2245 Preamp Recap Screwup - Help

[Aaron J.]

I have a feeling there's many answers to this, but are there any common mistakes made when re-capping the P400 preamp board in the 2245..?? It was the LAST board on this rebuild and now I'm only getting the right channel for output. The amp was working fine yesterday. I've used it for a minimum of several hours after each one of the boards was re-capped to make sure I didn't slaughter something. I finally did it this time. Is there at least a layout to the board for Left & Right which can help me look at one correct section for screw ups..??

 

[catrafter]

Here's a pic of a 2270 preamp which I think is the same. Look for broken wires, too.

Tom

 

[Fairlane]

Like catrafter said. Look for lifted solder pads too as this will cause the exact issue you have. Use a magnifying glass as they are hard to spot otherwise.

Good luck!

 

[Steven Tate]

I had a similar experience with a 2245 and after close inspection, I found a cap lead I had missed when soldering. It was sitting in the hole, but no solder. So I think these guys have you on the right track. There is probably a soldering or trace problem somewhere.

 

[Aaron J.]

Thanks guys. I'm looking at it now and I'm wondering if some of those bottom solders are bad. They look a bit odd. I found those connections to be a royal pain with nothing but a tiny piece of wire sticking through. I figured I'd show these (even if they're embarrassing) before re-soldering anything and making things worse.

 

[Steven Tate]

Any new solder joints that don't look shiny and smooth (pitted, "frosty" looking, etc.) should be reflowed with a dab of new solder. If very many of the new joints are looking bad, you might have the wrong kind of soldering iron or the wrong temperature.

 

[Aaron J.]

Any new solder joints that don't look shiny and smooth (pitted, "frosty" looking, etc.) should be reflowed with a dab of new solder. If very many of the new joints are looking bad, you might have the wrong kind of soldering iron or the wrong temperature.

I'll definitely reflow them. I think my iron is ok, and I only say that because I've used for the entire build with no issues until now. It's an OKi PS-900 if that helps.

 

[kln138]

I was listening to a 2245 after a recap. Literally I heard the right channel fade and die. I used some cooling spray on the transistors and it came right back. I'm thinking after a recap and some better voltages a transistor that was just holding on went away.

As you are looking at the receiver the channels are literally on the left and right side of the board. If you have a way to trace it, put a signal in and see where it stops in the audio path.

And of course check your solder pads.

 

[kln138]

Another thought is to run another receiver through the pre and amp inputs in the back to see if in fact it's the pre amp or output

 

[Aaron J.]

I was listening to a 2245 after a recap. Literally I heard the right channel fade and die. I used some cooling spray on the transistors and it came right back. I'm thinking after a recap and some better voltages a transistor that was just holding on went away.

As you are looking at the receiver the channels are literally on the left and right side of the board. If you have a way to trace it, put a signal in and see where it stops in the audio path.

And of course check your solder pads.

That's definitely a good point. I'm working on re-soldering all the wires first and will go from there.

 

[hirscwi]

Another thought is to run another receiver through the pre and amp inputs in the back to see if in fact it's the pre amp or output

or you can just cross the left output to the right amp input and vice versa.

 

[KutzlerTrans]

Did you smack it yet to see if its not a dirty switch or something?

Its probably something simple.
The real question is... Does your cd player work on both channels or is this a phono only problem???

 

[Aaron J.]

Did you smack it yet to see if its not a dirty switch or something?

Its probably something simple.
The real question is... Does your cd player work on both channels or is this a phono only problem???

I actually just tried all inputs, AM, FM, Aux, Tape, and Phono. Still no left channel. I just spent the last six hours double checking the connections from the outside, into the pre-amp board as well.

 

[Aaron J.]

I just pulled the jumpers on the back of the amp and went directly from my laptop into the MAIN IN. Both channels are working and sound great. I'm assuming something on the pre-amp board is screwed up..??

 

[KutzlerTrans]

Check the solder joints at the pins. Getting them hot on top probably loosened a joint. it will look like a ring around the pin and it will move when you manipulate it.

 

[Aaron J.]

Check the solder joints at the pins. Getting them hot on top probably loosened a joint. it will look like a ring around the pin and it will move when you manipulate it.

I re-soldered all those connections today and checked them on either side for continuity. This is what happens when a "mechanical" person (me) messes in the "electrical" arena....disasters.

 

[Aaron J.]

Are the transistors typically replaced on the P400 board..?? I didn't have those listed.

 

[kln138]

Some replace the transistors in the course of refurbishing. You can go to hifi engine and download a schematic listing the transistors.
A quick glance at the schematic I see two transistors listed.
2SC1000 replace with KSC1845
There is an error on the schematic. It list the other transistor as a 2SC493. Should be 2SA493.
2SA493 replace with KSA992
Many have said the 2SC1000 is problematic.

 

[Aaron J.]

Some replace the transistors in the course of refurbishing. You can go to hifi engine and download a schematic listing the transistors.
A quick glance at the schematic I see two transistors listed.
2SC1000 replace with KSC1845
There is an error on the schematic. It list the other transistor as a 2SC493. Should be 2SA493.
2SA493 replace with KSA992
Many have said the 2SC1000 is problematic.

Thanks..!! I'll research it.

 

[rBuckner]

Don't toss the 1000's though. I replaced them before with the 1845's and the phono pre "motorboated" so they don't work everywhere.