AU-9900 Stuck In Protect

[Segasonic91]

Continuing on from my thread about channels dropping out, I have started to recap as I was getting LOUD pops and clicks and it was then going into protection. As I was told it is resistors that cause this, I decided to start work with what I have on hand (still waiting for some backordered caps).

I replaced all caps on boards F-2567 and F-2568, as well as all A726 and A1313 transistors on F-2568.

After testing, I was not getting the relay kicking in. I am 100% positive all caps are in the correct polarities, I will not make THAT mistake again! So I will have to double check the 6 transistors I installed. Again, I am certain they are in correctly. I installed going off the readings of the transistors in the tester, but I will double check tomorrow.

The only caps I was not sure about where the 2 100uf, 80v caps on the underside of F-2567. I forgot to check before I took the old ones out. I lined up the old caps and it seemed like negative was on the outside, and positive were conected to the centre. Is that correct?

On another not, I discovered that F-2568 and the phono board (F-2570) were recapped. Terribly, I might add!! Every capacitor was the wrong uf value! What ever moron did the work, they linked two 470uf/160 caps together in place of the 220uf/10v bi-polar cap!!! No WONDER this thing has problems! All of those shitty, cheap caps are out and replaced with CORRECT value Panasonic FC caps. I guess this was yet another lie by the seller, I was told it had never been re-capped.

 

[Segasonic91]

Oh one other thing, I will be replacing the dreaded 798 transistors on the phono board, along with the rest of them. I tested a few 992 transistors tonight, and was getting 432hfe for all but one of them, I guess they were the same batch. Now I know that the pairs to replace the 798's have to be "matched", but do they need a low as possible hfe or just matching or close as possible?

 

[LBPete]

It would help to know what unit you are working on.

- Pete

 

[Segasonic91]

Oh yeah, good point. I put tags on the thread but stupidly forgot to write it in here. I planned to link to my old thread, but forgot to add it.

Thank you to the mod that changed the thread title for me

 

[Segasonic91]

Well, I re-watched the video of a AU-9900 re-cap on YT. I wanted to check that polarity and as I suspected, I was completely wrong. From the right side to left, it is + - + -. I fixed that and plugged in a cable I missed on the relay board and I got a click!..... which lasted for 2 seconds before it went back to protection mode. I think one of the fuses looks dodgy, so I will replace all three today and see how I go. I will re-cap and replace transistors on the phono board today, too. I suspect it is one of the 798s. Two have been replaced and two are original. The originals have glue on top from where they were glued to the big green capacitor next to them. Was there a point to that? Seems kind of strange.

The glue has been a complete pain in the arse because it has covered polarity on more than one spot. Had to watch the video again to make sure it was correct. Does that glue eat away at the board or is it okay to leave on there? It was very difficult to get off. What little I was able to get off that is.

 

[Segasonic91]

Anybody????

 

[Hyperion]

Does that glue eat away at the board or is it okay to leave on there? It was very difficult to get off. What little I was able to get off that is.

You need to get all of that glue off everywhere it has touched - every last speck. People have suggested a variety of methods on here to deal with it (do a search), perhaps the most common is the use of an Acetone based solvent cleaner, which seems to soften the glue enough to remove it. You have to be very patient as it is laborious and slow work to get it off. But worth it in the end because that glue becomes corrosive over time and eats through component leads. And sometimes the glue also becomes conductive ! - definitely something you don't want.

Two threads of many on here....
https://audiokarma.org/forums/index.php?threads/sansui-glue.407467/#:~:text=scrape scrape scrape!-,Gently of course..,and remove the Sansui glue.
https://audiokarma.org/forums/index.php?threads/au-717-worst-glue-corrosion-ive-seen.801276/

 

[Segasonic91]

You need to get all of that glue off everywhere it has touched - every last speck. People have suggested a variety of methods on here to deal with it (do a search), perhaps the most common is the use of an Acetone based solvent cleaner, which seems to soften the glue enough to remove it. You have to be very patient as it is laborious and slow work to get it off. But worth it in the end because that glue becomes corrosive over time and eats through component leads. And sometimes the glue also becomes conductive ! - definitely something you don't want.

Two threads of many on here....
https://audiokarma.org/forums/index.php?threads/sansui-glue.407467/#:~:text=scrape scrape scrape!-,Gently of course..,and remove the Sansui glue.
https://audiokarma.org/forums/index.php?threads/au-717-worst-glue-corrosion-ive-seen.801276/

Thank you. Exactly as I thought, that glue is terrible and bad for the boards.

Would the glue I described on the A798's on the phono board have damaged them? They were glued along the top of the transistor to the big green caps next to them on both sides. Seemed a strange thing to do to me, they do not need to be secured like one of those giant old caps.

With the unit being stuck in protect now, I was thinking it may one of the transistors on the main board (sorry, can't think of the number, 2580?? The one that slides in vertically where the power outputs are). I know they can be a problem and fail often. Would that be the most logical place to start? I was thinking that the horrible pops and clicks would most likely come from there. Of course, there are also those damned A798's on the tone boards, too.

EDIT: Forgot to say I am ordering replacements for everything on the F-2580, as well as new power transistors. Not in stock though, so will take a while. I should have posted pictures of the fuses. I think one or two are dodgy. Would the amp stay in protect if a fuse was blown, or not turn on at all? Not 100% sure how the fuses work in these. I know usually a blown fuse will stop power to things, but I am sure I read of blown fuses with amps still working. Albeit with problems.

Thanks!

 

[Segasonic91]

You need to get all of that glue off everywhere it has touched - every last speck. People have suggested a variety of methods on here to deal with it (do a search), perhaps the most common is the use of an Acetone based solvent cleaner, which seems to soften the glue enough to remove it. You have to be very patient as it is laborious and slow work to get it off. But worth it in the end because that glue becomes corrosive over time and eats through component leads. And sometimes the glue also becomes conductive ! - definitely something you don't want.

Two threads of many on here....
https://audiokarma.org/forums/index.php?threads/sansui-glue.407467/#:~:text=scrape scrape scrape!-,Gently of course..,and remove the Sansui glue.
https://audiokarma.org/forums/index.php?threads/au-717-worst-glue-corrosion-ive-seen.801276/

Started cleaning the boards tonight. Right pain in the arse it is, too! Some of the glue os so stubborn.

Also found two eaten traces on the underside of the phono board, right where those two small caps were glued.

 

[Segasonic91]

Well, I am stumped again. I changed the 1313 transistors and 1uf 50 caps on F2570. Also placed 2 A992 transistors together (matched pair), soldering the E legs together. Put it back together and it came out of protection and stayed out.

Plugged in one of my turntables, and got no sound from phono 1 or 2. Tried the CD player and it was fine. I thought maybe the A992's were no good so I put the old A798s back in. Tried again and it went back into protection mode when I tried the turntable again.

SO, I put the A992s back in, but when I de-soldered one of the 798s, the damn solderpoints lifted off with the legs. There was BARELY enough left on two of the 3 lifted pads to get a connection, but there was no continuity with the other. So I put a wire between the transistor leg and the two points it connects to and got continuity back again. Tried the amp again but it back to being stuck in protection. I would REALLY appreciate some feedback and advise, please. I am about to put the thing through a wall and be done with it!