nashou
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Post by nashou on Feb 19, 2016 21:22:33 GMT -5
Right, not the volume, or any of the switches. Most likely on the drive board or the board they are calling the electrolytic capacitor. Those pots are most likely for idle current or bias adjustment. I dont know if the scope will even help now. You are most likely going to have to start testing parts with your DMM. If something appears to be testing funny you can compare that reading with the adjoining good channel. I do not think it is the relay since the speaker and headphone use different contacts. But you can solder a wire across it if you want to make sure. Ok, I'm headed back now. Would introducing hum by touching the left input wire on the drive board indicate a bad ground connection some where? And I assume you mean I should test parts on the board with it powered off. That board is on one side of the unit , I think its just connected via the wrap around wires so I should be able to test both sides. If I remove the cover the populated side is facing out. I would have to partially remove board to test bottom points. Could I use an RCA splitter into one of the inputs and use my test tone from the LCR meter I have and prove the wave forms on my dual channel scope along different parts in the signal path? be home in 15 Nashou |
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Post by mastertech on Feb 19, 2016 21:40:21 GMT -5
Right, not the volume, or any of the switches. Most likely on the drive board or the board they are calling the electrolytic capacitor. Those pots are most likely for idle current or bias adjustment. I dont know if the scope will even help now. You are most likely going to have to start testing parts with your DMM. If something appears to be testing funny you can compare that reading with the adjoining good channel. I do not think it is the relay since the speaker and headphone use different contacts. But you can solder a wire across it if you want to make sure. Ok, I'm headed back now. Would introducing hum by touching the left input wire on the drive board indicate a bad ground connection some where? Not really.And I assume you mean I should test parts on the board with it powered off. CorrectThat board is on one side of the unit , I think its just connected via the wrap around wires so I should be able to test both sides. If I remove the cover the populated side is facing out. I would have to partially remove board to test bottom points. Could I use an RCA splitter into one of the inputs and use my test tone from the LCR meter I have and prove the wave forms on my dual channel scope along different parts in the signal path? You can try the scope but I think you are just going to find noise all over the place since the signal travels along many places. But give it a shot if you want.Have you checked for any DC on the signal lines? Maybe test at L101 and L102. Signing off for tonight.be home in 15 Nashou |
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nashou
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Post by nashou on Feb 20, 2016 9:30:47 GMT -5
Ok I am working from memory right now. I should again have taken notes. Ugh. I scoped the points along the Electrolytic where the main power transistors are connected. Pic below. Obviously the right channel 1khz wave is nice and clean at all points the wave was visible. Now here is where my memory fails, but i'll go back later today from work and re test all the points and give a detailed reading. there were some pints where the 1khz wave is not shown but another wave is, maybe I need to adjust the scope to see it better. But AB and AE on the left channel were not clean( fuzzier) compared to its right counterpart crisp wave. CE was clean on both left and right. Would this be the input to the transistors? I dont remember how CB,AC, or CC looked. I think there was a different wave there or it was off the screen. I may need your help with those settings on the scope as I am still not proficient using one. So that is what I have from memory. I think one of the left Transistors may be the culprit .  |
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nashou
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Post by nashou on Feb 20, 2016 19:07:43 GMT -5
Had a slight accident. But thank God When I was working on my other A-1 and I had a similar mishap I ordered Extra Transistors! I was looking at the schematics and decided to scope the signal at the point of entry to the Cap board at transitors TR133 and TR135, and compare to the right channel TR 134 and 136. I couldn't get a good contact using the safety cover on my probe so I removed it. Guess what? I slipped saw a spark and then smoke before I could shut it down. So TR134 is dead I think and R102 I should have some radio shack resistors of that value and I have another 2SC1913. I was thinking to scope the +0 line and -0 line and compare. If that was clean and then after each Transistor before it got the the main power transistors. I hope I was using proper deduction compared to my improper cautious probing  Nashou |
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nashou
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Post by nashou on Feb 20, 2016 20:39:41 GMT -5
Ok FR102 is also dead. Its a fusible type. I have regular 68 ohm 1/2 watt resters can I use that safely for testing or am I risking
frying the transistor.
Nashou
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Post by mastertech on Feb 20, 2016 21:05:25 GMT -5
Well it would only be a problem if there is still a problem. If you have any pico fuses you can put 1 in series with the resistor.
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nashou
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Post by nashou on Feb 20, 2016 21:20:08 GMT -5
Well it would only be a problem if there is still a problem. If you have any pico fuses you can put 1 in series with the resistor. Oh like the type that are on the 5 volt rails on a marquee Vim? I can steal one. So would a regular fusible 68 ohm 1/2 watt type work there? I am trying to look for the same type but not sure. The one that died is a 68 Ohm 60mA resistor. Would the mA rating be the same as the wattage? The original is a HW 29468 Micron 82( markings on resistor) Schematics say 68Ohm 60mA Nashou |
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Post by mastertech on Feb 20, 2016 21:26:44 GMT -5
No, ma not the same as wattage. I do not know the spec on the marquee fusible. The ma is a big concern, especially the 60ma. That is very low.
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nashou
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Post by nashou on Feb 20, 2016 21:33:27 GMT -5
No, ma not the same as wattage. I do not know the spec on the marquee fusible. The ma is a big concern, especially the 60ma. That is very low. That is why I didn't try it. I didn't check that one when the saw the 330 Ohm burnt. Also I removed the Power supply board to have more room to work. What I did was another stupid thing on my part. I plugged it in with no PS board, then the 330 ohm began to smoke again. then I decided to check the other parts and it is then that I found the FR102 open. I don't think anything else got hurt, at least I hope.  Nashou |
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nashou
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Post by nashou on Feb 20, 2016 21:45:40 GMT -5
Marquee is a 3 amp !! no go with that one.
Nashou
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Post by mastertech on Feb 20, 2016 21:46:51 GMT -5
well 3 amp for testing purposes is better then no amps.
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nashou
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Post by nashou on Feb 20, 2016 22:06:47 GMT -5
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Post by mastertech on Feb 20, 2016 22:23:57 GMT -5
Do you have any 20 ohm resistors?
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nashou
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Post by nashou on Feb 20, 2016 22:26:52 GMT -5
Do you have any 20 ohm resistors? I should have some. nashou |
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Post by mastertech on Feb 20, 2016 22:30:09 GMT -5
The phono section has a bunch of 47ohm 70ma resistors. Just series 1 of those with a 20ohm regular and you should be fine for now. The goal is to get it running properly first and then try to find the correct parts.
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