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The digital read out is very very dim.
- Thread starter srinath
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Flourescent displays generally do not go dim when they fail, there is a filament that goes open, and they fail completely. They require a 30V supply to the outer 2 terminals to work. Sometimes it's -30V. On Sony equipment there is a resistor in series with this supply. Sometimes the resistor goes open, sometimes the resistor gets hot and desolders itself or burns the pads on the board.
Jon_Logan
Addicted Member
Like any vacuum tube, VFD's can wear out and get dim.
The Cathode (heater) loses it's ability to emit electrons. There are ways to bias them harder. Sometimes a zener diode is used in the winding for the heater to DC offset is from the grids.
If it is a vacuum flourescent display, they do have finite lives.
The Cathode (heater) loses it's ability to emit electrons. There are ways to bias them harder. Sometimes a zener diode is used in the winding for the heater to DC offset is from the grids.
If it is a vacuum flourescent display, they do have finite lives.
OK I have since discovered a faint hum upon turning on. Very much thinking its that AC bleed over hum ... so I guess I open it, start searching for a bad ground and open resistors and 30V - it looks like LED display, it seems to have horizontal lines like its writing on college ruled.
Cool.
Srinath.
Cool.
Srinath.
Jon_Logan
Addicted Member
That sounds like VFD to me.
Here's a link to Noritake. they're maybe the largest supplier of these displays.
http://www.noritake-elec.com/vfd_technology_an.htm
Jon_Logan
Addicted Member
... or across the outer pins should be 3~5 V AC. Those filiment pins are usually "doubled up" too.
Thanks, Jon. I was going to post that too, but my memory was foggy and I didn't want to mislead if I was wrong. Yes, if the filament voltage is low, that can cause it to be dim.
OK filament pins getting bent - OK I'll look for that, then outer pins 3-5 Vac, and outer pins of display to ground should be 30V. Now off to search the manual for what you guys are talking about.
BTW the manual I pulled off the inter-web-ring is the coolest thing ever ... so detailed and has everything. Is it cos its a sony ? man I dont figure this out wiht that kind of manual and you guys, I am useless. Thanks a bunch.
Cool.
Srinath.
BTW the manual I pulled off the inter-web-ring is the coolest thing ever ... so detailed and has everything. Is it cos its a sony ? man I dont figure this out wiht that kind of manual and you guys, I am useless. Thanks a bunch.
Cool.
Srinath.
OK here is a very fundamental Q. So I remove the face plate. Then it has that full width PCB with various chips and what not in it. The VFD is on the back side of it - rather the fornt side of it as the amp is in operation. So I get that off and test the pins and what not right ? So I pull it apart and plug it in and power it on ? OK then, if you guys see a big puff of smoke up from the charlotte NC area ... its probably going to spell out sony ...
If there a way to get @ it from the front ? Like pull that protective face plate off and right there ? No ?
Cool.
Srinath.
If there a way to get @ it from the front ? Like pull that protective face plate off and right there ? No ?
Cool.
Srinath.
OK looking @ the circuit diagram -
It has a "indicator Tube Fluoroscent".
That has a scarcely believable 54 pins a side X 2 sides, top and bottom.
1. Basically I look for bent pins.
2. Then power it on and look for 3-5 VAC across the outer pins - More circuit reading needed here.
3. Either of the 2 outer pins to ground - 30 V ac or dc ?
Thanks muchly.
Srinath.
It has a "indicator Tube Fluoroscent".
That has a scarcely believable 54 pins a side X 2 sides, top and bottom.
1. Basically I look for bent pins.
2. Then power it on and look for 3-5 VAC across the outer pins - More circuit reading needed here.
3. Either of the 2 outer pins to ground - 30 V ac or dc ?
Thanks muchly.
Srinath.
Jon_Logan
Addicted Member
You (probably) can leave the VFD implanted in the faceplate. If you can get access to the VFD soldered leads from the back. If it's got pins on both sides (lengthwise) on the VFD, you should consult the manual. Generally, the tracks (PCB traces) that feed the heater are wider as they have to carry more current than the grid pins, and the heater pins get to a connector that goes to the transformer in a hurry.
Opened up the thing, got the PCB out from the face plate. Still dim and worse yet the VFD has a bulb like end - top left as you face the amp, I am guessing its supposed to light up, and its not. So I am guessing a VFD that isn't lighting up as well as it should.
Cool.
Srinath.
Cool.
Srinath.
Tinman
Super Member
Check the voltages.....
I used to fix a lot of consumer stuff years ago. If it's not AC on the filament, then it was often DC. In that case, the problem was almost always a bad capacitor that filtered the output of the supply to the VFD. But the schematics will tell you that.
Marc
I used to fix a lot of consumer stuff years ago. If it's not AC on the filament, then it was often DC. In that case, the problem was almost always a bad capacitor that filtered the output of the supply to the VFD. But the schematics will tell you that.
Marc
I didn't see a cap in that entire board. It could be else where obviously.
Its actually slowly getting better, and letting it stay on seems to help, but what appears to do more than that seems to be to turn it on, and a few seconds later off. A few dozen times of that and its now very readable in movie theater darkness. in a bright room its like you can tell its got lights.
Cool.
Srinath.
Its actually slowly getting better, and letting it stay on seems to help, but what appears to do more than that seems to be to turn it on, and a few seconds later off. A few dozen times of that and its now very readable in movie theater darkness. in a bright room its like you can tell its got lights.
Cool.
Srinath.
