DHC-EX77MD problem with display

[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!

[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

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!

[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:

[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

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.....

[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.

[R_J]

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?

[slayernn]

Re: DHC-EX77MD problem with display

Added new:
C309
C310
C301
C307
D310 (1N5230 instead of rd4.7esb2)
D305,D306 (1N4004 instead of 11es2)
Nothing changed. Sorry for spam, cant edit single post so to update results. Cheers!

[slayernn]

Re: DHC-EX77MD problem with display

New readings:
Q301: ~20v on collector , ~21,3v base, ~16v emitter
Q305: collector ~18.7v.
When i measure Q301, Q305 voltage start at ~15 and slowly increase to max, eg ~20v for collector voltage.

[slayernn]

Re: DHC-EX77MD problem with display

D309 is fine and also D305 & D306 fine. I have no clue, i tried everything, changed all caps related to VF1,VF2,-28v(B-) cn305 pins. Is C324 critical? I'm not sure,have to check out, but maybe that's the only cap i forgot to change. Mistery to me

[slayernn]

Re: DHC-EX77MD problem with display

Did you change C304? You should have -39.5v on Q301 collector, also check D309 to be sure it is not shorted.
Just to be sure the a/c coming in is ok, check the voltage across C302, it should be around -14 volts

"-28v third pin = 0v." Do you mean pin #3 of CN305?

I have changed C304 yes. Q301 collector show 0v. Voltage across C302 is 13.5v. -28v yes pin 3 (cn305), it show 0v .I will check D309 and will let you know. Regards!

[R_J]

Re: DHC-EX77MD problem with display

Did you change C304? You should have -39.5v on Q301 collector, also check D309 to be sure it is not shorted.
Just to be sure the a/c coming in is ok, check the voltage across C302, it should be around -14 volts

"-28v third pin = 0v." Do you mean pin #3 of CN305?

[slayernn]

Re: DHC-EX77MD problem with display

Update, in short. I changed:
c320,c324,c322,c323,c306,c305,c303,c302,c316. 0 volts Q 301,305, checked d305,d306 with diode test, seems to be ok. Checked D309,D310 ok. Checked some resistors, its ok. Display still very dim. Ac 3.2v between vf1,vf2. -28v third pin = 0v. Strange, what could be problem here? Best regards

[slayernn]

Re: DHC-EX77MD problem with display

The a/c coupling caps for the filliment are C315, C316, and you might want to check C322 & C323
C320 is the filter for the B- supply, remeber the cap will be + to ground, If C303 was bad (lower capacity) The B- would be very low.

I add new C315,C316,C322,C323 and also put back old 100uf 25v to position C303 (there was wrong mark C320 on copper side of pcb and i use C320 cap which is 100uf 50v). Everything is very dim, barely visible. I have check between VF1,VF2 ac mode and its 3.2v. Strange but -28v pin to ground shows 0v! So filament voltage is probably good but anode(-28?) is not and thats why it is so dim. Here i will add schematic of display pcb which i forgot to add in previous post. Thanx for all, cheers mate.

[R_J]

Re: DHC-EX77MD problem with display

The a/c coupling caps for the filliment are C315, C316, and you might want to check C322 & C323
C320 is the filter for the B- supply, remeber the cap will be + to ground, If C303 was bad (lower capacity) The B- would be very low.

[slayernn]

Re: DHC-EX77MD problem with display

Here is cd player manual, i belive i need to change C320 (33uf 50v)? I inspected main board and find out that there was wrong capacitor C303, 100uf 25V so i changed it to 100uf 50V (like one in manual). Beside that i changed few other caps with new one (except that c320 which i dont have). Now filament is not glowing visibly red like before but brighness/latters are even less dimmer then before, its bareilly visible. Any tips what to try for cd display? Thanx!

[slayernn]

Re: DHC-EX77MD problem with display

Ok, I understand it's the other display. With no a/c for the filament Check the caps C009, C007, Check if you have a/c (3~4vac) between C007 + and C009 +, If you have the ac voltage there, either one or both caps are bad or the resistors in that line are open.
That q522 is a simple regulator, its output voltage is based on the "base" reference, in this case a 33 volt zener, so the output will be aprox 33 volts, being a couple volts high or low will not effect the display where it would be noticed
measuring 33 volts on the acf1/f2 to ground is normal, It comes from B- via uzp-5.6b zener diode and through R532, there is no current drawn at the moment so there will be no voltage drop. Its there to apply a small dc voltage on the filiment, again it should not effect the display brightness

And........ it was C007! Everything work like a charm now! Man you rox !! Now im going to fix cd display dim with your tips and will update here. Do you accept donations or so? Cheers!

[R_J]

Re: DHC-EX77MD problem with display

Ok, I understand it's the other display. With no a/c for the filament Check the caps C009, C007, Check if you have a/c (3~4vac) between C007 + and C009 +, If you have the ac voltage there, either one or both caps are bad or the resistors in that line are open.
That q522 is a simple regulator, its output voltage is based on the "base" reference, in this case a 33 volt zener, so the output will be aprox 33 volts, being a couple volts high or low will not effect the display where it would be noticed
measuring 33 volts on the acf1/f2 to ground is normal, It comes from B- via uzp-5.6b zener diode and through R532, there is no current drawn at the moment so there will be no voltage drop. Its there to apply a small dc voltage on the filiment, again it should not effect the display brightness

[slayernn]

Re: DHC-EX77MD problem with display

Schematic