It LIVES.. sorta ;) The 2245 is out of ICU

Mike Sweeney

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Well, the left channel seems to be alive :) No magic smoke, It didn't blow the fuse and I have about 12 mVs across the speaker terminal before any adjustments. At least now it comes out of protection and the relay engages. Very faint sound if I crank it up all the way so I'm assuming the preamp is toast since it has not been touched yet. Well, not by me.. a few caps had been replaced at some point and if it was the same bozo who did the transistors and resistors .. oh well..

Now I need to wire in the right channel and test that next then mount it all.

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So when I wired up the right channel amp, it blew the fuse.. well hell.. I ended finding a short from a tiny piece of wire extending between pads that I missed after redoing the bias transistor install. I think thats it.. I have go buy some more fuses since I'm out right now. But, I wanted to check the power transistors and I had read some of Steven Tate's adventures with his 2245 so I decided to check the placement very carefully. I had taken pictures before taking anything apart and I had put the new transistors back as they came out.. which as it turns out was wrong :/ I'm not surprised given the rest of the work I have found on this system. According to the schematic and how the offset transistor sockets work out, NPN is on top, and PNP is on the bottom.. on BOTH sides. My right channel amp was backwards. PNP on top and NPN on the bottom. So, since I had everything apart to fix the short I found, I went ahead and swapped the transistors which tested good on the bench out of the circuit. I may have dodged a blown transistor by accident here with the short taking out the fuse before the protection circuit was enabled. I got off base because the LEFT channel was wrong when I took it apart. When I took the boards apart, I had used blue tape and marked NPN, PNP to keep track. At some point, I got the left side correctly wired up but didn't check/correct the right side. I just matched my tape .. dumb.

So note to self.. Don't trust what you see.. always verify ... I feel like a dope since I know better. But on to a better day assuming the fuse doesn't blow and no magic smoke gets loose.

The source of all evil in my 2245 ;) Someone had put the left channel 2514 ( PNP) on top when it should have been the 2513 ( NPN). This was verified by tracing the wires from the socket back to the board and checking the pin numbers
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The correct way which of course, I missed :/
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These are the pictures from the start.. I'll put up some once I get the right channel straightened out and both are wired back into the chassis.
 
Good job Mike!
The NPN is always on top (2245,2270) even though the boards are upside down from each other.
I always follow the red wire.

Tom
 
Whoot!!! Its ALIVE.. like with real sound and everything ;) The only thing is I cannot get the 5mv idle current adjustment as it says to do in the service guide. When I'm on pin J753 and J554, it's 37 volts DC. The DC off set zeros out just like it should with no load. Obviously I'm not understanding something here clearly..

Anyways.. I'm stoked that I've gotten the unit to fire up and use it's voice again. I still need to mount all this stuff and re-do the wiring some. Then I can tackle the P400 and P700 boards. I save the AM/FM boards till last.. they are such a PIA :)

Its a bit of an unholy mess with everything jumped into place. But it wont take too long to get put it back where it all belongs. The new shielded guitar cable is working well so I've got a winner there for re-wiring that part up. The right channel is still split from the chasing wires and verifying I didn't have any more shorts on it. I use the blue painters tape to keep the caps from shorting out by accident on something.
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ry J754 to J760, 10mV. The pins mentioned in the SM are wrong.
Yeah.. I went digging and I see people using this set of pins. Worked fine once I put some decent leads into the mix. My standard clipping with alligators didn't work well. But when I went to my BNC to alligator clips, life was much better :) 10.5mV after 30 mins of run time on this board. The drift after an hour is 1mV.. I can live with that. I need to swap it out and do the same now with the right channel board. Sorry for the fuzzy pic.. I didn't see that until I put on the desktop.

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I got both 750 boards into the chassis and wired in tonight. And she works well :) it took a while and some work to undo what someone else had done. It also took a new board ( thank you bob) and some new wiring.

I ended up replacing all four power transistors ( MJ21193/94), all caps except for the disk caps, all carbon resistors, both 10 ohm resistors, new 2.2 k pots, new shielded wiring and new bias transistors (2SC495).

Now to get to the tone board and preamp once my transistors arrive.

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Well now, what do we see here.. why am I not surprised :) This is what I found on the inspection of the preamp board. I wish this one could talk.. I'd love to hear just what happened to it .

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Jeesh, pad totally pushed off the board. How does that even happen?
 
Jeesh, pad totally pushed off the board. How does that even happen?
The cap looks like it had been replaced at one time.. ie.. glue on the board.. 1/8 inch gap from the bottom of the cap to the board and coupled with wrong parts, parts in backwards etc, this really didn't surprise me.

:::SIR!! Put the soldering iron down on the ground. no, not on your foot, on the GROUND.. :::
 
Ahh.. " well sonny, I only replace whats broken.. it disturbs the original sound" or some other drivel ;) This is why you want to replace 40 plus year old caps. You could not see this till you pulled the caps. But there was odd popping and crackling in the audio. These were on the outputs on the Tone Amplifier board. Leaking bulging caps. ESR meter says they are "Fine".. hardly.. Healthkit leakage test says they are worse than a sieve.. Its just another grumpy day over here.. where is my coffee..
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So the board is half done. All caps but I'm waiting on the transistors. But the caps cleaned up the crackling that was intermittent. I did change out the .22uf greenies to .47 Wimas. All the caps except three are films now. Cant wait to get the new transistors in to finish up this board.

Some notes of interest

The greenies which everyone says to leave.. measured in at .216uf and .214uf but each were over 2 ohms each vs the .52 ohms of the wimas
The Elnas .. the 3.3uf were clocking in 4.1uf at 3.2 ohms vs the 3.2uf at .3 ohms
The 1uf Elnas were not right.. 1.1uf but 13 ohms vs the new wimas at 1uf and .35 ohms

Just for an FYI at 1.3 volume.. the output transistors into 8 ohms were 89 degrees. The power supply was 109 degrees.. ambient was 74 degrees

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So what you do while waiting for the roast to finish cooking? Work on the P700 phono board :D
This was interesting.. the cap pushed and broke the trace. .It had not been replaced, the cap still had glue on it that matched the glue on the board. But there had to been a 1/16 of inch gap from the cap to the board plus the broken trace. The bottom of the cap was bulging and cracked. I'm guessing it overheated at some point? It's rated at 100 uf but tested at 147uf at something like .5 ohms.. not quite a dead short.

I jumped the broken trace. I think I'll put a dab of glue on it later today.

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You are having quite a day. I have ran into stuff that would curl your teeth.

It keeps it interesting. Yea interesting, that's it.:rflmao:
 
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