Sansui AU 7700 does not power up, no red light, and three fuses blown

[cicadasong]

I just purchased an AU 7700 yesterday that does not power up, no red light, and three fuses blown. I've been searching the "Exclusively Sansui" pages here and thought I would start a thread about this one. Here's a few pics fresh out of the box, haven't even dusted it yet. It was very well packed. Inside looks untouched and doesn't appear to have any obvious previous repairs. Other than the 3 blown fuses, I don't see any visible burns, discoloration or bulging caps, etc. The cover is missing from the voltage switch on the rear which makes me wonder if someone one moved it to 240 and plugged it in. Hoping to find a replacement cover. I had an AU 5500 in high school which sounded so amazing (although I recall it had a relay problem). I'm excited to to start troubleshooting and getting this AU 7700 working again. I have a service manual and I appreciate any guidance as to what my first steps should be to get started. Thank you! Jack

 

[Hyperion]

Congratulations on your acquisition, you may have blown OP transistors and other driver board damage, or possibly shorted main PSU rectifiers - to explain the fuses blowing.

I think I see the construction and use of a Dim Bulb Tester in your future...

 

[cicadasong]

Thank you! I'm guessing there are links or how to's on the site? Checking now...

 

[Overundr1]

Yes, you will need to build that dim bulb tester first, search dbt on AK, and welcome to the Sansui forum as well. I do not see any driver board burning, a good thing, so once you get a tester built stop by and we will be glad to help with trouble shooting. Nice looking piece, rebuilt several of them and they always impress when up and running.
-Lee

 

[cicadasong]

Yes, you will need to build that dim bulb tester first, search dbt on AK, and welcome to the Sansui forum as well. I do not see any driver board burning, a good thing, so once you get a tester built stop by and we will be glad to help with trouble shooting. Nice looking piece, rebuilt several of them and they always impress when up and running.
-Lee

Thanks Lee! Looks like I have all the parts I need to build a dim bulb tester, I'll start on it today and post when completed. I'm also looking at getting a Powerstat Variable Autotransformer. I've got a couple of amps I'd like to spruce up over time and thought it might be useful. Thanks again!

 

[Overundr1]

Assuming you live in a 120v area first thing before plugging in that unit is get that selector switch set to the correct voltage. Also will need to pick up fuses.
We reference the dim bulb tester and often neglect to say why. The dbt will limit current to the device under test. For example, with a 60watt incandescent bulb you will limit current to about 3/4 amp which will save expensive smoke signals to friends and neighbors. If it goes bright and stays bright you have a nasty short somewhere, gives you time to shut the unit down and proceed with repair. I also have a variac which I use extensively for tube work but the dbt is so quick and reliable for transistor work I use it constantly. Great for other things too like initial bias setting.

 

[cicadasong]

Assuming you live in a 120v area first thing before plugging in that unit is get that selector switch set to the correct voltage. Also will need to pick up fuses.
We reference the dim bulb tester and often neglect to say why. The dbt will limit current to the device under test. For example, with a 60watt incandescent bulb you will limit current to about 3/4 amp which will save expensive smoke signals to friends and neighbors. If it goes bright and stays bright you have a nasty short somewhere, gives you time to shut the unit down and proceed with repair. I also have a variac which I use extensively for tube work but the dbt is so quick and reliable for transistor work I use it constantly. Great for other things too like initial bias setting.

Cool, can't wait to get started! I also picked up an amazing 1962 Stromberg-Carlson console recently as well, so I'll be bringing it around by and by, sounds like a variac will be useful when working with it. The voltage switch is set to 117v, trick of the photo angle makes it look like it's set to 240. Where's a source(s) for parts, like the fuses, and capacitors, transistors and such down the line? I think we *may have one Radio Shack remaining, not sure how stocked they are on parts. Thanks Overundr1!

 

[Overundr1]

RS will have the fuses, make sure you get fast blow not slow blow. Most of my parts orders are through either Mouser or Digikey.

 

[cicadasong]

I picked up a few 1 amp fuses at the local parts store, they're not accustomed to selling to individuals anymore, so he just gave them to me. I'll check today to see if he or Radio Shack have the rest. I count 5 fuses total so far, looks like the 1 amps were not blown. I also got all the supplies (except bulbs) to make the Dim Bulb Tester. What wattage bulbs should I get?

 

[Overundr1]

I would use a 60w for this application at first.

 

[cicadasong]

I would use a 60w for this application at first.

Ok good to know! I just found a clear 55 watt bulb, I'll see if it's still good. Also, as a learning experience and just to get it clear in my head, I made this drawing of the Dim Bulb Tester using the parts I have, using a bulb socket that is wired and not plugged into the power outlet (seemed a little confusing to me). Let me know if I drew my wire paths correctly, (lavender = black = hot, also, I will probably use a 3 prong with ground). Not much mention of hot/neutral in all the way-too-many discussions of DBT I read, so I wasn't clear if it mattered,, but it seemed logical that hot was the wire to interrupt with the bulb filament. Thanks!

 

[cicadasong]

Ok, not at work today so playing a little catch-up on my Sansui AU 7700! I got all the fuses, except the only 7amp fuse radio shack had was rated for 125V, while it isn't written on the "original" fuse, nor in the repair manual, I'm guessing it needs to be 250V? These were the only two that were actually blown, the rest are fine. It says "Toyo" and has a triangle stamped on it.

 

[cicadasong]

RS will have the fuses, make sure you get fast blow not slow blow. Most of my parts orders are through either Mouser or Digikey.

I got all the fuses, except the only 7amp fuse radio shack had was rated for 125V, while it isn't written on the "original" fuse, nor in the repair manual, I'm guessing it needs to be 250V? These were the only two that were actually blown, the rest are fine. It says "Toyo" and has a triangle stamped on it. Thanks!

 

[petehall347]

if it is for the external fuse holder it is 6 amps not 7 .. 125v will be fine as your supply will be under that .

 

[Grbluen]

Subscribed.

 

[cicadasong]

if it is for the external fuse holder it is 6 amps not 7 .. 125v will be fine as your supply will be under that .

No, I have the fuse for the external fuse holder, (it was *not blown, but got spares anyway, see attached photo), it is the 7Amp fuses on the board I want to be certain of. I got all fast burn fuses as well. Thanks!

 

[Overundr1]

7A 125v will be just fine and yes they all are fast acting fuses.

 

[petehall347]

125v still ok .
voltage rating is for maximum voltage . they are rated for flash-over so anything above the voltage they will ever see will be fine .

 

[cicadasong]

Awesome, thanks!