Sansui AU-505 issue

[T1996]

Hi,

I picked up a lovely Sansui AU-505. Unfortunately, all the outputs where blown. So, I replaced them with the recommended replacement, the MJ21194G. Not too difficult you would think, however the problems are starting now….

I cannot get the 27v on the output caps (c819/c820). Changing the pot settings does not influence it all and it stays at +-54v. Checking and replacing tr815 with a ksc2690 did not solve this issue unfortunately. In the meantime, I recapped the power amp board, and the problem is still there.

For now, I do not know what the issue could be. Some help would be welcome, as I want to get this nice piece of equipment in working condition again.

Thanks!

 

[Hyperion]

You should be looking at TR807 & TR809 and TR808 & TR810 - damage like blown output transistors usually affects more than the OP transistors themselves.

 

[stereofun]

First off check the the TR815 replacement for correct pin-out. and check its solder points. Also if you replaced the output caps, carefully check their connection - in order to get new ones in, you usually have to jerry-rig the pcb as the old terminals are spaced much further apart, than new ones. On a general note, its a good idea to do a post recap check - visually run through your replacements and check +/- and ECB pin-outs, solder points etc.

The MJ211's are execellent replacements !

 

[T1996]

Thanks, TR810 & TR809 was damaged. Luckily i ordered already some replacement for those. So i could easily swap them with a ZTX795A.
Without the fuses in, I get the 27v on both channels now
but when i power it up my, 60w dim bulb starts to glow after a few seconds, not full but quite noticeable.
and the voltage is 14v on both channels now
I checked all the new connections and couldn't find any problems there.

btw, thanks for your excellent documentation of the restoration of your AU-505 @stereofun

 

[penmarker]

You should be looking at TR807 & TR809 and TR808 & TR810 - damage like blown output transistors usually affects more than the OP transistors themselves.

Hi Hyperion. Rather than creating a new thread I think I could reuse this thread instead. I have on my bench a 505 and TR807/808 are also faulty. They crackled terribly with freeze spray. However 2SA532 TR809/810 (their complementary pair) are fine. I haven’t found a suggested replacement for these yet.

Is it ok to only replace TR807/808 and leave the complementary pair alone?

 

[Hyperion]

Is it ok to only replace TR807/808 and leave the complementary pair alone?

The named transistors above are one in each channel, they are half of a complementary pair, the pairing is TR807/809 & TR808/810 - you should replace each pair if either/both of the transistors in a pair are faulty.

 

[penmarker]

The named transistors above are one in each channel, they are half of a complementary pair, the pairing is TR807/809 & TR808/810 - you should replace each pair if either/both of the transistors in a pair are faulty.

Thanks, I've ordered a bunch of ZTX694B/ZTX795A on digikey to replace them. This 505 sounds amazing on the good channel.

 

[penmarker]

I checked my parts stash and found BD139/140. After checking they're:

• Ratings: both are 80V, 1.5A. the 2SC875 is 75V and 2SA532 is -50V, so voltage is on par with the original.
• Speed: the BD139’s fT is about 190MHz typical, near the 2SC875’s 170MHz. The BD140 is about 75MHz, higher than the 2SA532’s 45MHz. But that unequal pairing resembles the original pair (am I right to think this way?)

Either way I installed the BD139/140 into one channel, dim bulb shows healthy sign, and did the biasing. During listening it actually sounds pretty dang good.
So I swapped the other channel too. Now I'm letting it play for a while. I like it.