nashou
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Post by nashou on Feb 20, 2016 22:41:25 GMT -5
I'll try tomorrow. Off to bed have to get up at 4:50 am I could take one out of my good A-1  but i dont want to mess that up. I sent an RFQ at this place www.afrenterprises.com/parts-search?partno=HW294680Lets see what they come up with. I asked for 10 Thanks Mac |
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Post by mastertech on Feb 20, 2016 22:46:26 GMT -5
Welcome.  |
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nashou
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Post by nashou on Feb 21, 2016 6:25:30 GMT -5
I got this responce from some one on AudioKarma "You will not find this kind of fuses resistors on MOUSER . You have to choose modern type if you don't have original type . I am sure that you know U=R x I and P = U(2)/ R so you have your answer 0,244 W !" So a 1/4 watt fusible should work? Here is the transistor datasheet.pdf (123.19 KB) But I am not much into the math part of this repair stuff So where do you get the values for this formula? all We know is the resistance 68 ohms and current 60mA. What Is U? Another member there also said to use a 68ohm 1/4 watt fusible flame proof. I think there are some on a few marquee boards actually( I hope) Just looked, the CVA board on a Marquee has 68ohm but I think they are 1/2 watt. What do you think? Nashou |
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Post by mastertech on Feb 21, 2016 9:57:15 GMT -5
Well you can dance this dance until the sun goes down. You can ask the question to 10 different techs and get 10 different answers. In the end it is the tech that has to decide what he is comfortable with since he is responsible in the end.
In my opinion, a fusible resistor is just that. A fuse and a resistor together. I would not consider a low wattage resistor fusible. It has to heat up and break to blow open.
If it was my project, in the end if i was not able to get the proper replacement then I would use a regular 68ohm resistor with a .062a pico fuse soldered in series.
Even for testing purposes I would try to get close to the ma rating. Cause who knows how many parts can get damaged in the event of another failure during testing.
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nashou
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Post by nashou on Feb 21, 2016 14:59:47 GMT -5
Well you can dance this dance until the sun goes down. You can ask the question to 10 different techs and get 10 different answers. In the end it is the tech that has to decide what he is comfortable with since he is responsible in the end. In my opinion, a fusible resistor is just that. A fuse and a resistor together. I would not consider a low wattage resistor fusible. It has to heat up and break to blow open. If it was my project, in the end if i was not able to get the proper replacement then I would use a regular 68ohm resistor with a .062a pico fuse soldered in series. Even fo r testing purposes I would try to get close to the ma rating. Cause who knows how many parts can get damaged in the event of another failure during testing.Thats what I was thinking too. I am ordering a bunch of resistors that are common in Amps so I'll add a few different values of axial lead pico fuses to have in my stock bins. |
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nashou
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Post by nashou on Feb 21, 2016 22:32:01 GMT -5
Well I decided to Check the main Power Transistors, and the once good right channel has both TR1 and TR2 blown. 0.000 reading on some leg combinations 0.00075 on others , they are shot. Now not sure how they are suppose to read but from the channel i was first trying to get rid of the distortion( left) TR2 - probe on C B=.578 E=.818 +probe on C B=.525 E=OL - on B + on E .534 +on B - on E .934 TR1 - on C E=.861 B=.500 +on C E=.821 B=.608 +on E - on B .904 - on E + on B .505 Not sure if that is normal reading for those or not. But the other channels that WERE GOOD are not shot due to my slippage.  Nashou |
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nashou
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Post by nashou on Feb 21, 2016 23:28:27 GMT -5
Well I ordered 2 of each from UTSOURCE. I ordered Marquee VDM parts from the before . Hope there not counterfeits. Nashou |
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Post by mastertech on Feb 22, 2016 9:59:49 GMT -5
Now not sure how they are suppose to read but from the channel i was first trying to get rid of the distortion( left) TR2 - probe on C B=.578 E=.818 +probe on C B=.525 E=OL - on B + on E .534 +on B - on E .934 TR1 - on C E=.861 B=.500 +on C E=.821 B=.608 +on E - on B .904 - on E + on B .505 Not sure if that is normal reading for those or not. But the other channels that WERE GOOD are not shot due to my slippage. Nashou I am assuming these are still in circuit? |
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nashou
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Post by nashou on Feb 22, 2016 11:40:45 GMT -5
Now not sure how they are suppose to read but from the channel i was first trying to get rid of the distortion( left) TR2 - probe on C B=.578 E=.818 +probe on C B=.525 E=OL - on B + on E .534 +on B - on E .934 TR1 - on C E=.861 B=.500 +on C E=.821 B=.608 +on E - on B .904 - on E + on B .505 Not sure if that is normal reading for those or not. But the other channels that WERE GOOD are not shot due to my slippage. Nashou I am assuming these are still in circuit? Yes they are. I could desolder the lead wires at the cap board and then just hook it up to my Parts tester I have. Then I'll know for sure whats up. Nashou |
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Post by mastertech on Feb 22, 2016 17:43:33 GMT -5
The numbers as they appear would indicate they are not blown out but would not be totally removed from suspicion. If they were on the good channel I would except it but if they were on the problem channel they would need to be tested out of circuit.
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nashou
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Post by nashou on Feb 22, 2016 19:56:38 GMT -5
The numbers as they appear would indicate they are not blown out but would not be totally removed from suspicion. If they were on the good channel I would except it but if they were on the problem channel they would need to be tested out of circuit. I tested one it was the PNP , so it seem like it is at least identified as working transistor. I have to run for a bit but i'll test the NPN and I'll take pics of the readings from my tester. And I'll test with the DMM as well if you want. Nashou |
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nashou
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Post by nashou on Feb 22, 2016 23:12:01 GMT -5
 - Probe on B C=OL E=OL - Probe on C B=.506 E=OL - Probe on E C=OL B=.509  - Probe on B C=.542 E=.543 -Probe on E C=OL B=OL -Probe on C B=OL E=OL Now I'm going to test the ones I blew just to be sure as I tested those in Circuit as well. Nashou |
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Post by mastertech on Feb 22, 2016 23:14:10 GMT -5
- Probe on B C=OL E=OL - Probe on C B=.506 E=OL - Probe on E C=OL B=.509 - Probe on B C=.542 E=.543 -Probe on E C=OL B=OL -Probe on C B=OL E=OL Now I'm going to test the ones I blew just to be sure as I tested those in Circuit as well. Nashou Looks fine. |
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nashou
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Post by nashou on Feb 22, 2016 23:27:09 GMT -5
Yep the other two are dead.
While waiting for the parts of the right previously good channel is there anything I can test while powered up? I can de solder the bad power transistors and add a 68 ohm 1/4 watt resistor in the fusible resistor location as I am not worried about loosing the main amps as they are dead now.
then I should be able to at least search for the distortion on the left.
Right? Or should I wait?
nashou
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Post by mastertech on Feb 23, 2016 12:31:30 GMT -5
I don't see why not.
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but i dont want to mess that up.
