Low output on left ch.

[Blad09]

Just did a cap change on a zx250. Powers up fine and right ch. sounds great but I can hardly hear the left ch. Any ideas what to check?? Bridge mode works fine. Tried switching L/R rcas and different speakers, still very low output on left ch.

[ajaye]

Have you checked dc output levels of each channel? I'm sure one of the experts working on these ZX boards will chime in, but could be as simple as needing bias adjustment.

[Blad09]

I have not checked DC levels, but I have read the tutorial in the how-to so I will go over it again and take some readings.

[trickyricky]

Have you messed with the bias pots? Post some good (hi-resolution) pics maybe one of us can spot something out of the ordinary.

But do as ajaye stated, check for DC on the speaker terminals (do this with no signal and no loads/speakers).

[Mr. Wild]

Adjusting bias and DC have nothing to do with low output on a channel as far as I understand.

There might be something wrong on the crossover board or maybe the gain pot is dirty. You might have loosened a connection on the ribbon wires when taking the amp apart.

If bridge mode works then we know that the output stage is fine on both channels and the fault is on the input side.

[trickyricky]

Your corrent Mr.Wild, especially if there is ABOSLUTLY no output, lol.

Blad09- can you give use some number regarding how much AC voltage the right channel is putting out vs left channel, you'll have to do this with a sinewave - an make sure your not clipping. Just to get an idea of how low is the left channel.

Could be the RCA inputs (broken pin or loose solder?) or like Mr.Wild stated....crossover, input section.

[MW3]

Possibly a bad freq potentiometer, a very common issue with ZX series.

Turn the crossover off and see if left channel returns to normal.

[Blad09]

Have you messed with the bias pots? Post some good (hi-resolution) pics maybe one of us can spot something out of the ordinary.

But do as ajaye stated, check for DC on the speaker terminals (do this with no signal and no loads/speakers).

Have not touched the biased pots. Will get some pics up as soon as I get a chance to take some.

Adjusting bias and DC have nothing to do with low output on a channel as far as I understand.

There might be something wrong on the crossover board or maybe the gain pot is dirty. You might have loosened a connection on the ribbon wires when taking the amp apart.

If bridge mode works then we know that the output stage is fine on both channels and the fault is on the input side.

Forgot to mention, there was some scratching on the FREQ pot when I first tried it, but after 10-15 rotations it went away. I will check the ribbons.

Your corrent Mr.Wild, especially if there is ABOSLUTLY no output, lol.

Blad09- can you give use some number regarding how much AC voltage the right channel is putting out vs left channel, you'll have to do this with a sinewave - an make sure your not clipping. Just to get an idea of how low is the left channel.

Could be the RCA inputs (broken pin or loose solder?) or like Mr.Wild stated....crossover, input section.

I will get all necessary readings as soon as I re-install the amp back in the vehicle.(don't have a power supply )

Possibly a bad freq potentiometer, a very common issue with ZX series.

Turn the crossover off and see if left channel returns to normal.

Will try crossover off along with all other tasks.

I will get to all of this as soon as I have some free time. Thanks everyone, I will report back with pics and readings when done. Thanks again,
Brad

[Blad09]

I would have to guess the x over card is a replacement. It's the only thing I can find that doesn't look right/normal. Right where the ribbon cable is soldered to the card.

Everything else looks fine in the means of solder joints/connection points. Meter readings will be up in next couple days.

[ajaye]

My 350 has the same thing, leftover flux where the ribbon cable attaches. It was upgraded to V2 by PG before I bought it so I assumed that was done while it was being serviced.
http://phoenixphorum.com/download/file. ... &mode=view

[Blad09]

I don't think its flux, I cleaned any spots I could find with laquer thinner and it didn't come off. It's almost like epoxy and the solder is definetly different than the rest of the amp(shinier). Also, mine doesn't have the v2 fan (7 blade) it's still an 11 blade, which I thought was part of the upgrade. Anyways, I'm sure once I get some readings with my meter it'll give u guys a better idea whats going on. The joints on the ribbon all look fine, I just noticed the difference in solder. Hope to get the requested info by tomorro.

[Eric D]

That style of ribbon cable is very unreliable. I have had more than one ZX amp with a low output channel due to broken connections on the ribbon. You should take a DMM in continuity mode and check each line of the ribbon from the bottom of the main board to the top of the daughter board. If you find one with a resistive connection, or no connection, it needs to be replaced. I typically use computer IDE cables cut up into shorter lengths and widths to replace ribbon.

Also, if only one channel works, I doubt the amp works in bridged mode. When you bridge the amp you are just getting half the voltage (due to one channel not working). Yes, you can wire it that way and hear sound, but at half the voltage, bridging the amp is not accomplishing anything.

[Blad09]

Okay.... everything seems to be working now must've been baked or something. I did get lots of readings tho if anyone cares lol. First off, DC offset-
Right ch. (-) 9.2 mV
Left ch. (-)30.7 mV That seem OK to everyone? Both negatives

Next, speaker output voltage @ minimum gain (6v), crossover bypass ON (0db 55hz tone)
Right ch. 3.0 v
Left ch. 2.8v
@ +/- 3v gain (halfway),crossover bypass ON
Right ch. 6.5v
Left ch. 6.3v
... with x over bypass off, HP at 30hz
Right ch. set to 14.3v
Left ch. 13.6v
Bridged 27.8v

Hooked up my 6x9's after all tests and it sound FANTASTIC! Don't know what happened the other day, but seems to be good now. Oh and Eric, ribbon cable tested fine, obviously lol. I thank everyone for the guidance and also apologize for the false alarm. Now just gotta find some gate resistors for my zx350 so I can start repairing it too . Thanks again u guys!