Differences in F-2655 Dolby boards (9090DB compatibility)

[burrmanchu]

Hey guys... Wanted to swap out the DB board on my 9090 (troubleshooting for intermittent sound from one channel). I found a couple inexpensive replacements, and just grabbed them without being too particular. Upon actually checking them out, it seems like both replacements have different placement of jumpers, resistors, etc than the original board in my 9090.

Can anyone tell me if these are modded, or post-repair, or just from different versions of the 9090? Or just what's going on with them in general? Lol... I honestly didn't know there would be multiple iterations of this same board. One of them even has multiple single wires instead of the ribbon cables. I didn't want to spend 6 hours soldering just to find out I used the wrong replacement board.
Pics attached. Thanks!

 

[AE Bob]

It does not look as though any of the Dolby boards in your photos has had the feedthrough's reworked. It is the MOST common issue with that board. There are plenty of posts about intermittent Dolby boards in the x0x0DB units. I have repaired MANY. I DO NOT pin the feedthroughs (as many do), but I do remove the Dolby board, and remove the switch from the board, so I can get to all of the feedthroughs on the top. I then resolder all of them on both sides, leaving a good thick fillet of solder between the foils and rivets, as the original thin wave solder membrane is what fails. I usually go back and forth between sides a couple times to be sure the solder connections look good and thick on both sides. I then reinstall the switch and reconnect the ribbon etc., and reinstall the board. The process still takes a damn long time. I have NEVER had one come back with an issue.

 

[Gary Sansui]

It does not look as though any of the Dolby boards in your photos has had the feedthrough's reworked. It is the MOST common issue with that board. There are plenty of posts about intermittent Dolby boards in the x0x0DB units. I have repaired MANY. I DO NOT pin the feedthroughs (as many do), but I do remove the Dolby board, and remove the switch from the board, so I can get to all of the feedthroughs on the top. I then resolder all of them on both sides, leaving a good thick fillet of solder between the foils and rivets, as the original thin wave solder membrane is what fails. I usually go back and forth between sides a couple times to be sure the solder connections look good and thick on both sides. I then reinstall the switch and reconnect the ribbon etc., and reinstall the board. The process still takes a damn long time. I have NEVER had one come back with an issue.

I have a post up F-2654/F-2655 Dolby modification. In some units like the one the previous post has pictured, the k terminal from the calibration pots is bypassed and wired directly to the bottom trace of the board. If you have the experience and technical background to explain this I do believe it would be helpful to others to understand how to interchange boards from different model years. And yu can see in picture #5 Sansui made the F-2654 different for this model year and the switch board has to be wired this way to work correctly.
Thanks, Gary….sansuioldaudiophile