Sansui 8080DB fixed red light

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Conte
Posts: 2
Joined: Sun May 02, 2021 7:36 pm

Sansui 8080DB fixed red light

Post by Conte »

Hi everybody!

As a newcomer to the forum, I failed to find any entry on the wonderful amplifier Sansui 8080 DB,
which suprises me because the bug it suffers from is very nicely described
in the Blueglow video
https://www.youtube.com/watch?v=w6RAAUlhkdw

We just followed the instructions of this video
aimed at fixing the bug labeled BG090
(flight flashing red fix instead of green fix),
but failed to find any faulty resistor.

So, may I ask where to search next among the quite many parts?
Some transistor?

The device is a Sansui 8080DB bought in 1977 when I was in Berkeley
(I am now in France, 220 V),
which performed quite well until this flashing problem.

We measured all the resistors which we could see on the board
labeled F-2624 SANSUI at its top and GCMK-45EY at its bottom, with the results

R18 8.2
R24 39
R26 3.3
R33 R34 both 190 ohms
R36 5 ohms
R38 3.8
R39 R40 both 10
R41 153
R42 164
R45 5
R47 5.3
R48 4.9
R49 4.9
R50 4.9
R56 472
R59 23 kohms
R60 22 kohms
R under some plastic 29.

All these seem to be within the limits described in the chart visible in the video.

The board seems in quite good condition.

Any hint?

PS. I also failed to "introduce myself", probably keeping clicking the wrong link, sorry.
Robert.
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Hipocrates
Posts: 12
Joined: Wed Feb 24, 2021 7:11 pm
Location: Costa Rica

Re: Sansui 8080DB fixed red light

Post by Hipocrates »

Your unit is in protection mode (red light)
F2624 problems are quite common.

1. Look fo the service manual on internet and check page 15 regarding fuse resistors, is good practice to replace them.
2. look for ''fuse resistors f-2624'' on internet.

Sansui have some diferent versions, some use trasistors on the bias circuit and others use STV diodes... post some pictures of your board.

Be carefull with that board, pads a very delicate.
Be carefull when installing the board back, mis place it will cause some cool sparks and smoke.

Did you check bias?

Finally You will have more luck asking on the sansui sub forum in audiokarma, that unit is one of the most documented one.

If you wan't keep asking here, I'll let you a hand, but this unit can be tricky and that video that you are watching is just a hint about what this units problems usually are.
Conte
Posts: 2
Joined: Sun May 02, 2021 7:36 pm

Re: Sansui 8080DB fixed red light

Post by Conte »

Many thanks Hipocrates for these useful hints and kind offer to help!

We ordered transistors and, yesterday, changed TR 11,12,13,14 of F-2624.
We also changed all those resistors (R33 to R50) which are listed in "Parts list" section 5-5 of Service manual
(other resistors have not been changed)
Also changed C07, C08 and will change (tomorrow) VR01 02 03 04.

But the red light still flashes!

Bias not yet checked, will do.

The F-2624 driver circuit board (.jpg attached, before any part
Sansui.8080DB.F-2624.full.242kb.jpg
Sansui.8080DB.F-2624.full.242kb.jpg (241.12 KiB) Viewed 66 times
replacement) looks identical to that of the Service manual.

What about F-2657 (protector circuit), section 2-1?

Robert.
User avatar
Hipocrates
Posts: 12
Joined: Wed Feb 24, 2021 7:11 pm
Location: Costa Rica

Re: Sansui 8080DB fixed red light

Post by Hipocrates »

Sorry I haven't checked this forum in a while.

On F-2657 R12 (1.5K) goes high/open quite frequently.

Info about f2426
https://audiokarma.org/forums/index.php ... 24.709267/

Does the unit comes out of protection without F-2426 in place?
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