Discussion in 'Exclusively Sansui' started by Hipocrates, Apr 17, 2017.
This video is from a fellow AKer ( @Blueglow ) youtube channel. (good stuff there)
SUBSCRIBED due to having troubles with my own Dolby board after a full resto. Grrrrrrr.
I like all the videos by @Blueglow especially the Dummy load and Analog discovery 2 testing videos...
Although it's a bit long, it's a very well produced video and it was very nice of him to reference my AK posts on Dolby board repair. The image you see above as the background for his video is from my AK post.
That said, he made the classic mistake of jumping right to the Dolby board. He never verified that the Dolby board was the cause of the signal drop. Late production units with the factory wire ribbon cables, like that one, are much less likely to have Dolby issues. All of the work he did there may have been unnecessary. Also, if you do need to rebuild the board, it's not necessary to remove the Dolby switch. With a little patience you can resolder the pass-throughs under it with the switch on the board.
Sadly, this video is going to greatly feed the myth that the Dolby board on these units is the cause of all channel drop issues on these models.
Too bad, I though it could be useful for those in need to deal with that board.
That's not true Pete. I did verify the dolby board was the problem before jumping to fix it. I guess I could make another video covering how to diagnose the front end of any receiver and find where the signal is dropping out. Like yourself, I've worked on a lot of Sansui units, and have found this board to be the problem a good bit of the time. Like you said, lets avoid jumping to conclusions...
How did you verify that the drop out was a pass through? You didn't show it in the video, only that if you had drop out, 90% of the time it was a Dolby board problem.
Decided not to get into a battle on a forum that I appreciate too much to do so.
Back to making videos...
I care deeply about this place too. Almost all vintage audio equipment will have channel drop issues especially if it has been unused for a long time. The majority of these cases all that is needed is a deep cleaning of the controls. I've been helping people with their 9090DBs for almost as long as this forum is old. The 9090DB has a lot of controls, more than most receivers to support the Dolby function. Like any receiver, almost any one of the controls can cause a channel drop issue. I've been involved in countless threads where someone will post that they have a channel drop issue with a 9090DB and immediately the voices chime in Dolby Board, Dolby Board, Dolby Board ignoring all other possibilities. Here's a recent example: http://audiokarma.org/forums/index....lume-in-one-channel-in-preamp-section.765088/
With all the focus on the Dolby board, a lot of guys quickly get in over their head trying to fix it and in many cases introduce a range of new problems. Then it either gets put on the shelf or parted out and we loose another great receiver.
I have no issue with your video other than the statements you make about the Dolby board support the myth that the Dolby board pass throughs are the cause of all 9090DB channel drop issues. Rather than get defensive, you would do better to listen to your critics. They will help you make better videos.
Never got defensive, never said I didn't listen or learn. Just rose above public forum debates many years ago.
I'll make a video on how to determine if you have a dolby board issue with your 9099/8080db to better help the community.
Here you go...
Thank you for the latest vid mark.
You are a good educator in your manner, humble to boot.
Thank you for your videos as they went a long way in forming a sense of awareness to grow from and investigating a few of those towards servicing further. (Have been fortunate in finding them and have one regular 9090 running well so far.)
Same troubleshooting and repair methodology apply to the QRX 8001 and QRX 9001 quad units as well ... more or less anyway.
Only thing I'd add is, the quad units have the push button switches sandwiched between a couple boards, and the only way to clean them right is to break down the stack ... and half the battle is getting that far, so you might as well pin the pass throughs while you're there.
Agreed, I have worked on a few QRX 9001 units. PITA...
And I agree with what you said about might as well do the pins by then.
... and with a 9001, you don't have to remove the board from the receiver either ...
(You just have to remove the receiver from the board) <G>
If you're still auditioning desoldering tools, I'm really liking the Jameco BenchPro SA6R. That's conservatively rated at 30 watts, but mine measures out at 42. Plenty of heat, good recovery, and I seldom need to go more than one click of the button for a clean joint. I went with the trusty old RatShack for years, but this runs rings around that, especially for getting into tight spots.
Just viewed the video, and one BIG difference between our repairs is the pinning method used. I went an extra step and scraped the traces next to each pass through for a more solid mechanical connection. Tin the traces, keep the pins long on each side, solder them in the holes, then bend each side to conform to the trace and solder that. Maybe overkill, as there's plenty bare copper around the rivets already, but as mentioned, this ain't something I wanted to have to do twice.
I used an old X-Acto fine point blade dulled and ground flat at the end for a scraper ... worked nice!
PS ... good closeup of the rivets for anyone who hasn't had a close look at what we're talking about. Also shows what an outstanding job the Jameco desoldering tool does. These are pretty much factory fresh.
I've done the trace scraping a long time ago, added a good bit of time to the process. Then I tried a few without doing it and found it worked out well. As you said, typically there is a good amount of solder there to grab to. If I ever see one that doesn't look good, I do the scraping but not on all, just the suspect ones.
I'll check out that desolder tool.
How do you go about cleaning out the solder in that unit while using it hot?
The tip sits into a fairly long metal sleeve that keeps the solder molten ... Just push the plunger, and excess squirts right out. Tips are replaceable too ... I got an extra just in case, although mine already has some pretty good miles on it and still working the original tip.
One warning ... I was using an old iron holder with a full metal jacket, and the plastic barrel softened up and deformed. The holder didn't vent worth a crap and funneled all the heat straight up. Contacted Jameco, and they sent me a new iron, free of charge. I've since changed out to one of them spring things and no problems since.
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