I have a PPI PC450 that I want to repair. Please help me if you can.
Here's what happened to it. I had this in my ex-gf's truck and her stupid boyfriend <not me; this was after we broke up> removed the speaker enclosure and didn't tape off the ends of the speaker leads. When I later removed the amp out of her truck I found that the fuse was blown.
Several months later I tried to install the amp in one of my cars and the amp comes on, but only plays for about half a second before going into protection. That last for about 2 seconds and then it plays for half a second and the pattern continues.
Common sense tells me that some of the transistors are blown, but I don't know how to begin testing them. Is there anyone that can help me out?
FYI. The sub box was running 4 ohm mono, bridged on channels 3 and 4 of the amp.
Thanks
Here's what happened to it. I had this in my ex-gf's truck and her stupid boyfriend <not me; this was after we broke up> removed the speaker enclosure and didn't tape off the ends of the speaker leads. When I later removed the amp out of her truck I found that the fuse was blown.
Several months later I tried to install the amp in one of my cars and the amp comes on, but only plays for about half a second before going into protection. That last for about 2 seconds and then it plays for half a second and the pattern continues.
Common sense tells me that some of the transistors are blown, but I don't know how to begin testing them. Is there anyone that can help me out?
FYI. The sub box was running 4 ohm mono, bridged on channels 3 and 4 of the amp.
Thanks
With no power applied to the amplifier...
Measure the resistance between legs 2 and 3 of the output transistors. None should read near 0 ohms. I think they were using 2N6488s and 2N6491s for the outputs.
You should not apply power to the amp without the bottom cover in place and tightened. If you do, you need to monitor the temperture of the heatsink mounted semiconductors VERY closely. They can overheat and fail in seconds if there is a problem.
Try to find the original threads when replacing the bottom cover screws. They can be stripped relatively easily if you don't find the original threads and cut new ones each time you replace the screws.
Measure the resistance between legs 2 and 3 of the output transistors. None should read near 0 ohms. I think they were using 2N6488s and 2N6491s for the outputs.
You should not apply power to the amp without the bottom cover in place and tightened. If you do, you need to monitor the temperture of the heatsink mounted semiconductors VERY closely. They can overheat and fail in seconds if there is a problem.
Try to find the original threads when replacing the bottom cover screws. They can be stripped relatively easily if you don't find the original threads and cut new ones each time you replace the screws.
Try digikey.com or mouser.com.
If the amp uses two 88s and two 91s per channel, you should replace both the 88s and 91s in the defective channel.
There's a good chance that only one of the 91s is damaged. If you pull one and find that only one is defective, you can reinstall the good one and test it at low power to see if there are any other problems. If it plays cleanly, you can replace the 88s and 91s and likely be done. If it's still distorted or goes into protection when the defective transistor is removed, there may be defective driver transistors.
Remember, you need to replace the bottom cover before applying power.
If the amp uses two 88s and two 91s per channel, you should replace both the 88s and 91s in the defective channel.
There's a good chance that only one of the 91s is damaged. If you pull one and find that only one is defective, you can reinstall the good one and test it at low power to see if there are any other problems. If it plays cleanly, you can replace the 88s and 91s and likely be done. If it's still distorted or goes into protection when the defective transistor is removed, there may be defective driver transistors.
Remember, you need to replace the bottom cover before applying power.
I took the 2 2N6491's out and went up to the local TV repair shop. They tested them and agreed they were bad. They don't keep those up there so they had to order them for me. They told me that the alternative transistor was a TIP42 NTE332. I did not know there was more than one model number for the basically the same transistors.
The TIP42 is not a good sub. I'd avoid using NTE or similar generic replacements.
Order the correct replacements. Replace all 4 outputs in that channel (88s and 91s).
Pick up some heatsink compound from Radio Shack (276-1372) and apply it between the transistors and the insulators. Be sure to clean the area before applying the new compound.
Order the correct replacements. Replace all 4 outputs in that channel (88s and 91s).
Pick up some heatsink compound from Radio Shack (276-1372) and apply it between the transistors and the insulators. Be sure to clean the area before applying the new compound.
If you use a TIP42, it could blow before the end of the first song if you drive it hard into a 2 ohm load. If you only use it to listen to talk radio at a low to moderate level, the TIP42s may survive for years.
Order the correct parts. The total will likely be less than $10 including shipping.
http://www.mouser.com/search/ProductDetail.aspx?R=2N6491Gvirtualkey58410000virtualkey863-2N6491G
http://www.mouser.com/search/ProductDetail.aspx?R=2N6488Gvirtualkey58410000virtualkey863-2N6488G
Order the correct parts. The total will likely be less than $10 including shipping.
http://www.mouser.com/search/ProductDetail.aspx?R=2N6491Gvirtualkey58410000virtualkey863-2N6491G
http://www.mouser.com/search/ProductDetail.aspx?R=2N6488Gvirtualkey58410000virtualkey863-2N6488G
You got a point there. The channel that has the blown transistors I use for bass, 4 ohm mono <which is the same as 2 ohm stereo>. I could swap the chips from channel 1, since those I would only run 4 ohm stereo for mids and highs.
We'll just see. The TIPs came in today so I'll play with it after work. If I things don't work our right, oh well. The fun of it is learning how this whole thing works.
Thanks for all you're help. I'll let you know what happens.
We'll just see. The TIPs came in today so I'll play with it after work. If I things don't work our right, oh well. The fun of it is learning how this whole thing works.
Thanks for all you're help. I'll let you know what happens.
I put the 42's in and it is still doing the same thing. I wonder if there is some power supply damage.
I e-mailed one of our technicians that works in the repair center and will see what else he can tell me.
Of course the easiest and cheapest thing for me would be to employee purchase me an Eclipse amp.
I e-mailed one of our technicians that works in the repair center and will see what else he can tell me.
Of course the easiest and cheapest thing for me would be to employee purchase me an Eclipse amp.
ppia600 said:Wow, I didn't know the nte cross would be crappier. They (nte) always brag about their crosses being as good or better than the original.Is this only in some cases? I do notice the cases of the nte crosses looking poorly made sometimes.
What would say if your were selling crap ?
Do as Perry says and use original parts only and your life will become a smoother trail. I have been doing this myself for over 20 years and both Perry and I know from real life experiences original parts rarely let you down
I've repaired a few amps, maybe thirty in the time I've been learning. Most of the time they were simple problems like bad solder joints or outputs or power supply transistors. I like working on american made amps (the older ones) and the alpine, sony and kenwood seem to be pretty straight forward and easy to repair.
Hello perry I have a pc4400.2 with a simpler problem q69 q70 q72 q73 appear defective have almost no resistance between pins 1 and 2 also the emoter resistors appear bad also I could use your help if you have time
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