Aarrggghhhh...
I set it up to let it play awhile.
After playing nicely for a while, it developed a nasty static sound in the right channel. Minor at first, but then the minor became major.
So...back to the old drawing board...some circuit tracing is in order. Maybe later. I've put it back on the shelf for now.
Gotta be some crap in the balance/volume control that needs to be blasted out with Deoxit, or a not yet replaced carbon resistor, or a crappy trace but You are the pro. Find it! Best !
Thanks, Bill...
I suspect it is somewhere between the volume control and the final audio amp board (rebuilt). The static is present regardless of position setting (AM, FM, PHONO 1, PHONO 2 or AUX) and regardless of volume or balance control settings, so it must be after both controls.
I kinda doubt it is a control, those exhibit crackles when moved, not in steady state.
A cold solder spot, a cap on its way out.....
In fact if you make yourself a hi-impedance tracer with earphones, that can pinpoint it.
It isn't the volume control itself, no. I was saying the problem should lie somewhere between the volume control and the input of the final audio amp board which is freshly rebuilt.
I have a signal tracer.
If you have signal tracer (I take it, it is a tube type; provided it does not do anything dumb when used with solid state; shouldn't, but check first) - should be a piece of cake eaten while walking in the park.
As Wilbur G. would say: "...indeed..."
My signal tracer (Eico) is tube-type, but I've used it on Fisher solid state gear without any issues.
Well, sometimes old advice works best. Start from speaker and work backwards to antenna to isolate stage where problem is at. Always nice to have an auxiliary amp (well isolated of course) on the bench to help with differential diagnostics.
I haven't forgotten about this - it's just difficult to do anything during the week.
I plan to do some signal tracing tomorrow.
Not so easy, as it turns out...
I hooked it up to a pair of speakers last night and had my signal tracer ready.
This morning, I turned it on and let it play.
After an hour or so, the static began, so I started the signal tracing process.
Unfortunately, I could not find the source of the static. It goes back before the volume control...all the way back to the function switch. I traced as far back as the W15-081 push switch board which is located in between the function switch and the volume control. Static all the way.
I am now wondering if the problem could be in the power supply...something which is in common with all functions (AM, FM, phono, tape, aux). I replaced the electrolytics and the semiconductors on the power supply board...but I didn't touch any of the resistors. Maybe I should have?
This is obviously a thermal problem in that it does not manifest itself until the unit has thoroughly warmed up.
?????
If any of you want to follow along, you can find road maps here:
http://www.philcoradio.com/images/SX1500TD_manual.pdf (WARNING - LARGE FILE - 3.6 MB)
http://www.philcoradio.com/images/SX1500TD_schem.pdf (WARNING - LARGE FILE - 4.7 MB)
Looking at the three B+ outputs from the power supply...
B1 - 65V - measures 78V
B2 - 40V - measures 38V
B3 - 25V - measures 22.5V
Odd that B2 and B3 are a bit low, while B1 is high.
Quote:This is obviously a thermal problem in that it does not manifest itself until the unit has thoroughly warmed up.
Sometimes a hair blow dryer to accelerate the process and a can of freeze mist to cool down components can be helpful to isolate thermal problems.
http://www.amazon.com/Professional-Freez...B000Z99ZCA
Thing is, unless I'm mistaken the power is common for both channels and the problem is in only one, no?
It was, Mike...but while I was tracing the signal, the static switched to the other channel...then back to the first.
I dunno. May have to hoist the white flag of surrender on this one.
This is while playing the radio or records?
In any case if it jumps channels, forget the power, it is something else.
It produces static no matter what position the function switch is in - AM, FM, Phono or AUX. This is what initially led me to believe the problem was somewwhere between the volume control and audio output, or more correctly, between the function switch and the audio output. But I traced the static all the way back to the function switch.