+1but I could swear the 9090DB is a tad more punchier
Yeah, it's kinda stuck there like a tumor. There's a FAQ sticky about how to service it. Once you do that, it becomes transparent, but it's still a royal pain to do.it seems that everything runs through this board,
I think a lot of the issues with the Dolby board pair on the 9090DB is related to how people at times try to clean the controls and switches sometimes resulting to damage to the connections board to board, as well as making the feed through connections worse by trying to squeeze the boards out as a pair. I have seen some that have no issues and haven't been repinned. I have seen some that were repinned, and are a mess because of damaged connections as well as shorts created by the repinning. Extreme care needs to be taken when repinning near the multi section rotary switch as there are a number of locations where it is easy to short the connection to the metal frame of the switch, or to an adjacent foil run. I have always looked at it with the "If its not Broken, don't try to fix it" attitude. Of course you need to verify that there aren,t any problems usually by slowly rotating the controls for the board set, and loosing the 1 non grounding screw on bottom and flexing the board a little to see if you lose any signal in any of the 6 or so functions
One more suggestion. Currently the Serial Number Database has not been tracking the production changes mentioned here. I can tag notes to the serial numbers so we can start trying to determine approximately when in production these changes occurred. I think the driver board version is a good place to start. For the 9090/8080 does it have glass fuses on the driver board? For the 9090DB/8080DB does it have a bias transistor or bias diode? Additional items for the 9090DB/8080DB are: ribbon cable or the flex pc board on the Dolby board? Fuses on the protection board? Gold chassis? Multi voltage or single voltage. We can get a pretty good idea if we get enough accurate report. So if you have a new serial number or have already reported a serial number and want to state I'm all ears.
To report this additional information, please put it in the 2017 Serial number thread in the database link at the top of the Sansui Forum main page. To get there you can just click on the link in my signature block.
Thanks,
- Pete
All I,ll say is of all the 9090dB's I've repaired, only one had the improved feed thrus on on the Dolby board. All the rest of them had to have the Dolby board rebuilt to get rid of intermittent channels. There is no way to know before opening the receiver if it has had the changes, so I always advise people to buy the 9090, NOT the dB. Also, the dB has the audio signal running in and out of the Dolby board several times, adding un-needed circuitry and cabling in the signal path to degrade the signal.
9 times out of 10 if you tap on the Dolby board a channel will drop out, revealing bad feed thrus. The 10th one has either already been fixed or has the new feed thrus. I don't like recalls.A couple of notes. On 9090 the newer driver boards will work in older units but not vice versa. The older units without the fuses on driver board had a jumper on board connected the fuse replaces that jumper so and older board will not work in newer chassis without the jumper being added. I believe the cadmium plated chassis was added mid year 1977, might be wrong I have to see what I have.
The fuses replacing the fuse resistors were added to make the units shipped directly to US, UL approved. Most multi voltage units were built for the US Military with some for Europe. Single voltage units were built exclusively for NZ/AU, GB, which did not have outlets in rear of the unit.
Yes those printed circuit “cables” between switch board and Dolby were a nightmare.
Some of the really early driver boards used in 9090 had the suppressor coils mounted on driver board but these may have only been used in other Sansui amps same vintage. I have found that the printed board for the 8080/9090 is much more subject to soldering damage the most other PC boards.
Pete unless I am doing a complete restoration, I only fix Dolby board feed thrus that are defective.