Phoenix Gold ZX500 no low pass!! please help! - diyAudio
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Old 6th March 2013, 01:54 PM   #1
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Default Phoenix Gold ZX500 no low pass!! please help!

Hi everyone,

I have a Phoenix gold ZX500 on my bench and i am having trouble getting it to go into low pass. i am not very familiar with this amp and help would be appreciated.

This is what i have checked

all IC's have a good +LV and -LV rails (+15v and -15v), with no dc on any other legs.

i dont have any burnt marks.

i have read in other post that say the push button switcher are usually the reason for this issue, but i do not see the LP signal going into the switcher so i don't want to take it out unless i no for sure.

if some one could please tell me which IC'c control the LP signal or even a schematic for this amp, i would be very appreciated.

thanks!!
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Old 6th March 2013, 05:28 PM   #2
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If there is a switch for LP operation, you can safely assume it's an active part of the circuit. The switch can be tested with a continuity check, amplifier powered down of course. A signal injector and a DMM (or ideally a scope) should at the very least narrow you down to a specific area to test further if it's not the switch. You can even draw up a small 'block diagram' of the input and filter stage using these techniques and the data sheet(s) for the op-amps in the area.
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Old 6th March 2013, 05:36 PM   #3
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Quote:
Originally Posted by MatthewS View Post
If there is a switch for LP operation, you can safely assume it's an active part of the circuit. The switch can be tested with a continuity check, amplifier powered down of course. A signal injector and a DMM (or ideally a scope) should at the very least narrow you down to a specific area to test further if it's not the switch. You can even draw up a small 'block diagram' of the input and filter stage using these techniques and the data sheet(s) for the op-amps in the area.
Yeah, i kind of figured that i might have to do that, but i just thought someone might have a schematic. Or maybe had this issue before with any of the Phoenix gold zx series style amps.

i even tried contacting phoenix gold via e-mail to request schematic, but no response...might call next time
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Old 7th March 2013, 02:29 AM   #4
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The ZX and Ti lines of PG amps both had gain pot failures and mode switch failure issues. The push buttons are input select switches so yes unless they are set correctly also you will not get any signal < which RCAs feed what channels >

Schematics won't be helpful unless your use to and have access to the gear needed to signal trace the entire crossover board that floats above the amp channels just underneath the top cover plate. The selector switches are the main suspect, and they can open up internally and need to be replaced with original parts from PG. I have seen the gain pots for the crossover set points also go bad due to over manipulation.

Only on rare occasions have I seen burnt resistor behind the RCAs but this caused no signal at all in any mode. And a few bad LPL input control chip < LM13600A > which caused no bass in any mode since all bass passes thru this VCA with remote input to control Lo Pass Level.

Your best suspects are the Switches and crossover pots, then possibly the LPL VCA chip. I have never really seen any other failures of that part of these amps, so its my best opinion based on many amps I have repaired....hope this helps some..

PS there is a seller on ebay Altser-llc I believe you will find they can supply you parts and service. They are PG engineers and tech's from the Oregon days...here is the link to your crossover pot i believe; http://www.ebay.com/itm/NEW-VIMEX-10...item460a218a4e

Last edited by 1moreamp; 7th March 2013 at 02:39 AM. Reason: Altser-llc info
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Old 7th March 2013, 04:01 PM   #5
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Quote:
Originally Posted by 1moreamp View Post
The ZX and Ti lines of PG amps both had gain pot failures and mode switch failure issues. The push buttons are input select switches so yes unless they are set correctly also you will not get any signal < which RCAs feed what channels >

Schematics won't be helpful unless your use to and have access to the gear needed to signal trace the entire crossover board that floats above the amp channels just underneath the top cover plate. The selector switches are the main suspect, and they can open up internally and need to be replaced with original parts from PG. I have seen the gain pots for the crossover set points also go bad due to over manipulation.

Only on rare occasions have I seen burnt resistor behind the RCAs but this caused no signal at all in any mode. And a few bad LPL input control chip < LM13600A > which caused no bass in any mode since all bass passes thru this VCA with remote input to control Lo Pass Level.

Your best suspects are the Switches and crossover pots, then possibly the LPL VCA chip. I have never really seen any other failures of that part of these amps, so its my best opinion based on many amps I have repaired....hope this helps some..

PS there is a seller on ebay Altser-llc I believe you will find they can supply you parts and service. They are PG engineers and tech's from the Oregon days...here is the link to your crossover pot i believe; New Vimex 10K Dual Potentiometer for Phoenix Gold Amps Logarithmic Taper | eBay

Wow! thanks 1moreamp for the info!

Yeah i have most of the equipment needed to trouble shoot an amp (i.e. fluke DMM, Leader O-scope, 5 astrons VS-50M, spectrum analyzer....)

my friend just dumped off 10+ PG Z series and MPS series amps on me and I'm trying to get some fixed for him. PG's arent really my specialty, but an amp is a amp...

Schematics would be very helpful for the Z series or mps amps, if anyone has any please PM me! willing to trade schematics..LOL!

Does any one know where to get any of the 12 pin push button switches (HP/LP switch)?

Last edited by killerkeoki; 7th March 2013 at 04:25 PM.
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