The PHILCO Phorum

It's been a year and a half since Mike rebuilt his Pioneer SX-1500TD. I've owned one for a little while longer than that, and used it regularly until it developed audio issues.

I've decided to completely rebuild the audio amp board with all new electrolytics.

This required pulling the board from the chassis...which is mounted in such a manner that the output transistors and heat sink are all mounted to the audio amp PC board.



This is a view of the audio amp board from underneath.

Removal required unsoldering and removing eleven wires, removing the metal cage on top covering the output transistors, removing two screws holding the whole thing in place, and pulling it out from the top.

I ordered the parts from Mouser tonight.

I've put this job off far too long. I'm looking forward to getting this one running again. I had previously replaced all of the dial lamps, and it looked good and worked well until it lost one audio channel. It's rated at 58 watts per channel into 8 ohms.

You forgot the pic.

I didn't forget...I don't have a good "before" shot of the entire unit right now.

OIC. It's just that you indicated there was one. These Pie-in-ears are certainly a PITA to work on, but, IMHO, well worth the effort.

Most Pioneers (pie-in-ears...I like that ) are desirable receivers. One like mine is less so, from what I have read, only because of the speaker plugs they used on early 1970s and older models.

I'll post more photos, chiefly that of the audio amplifier board in question, once the parts arrive from Mansfield, Texas.

 Look forward to your rebuild Ron. Thanks to you and morzh/Mike it is my daily driver in the work room and still playing very well.

I did post a "how-to" on AudioKarma showing how to replace the fuse lamps in one of these receivers with LEDs some time back:
http://www.audiokarma.org/forums/showthr...=SX-1500TD

And Brenda, I did find a frontal shot of my SX-1500TD in my AudioKarma thread:



This photo was taken before I replaced the meter bulbs, and replaced the indicator bulbs above the dial with LEDs.

While I wait for parts...



Here's the audio amp board with the output transistors and heat sink. The two output coupling caps (1000 uF) have both been removed already, and the remaining electrolytics have been desoldered and are waiting to be pulled and replaced with new Nichicons.

Nice to see you still have the original matched output transistors.

Mike

...yes, but not for long...new MJ21194Gs are arriving today...

Any reason you are changing them, Ron? (unless bad?) Transistors do not go bad from age...for the most part (there is that legendary whiskers growing in Ge).

Acked. I know. One audio channel is bad. If the original outputs happen to still be good, I'll save the MJ21194G transistors for another project. But if outputs are bad in one channel, I'll replace the whole set.

Well...

I decided to just dive in and replace all of the old electrolytic capacitors...and transistors (including the outputs).





This way, this board should be in good shape for another 40 years.

I carefully compared the operating specs of the originals before choosing replacements, since the new transistors do not have the same type of bodies as the old ones (excluding the four output transistors, that is).

Success - I have audio in both channels again! (At least, through headphones...I have no reason to believe that it will be any different with speakers, though.)



I really should give the same treatment to the power supply board now.

And I now remember that I need to replace the wee little bulb that lights up the dial pointer. That should be fun.