SA-9800 fluorescent display issue
- Thread starter Backlight
- Start date
Just want to know, how this ended? did you find reason for dimmer display? I have the same problem over here, display is dimmed and it goes left to right more darker. Pin 10 is over 60 volts. And everything looks to be fine on PS side. My opinion is, that display unit has been damaged and current drawn is not ok any more. Thats why voltage level is so high.
locoworksnorth
New Member
Having bought a 9800 and after finally having got it up and running ' I find myself in the same boat....duff display. I've had a good look and come to the conclusion that just like a valve my old display has gone " low emission".
Driving the heater to dull red improves the brightness, or lowering the centre tap of the heater transformer below GND improves brightness.
The voltage at pin 10 on the vfd board goes higher with lower tube emission (lower current)
Temperature of the display vfd is the reason for fade over time if the voltage is reconnected to pin 10.
Although not really a solution (that would need a new vfd) what I have done is regulate the voltage on pin 10 and bias the heater centre tap below GND.
I have a usable ( not perfect) display without driving the heater to red hot.
If anyone is interested in details just ask.
Driving the heater to dull red improves the brightness, or lowering the centre tap of the heater transformer below GND improves brightness.
The voltage at pin 10 on the vfd board goes higher with lower tube emission (lower current)
Temperature of the display vfd is the reason for fade over time if the voltage is reconnected to pin 10.
Although not really a solution (that would need a new vfd) what I have done is regulate the voltage on pin 10 and bias the heater centre tap below GND.
I have a usable ( not perfect) display without driving the heater to red hot.
If anyone is interested in details just ask.
Backlight
Active Member
Hi all,
For the curious poeple: I still have this SA-9800 as my main amplifier. The display still works sufficiently well, and has even slightly improved since I changed both Q1 (replacement BD139) and Q2 (original 2SC1735) on the PSU board with 2 KSC2690AYS transistors. I came to this upgrade because I got a 50Hz hum on both channels due to a dead 2SC1735.
Running both + and - regulated 52V supply with these transistors slightly increased the brightness on the right side of the display somehow. Any clues?
But!! I also I heard a clear difference in sound on the bottom end: More presence in low frequencies and controlled very well, even when bass is exaggerated turning on loudness and bass to the max. Could be the BD139 was just not cutting it, providing decent (fast response) +52V to the EQ circuit. I did not have this bass response before I installed the KSC2690AYS transistors.
I now have another SA-9800 which is waiting for a recap, but also has an almost dark display...
Thanks for reading this update!
Cheers
For the curious poeple: I still have this SA-9800 as my main amplifier. The display still works sufficiently well, and has even slightly improved since I changed both Q1 (replacement BD139) and Q2 (original 2SC1735) on the PSU board with 2 KSC2690AYS transistors. I came to this upgrade because I got a 50Hz hum on both channels due to a dead 2SC1735.
Running both + and - regulated 52V supply with these transistors slightly increased the brightness on the right side of the display somehow. Any clues?
But!! I also I heard a clear difference in sound on the bottom end: More presence in low frequencies and controlled very well, even when bass is exaggerated turning on loudness and bass to the max. Could be the BD139 was just not cutting it, providing decent (fast response) +52V to the EQ circuit. I did not have this bass response before I installed the KSC2690AYS transistors.
I now have another SA-9800 which is waiting for a recap, but also has an almost dark display...
Thanks for reading this update!
Cheers
Really to bad they went with VFD technology instead of the old analog meters which seem to last longer. I guess you could mod the meter circuit to drive LEDs instead but making it look good is an issue.
The KSC2690A/A1220A are good devices to use as driver sub parts. I used them on a Yamaha RX-900U recently to replace some obsolete Toshiba parts.
The KSC2690A/A1220A are good devices to use as driver sub parts. I used them on a Yamaha RX-900U recently to replace some obsolete Toshiba parts.
Could it replicate the original display? That would be HUGE!I think a rather simple solution would be to replace the VFD with an LCD TFT display or OLED display.
I don't know the size of the Pioneer display, but I'm saying it would be a big deal to be able to replicate these displays that have faded out over years. Oddly, some seem fine after 30-40 years. I have a Heathkit clock that I built in 1980 that still is used today, 38 years later. Sure the display is a little dimmer than when new, but is still usable. I have a JVC R-X40 receiver from 1982. The VFD display looks new. I have a VCR that I bought in 1987 and as of a couple of years ago, the VFD display is so dim, you can hardly see it anymore. It is not in use right now though. I want to try that rejuvenation trick on it where you heat up the filament red hot for a couple of seconds. Just haven't gotten around to it yet.
restorer-john
Addicted Member
TXturbo, I have one here, complete but non-functional, including the steel support brackets, VFD and PCB. Do you want details/measurements?
IIRC, the PCB overlay in the S/M is full size or very close to it.