[morzh]

Is it mechanical or electronic?
Can it be inspected, cleaned?

[PhilcoMike]

Ron,

Try tapping on the resistors in the power supply section while this is occurring and see if you can get it to stop.
Could be a crack in one of them letting values change when warm.

Mike

[Ron Ramirez]

Is it mechanical or electronic?

I wish I knew...

...oh, you mean the function switch. Mechanical. This unit dates back to around 1969 or 1970.

Can it be inspected, cleaned?

Yes...and it shall be cleaned tonight.

Try tapping on the resistors in the power supply section while this is occurring and see if you can get it to stop.
Could be a crack in one of them letting values change when warm.

Thanks, I will.

[Ron Ramirez]

Waallll, this is a very interesting situation here...(spoken in my best Jimmy Stewart drawl)

I removed the shield from the function switch and cleaned it, letting it dry out for a little bit before trying it out again.

The static returned after about five minutes of playing - first in the left channel only, then in both.

I had left it right side up so I could check the outputs of the AM and FM boards.

Both were clean, no static.

I then turned it upside down again and retraced the signal.

The sound was clean at the volume control...but the static was present at the input to the W15-079 control amp board. The static was much louder, of course, at the output of the control amp.

So now I am wondering...could the control amp be the originator of the static, and is it severe enough to make it reflect at the inputs of this amp (yet not show up at the volume control)?

Forgot to mention...tapping on various components made no difference.

[Ron Ramirez]

I'm thinking that the next time I go to the bench, I'll see if I can find my test leads with alligator clips, disconnect the inputs and outputs of the control amp, and run the sound from the volume control direct to the main amp.

I know the volume will be low, but that should tell me whether or not the static is originating in the control amp board.

[Ron Ramirez]

Europa! ...er, Eureka!

I do believe I have localized the trouble...

I disconnected the input and output wires from the W15-079 control amp board and connected them together, not touching anything else, so there are no wires connected at the inputs or outputs of the control amp.

Yes, as expected, I had to turn the volume up, but it produced clean sound when connected in this fashion.

As the control amp is still "live" in that it is receiving voltage, I connected the signal tracer to the control amp's left channel output.

There it was...loud static...

I'm going to let it play for awhile to make sure the static does not reappear elsewhere, but at this point I believe I've found the problem - and I will have to rebuild the control amp board.

I think I will replace everything on this board, including resistors.

[morzh]

Cold solder spot.

[Ron Ramirez]

Maybe...but with a unit that is at least 43 years old, I want to do this once and do it right...and not have to be concerned about it again for another 43 years.

(Depending on who you believe, the SX-1500TD was built between 1971 and 1973...or as early as 1968...who's right???)

[Mondial]

Before you change all the components, why not try hitting each with a bit of of freeze spray when the board is warmed up and making noise. At least as a matter of interest, you may find out which part was causing the problem

[Ron Ramirez]

I don't have any. Perhaps I'll get a can when I order parts to rebuild the control amp board (which I am still going to rebuild).

Oh, I let the unit play for over two hours with the control amp bypassed...it never produced any static except in the control amp board itself when it was checked with a signal tracer (inputs and outputs disconnected).

[morzh]

I would just troubleshoot it. How complex can it be....just out of pride.

Does it have solder posts for power wires? If yes,they develop cold solder joints.

Wiggle some wires there, tap on it. It is more likely to be a joint than a bad component.

[codefox1]

Just replace the parts if you'e got 'em. I've spen enough hours grinding down old flimsy circuit boards, replacing failed traces by fine wires wound around components stuck through remaining holes in the plastic, and washed away again with whatever solvent would work without melting the plastic. The components themselves, unless unobtanium, were never of any concern.

Can't think of any story told here or anywhere else that Freeze spray actually helped anyone beyond the cost of the can and time spent using it, but we'll hear some stories I'm sure.

One technique I have used especially on smaller circuit boards is to use an old pencil iron, maybe file down it's hopelessly corroded tip to nearly a point, plug it into my stupid ancient lamp dimmer outlet, get it to the point where I can work the thinnest multicore solder I have to the beast at hand, get the bench well lit, use a pair of magnifying glasses and take it slow and even. If you can create or recreate a silvery band across the original traces from point to point, you are probably OK. Seems like patience is a virtue, but sometimes, a step happens all at once, so just back off then, and see if you have it.

All bets are off on multi circuit layer printed circuits, that's above my pay grade. You'll probably be charged to dispose of that stuff.

[Ron Ramirez]

Okay folks, due to popular demand, this topic is open again.

I apologize for getting angry. However...let's limit the Ooooh, eh eh, you should troubleshoot at the compoooooonent level comments, okay? It would be different if this was a 5 or 10 year old unit. But it's well over 40 years old; electrolytics are drying out; parts are failing; it was time for some major work and so this Pioneer received it. Get back with me when you have a 40+ year old piece of electronic equipment and you've gone in multiple times to replace one part at a time at the component level.

Now, boys and girls, when we last left off, I was waiting for parts from Mouser to rebuild the control amp board. That was enough in itself to drive me crazy. As you know, Mouser purports to ship orders the same day if the order is placed before 8 pm Central Time. Well...I posted an order a week ago this evening, and it was placed by 5:30 pm CDT. Guess what? They sat on the order until the next day. Then they thought they were doing me a favor by changing the shipping from FedEx Ground to FedEx 2 Day Deliver Weekday. Guess what? This guaranteed that I did not receive the order until Monday, so I was unable to use the parts this past weekend as I had planned.

I've placed enough orders with Mouser that I know if an order goes out on, say, a Monday night via FedEx Ground, that I will have the order on Wednesday as it takes just two days to get here. But by their using 2 Day Deliver Weekday and not shipping until Thursday night, the order sat in Louisville from Friday afternoon until Monday. Had they used FedEx Ground and shipped the order Thursday night, FedEx would have delivered on Saturday.

Oh well...</rant>

[Ron Ramirez]

So anyway...

Since I did not have the parts I needed to completely rebuild the control amp board, I went ahead and removed it. Just for fun, I also removed the head amp board (phono preamp). Here's how the two looked when pulled from the receiver:

[Image: http://www.philcoradio.com/images/phorum..._00032.jpg]

After several hours and more than a few feet of desoldering braid, the control amp board looked like this:

[Image: http://www.philcoradio.com/images/phorum..._00033.jpg]

[Ron Ramirez]

Finally, the parts arrived on Monday.

I immediately set out to completely rebuild the control amp board. As you noticed above, everything was removed - so it received all new parts including resistors.

When I was finished by last night, here's how the control amp board looked:

[Image: http://www.philcoradio.com/images/phorum..._00035.jpg]

Last night, I also partially rebuilt the head amp board. This time, I did not bother any of the resistors, replacing only the transistors and all capacitors.

On both boards, any electrolytics of 1 uF and below were replaced with WIMA or Nichicon polyester.

This photo shows the completely rebuilt control amp board, and the head amp board with a few new transistors:

[Image: http://www.philcoradio.com/images/phorum..._00034.jpg]