ZPA 0.3 "good working" ebay deal.

yeddy · Post by **yeddy** » Sat May 29, 2010 8:44 pm

So I bought this 0.3 off ebay, while testing it I found it gets really hot on the left side of the amps middle heatsinks, the right would stay cool to the touch. It does play and sound good, but my other 0.3 stays a lot cooler and the temp is even on both sides. There was also a high pitch squeal coming out of the amp somewhere, it would go away or change a little if I would press on any part of the board or component. After stripping the board down, all the components look good. I probed around finding nothing out of the norm. I cleaned everything underneath the heatsinks and reapplied new thermal paste. The amp hasn't gone into protection at all, I just want to fix the problem before it becomes bigger. Anyone have any ideas?

Post by **joerg** » Sun May 30, 2010 1:53 am

Are both of the fans working? Might be a dumb questition but sometimes i forget about looking for the easy solutions myself.

thedeal7235 · Post by **thedeal7235** » Sun May 30, 2010 5:02 am

the left input cap looks diff. than the rest, in the pics it looks like the top of it is black and discolored- ive only ever replaced caps&output trans., so .y experiemnce is limited on heat&noise issues

Post by **joerg** » Sun May 30, 2010 5:10 am

Now that christian said it i say that the marked cap is pretty much done and screams for replacement!!!

shawn k · Post by **shawn k** » Sun May 30, 2010 7:23 am

Everytime I've encountered squealing from an amp it's always been a transformer. While the amp is powered up try sqeeazing each transformer while twisting slightly to see if you can get rid of the noise.

The cap may be bad, as suggested, but it looks like there's just a piece of tape over the top for some reason. Either way it still warrants an ivestigation.

Good luck!

waynehead · Post by **waynehead** » Sun May 30, 2010 7:50 am

shawn k wrote:Everytime I've encountered squealing from an amp it's always been a transformer. While the amp is powered up try sqeeazing each transformer while twisting slightly to see if you can get rid of the noise.

The cap may be bad, as suggested, but it looks like there's just a piece of tape over the top for some reason. Either way it still warrants an ivestigation.

Good luck!

Exactly what i was going to say to the T. Thanks for saving me the time. lol

Post by **Eric D** » Sun May 30, 2010 8:14 am

Just a guess, but the tape on the input cap is probably there to keep the plexi REM kill switch from touching the cap, or the screws for it. It has been a long time since I have taken apart a 0.3, so I can't remember just how far down the switch rests.

If one side is getting significantly hotter than the other, I believe something is wrong. The bias on that channel may be set too high (someone may have turned the bias pot up, instead of the gain pot for example).

Maybe one of the 4 output transistors is failing or has failed. I have seen amps which work and sound great, but one transistor is shorted and has a high enough resistance to not cause the amp to shut down. The amp's power supply is tough enough to keep feeding this short and allow the heat to build.

thedeal7235 · Post by **thedeal7235** » Sun May 30, 2010 8:52 am

now that eric mentions it, YEAH check the bias , ive found that some people have also turned those up thinking it is a gain, but ive always been told LEAVE IT ALONE-would prob. need a ossc. scop like eric to really even think about setting bias???!!!

shawn k · Post by **shawn k** » Sun May 30, 2010 10:15 am

Eric D wrote:If one side is getting significantly hotter than the other, I believe something is wrong. The bias on that channel may be set too high (someone may have turned the bias pot up, instead of the gain pot for example).

Maybe one of the 4 output transistors is failing or has failed. I have seen amps which work and sound great, but one transistor is shorted and has a high enough resistance to not cause the amp to shut down. The amp's power supply is tough enough to keep feeding this short and allow the heat to build.

Good call Eric!! Also keep in mind that if you don't find a short for one or more of the transistors there could be one (or more) that's leaking(will not show a dead short). Only way to check for a leaking transistor is to remove it from the circuit and charge/discharge them with a meter. Check the outputs for a short first. If you still have problems let us know.

yeddy · Post by **yeddy** » Sun May 30, 2010 11:01 am

Thanx for the input guys, Eric is right about the tape on top of the cap, the tape is put on from factory to protect shorting from the kill switch, both 0.3's of mine have it. After looking over the other pots, the one on the hot side does look like its turned up slightly more. Any tips on how to set these? The joys of old used equipment, you never know what your going to get.

thedeal7235 · Post by **thedeal7235** » Sun May 30, 2010 12:06 pm

upon opening a couple of my zx amps its always appeared they r both at same setting/level/direction- i dont think in ur case going back on that bias pot is gonna hurt, i beleive it is decreasing that setting, pls. dont quote me on that, but counterclockwise on that is a decrease

yeddy · Post by **yeddy** » Sun May 30, 2010 1:44 pm

I turned down the pot on the left side to match the right one, now each side warms to the same temp, not hot and cold no more, just warm!

Post by **ttocs** » Sun May 30, 2010 2:09 pm

hmmmmmmmmmmm

thedeal7235 · Post by **thedeal7235** » Sun May 30, 2010 3:15 pm

hopefully Eric will chime in soon: i run a rsd 500.4 on my bench w/ a dvd player for my daughter & it gets warm, not hot, not cold- the brief period i used it in my car it was never once warm like on the bench, is the noise still there? as i mentioned before it has always appeared both bias pots in same direction, but wait for Eric, stipud, or jacampb2 to chime in, i have always trusted any info. from either 3 of those guys, & theyve always steered me in the right direction

Post by **Eric D** » Sun May 30, 2010 6:18 pm

yeddy wrote:I turned down the pot on the left side to match the right one, now each side warms to the same temp, not hot and cold no more, just warm!

I think you solved it. Does it still sound fine?

The bias adjustment is not really all that critical. The only problem is if it is too high, then you can get thermal runaway.

On some amps turning it down is actually up, but I really don't think this is the case on your ZPA.

yeddy · Post by **yeddy** » Sun May 30, 2010 6:27 pm

Ya the amp sounds awesome, and stays really cool. I have been running it without the fans no problem! well at lease running my xm radio into it. The high pitch sound was coming from one of the transformers, I was thinking some hot glue or crazy glue would solve the vibration problem. I have a few other PG amps that have the high pitch sound problem too, must have been common, I'm surprised I haven't seen too much talk about this issue.