Well, I'm not sure what I've learned. I opened the unit & looked for a short. I couldn't find anything. I decided to see if it would power up enough to check the voltage across the .047F cap that I replaced. I removed it, and I was watching R164 closely as I powered up. It is a 2W 18 ohm flame proof resistor, so I reasoned that it could still be operating correctly (Even though it had gotten red hot). The resistor shows some discoloration, but not as much as I expected considering the heat it had seen. It got almost red hot in about 15 seconds, so I never got a chance to check the voltage across the .047F cap. I had about a half a beer contemplating the situation & decided to lift one leg of R164 & check it. It shows 67 ohms.
One other bit that bears mentioning again: this unit was being frequently used & worked fine until I unhooked it about 3 months ago.
I'm thinking that I should replace the resistor & see if it will power up any differently. I ordered two of the resistors... I'm not sure if any of what I saw tonight tells me anything. Of course, I'm probably wrong.
I'm open to recapping this receiver, if I think that'll fix the problem. I just have trouble thinking the caps failed since I last used it 3 months ago. It would be good practice for me, though.
One other bit that bears mentioning again: this unit was being frequently used & worked fine until I unhooked it about 3 months ago.
I'm thinking that I should replace the resistor & see if it will power up any differently. I ordered two of the resistors... I'm not sure if any of what I saw tonight tells me anything. Of course, I'm probably wrong.
I'm open to recapping this receiver, if I think that'll fix the problem. I just have trouble thinking the caps failed since I last used it 3 months ago. It would be good practice for me, though.
Your resistor is wrong value, but resistors don't usually deteriorate based on time, just from abuse. Electrolytic capacitors have rubber seals and water inside, and like tires, start deteriorating the day they come off the machine. One day the water is gone, and poof! My H182 organ built in 1968, the motor capacitor shorted in 1997 and burnt the wire harness from the power plug. I can tell the date because the dealer tech replaced that cap and one other on the power supply with Hammond factory parts- the date code is YYWW where years is 19YY. You should hear my thunderous screaming 1968 H182 organ with 70 new caps and the destroyed case (helper ran away after I rented the truck). Next to it sits a 1969 H182 organ with beautiful case and a new motor cap. Sounds like a kazoo, and has about as much power.
I recapped my ST70 tube amp in 1983s with parts from the Dynaco bankrupcy auction (stereo cost cutter), then quit using it because the power tubes were tired and replacements came from the USSR- the entity I had been driving around the Fulda gap in a 5 ton truck staring down. In 2010 I'm retired and JJ is making power tubes in Slovakia, so I bought some and installed them in the amp with the practically unused 1983 cap- a Cornell Dublier cardboard tall can simulation. First night it sounded great! Poof- next day it blew the fuse- the cap had leaked out. Oxygen and rust, they never sleep.
I recapped my ST70 tube amp in 1983s with parts from the Dynaco bankrupcy auction (stereo cost cutter), then quit using it because the power tubes were tired and replacements came from the USSR- the entity I had been driving around the Fulda gap in a 5 ton truck staring down. In 2010 I'm retired and JJ is making power tubes in Slovakia, so I bought some and installed them in the amp with the practically unused 1983 cap- a Cornell Dublier cardboard tall can simulation. First night it sounded great! Poof- next day it blew the fuse- the cap had leaked out. Oxygen and rust, they never sleep.
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I don't think so... something else has happened.
It needs methodical fault finding now along the lines of isolating the rails that the 14 volt reg feeds and seeing where the excess current is being taken.
OK, I think I follow. I need to figure out what is on the other side of R164 & then start disconnecting each branch until I fugure out what is drawing so much current? I'm looking at the schematic right now, but I'm having a hard time with it. It looks like R164 is part of the voltage regualtor part of the board, but I'm having a hard time tracking down what it feeds. It is obvious to me that my schematic skills aren't up to snuff... I'm going to have to spend some quality time looking at the schematic & actual circuit to figure it out.
The good news is that I'm off after today and won't have to come back to work until Tuesday. In between my more interesting projects (Custom 2-way speaker build & extremely retro cabinet for the my NAD pre-amp & Carver amp made from a pre-prohibition wooden beer case) I hope to be able to come up with something.
The good news is that I'm off after today and won't have to come back to work until Tuesday. In between my more interesting projects (Custom 2-way speaker build & extremely retro cabinet for the my NAD pre-amp & Carver amp made from a pre-prohibition wooden beer case) I hope to be able to come up with something.
To begin with I would check for obvious shorts. Although you can not reliably measure most resistances in circuit when checking for shorts you can.
So with the unit off and your meter on a low ohms range measure between ground (chassis) and point A in my diagram. Also do the same for the end of R164 that feed the reg. If either reads short or very nearly (that's 0.00, same as when you short the meter lead together) then it needs investigating.
So with the unit off and your meter on a low ohms range measure between ground (chassis) and point A in my diagram. Also do the same for the end of R164 that feed the reg. If either reads short or very nearly (that's 0.00, same as when you short the meter lead together) then it needs investigating.
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