DHC-EX77MD problem with display

[slayernn]

Re: DHC-EX77MD problem with display

In post #16 you had 0 volts on Q301, In post #18 you now have ~20 volts on Q301 collector, what did you do to go from 0 to ~20v?
That Q301 collector needs to be about negative 40 volts. What is the a/c voltage measured across CN402, pins 2 & 4?

Well i just changed all what i think off.. most caps that i mention. Ac voltage on CN402 across pin 2&4 is 20.5V. What i realised now is that B+ line that goes to pin29(cn305) +5v is 0V! So display IC gets 0v on VDD. IC301 also draw 0v. Maybe faillure in D301,D302,D315,D316? Best regard friend.

[slayernn]

Re: DHC-EX77MD problem with display

I made huuuuuge mistake so far.......i used "LP301" lead with connector (which connect to chassis) as ground for measuring!... Now i have used chassis as ground and ...everything is good on board, ~-29V (pin 3) and +5 (pin29) of cn305. Everything is fine with main board apparently. Problem lies on display board.. im not sure what i did so that fillament is not glowing red like before, but voltage across filament is ~3.3v which is fine. Maybe some caps on display board is critical and is off? Probably anode voltage is very low or so. Next day i'll remove display board and try to fix. Thanx for all your help and sorry for my stupidity.....

[R_J]

Re: DHC-EX77MD problem with display

Not to worry, I hope you can track down the problem, I will help if I can.

[slayernn]

Re: DHC-EX77MD problem with display

In post #16 you had 0 volts on Q301, In post #18 you now have ~20 volts on Q301 collector, what did you do to go from 0 to ~20v?
That Q301 collector needs to be about negative 40 volts. What is the a/c voltage measured across CN402, pins 2 & 4?

Everything looks fine with display board, voltage on check points etc, its probably that display is worn out? If im correct i have two choice, one is to put higher voltage on VF1,VF2 so filaments glow light red and then display is more visible by its light (which was in original state, probably ex owner did that with purpose). Or second choice is to add much more voltage across filament so that it burn phosphorus layer, that trick seems to help many ppl. Btw i have removed display board and checked VF1 to ground and VF2 to ground (on main board) and its read 26.6v, sholdnt it be 30v?What do you recommend? Can i change something on board so that i get much more volts to VF1,VF2 or i need external PS for that job? Cheers!
PS:

[slayernn]

Re: DHC-EX77MD problem with display

Not to worry, I hope you can track down the problem, I will help if I can.

One more question and im finished. I tried trick with 9v battery over fillament. Did it for around ~10sec glowing red and results are ~10-15% improvement but still uneven. I check out again voltages on display board/ic to compare with datasheet. Some voltages is not like it should be. Can you look at image and tell me what is posible reason for that? Is X1,X2 (resonator 5mhz) normal? Best regards!

[R_J]

Re: DHC-EX77MD problem with display

You are lucky you did not burn out the filament with 9 volts, I suspect the display is just worn out. The voltages seem ok, they are not that critical, you would need to use a scope to check for a proper data pulse. The voltage on the resonator are ok, If the resonator had a problem you would not get any display, ic501 would not be operating at all.

[slayernn]

Re: DHC-EX77MD problem with display

You are lucky you did not burn out the filament with 9 volts, I suspect the display is just worn out. The voltages seem ok, they are not that critical, you would need to use a scope to check for a proper data pulse. The voltage on the resonator are ok, If the resonator had a problem you would not get any display, ic501 would not be operating at all.

Thanx. Thats it, display is near end, probably fillament that was red glow caused by bad caps, burn phosphorus layer over time. But, md is alive and that is more of importance thanx again. Hope that this tread will help someone in repairing own display. Cheers!