[morzh]

In both boards or just one?
Can you put a photograph of the cap, in circuit, out of circuit put aginst a ruler, and blowup of markings?

[KCMike]

Its just one board. The caps are on each side one for IN-1 and one for IN-2 and in series with 1K resistors that goes to the bases of Q1 & Q2 respectively. I will get a pics for you but will be tomorrow. By the way they are 25 volt caps and 25v is what schem. calls for. Thanks

[KCMike]

Mike. forget everything I just blathered out. Rechecked the schem. and the 47ufs replaced C17 & 18.
which called for 50uf/25v. on schem. Got to quit working when tired.

[morzh]

OK, good then....

[KCMike]

Heres an update on the sx1500td.
Installed the main amp. back in chassis.
Rebuilt the control amp.( all new caps) tested transistors out of circuit. they test good,so reinstalled them. Resistors ck. good. Changed the caps on the Mic. board. Changed the caps on the muting unit, and indicator unit. I did these boards 1 at a time with power up after each board was done. Still very low audio on FM.

So I now get FM but at very low sound out of speakers. I did try moving the speakers to the B & C plugs with no change. It is getting stations across the dial. I recleaned all the switches this is 3rd time. The AM band plays very good, and loud or quiet as you want with the vol. control.
So I still have something amiss in the FM section. But at least I'm now getting FM.
Any FM experts? I need advice what to check next. Thanks

[Ron Ramirez]

Without looking at the schematic, my first two guesses would be the FM IF strip, or the multiplex decoder.

[KCMike]

Thanks Ron. I was afraid I might end up there. I don't anything about the mpx board or the IF strip except that the IF board has 4 metal can ICs (LM703L) they have 6 legs on each one. and the mpx board has a 14 pin. IC (mc1304)
I just started to take some transistor readings on the control amp unit. Although I had previously tested them.
When I went to check V/BC of Q1 with just (one) lead of the Dmm. touching the base, I got a loud hum at the speakers. I had nor yet touched the other lead to anything.
I'm going to go ahead and change the 4 transistors on the control board and see where I'm at.
NOT giving up!! and appreciate all the help I can get. Big thanks to morzh/Mike for his help.

[morzh]

I woud leave Ctl board alone.
As your AM is OK, the FM goes through the S1/S2 switches to the same input as the AM does so if any of the amps were bad, it would affect both AM and FM equally.

Stupid question, are any of your muting switches etc engaged by chance?
To rephrase, are all switches in proper position for you to listen to unmuted FM?

[KCMike]

Yes the switches are off./unmuted. I have tried pushing the switches in and out with it playing. Still low volume. The loudness button does function on AM. Can't really tell on FM.
I have the mode selector in normal stereo setting.
I do have to ask if you know why the base of the transistors on the control board make a loud hum through the speakers when only being touched with the tip of one probe of a DMM? I don't see how you could ever check voltages on the transistors with this condition.
I did check all the B+ voltages to all the boards and they are very close to, or are correct.
I think Ron might be right that its in the FM IF. section or the MPX. I have not messed with or turned any adjustments in regard to FM/tuner/ or AM boards. I do know better than to mess with any of them.

[morzh]

The hum is upposed to happen when a high enough impedance input is touched (which is whart the base is). Or if you simply touch an input connected to that base you will also hear it though possibly not as loud.

Should be the case in both channels.

[KCMike]

Thanks for that info. makes sense now. Would you know how to go about trouble shooting the FM, IF. and MPX section?

[morzh]

No, ain't no expert in that.

But before going inside, I would try to (even though I think they are OK) bypass all circuits between MPX unit and control amp by disconnecting everything first from MPX's L/R outputs, and from Con amp IN1 and IN2 inputs and then connecting them respectively L to IN1 and R to IN2.
If it is still low vol, then further exploration into FM circuitry is warranted.

[KCMike]

Okay great I will try that tomorrow. I did take some volt readings of the 14 pin IC chip
Pin 1-11.60v DC

'' 2- 2.16
'' 3- 2.94
'' 4-.958
'' 5- 1.1
'' 6- 10.80
'' 7-0
'' 8- 4.47
'' 9- 11.95
'' 10- 3.73
'' 11--11.94
'' 12- 11.94
'' 13-3.75
'' 14- 0
These are all dc volt readings. The schematic doesn't say what they should be.
Thought maybe someone might know if they are ok.
I did hook up my JVC disc player to aux. of stereo and it plays very strong and listened to Jonny Cash /Folsom prison
it will be a good stereo if I get the FM going.

[KCMike]

No, ain't no expert in that.

But before going inside, I would try to (even though I think they are OK) bypass all circuits between MPX unit and control amp by disconnecting everything first from MPX's L/R outputs, and from Con amp IN1 and IN2 inputs and then connecting them respectively L to IN1 and R to IN2.
If it is still low vol, then further exploration into FM circuitry is warranted.

I tried what you suggested. But want to be clear on if I did it correctly.
Unhooked the L & R wires from MPX output pins. Unhooked Con. amp IN 1 & IN 2 wires.
Used jumper wires and connected one to each wire that I had removed from MPX board L/R .Then hooked the other end of each jump wires to each pin( -L to IN 1) & (R to IN2) of Con. amp. I powered up this way on variac and all I got was a hum from the speakers.
I don't know if this is helpful but touching/scratching/tapping, the chassis or the switches with no knobs causes a scraping and or tap sound out of speakers.

[morzh]

Yes you did that correctly, and a possible reason for the hum is maybe the wires being unshielded (does it use shielded wires between amp boards?)
Another - you are bypassing the volume regulator V1 (a-d) at the control input and that one provides some DC pulldown to GND so the wire would not float. Not sure what we are dealing with in there.

As for the tapping, there are plenty of elements that will exhibit microphonics.....

In short, I do not know enough about FM tuners and the apparatus being remote from me does not help, so maybe someone who knows it can troubleshoot it remotely.