across C57 and C56.

[Agent24]

Re: Infinity 475a car amplifier 75Wx4Ohm

Can't you test for voltages on leads of components at the top side?

Try the discharge ideas here: http://www.repairfaq.org/sam/smpsfaq.htm#smpssafdc

[tibimakai]

Re: Infinity 475a car amplifier 75Wx4Ohm

OK, I have tried measuring with Min/Max Peak and it showed 30V, but then shut it off.
I'm trying that way to measure, but not all components can be reached.
For example C56, is against the toroidal transformer and C55 against it.
So, I'm guessing that something is still shorting in the amp section, to cause this shut down.

[tibimakai]

Re: Infinity 475a car amplifier 75Wx4Ohm

I'm about to quit on this amp.
It's so nerve racking to follow the PCB and the schematic. I feel like I'm not capable of following the PCB.
Why they made it so complicated, I don't know.
It seems, like the schematic is not the same as the amp.
I can't fine those diodes at each amp's VH voltage. There are a bunch of ZD diodes on the PCB and in the schematic I can't find them.
There are some diodes like D2, D14 and D1, D3 on the pcb, but I can't find these on the schematic. There are other diodes D2, D3 on the daughter board, which I can't even find on the schematic.
There are so many jumpers, that my head hurts just following them.
I have repaired a couple amplifiers lately(home and car amp), but this one will beat me and I will have to quit.

[conan981]

Re: Infinity 475a car amplifier 75Wx4Ohm

hi, i just took in my hands this exact model of amplifier, with the same error.
it light up PROTECT led as soon as i give power. Amplifier has connected only power cables. now i read discussion and infos from Budm and others and found Q7A-B-C-D transistors and RT100 thermal switch, and another thermal switch that is noted with CN4 (i think an error).
now, i can do measurements but i don't know what to check to try what Budm was suggesting (give vcc off one amp at a time).
Also, RT100 thermal switch is an JUC-31F i would know if it is normally closed or opened, since it is always open with over 2MOhm.
Let me know if someone wants help me, i would be happy to follow istructions to repair.
thanks
Conan

[stj]

Re: Infinity 475a car amplifier 75Wx4Ohm

[tibimakai]

Re: Infinity 475a car amplifier 75Wx4Ohm

I still have the amp, I have just put it away.

[conan981]

Re: Infinity 475a car amplifier 75Wx4Ohm

on service manual is written only Temperature Switch JUC-31F65℃ ±5℃ TO-220 1 RT100
i don't know if it is normally opened or closed. maybe tibimakai that removed the clips that block these ones to cooler can give more infos

[tibimakai]

Re: Infinity 475a car amplifier 75Wx4Ohm

CN4 shows 32.12Kohm and the RT100 starts around 480Kohm and is going higher and higher.
This is how I have it set up for easy testing. Some Aluminum strips, some clamps.
To remove the original clips, use a bent screwdriver, like one I made one for myself.

[budm]

Re: Infinity 475a car amplifier 75Wx4Ohm

Post 21 (if the circuits are drawn correctly) " or if the thermal sensor RT1 resistance goes low to cause pin 2 to be lower than pin 1 which will cause pin3 output to swing HIGH (it is normally LO)." So if the RT1 is closed the unit will go into shutdown.

[conan981]

Re: Infinity 475a car amplifier 75Wx4Ohm

ok, so the RT1 and RT100 are normally opened and mines and tibimakai ones are ok.
CN4 (RT1) is measuring 32kohm and RT100 is over 2M Ohm (open circuit).
Should we check in some way the 4 transistors?

[tibimakai]

Re: Infinity 475a car amplifier 75Wx4Ohm

I had blown transistors and I have replaced them already.
I even had blown off traces at the transistors. All that is done and I still have the protection on.

[CapLeaker]

Re: Infinity 475a car amplifier 75Wx4Ohm

Did you check all the transistors mounted on the heat sink for shorts? If they are none, check the big resistors on each output transistor and their driving transistor. If the driver is bad, unit will stay in protection too.

[tibimakai]

Re: Infinity 475a car amplifier 75Wx4Ohm

On mine, I believe that in the power supply section is something bad.
I had a couple FETs blown there, too.

[tibimakai]

Re: Infinity 475a car amplifier 75Wx4Ohm

Can you believe, that I'm back to repair this? It's been 5 years already!?
I have found a leaky transistor, Q12B.
Replaced it and the first time I turn it on, it turns on OK(blue LED is on). The power supply is only a 5A one. That could be a problem? Turning on this amp, maybe spikes higher then 5A?
If I turn in off and then on again, it goes into protect mode.
I have soldered two wires, at the pin #9 and #10, at TL494 and when it's not in protect mode, I have two nice square waves.
If I turn it off and then on again, protect mode is on and the two square waves are gone. It shows a negative straight line, at both outputs. -29V is gone. +29V is always present.
I have even replaced TL494 again, just in case. All the transistors/diodes, on that daughter board check out OK. It could be a bad capacitor somewhere?

[tibimakai]

Re: Infinity 475a car amplifier 75Wx4Ohm

It is all good. I guess, it was my power supply, as it was discharging, "causing" the protect mode?!
If I kill the power instantly and apply it again, no more red light.
It is fixed.