blown two zx 700.5s and two deq 9200a

[rolexcomm]

Hey guys, after some time researching and finding out what is the cause of all my system failures, which I pretty much narrowed it down to a defective head unit, I have a zx 700.5 that is protecting itself. Knowing a lot about electricity but not a lot about electronics I would like to get some help fixing this amp and maybe moving on to the deq 9200. Please forgive me upfront if I ask too many questions as I don't have a lot of electronic background just what I have picked up over the years in classes for automotive repairs.

Now I have taken my zx apart and have not found anything obviously burned and have not dismounted anything except for a few resistors because some are out of range, they are suppose to be 2 watt and .1 ohm resistors and most read almost one whole ohm. So I will start by replacing these. I have voltages all across the board and on one set of rca's I have 7+ volts on the outer edge...The problem with this system was that the ground circuit in head unit was never connected and after time kept blowing other items. We replaced the ground and fuse inside the head unit and that seems to be working fine for now. Any help would be appreciated thanks in advance

[Perry Babin]

Touch your meter probes together. Subtract what you read with the probes shorted from the resistor readings. Do you still get near 1 ohm for the resistors?

[rolexcomm]

Hello Perry I took into consideration for the calibration of the meter yes I do get almost an ohm on 6 of the resistors. there is a group of 8 of them and two apprear to be within specs but I will replace all of them. they range from almost .5 up to an ohm. Also, fyi I have checked most of the transistors onboard and none seem to be shorted together or open. I have high resistance readings on all legs of the transistors. Also I checked a majority of the resistors and diodes and all seem to be working well, of course I checked these on the board. Now I power this thing up with my own little box that gives off fused 14.4 volts and while I am checking the transistors on the board the whole input side gives me b+ but the output side only has 7v. I might have these sides backwards but I think that tells me that I am not getting enough power??????????? and this would mean a power supply problem??????????? just asking questions to understand.... thanks again

[amc32]

what exactly do you mean as the input/output side,do you mean the input jacks on the amp or one leg of a transistor?

[rolexcomm]

power supply and output sorry for the confusion.....

[Perry Babin]

What is the current rating on your power supply (little box?)?

It's very strange to have burned emitter resistors without having any shorted outputs. Are you sure that no individual output transistor has anything near 0 ohms between any of the legs (1-2, 1-3, 2-3)?

[rolexcomm]

I am pretty sure, I checked all of them twice on both the power supply and output sides, but like I said these are mounted on the board. The current rating on my box??? I think if I remember right it is rated at 15 amps. But don't quote me on this as we use it to power up blower motors, electromagnetic clutches from ac compressors, and I used it once to power up a head unit and amp at idle......

[Perry Babin]

With the amp connected to nothing, measure the resistance from the B+ terminal of the amp to the RCA shield. What's the resistance?

[rolexcomm]

It shows 4.2M ohms resistance on the b+ to the shields of amp 1 that has 7v when powered up. The other two amps have no resistance they show out of range. I also checked the ground side and it shows continuity on the same amp with a reading of 22K ohms..

[Perry Babin]

With one probe on the B+ terminal and the other on the input RCA shield, twist the power transformer to see if the resistance ever goes to ~0 ohms. It's a strange coincidence that the power supply is pulled down to 7v and you have 7v on the shield (which should essentially be at 0v).