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Sansui SE-88 Dimmed Display

Enrique Vega

Enrique Vega

New Member
Hello guys
I'm new to this forum, I have a Sansui SE-88 that has a dimmed display and I want to try to fix it before sending it to service. I have fixed some amps and other EQs my self but I do not do this for living and I might not have all the knowledge to troubleshoot this right away.

Here is what I have done:
First I got the service manual and checked the power supply voltages, since it's hard to measure with the EQ assembled I carefully took it apart and got the power supply unit alone.

I was expecting to see some lower voltages but surprisingly is not the case voltages are mostly right matching the service manual.

But this was measured disconnected the rest of the components only the power supply board that includes from the transformer up to the final DC supply pins.

So now I guess the problem is in the same board that is attached to the displays and is a little too delicate to mess and play with it without having a real idea how to find the reason why the display is dimmed.

Any suggestions would be really appreciated, I really want to get it back to the normal display.


I'd like to hear from other members in this case normally what I would do is try to visually check for bad caps or resistors but I was not able to see any potential issue, I want to avoid desoldering one by one caps or res to check which one is bad.

Can someone if possible suggest me a way to find the issue without desoldering or risking the display?

The service manual file is too large to be attached here is the link
https://www.manualslib.com/products/Sansui-Se-88-5886472.html


I also attached a picture comparing to a Kenwood GE-920 to show how dimmed it looks.

Thanks !!!
 

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Based on the pictures, it isn't a power supply issue. The bad newscis the display tube is failing from age and use. This is vacuum flourescent display, and relies on electron emission for its luminosity. With many hours of use, they lose their brightness. The "end of life" is generally considered the point at which the display has lost 50% of its original luminosity. As it is a sealed glass envelope under vacuum, there is no repair for that condition.

That having been said, you might render some improvement by briefly applying a low DC voltage (a 9 volt battery is usable for this) to the filaments on the display. This has the effect of "cooking off" the fouling that develops over time and use on the surface of the filaments, thereby increasing electron emission and increasing the brightness to some extent.

You willxneed to identify to the two pins on the display that are attached internally to the filaments (very fine wires stretched horizontally across the display) and apply the voltage from the 9V battery very briefly. Polarity is not importantm be very careful not to leave voltage on the filaments for more than a second or two, as they can heat up and break, much like the filament in a standard light bulb. You may need to pulse the voltage to the filaments multiple times with rest time of several seconds in between each, to avoid over heating and damaging them.

I cannot stress enough that this is a very delicate operstion, and even if exeedingly careful, the display can be ruined quickly and irreparably if one or more of the filament wires break. However, that is really the only option to try and increase the brightness on an old VFD like this.

I'll look at the sevice manual when I have a chance later and ID the two pins for the filament supply on the display. There may also be a VR that can slightly adjust the brightness, if so I'll post that info. I know the SE-99 has brightness adjustments, but not sure about the SE-88.
 
Hello @Sansuiman thanks for the feedback, I guess I can make a last try by measuring the voltages right before it goes into the display if voltages are ok then this display is done as you explained.
I have one more question for you looking into the manual it shows two lines directly from the Transformer called "Fil" that goes directly from the transformer to the display this is AC never seen this before, what is this for? the service manual does not specify a specific voltage for these lines I was trying to check if this could be the issue if the transformer was bad, which I doubt since all the other outs are measuring fine.

I'm just trying to see if by any chance something can be replaced before it put it for sale


I'll be waiting for your reply, appreciate your time

Thanks !!
 
Those marked "FIL" are the filament supply lines. AC is used to energize them, while the grids and anodes are powerd by DC voltage. If you follow those leads marked "FIL" that will lead you to the two pins on the display that power the filaments. Those are where the 9VDC would get applied as I outlined previously. Make sure the wiring back to the transformer is disconnected if you choose to try doing that procedure.

I believe the filament supply from the transformer is about 6 volts.
 
Just measured the AC voltage on the Fil pins and is giving 7.2 volts, so I guess then there is nothing else to do other than sell it and find another one.

What a shame because is functioning perfectly fine with great sound, and is aesthetically great anyway I hope to find another at a reasonable price.

Thanks for your help !!!
 
No problem. Wish I had a better solution to offer. I have an SE-88 here now with a bad power supply awaiitng rebuild, but at least the display is good. Really need to get to it one of these days, it has been sitting fo over a year while I whittle away at other projects.
 
just repair this in a 9900z. turned out to be the op amps. I used a signal tracer I made to verify the ic's were bad. How many frequencies are dim? It also had a shorted diode on the main power line
 
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tonysrep said:
just repair this in a 9900z. turned out to be the op amps. I used a signal tracer I made to verify the ic's were bad. How many frequencies are dim? It also had a shorted diode on the main power line
Click to expand...
All of them are dimmed , do you have some pics or more details exactly what parts did you replace
 
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