Phoenix Gold ZX475ti problem with 1 channel - diyAudio
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Old 17th June 2007, 04:06 AM   #1
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Join Date: Jun 2006
Default Phoenix Gold ZX475ti problem with 1 channel

I Need help!!! I decided to put it in separate thread. This PG 4-channel amp is having a problem:
one channel is going out after 1-2 minutes of fine working. And I am going totally bananas trying to figure out how to fix it. This is what I found so far:
- It is easy to shutdown a channel by heating driver circuit with hairdryer. Then you need to wait a LONG time with power off until it starts working again.
- heating outputs do nothing, channel works
- 2 LED's in driver circuit for this channel is going off when channel is hot.
- tried swapping all big transistors in driver circuit (6 of them) with another channel. Problem is not moving.
- all resistors specs seems to be ok, all other transistors measures fine (without removing from board)

Driver circuit looks like to have a very fragile balance of two symmetrical circuits, and what happens, it's going out of balance...

Totally lost... I need any ideas. Thanks in advance!!!
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Old 17th June 2007, 04:49 AM   #2
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Join Date: Dec 2005
Location: Northern California
Sounds kind of like a bad circuit trace issue maybe. The RED LEDS are indicators that both + & - rails are intact and feeding the driver of the Triple Darlington output stage.

what does the 12 volt current draw look like before and after shutdown ? I would check immediate turn on with the blue LEDS on , then the current reading just before shutdown, and then the shutdown current draw.

It should turn on, then idle, then stay constant up till shutdown then the idle current should drop the same amount as the idle bias of that channel. Any other readings may be indicative of other issues.

By the way have you compared the idle bias settings and readings against each other. There is a little pad for each channel in between the drivers just at the sink. You can read the idle set here for each channel, and compare the settings.

The balance thing your referring to sounds like a bias idle issue < like Too much bias maybe.

What does the DC offset look like for that channel , and as compared to the rest of the channels ???

If it keeps bugging you, send it to me I will get it straight for you lol lol lol. I love PG amps. You can always find me on the Phoenix phorum.com
You can't miss it, it has the PG logo on its home page
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Old 18th June 2007, 02:36 AM   #3
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Join Date: Jun 2006
Thank you for reply and your offer! It made me much more motivated I just fixed it, spend too much time on it though. I hope it will prove to be worth it. So list of things wrong:
- two resistors was way out of spec
- one diode was awfully leaking
-and... the most interesting part of random, temperature-dependent turn-off: one of the red LED's was faulty!!!!! I had a similar case with JL amp before where LED was a part of driver circuit and lived his own, independent life.

P.S. I love PG amps too. They engineered great, performed beautifully, and a hugest pain in the bottom to disassemble/reassemble and work on it
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Old 18th June 2007, 08:54 AM   #4
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Join Date: Dec 2005
Location: Northern California
You must have never worked on Zapco amps hey?? Especially some of their art deco stuff, oh I hate them so bad. But anything made overseas nowadays is just as bad. I had to remove 38 screws the other day just to do a 10 minute repair.
Asian assemblers are working there bottoms off building this stuff

Those LEDs are a fairly common issue, along with the transistor just before it in the circuit. They run hot to the touch. On mine I removed them and reinstall on the bottom of the board so they touch the sink. On clients I leave them stock, no mods on original work to my clients.

Your amp must have seen a huge over current situation to cause what you found. Glad it all worked out for you. I see the diode issues more on their lower line stuff like Tantrums and XS amps. You have to give them credit though they don't copy anyone else's work. They truly design their own equipment. Thats more than I can for most of the rest nowadays...
Happy trails
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Old 21st June 2007, 02:53 AM   #5
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Join Date: Jun 2006
Beautiful amp. It's been 2 days installed in my car together with Ti800.1 + JL 10w6v2 and it's the best sounding setup I've ever had in my hatchback It's definitely not that 'sterile' sound, it's got a specific warm character, and seems to be I like it a lot.
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Old 21st June 2007, 04:12 AM   #6
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Join Date: Dec 2005
Location: Northern California
great Glad to hear its worth the effort. I run all PG in my car always have since 1992 when I first was introduced to them. I was a PPI fanatic before PG. I have and see all brands of amps being in the business I am in. I'll stick with what works and works well, PG..
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Old 24th June 2007, 07:36 AM   #7
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Join Date: May 2007
I'm also using PG Ti amps in my car.

I have been busy upgrading the Ti 500.4
Here you can see the things i did.

http://world.altavista.com/tr?tt=url&text=&done=doit&url=http%3A%2F%2Fforum.s howyoursound.nl%2Ftopic.asp%3FTOPIC_ID%3D58546&lp= nl_en

Translated to English

This is the original:

http://forum.showyoursound.nl/topic.asp?TOPIC_ID=58546

I replaced al opamps to better ones, removed the filter and bassoost section, upgraded the elco's and added a Musical fidelity Tube pre amp.
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Old 26th June 2007, 03:39 AM   #8
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Join Date: Jun 2006
Nice crossover board you have there
I like how you have a bottle of Heineken on your work table Ironically, mine has the similar bottle right now
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Old 23rd August 2007, 04:59 AM   #9
genes66 is offline genes66  United States
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Join Date: Aug 2007
Default zapco ag 350 car amp

anyone know anything about these amps
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Old 23rd August 2007, 04:59 AM   #10
genes66 is offline genes66  United States
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Join Date: Aug 2007
Default zapco ag 350 car amp

will not power up and does not blow fuse can you help
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