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Problem with Fisher CA-272

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tyler657recpro

New Member
Hey guys, I'm new to this board, but it looks like this might be helpful. Alright I have Fisher CA-272 Power Amp which only has one side working. There are no blown fuses, and I glanced at all the caps and they all looked fine. When I turn it on, the lights on the left meter (the broken channel) light up for a few seconds, and then fade down, if i remember, before the safety thing clicks off. The other channel remains unlit as it should. I don't think its the amp that's blown because when I pump it all the way on that channel, there is no distorted sound or anything. And when I hit the switch that changes the meter from 7watt range to 100watt range, the same light thing happens. No sound is produced which might coincide with the meter level jump, and the safety switch is off at this time. What possibilities are there and is this amp even worth fixing? Also the low end on the working channel sounds kinda shitty. I'm not sure if the speakers are just a bad combo for this amp or if it needs to be re-capped, or if it's something else. My guess would be its an OpAmp problem. But I'm not really very educated in this field. Any help would be greatly appreciated.
 

Gene

New Member
There are a great number of things that would result in the problems you describe. If the lights you are referring to are simple illumination bulbs, I would assume that there is a power problem that is either inoperative or is being shut down through a protection circuit. I would start with a schematic and trace the voltage points through the circuit one-by-one. This might give you more clues. If you don't have a schematic, you could test the voltages at various points in the channel that is working and compare the result to the same point in the channel that is not working. If all the voltages check-out, the problem is with a component and becomes more difficult to diagnose without specific test equipment.
 

tyler657recpro

New Member
I think I got it figured out. I'm pretty sure its the power transistors or whatever the things under the cooling fins, because, after running the amp for a while, I felt the two sets of fins wiith my hand. One was warm and one was cold. And the energy spike is after the saftey switches off by the way. But i think it would be possible for these transistors to emit such an energy spike which is not audible. I'm probably gonna try putting in the transisters from the other channel and see what happens. If it works, then I'll order new ones. It looks like they're only a few dollars. Does this sound plausible?
 

riteet

New Member
If you have an ohm meter, I'd take a measurement from the good (warm) trans. and then the bad one... be sure to allow for some cooling/discharge time. If they're different 80% chance you've found the problem!
 

riteet

New Member
I'm not sure what model trans. your measuring so I'm not sure as to the pinout of it... But I generally know these devices to short out (sometimes they do pop).

Simple answer, keep one lead to the center, and then measure each side.
 

tyler657recpro

New Member
Alright, I tested the resistance of both the transistors on each channel. Both on the dead channel had no resistance at all. And both on the good channel had like an ohm or so.
 

olly_k

Member
Well, I would say taking the resistance of trannies is a bad idea if you don't know what range to put your analogue? meter on, and also what to expect, better using the diode range instead. but it seems you have found a problem...
1. Did you take this measurment with the transistors still connected? It certainly sounds like they may be duff but if that's the case they may have taken somthing out with them... Also they may be ok if still connected and it maybe some other component that is short-circuit. unlikley though.
One of the first things I do when suspecting the power output stage is to measure for DC voltage at the speaker terminals on switch on. If there is more than couple of volts present you can bet the output trannies are dead. If this is the case you can nearly guarentee the speaker is as well!
Welcome to the world of hifi repair! and YES it is definatly worth a try because the feeling of satisfaction when you have fixed it is worth all the headaches and hair loss! Just don't be too dissapointed if you fail!
 

tyler657recpro

New Member
I did disconnect the transistors before testing them. I will try that voltage test. I did some hunting and found a place that has the parts. And they total 50 bucks plus shipping, and im not intending to keep this thing. If I could get 100 bucks for it, that'd be fine, but I don't know if i can. I'm not positive its worth repairing.
 

olly_k

Member
50 bucks??? What are the part numbers. We are talking transistors here and not an I.C. i.e. STK#### MkII or similar? I know some of them can be pricey!
 

Gene

New Member
If your output transistors cost $50, toss the thing out or use it for parts. After all, this may or may not solve the problem. The only thing for sure is that you will be out $50. I would look for another source of parts.
 

tyler657recpro

New Member
olly_k said:
50 bucks??? What are the part numbers. We are talking transistors here and not an I.C. i.e. STK#### MkII or similar? I know some of them can be pricey!
Yeah that's what I was thinkin. I thought it would only be a few dollars.

The original part numbers are 2SA1302 and 2SC3281 both from Toshiba. The replacement parts from fisher would cost 50 bucks. On a website somewhere, I found these parts for like 3 bucks, but somewhere else it said that if I found these parts, they were probably counterfeit, and that I should use the 2SA1943, 2SC5200 or the MJL21193, MJL21194 as replacements. Does anyone know where I can get these things? Or if those second number will be good replacements in the case I can't find the originals at a reasonable price.
 

seeker

New Member
Hey tyler,,

if these are transistors look around a little bit.
2SA1302

http://www.donberg.ie/descript/2/2sa1302.htm
Don't know where you live but they sure ain't 50 bucks around here :shock:
and P.S.....not too many people are gonna fake a 3 dollar transistor
 

Dremarcus

New Member
Problem

Hello,
I have this amplifer, but it is maybe dead. First chanel not funftion and second already too no. Maybe it has been broken fuse. In order to I wont ask You, if You accient have schematic this amplifer. SORRY for my English. I Am Czech... Please answer in very simple English. Thanks.
;)
 
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