1-2 is 0
2-3 is 0 turned counter clockwise
2-3 turned full clockwise doesn’t register unless I bump the MM up to 200k and then it bounces all over the place. From 11.4 to 19.4 and everything in between. It never stabilized.
Barn find Sansui AU-7900
- Thread starter Kylek1443
- Start date
2-3 is 0 turned counter clockwise
2-3 turned full clockwise doesn’t register unless I bump the MM up to 200k and then it bounces all over the place. From 11.4 to 19.4 and everything in between. It never stabilized.
Could you point me in the direction of a model number for a trimmer that would work? It’s no problem to replace the trimmer. I’ve used D100 on it before and didn’t make a difference so I’m sure it needs to be replaced.
I’ll look around and check with you before I buy something.
How does this look to you?
Attachments
Ok great! I’ll get it ordered and get back with you in a few days when I’m ready to install it. I’ll get 3 of them but we really should just worry about replacing the one, and then testing, right? I don’t want to get ahead of myself. Stick with me. I’ll have them in a few days.
I’ll do that! Hey on a side note, I wanted to show you what I dug out of a barn today. It’s a mess!! Bose 1800 with a mouse nest that’s seen 100 generations of mice! It’s awful. But most everything (except the two front handles) is here.
Attachments
While we are waiting on those parts I wanted to show you a few more things I pulled out of that barn! Thought you might like seeing some cool finds.
1968 fender bandmaster!
Tons of new/old stock resistors and ceramic caps
A pioneer sx 780
An oscilloscope from tektronix
Tons of cool stuff.
Attachments
Yes also have the kenwood KR-9000GX. I have 2 sets of Bose 901 IV, and a set of series I 901, which is why I would love to get this 1800 fixed. I’ve cleaned up most of the mouse debris to see the extent of the damage. The amplifier boards were already unplugged and unbolted from the heatsink. It’s a mess. BUT it actually looks fairly simple to put together. All the wires are modular. One of the amplifier boards has 2 power transistors missing. It came from a barn, the guy owned an audio/music/repair business from the 70s to 90s. He closed shop in 1994 and passed in 06. This amp has been in that barn 25 years at least.
Attachments
GrisPato
Super Member
Nice collection you have there. Even though no Sansui's. Here in the Netherlands the distributor of Sansui and Bose were the same.
There is a schematic available from the Bose 1800 so should be possible to repair it. Will have to find out what are the correct output replacements.
Circuit wise not especially simple though. High rail voltages. Would probably be best to start with a physical restoration. Cleaning, verifying connections ar correct and solid. Checking al traces and solderpads, etc. After that you can start looking at the electrical part.
Do I understand correctly that this amplifier is supposed to drive the 901 speakers?
There is a schematic available from the Bose 1800 so should be possible to repair it. Will have to find out what are the correct output replacements.
Circuit wise not especially simple though. High rail voltages. Would probably be best to start with a physical restoration. Cleaning, verifying connections ar correct and solid. Checking al traces and solderpads, etc. After that you can start looking at the electrical part.
Do I understand correctly that this amplifier is supposed to drive the 901 speakers?
Last edited:
I’m well into the physical cleaning of it. I have the mouse nest out finally, heatsink off, found as many screws as I could in the mouse nest. It was halfway in repair when it got thrown in storage. So screws are missing, connections have been removed, wires are chewed off, corrosion, the damage is extensive. I’ll be in the cleaning stage for a while. Yes! The 1800/1801 amplifiers and 4 or more 901’s make up what they call the Bose super system. I know the bad rep they get. I know there’s worlds better. But I like them. And this amplifier is the holy grail of Bose amps. I also have the spatial receiver to use as a pre-amp. On the lookout for a 4401 pre amp! It will be a fun project. I’ll definitely need you after we get this Sansui fixed. My next two major restores are this Bose and a pioneer sx 780. I’m going tacky with that pioneer. Purple LED lights and cocobolo veneer. It’ll be beautiful!
Attachments
Hey Gris! Hope all is well. I’m supposed to be getting those parts for the Sansui today. I had a few rookie questions I wanted to ask you. Is it necessary to turn the bias down on both VR before I pull them from the board? Since VR01 is the one giving us trouble, should I replace it first and test to see if the bias adjusts before I replace VR02, Or just replace them both, then test?
My last question is, when I get the parts can you help me make sure the leads are in the correct 1,2,3 order when I install them? Thanks again! Hopefully today might be the day the Sansui sings again!
GrisPato
Super Member
If you remember which way is turning up the current, clockwise or counterclockwise, put them as low as possible. Change them both at the same time. Should be self-explanatory how to replace them. Check them before installing with the DMM.
Most important, always start from the DBT after component replacement!
Most important, always start from the DBT after component replacement!
Just got them in the mail. Haven’t made any moves yet. How should I check them with the MM? It should be on 200DC and checking pin to pin right?
