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Sansui AU-7500 relay not clicking after partial recap/transistor replacement

You genius! That was it. Scrapped a little on the trace to make it take on solder and added a bit more to fix it. Turned it on and "CLICK." Sounds great. Can't thank you enough!!! I never would've found that.
 
Unfortunately, the saga continues... I am going to never touch this thing again when I am done!

I got a few more caps for the driver board and the tone/eq board, and also replaced a few transistors on the tone/eq board. I replaced the last non bipolar electrolytic on the relay board as well. Doubled checked the transistor orientations, all good. It’s possible a pair of transistors is bad, they were from my parts box but were new. That is unlikely, thought, and wouldn’t cause total silence.

Since the last post where the relay was fixed, I replaced:
C811/C812
C703/C704
C709/C710
C707/C708
C741/C742
TR705/TR706
TR703/TR704
C906
C743
Unamed cap on underside of relay board

Now I get a relay click, but no sound (not even an idle sound) coming out of the speakers. I checked the DC bias from the rear fuses and it is just where I set it, around 30 mA. DC offset close to 0 for both. My thought is another open somewhere from soldering--these boards seem quite fragile. I don't see anything, though. DBA fades quickly and behaves normally when turned on. Fuses are good.

Curious as to the dead silent aspect--volume knob does nothing. It sounds like the relay isn't working, but it is clicking.

Things I should check for voltages if there is no sound, but the relay clicks? I get music in headphones but it is a bit quieter than it should be.
 
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Start by narrowing down problem. Find a source (tuner or or other sound source with volume control, and go directly into the amplifier input jack. (Is the jumper between pre-out and main-in installed?) Since you have relay click, my bet is that amplifier part works, and problem is preamp related.
For preamp, start with the simple or obvious. Is four channel switch in right position. Tape monitor switches in right positions. Knobs on selector switch in right position (this can drive you crazy if it is off and not indicating the proper input.) Make sure you didn't put a shorting plug into one of the output (tape, 4 channel, or main out) Shorting plug is just an RCA plug where center is connected to ground, and are normally only used in unused phono inputs - not useful anywhere else) Check for negative supply voltages to preamp boards.
Trouble shooting will get tougher if no problems are found - you need something to follow signals, as voltages may not tell you the answers. Standard equipment is oscilloscope - although there are ways to trace signals without one. Several people have done it using a capacitor coupled lead and a tape deck....
 
sregor said:
Start by narrowing down problem. Find a source (tuner or or other sound source with volume control, and go directly into the amplifier input jack. (Is the jumper between pre-out and main-in installed?) Since you have relay click, my bet is that amplifier part works, and problem is preamp related.
For preamp, start with the simple or obvious. Is four channel switch in right position. Tape monitor switches in right positions. Knobs on selector switch in right position (this can drive you crazy if it is off and not indicating the proper input.) Make sure you didn't put a shorting plug into one of the output (tape, 4 channel, or main out) Shorting plug is just an RCA plug where center is connected to ground, and are normally only used in unused phono inputs - not useful anywhere else) Check for negative supply voltages to preamp boards.
Trouble shooting will get tougher if no problems are found - you need something to follow signals, as voltages may not tell you the answers. Standard equipment is oscilloscope - although there are ways to trace signals without one. Several people have done it using a capacitor coupled lead and a tape deck....
Click to expand...

OK--all switches and connections are the the correct positions, jumpers installed. I switched to the phono preamp to test it--it works. So, I should focus my attention on the tone board (F-2014) correct?

As for checking negative voltages, do you mean like checking for -20V at one side of C706 as listed in schematic?

I do have a signal probe that I use with a small guitar amp, so I could use that if needed. I'm never great at following the signal path on the schematic, but I could try.
 
Oh Man. I had reversed TR705/TR706. Something about the board orientation messed me up even though I knew they are ECB. Flipped em and it works great.
 
Noticeably less bass response in the left channel and possibly slightly lower volume. Tested out with a record and the same track digitally to make sure it wasn't just the phono stage. So maybe something is uneven in the tone board. I still have more transistors to replace, but ran out. It seems like a big enough difference that I can't imagine variances between transistors would cause it. (Unless I damaged one of the transistors by running power through it when it was reversed?).

It is possible this imbalance existed before and I did not notice it, I'm not sure. I sort of don't think so, however.

The left channel sounds weak even after swapping the left pre out to right amp in, and vice versa with the jumpers on the back, and even when on the Stereo Reverse, or either mono settings.

EDIT: After much back and forth listening, I swapped the speaker connections and the problem stayed in the left speaker. It must be an issue with my KG4, not with the sansui. Headphone L channel has full bass. Odd.
 
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Just saw this post while searching around since I am having the same issue on my au7500. Did you ever resolve the issue with yours? I have recapped the driver block F2034. I went to test and the relay would not click on. I have also recapped the protector block F2041 and F1215A. Issue still not resolved. I even removed the relay and cleaned contacts and reinstalled. Still no luck.
 
Oscar66 said:
Just saw this post while searching around since I am having the same issue on my au7500. Did you ever resolve the issue with yours? I have recapped the driver block F2034. I went to test and the relay would not click on. I have also recapped the protector block F2041 and F1215A. Issue still not resolved. I even removed the relay and cleaned contacts and reinstalled. Still no luck.
Click to expand...
Have you checked the voltages on the relay protect board, as in posts 3 and 4? Rare for relays to actually be bad, commonest problem is there is DC on the output, and protect circuit is doing its job. Post some measurements on the protect board so we can get an idea of what's going on.
 
Thanks for replying. While checking the transistors I heard the relay kick in. After removing and testing transistors tr901 and 902 it looks like they are open on one side. Also looks like they were installed backwards according to the spec sheet. I have ordered replacements, All diodes checked good as well. I will check input voltage again and post.
 
Your meter is your friend. Quick sanity check is to figure out the base lead with your meter. Japanese transistors normally have collector in the center, so all three leads can be easily checked. Transistor checkers will also verify leads.
 
So after going back and double checking transistors 901 and 902 they look good. It is ecb configuration, so base is on one of the outside leads. Checked all the diodes and resistors as well. All look good. Input voltage good as well. So I decided to reinstall everything and bingo! Relay is now activating. My only guess is it might have been some bad solder joints. Thanks for your input. Much appreciated.
 
Update. After testing several times relay is turning on intermittently. Checked voltage on 9y and 9z using 9u for ground. getting around 60mv on 9z and 250mv on9y. could this be an intermittent issue with transistors 901 and 902? Have replacements on order.
 
So my relay was not kicking on originally due to a lifted trace from replacing a cap or transistor--the boards on these are fairly delicate. I found it by checking continuity and tracing out the circuit with a DMM.

I still have not fixed my issue with popping when I switch to the phono stage--there seems to be DC on the switch. I still have some noisy transistors to swap out, but I'm also looking for pointers on tracking down the loud pop on the phono switch... does this mean the issue is on the phono board?

Sorry I am not more helpful Oscar--I am not very experienced with troubleshooting circuits. Mostly, I have been able to restore units due to the generosity and experience of people on the this form helping me fix my mistakes... :)
 
So it turns out once the relay clicked on I went ahead and did the alignment by adjusting the variable resistors and once that was done I didn't have any other issues with the relay. In the past any pops were resolved after doing a full recap on past amps I've worked on. If it's only on the phono switch that pops I would look at the schematics and trace out that particular section. If I have any info I'll let you know. Alot of my fixes have just been trial and error. My Sansui is sounding great now!
 
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