Need Help Sansui AU-20000 protect mode
- Thread starter compworld
- Start date
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Check all fuses.
Pull the driver boards. Make sure it comes out of protection.
Replace the Sony transistors on the driver boards. Use KSC3503 and KSA1381.
That very well could solve it. From there I would replace the input diff pair with KSC1845.
You sure you know enough to be working on this very large and expensive amplifier? This is pretty basic troubleshooting.
I've seen too many things absolutely ruined by inexperienced techs.
compworld
Active Member
Im not going to say im a expert on this but know some of the basics and just went through a sx-1250 that had a short and blew a lot of parts on the stabalizer board and worked with a seasoned tech on here for a few weeks and got it going. i will pull the driver boards and check for protect mode. The stereo is ap my computer shop so i need to get it home to work on it. I feel likes its always best to check for similar issues to aide pointing in the right direction.
Sounds good. Just wanted to make sure.
I don't think there's any common failures for the 20000, but those Sony's have given me issues in other Sansuis.
compworld
Active Member
Finally got back onto this unit and pulled the 2 driver boards and still only getting the first click, speaker protect remains open, any suggestions on what I need to check?
william
Relay drive transistor had died in my BA-3000. Replace that and see.
compworld
Active Member
I was thinking that with both driver boards out that would rule out a bias/dc offset no protect issue?
compworld
Active Member
You happen to know what transistor drives the protect relay? think there are only 4 on that board?
I’m not sure how it would react without the driver boards but you could very well be right that it would eliminate the possibility of high offset or bias keeping it in protection. It was more of the “test what you know” comment than anything else. I’m not at all trying to sound condescending but sometimes it’s helpful to be reminded to “keep it simple”.....but you may be past that point already.
All the transistors on the protect board are the same. Schematic shows 5 x 2sc1364 and if I remember correctly the board has to be pulled and flipped so If you suspect one has failed you may as well change all 5 while you are in there.
Your issue may be found in the output section. Is there evidence of the heatsinks being removed and worked on before? Im sure you have done some reading and know all about the passthrough connections on these boards which need to be pinned and re-soldered. The thermistor is located in there also and if it is acting up can hold the amp in protection. Could also be the thermistor connection to the wires going to it which connect to the F2511 board. I think the board number is F2479 and the thermistor is a roundish yellow looking device. Maybe try to test the 2 wires going to the thermistor to make sure they are not OL on your meter.
compworld
Active Member
I did some poking around and unplugged 18,19,20 and 21 and no driver boards in and low and behold both relays click, I plugged 20 and 21 Which led down to speaker select board back in and it still clicked. So 18 and 19 lead to pin 3 on the 2 boards in output section. I tested those thermistors and one was 198 and the other was 302 ohms
Well it looks like you've narrowed it down to the output section. Out of curiosity did you run this thing with a DBT already to see if anything is shorted? It looks like you are going to be pulling the output section out of the amp for inspection/repair anyways but before that you might want to see what happens using a DBT.
compworld
Active Member
DBT went perfect and i still have the driver boards out. we recapped the driver board and i actually dim bulbed driver board separately and one board the bulb dimmed right out and the other was a very slight dull bulb, trying to fix this unit slowly and carefully and would like the relay to click on with 18 and 19 pin connected then will check into the one driver board. I was hoping to not have to pull the output stage.
richardpp
Well-Known Member
Terminals 18 and 19 are the left/ right channel audio signal connections from the main amp to the protection board. Check for DC voltage on those connections, anything above a few hundred millivolts is a problem. If the relays are closing with 18 and 19 disconnected then the thermistors are ok for now.
compworld
Active Member
I was thinking with both of the driver boards removed it shouldn't have dc on the speaker outputs? I will check for dc voltage on the 18 and 19 pin tomorrow.
compworld
Active Member
Ok so tested the 18 and it was 2.6v with wire connected and 19 was 3.2v! Removed the wires and checked pin 18 and 19 f2511 with no wire attached and they were .2 volts on both.
Please list the serial number so we can post it in the Sansui S/N database.
That helps us get an idea of how many of each we’re built.
BTW - I have the lowest S/N AU-20000 listed.
There are several AU-20000 rebuild threads that might give you further insight.
That helps us get an idea of how many of each we’re built.
BTW - I have the lowest S/N AU-20000 listed.
There are several AU-20000 rebuild threads that might give you further insight.
