zapco ag 350

[Perry Babin]

You said earlier that the voltage on leg 3 of Q30 would drop when you applied remote voltage. The jumper will prevent the voltage from dropping (assuming that the trace is damaged/corroded under the caps).

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[genes66]

you are correct about that sorry!! now i understand. what is Q30 used in the circuit for?I have another ag 350 hooked up in car that works can i use it to troubleshoot this amp i am trying to repair? iam worried about possibly damaging the good one any suggestions?.

[Perry Babin]

Leave the good one alone.

The next hing you need to do is to connect the jumper (fused) across those points.

[genes66]

i will get some fuses tomorrow and do that and give you the results thanks for all your help

[genes66]

hey i ran a jumper like you told me and the power led came on whats next ? you said replace caps does it matter who makes the caps and what brand do you recommend?

[Perry Babin]

You need to pull the capacitors so you can examine the board and the caps. If there is an odor that smells like antifreeze when you apply heat to the terminals of the capacitors, there is electrolyte on the board and that means the caps must be replaced. This is likely what you'll find.


I'd suggest the FC series capacitors at Digikey.com. You'll need to measure the diameter, height and lead spacing to get the correct capacitor. Do an initial search like this (replace the values with the ones from your capacitors):

capacitor FC 1000uf 35v

Then go to the catalog pages for each cap to see which fits your amp.

You will need to run another jumper permanently. It doesn't need to be fused. The fuse was to help prevent additional damage in case there were other problems.

[genes66]

i have to run a jumper from d6 and d7 to Q30 permanantly?why?

[twon007]

or can't he just get a trace repair?

[Perry Babin]

The jumper replaces the trace that's likley been eaten away by electrolyte. The trace is under the capacitor. There is no practical way to repair the trace since the cap must sit directly on the board. The original trace was only ~0.002" thick. Virtually any repair will be much thicker. The jumper is the only practical repair.

When you run the permanent jumper, you should tack it to the board at several points with an adhesive. This will prevent it from moving which would eventually lead to it breaking near the ends.

[genes66]

sometimes it cuts off and you can hear a buzzing inside amp i opened it to listen cannot trace wear sound might be coming from maybe caps its hard to say does any one know about this