Need help for dim flourocent display sony FH-B170

[Hussain1255]

I already replaced florucent display with newone but it doesn't help its al due when i had pin main transformer board pins wrong with main power PCB.

 

[Hussain1255]

It was running totally bright after even 18years ane made just got dim due my wrong pin replacement between transformer pcb clips to main power pcb board.

 

[Hussain1255]

the 32 volt supply is a voltage doubler, and zener referenced pass transistor on the power pcb (grid square J-29 on page 2 of the pdf). those electrolytics should be replaced, as well as C1050 on the display pcb. you might be reading 32Vdc, but if there's a lot of ripple on it, the display could be affected by that. you can use your meter to check for ripple on the 32V rail, just switch it to AC. you should see less than 1V of ripple (actually because of the regulator, it should be even less than that, but zener referenced pass transistors do tend to float with the load a bit more than a regulator controlled by a diff amp). if you have an oscope to look at the 32V rail, even better. also, replace the capacitor in parallel to the zener, because if it dries out, you will get noise in the 32V rail (it won't cause much of a problem, but it's not normal operation of the circuit).

since i can't find a datasheet for the display driver chips, i have to assume from the signals going to them from the processor, that the brightness is either not variable at all, or there's a setting sent from the cpu, and the data going to the display drivers (IC1006 and IC1007) is serial data. i would try recapping the 32V supply first and see if that helps before assuming it's a chip problem.

Please guide where that J-29 gridsquare?

 

[unclejed613]

page 2, power board, lower right from IC901

 

[Les Jones]

If you can remember the way the power connector was plugged in incorrectly you may be able to work out which voltage rails had voltages on them that would damage components and possibly which components may have been damaged.

Les.

 

[Hussain1255]

Dear all thanks for your help but issue still not resolved as i changed almost all capacitors too but no improvement please guide me do i need to change the display driver ICs 1006 and 1007?

 

[unclejed613]

depending on where you got your "new" display tube, it could be as old and as used as the one you replaced. there are, however techniques for "rejuvenating" the filament to improve the cathode emission (the filament is the cathode in a display tube), which usually work by running the filament 10 to 15 percent over normal voltage for about a minute or two in order to get fresh material to the surface of the filament. this works with vacuum tubes that have filaments that are hot enough to glow orange. in a display, the temperature of the filament is below the point of emitting much visible light. there are some methods for doing this with VFD tubes, with a word of caution: if the filament has a physical weak spot in it, rejuvenation may burn the filament out. the most successful method i've found is to use a constant current supply to run the filament up to a temperature where it's bright orange, yellow, or white hot for a few seconds, with one method leaving it in white hot operation for up to a minute, or others where the temperature is ramped up slowly to white hot, then ramped back down after being white hot for a few seconds (ramping the temperature may allow for thermal expansion/contraction of the filament without sudden mechanical stress). i highlighted constant current supply, because there is one slight thing that could go wrong using a constant current supply to heat up the filament: there are several sections of filament in parallel in the VFD tube, if one strand fails because it was ready to go anyway, the current will redistribute through the other strands suddenly, and you might end up with all of them burnt out. i think this would actually be done better by an adjustable voltage supply. this should be done with no other voltages applied to the tube, preferably with the tube removed from the circuit board. you can find various methods for doing this, but i would avoid methods that keep the filament white hot for more than a few seconds. with the diameter of the filament wire used in VFD tubes (it is very small compared to other vacuum tube types), if it doesn't happen in a few seconds, it won't happen (i.e. burning off "poisoned" material, or boiling fresh material to the surface of the wire). also, every VFD tube, like regular vacuum tubes, have an area of getter material (looks like a metal coating on the inside of the glass, some people mistake it for the tube being "blown"). if the getter material has visibly reduced in area from when the tube was new (you can see the outline of the original getter spot) or the getter spot has turned transparent or white, the problem is not the filament, the problem is oxygen in the tube.

 

[Hussain1255]

depending on where you got your "new" display tube, it could be as old and as used as the one you replaced. there are, however techniques for "rejuvenating" the filament to improve the cathode emission (the filament is the cathode in a display tube), which usually work by running the filament 10 to 15 percent over normal voltage for about a minute or two in order to get fresh material to the surface of the filament. this works with vacuum tubes that have filaments that are hot enough to glow orange. in a display, the temperature of the filament is below the point of emitting much visible light. there are some methods for doing this with VFD tubes, with a word of caution: if the filament has a physical weak spot in it, rejuvenation may burn the filament out. the most successful method i've found is to use a constant current supply to run the filament up to a temperature where it's bright orange, yellow, or white hot for a few seconds, with one method leaving it in white hot operation for up to a minute, or others where the temperature is ramped up slowly to white hot, then ramped back down after being white hot for a few seconds (ramping the temperature may allow for thermal expansion/contraction of the filament without sudden mechanical stress). i highlighted constant current supply, because there is one slight thing that could go wrong using a constant current supply to heat up the filament: there are several sections of filament in parallel in the VFD tube, if one strand fails because it was ready to go anyway, the current will redistribute through the other strands suddenly, and you might end up with all of them burnt out. i think this would actually be done better by an adjustable voltage supply. this should be done with no other voltages applied to the tube, preferably with the tube removed from the circuit board. you can find various methods for doing this, but i would avoid methods that keep the filament white hot for more than a few seconds. with the diameter of the filament wire used in VFD tubes (it is very small compared to other vacuum tube types), if it doesn't happen in a few seconds, it won't happen (i.e. burning off "poisoned" material, or boiling fresh material to the surface of the wire). also, every VFD tube, like regular vacuum tubes, have an area of getter material (looks like a metal coating on the inside of the glass, some people mistake it for the tube being "blown"). if the getter material has visibly reduced in area from when the tube was new (you can see the outline of the original getter spot) or the getter spot has turned transparent or white, the problem is not the filament, the problem is oxygen in the tube.

Its not the issue with tube as i checked it before replacing.

 

[Hussain1255]

Guys issue resolved it was due to ICs issue of LCD Drivers IC#1006 & 1007, IC#755703FT

 

[Nigel Goodwin]

Guys issue resolved it was due to ICs issue of LCD Drivers IC#1006 & 1007, IC#755703FT

Well done, thanks for letting us know.