Need help on broken ZPA .5 amp

[Virtue]

Awhile back I bought a ZPA.05 on Ebay... Used it in bridged mode but never set it up properly. I never had enough input signal. I also had 2 others hooked up the same way. It was only after I put the right input into the amps, that I noticed the one sub only moving half what the other subs were doing. I removed it and one channel was not working and never had worked from the beginning.

I have opened it and realized the one side had been repaired. It was done properly. I know electronics really well, so, I've checked every output transistor and practically everything else. Now, when I power up the amp, everything turns on. All lights on the pre-amp turns on. The output transistors all warm up, equally with the working side. But, no sound signal comes out. When the speaker is hooked up, one can here that there is a connection, a slight hiss, so I know the output transistor side is working fine... But, the input signal is just not going through. Any thoughts? Is there a circuit on the pre-amp part that I need to check? I am not to sure how the 'over temp' circuit works, but, is it possible that it could be preventing the sound signal from going through? And on the same note, if the 'over temp' circuit engages, does it only cut back the sound or does it also turn off the output transistor section too? Really puzzled.

So far I have eliminated the whole output section and the two up right boards in the pre-amp side for issues, that is the two boards are on either side of the plug in cross over board. Also, I have just the full range crossover board.

Any thoughts?
Thanks!

[trickyricky]

If the over temp protection kicks in, the amplifier would shut it self off and will not turn on until proper temperature has reached. So I doubt that the temp circuit would just cut off the audio path.

So let me get this straight, so now you have NO output from both channels? You would have to make sure your sending proper signal (8v) through the RCA's, so I would check that first and confirm the input signal is good.

How do you know the over temp circuit is engaging?

[Virtue]

Ok, one side works 100%. The other side is not. It powers up and I will get perfect sound from the working side, but, no sound comes out of the other side. When the speaker wire is connected to the 'non' working side, I can tell it makes a connection. When I turn the volume up full, I can just get a faint signal out on the speaker. As if it was powered up, but the RCA are not connected. Hope this makes sense... So, from what I can see, the music signal is not making it to the output stage... I believe...

I asked about the temp circuit, because I was wondering if it was keeping the music signal from traveling through the one side and leaving the other side alone.

Any other thoughts?

[vwdude]

I wonder if maybe the gain potentiometer for that channel is bad. Do you have a dmm to check it?

[Virtue]

I just checked the pot, it is good. So, somewhere between the twin up right circuit boards and the output transistors is where the problem is. I wish I had a schematic as to how the sound travels through the amp. It would make my life a lot easier.
Any other suggestions?
I do appreciate everyone's time... I really want to use this amp in my vehicle.

[trickyricky]

You could trace it, starting @ RCA inputs. But its not east if your not familiar with components.

[Virtue]

Wow, after two weeks of non stop testing soldering and desoldering, I actually got this thing to work. From what I can gather, the fault was, either one or two transistors that are soldered, but, the pins were not quite sticking through the circuit board to make a good connection to the solder. I suspect when the one side had burned out, it must have created enough heat to loosen the solder connection. I can tell these were never replaced, so, it was a little off from factory. Funny thing is that everything I pulled off and tested, the previous owner had also checked and finally gave up and sold the amp, which I bought unknowingly.

My fingers are on the transistors that I swapped with the other side and resoldered them. Hope this helps someone else. If nothing is burnt out and the lights all go on but no sound, resolder everything even if it looks good!

[trickyricky]

The ones next to those are rectifiers, which makes me believe the ones your pointing could be voltage regulators (I could be wrong, I don't have a ZPA to go off of).

If so then that would explain why you didn't get any output, the op amps where not getting power and therefore where not amplifier the signal from the beginning. Can you please post the components numbers that where on the transistors, hoping am right lol.

[zeropoint0.5]

Wow, after two weeks of non stop testing soldering and desoldering, I actually got this thing to work. From what I can gather, the fault was, either one or two transistors that are soldered, but, the pins were not quite sticking through the circuit board to make a good connection to the solder. I suspect when the one side had burned out, it must have created enough heat to loosen the solder connection. I can tell these were never replaced, so, it was a little off from factory. Funny thing is that everything I pulled off and tested, the previous owner had also checked and finally gave up and sold the amp, which I bought unknowingly.

My fingers are on the transistors that I swapped with the other side and resoldered them. Hope this helps someone else. If nothing is burnt out and the lights all go on but no sound, resolder everything even if it looks good!

the transistors you're fingers are on can be replaced with a irfz44 or better irfz48...... i had one time an amp with one non working channel, it was

probably the same issue...... if i was you i would replace them in both channels while you're busy............

and please take out first those original ps caps and start with replacing those ...........

[Eric D]

In the above photo, just above your fingers there are two axial resistors which were used to replace two radial resistors. This is not a good sign. All of those resistors need to be the same or close too it. Generally if these are replaced, it is a sign that their connected transistors have also been replaced. If that is true, you need to make sure that ALL of the transistors for that channel are replaced, so they match. Otherwise you will find that under load, the weakest transistor will fail.

[trickyricky]

The transistors that got replaced are CIRCLED IN RED.

[Virtue]

I'll be doing all that is suggested, thanks guys!

[Virtue]

Just curious, I have the P55N06 fets in my power supply side, IRFZ48 actually has less current... Should I still switch them to IRFZ48? Maybe I have a different version?

[zeropoint0.5]

Just curious, I have the P55N06 fets in my power supply side, IRFZ48 actually has less current... Should I still switch them to IRFZ48? Maybe I have a different version?

if you switch them to irfz48, you have to replace the 16 gate resistors of 33ohm by 330ohm....otherwise it won't work and the resistors and some fets

will burn immediatly........if the powersupply is totally fine you can start with leaving them in................

normally the irfz3205 should work with 33 ohm gates, personally i haven't tried those out...some members here have.........

[freshkryp69]

To be on the safe side, Ive installed irf3205's in 1 of my .5's and its doing great on the bench. Been wanting to try them out as they have a higher rating that the 44's that come stock.. If everything goes all right, im going to install them in a couple of my unicorn's that use to220's. Im hell bent on making the PS rock solid.

[zeropoint0.5]

http://download.phoenixphorum.com/Manua ... a2chan.pdf

a zpa has no internal fuse, the owners manual recommands a 80A fuse for the 0.5 amp.......

If you wanna stay safe on the powersupply, even on a voltage drop the fuse should blow before the fet's will.....

Maybe you can go even up to a 100A fuse, but i never tried it ( to burn a powersupply , lol )

if you're planning to use the amp for speakers, probably you're fine with a 80A fuse.....

a modded zpa on a 2ohm brigded load will be another story.......................