TA-500 with No Phone Stage

Yes. Originally, I had good output from auxiliary and from the tuner. Now nothing. I ran some voltage tests on the power supply. Looks like I have correct DC voltage just past the rectifiers. None of the outputs show more than 10 or so volts. R05 (fusible resistor is definitely bad. I'm going to rebuild the power supply. I have a list of all capacitors, fused resistors and transistors but am unsure of exact replacements for all transistors. Below is my list or transistors and what I can find for replacements. Does my partial list look correct? And for the two in question, any suggestions?

Thank-you.


Original Replacement
2SD313 AL ……... TIP41C
FS7815M …….. ?
2SB507 …….. ?
2SA992...….... KSA992
2SC1845....…... KSC1845

I agree with Slimecity. Also, Sansui used their own part numbers for a lot of their chips. If you can read a different number directly from the IC or transistor you may be able to search for a cross reference that way. Make sure it is not functioning before replacing it though.
 
OK. Tested and replaced all capacitors on the power supply. I found 2 suspect caps: Both were 330uf caps that were measuring at around 260 uf. Also replaced the 3 4.7 ohm resistors and checked functionality of the transistors. All transistors are working properly. I hooked back up last night and ran through DBT and have good output on aux and tuner. Will set DC offset and bias voltages tonight and test out the phono stage. Fingers crossed.
 
Well, getting closer. I dialed in DC offset and bias voltages and gave her a test. Auxiliary output: Check. Tuner output: Check. But as for the phono section, it is working but only at low volumes Anything into moderate volume levels causes the sound to sputter and panel lights to flicker. I notice the issue is exacerbated by increased bass, loudness function on. Problem is less noticeable with subsonic filter on but is still present. Any ideas out there?
 

Attachments

  • upload_2019-2-8_23-27-32.png
    upload_2019-2-8_23-27-32.png
    342.4 KB · Views: 20
Last edited:
Well, getting closer. I dialed in DC offset and bias voltages and gave her a test. Auxiliary output: Check. Tuner output: Check. But as for the phono section, it is working but only at low volumes Anything into moderate volume levels causes the sound to sputter and panel lights to flicker. I notice the issue is exacerbated by increased bass, loudness function on. Problem is less noticeable with subsonic filter on but is still present. Any ideas out there?

View attachment 1413816
Since you recapped I believe, most likely one of the transistors is weak and breaking down. I replaced all with no problems after that. Check for cold solder joints as well. Caps all in correctly?
 
Well, getting closer. I dialed in DC offset and bias voltages and gave her a test. Auxiliary output: Check. Tuner output: Check. But as for the phono section, it is working but only at low volumes Anything into moderate volume levels causes the sound to sputter and panel lights to flicker. I notice the issue is exacerbated by increased bass, loudness function on. Problem is less noticeable with subsonic filter on but is still present. Any ideas out there?

View attachment 1413816

Hi,

Do you have the unit running through the dim bulb when this happens - you will have the symptoms you describe if the dim bulb is in circuit and you are trying to run the unit at normal listening levels, the dim bulb is limiting the amount of power that can be drawn.

Cheers

John
 
The dim bulb was not connected at this time. I have re-capped the power supply but have not re-capped the phono board. The only thing I did to the phono board is replace the 4 fusible resistors. Looks like I'm on to re-capping and replacing transistors on the phono board. I will say that what I have heard so far through the Aux. port is very good so this encourages me to keep moving forward with the restore. Very happy with the quality of sound.
 
I really liked the sound of mine when finished as well. Pay clause attention to cap polarity and ECB pin outs of BJT’s. Your almost there. Don’t want to fry those nearly unobtanium AN7070 driver amp IC’s on this last leg of your journey!
 
Getting ready to do some more work on this project. I checked voltages on the phono board last night. All match the schematic except at the transistor as hi-lited below. I am getting about -.4 volts here. I'm assuming the +40volt label shown below is incorrect?


upload_2019-2-18_11-5-40.png
 

Attachments

  • upload_2019-2-18_11-5-31.png
    upload_2019-2-18_11-5-31.png
    312 KB · Views: 2
I wouldnt assume its incorrect - rather it suggests that F3015 isnt getting the power it shoudl be getting at pins 5 and 6.

To double-check - measure the voltage that you are getting at the collector junction with R33 of the equivalent transistor (shown above the transistor you reference in the schematic) and tell us what it is.
 
At the junction of R33 and its related transistor, I get -3.87volts.
There is no chance of it being 40 Volts at that point - I think it is a misprint for 4 Volts, or actually -4 Volts, judging by the reading you are getting. ;)

How about the other voltages - all correct?

Have any of the electrolytic capacitors in the EQ amp been changed yet?
 
Last edited:
Here are the voltages on the board that I have gathered. I've replaced all the electrolytics and transistors. I have not changed out the ceramic and polystyrene cap's which are C15 through C20.

upload_2019-2-21_8-28-35.png
 
OK, those voltage readings look ok - As I understand it all inputs sound good except Phono, which is still as per your post #23 ?

And what are you using as an input to test the Phono input?
 
Correct. All inputs except phono are good. I'm using my turntable which plays fine at all volume levels through my standard receiver. On this TA-500, phono output is OK in the low volume range, but at medium to medium-high listening levels, that is when the problem starts. Sound cutting out and the display lights simultaneously flickering. The problem gets worse as volume is increased. Problem also gets worse as bass is increased.
 
Sound cutting out and the display lights simultaneously flickering. The problem gets worse as volume is increased. Problem also gets worse as bass is increased.
That really sounds like something power supply related - but I'll be danged if I know what!

My first though was that the phono input is being severely overdriven, :idea: but you say it works fine with another receiver - Soooo, what turntable, cartridge, and receiver do you have that work OK together - and what input on the receiver are you using. :idea:
 
Last edited:
Correct. All inputs except phono are good. I'm using my turntable which plays fine at all volume levels through my standard receiver. On this TA-500, phono output is OK in the low volume range, but at medium to medium-high listening levels, that is when the problem starts. Sound cutting out and the display lights simultaneously flickering. The problem gets worse as volume is increased. Problem also gets worse as bass is increased.

I wonder if you have a lot of rumble from your turntable, or possibly acoustic feedback from the speakers, which is causing the amplifier to be overloaded when you crank it up. How does it sound, when you listen to a record using headphones, speakers off, and turn it up loud?
 
Thanks for all the great help and information everyone. yet another great learning experience. I'm using the phono input on my receivers. My daily receiver is a Marantz 2265 with a Pioneer PL-630 TT (no discernible rumble) with Audio Technica AT14sa pq cartridge . I've run many different receivers with this setup down to 15 watts and have never had a similar problem. I will try the headphone test this weekend. Could it be an issue with the input switch? I'll see if I can isolate it further by cutting out one channel at a time and see if the problem persists on one channel vs another. I will test for acoustic feedback problem too. I'll move my speakers to a more remote location and retest. Feedback would give a nasty bump to my woofers. Now the problem does still exist with subsonic filter turned on, but not as noticeable. Maybe weak filter capacitors might explain this? I have replacements for these but haven't changed them out. Looks like I have to more than likely remove the tone control/power amp board to replace those. They are glued down pretty good and no room to remove the adhesive with the board mounted in place.
 
Last edited:
I replaced the main filter caps this weekend. Had to make a small hot knife with a bent tip at 90 degrees that I used to melt the adhesive around the edge of the cap just enough to break it loose without having to tug on the capacitor too much. Switched them out and took the receiver for a test run. Playback when my receiver is switched to Subsonic Phono is excellent! Sound/light cutout still happend on regular Phono but it takes a higher volume for the problem to appear. That's as good as she's going to get I'm afraid. Thanks again to all for your help.
 
Back
Top Bottom