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Need help for dim flourocent display sony FH-B170

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Hussain1255

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Hi i have sony old model deck FH B170 its running perfectly but display got dim due i mistakenly attach main power board with wrong pins order but when i correct them my deck display got dim as i changed the LCD florucent display having same model with a friend but it glow same dim as mine,please help me out.
 

Nigel Goodwin

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It's almost certainly that the displays are worn out - they only have a fairly short lifespan - and it's an EXTREMELY common fault (in fact it's rare to see one that's anything more than barely visible).

On some models there are a couple of electrolytic capacitors, associated with the heater feed for the display, and these 'can' give problems and cause a dull display - however, it's very rare that changing them makes any difference.

Essentially it's just a valve, and these only have a limited lifespan, and emission drops off as they get older.

It's rather disappoining, as when new the displays look pretty good - but their lifespan is just so poor.
 

Hussain1255

New Member
Thanks for reply but in my case my display is brandnew its just i pinup the main transformer supply board in wrong order and deck didnt on and when i again place jeck as it need to be it got on but display got dim and above i have extra new front display too and solder it with new one but still brandnew even working dim. Please check diagram of FHb170cd and guide which power board capacitor i would change so might get it full glow.
 

Les Jones

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You may get a better responce it you posted a link to the service manual rather than expecting members to go searching for it.

Les.
 

unclejed613

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with VFD displays, there's a 30V supply rail (or -30V bias applied to the filament). it's usually about 30V, but can actually be anywhere from 12-35V. most often, it is a negative bias on the filament, but that's not always the case, because the anodes can be individually driven, so the display can be multiplexed in the same way LED displays are.

if the electrolytic caps in the 30V supply are dried out, the average voltage on the display will be lower, making the display dimmer.
 
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Les Jones

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I suggest that you start by checking that you have 3 volts AC between pins 1 & 2 of connector CN10D4 and that you have +32 volts with respct to ground on pin 5 of connector CN10D4.

Les.
 

Les Jones

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I was expecting to fond a DC path to ground to a centre tap on the 3 volt winding of the transformer but there is no centre tap. the only path to ground I can find for the display filiment is from pin 12 of IC106 that may have a PWM signal on it to control the display brightness. I have very limited knowledge of florescent displays so I have reached the limit of my ideas. Someone with more knowledge of these displays may respond.

Les.
 

Les Jones

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I would want some firm evidence that that IC was faulty before changing it. First it is only a suspicion that the signal from this IC is a PWM brightness control. Wait for someone with more knowledge of this type of display to respond. You could check that the signal on pin 12 of that IC has an swing from close to zero volts to close to +5 volts and it is the inverse of the signal on pin 13. ( IC106 is a hex inverter.)

Les.
 

unclejed613

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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.
 
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Hussain1255

New Member
Pls guide where i find J29 on main power pcb and pls give number of the replacing parts to just i could replace and play at present ill be able to find just C1050 on main display pcb.
 
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