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Old 11th March 2006, 01:38 PM   #1
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Unhappy Zapco Z400C4-SL

I'm working on this amplifier and need to find info on some semiconductors that zapco used in this thing. They are to92 type and they are on the front end of the amp. I can take some pics if need be. The part numbers on the transistors and locations on the board are; Q41-c436aj, Q48-c436aj, Q49-c448ab, Q54-c436aj, Q55-c448ab, Q60-c436aj, Q65-c448ab, Q72-c448ab. I've tried to cross them and find data sheets with no luck. With them out of circuit, two of the three legs show about 4ohms in either direction on both types and on the exact two legs. The middle leg to the third leg shows high resistance. I'm stuck. Don't know if they are regulators or some kind of mosfets or just bad transistors. The four 100uf caps in the same section did leak their electrolytic fluid. All the surface mount transistors in the area do not show any shorts. Would like to know what could work in there place. Any help would be greatly appreciated.

Scott
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Old 11th March 2006, 01:42 PM   #2
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Try adding 2S in front of all the part numbers:

http://www.google.co.uk/search?hl=en...e+Search&meta=
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Old 11th March 2006, 04:53 PM   #3
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Thanks for the responce, I've tried that and it comes up with T03 type case. These are T092 type. I will post a pic of the devices and where they were on the board. I know companies somtime have onetime part numbers for parts. I've run into this for kenwood amps.
Scott
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Old 12th March 2006, 02:52 AM   #4
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Default Pics

Here is a pic
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Old 12th March 2006, 02:52 AM   #5
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Another pic
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Old 12th March 2006, 02:52 AM   #6
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Old 12th March 2006, 02:52 AM   #7
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Transistor pic
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Old 12th March 2006, 03:13 AM   #8
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From the meter readings, it sounds like they're some sort of jfet but I've never seen a jfet with 4 ohms of on resistance. ~20 ohms is the lowest I've seen.

It's virtually impossible to have 8 transistors fail and give precisely the same readings.


What sort of problems were you having with the amp?

Were all 4 channels out?
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Old 12th March 2006, 12:52 PM   #9
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I benched it and it does power up about half the time. When it does power up, idle current is a little over 2 amps, preaty normal. When it doesn't power up correctly, it flashes the clip and fault LEDs on a 1 or 2 second cycle and stays that way until turn on power is removed. Nothing is burned on the PCB. I've replace all the finals and the power supply mosfets. Zapco told me-"Usually Zapco has bad electrolytics, value about 100uF is the usual suspect. Change all these small caps; if you have time, they are up to their time. Usually the "bad" residue is not white, but brown. And it is semi liquidous. Usually you cannot see them until you remove the SMD component first. They are corrosive to the copper PCB tracks. After you clean the suspected sections, spray all the pcb with contact cleaner, and brush them with used tooth-brush. This way will clean all."

I still wish I could find out what those eight transistors are
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Old 12th March 2006, 02:14 PM   #10
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I found a similar component in the Xtant I'm working on and found similar readings that confirmed that they are jfets. I attached a photo of the one I have. The part number is J108. Here is its datasheet:

http://www.vishay.com/docs/70231/70231.pdf


I was suprised to see that they have jfets with Rds-on of 3 ohms.

I believe that your components are good and you can look elsewhere for the problem.

When you have leaky capacitors, the residue of corroded copper and electrolyte is conductive. If the area under the capacitor doesn't come completely clean, make sure that you scrape the area between the capacitor's pads to break any conductive path.

If you have to remove any surface mount resistors or small surface mount capacitors, you need to use silver-bearing solder when replacing them. This goes for any surface mount component that has ceramic base material.
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