DHC-EX77MD problem with display

[slayernn]

Re: DHC-EX77MD problem with display

If the heaters are visible in post #2 then you must have acf1 and acf2, it is usually around 3~4 volts ac measured across them, not to ground
The schematic is not correct, D521 is a 33 volt zener diode, so the voltage on Q522 collector should be about -33~-34 volts.
Check the zener diode (covered by arrow) and make sure it is not shorted. If you have a scope check the ripple on the B-. If C521 and C522 or C003 are bad that will cause a dim display. I would try bridging them with another 47µf and see if it helps
I see part of the display is bright [1 ~ 10], it could be that the display is bad, if it was a problem with the voltage it should effect the whole display not just part of it.

Hello. Well post #2 is cd display which is second problem but still, its working so for now im not touching it. I'm talking about md display and schematic is related to that. I have check diode covvered with arrow (uzp-5.6b) with simple multimeter diode check and its not shorted. Q521 collector voltage is 32.3v now and should be 29 (-29) as display IC driver pin (-VG to VFL pin) get 32.3v now so i assume schematic is correct. Between acf1,acf2 i dont have reading, 0v ac. Still acf1 to ground and acf2 to ground dc i have reading ~29/30v if i remember. Thanx for effort and im looking forward. I'll check caps c521,c522,c003.

[R_J]

Re: DHC-EX77MD problem with display

If the heaters are visible in post #2 then you must have acf1 and acf2, it is usually around 3~4 volts ac measured across them, not to ground
The schematic is not correct, D521 is a 33 volt zener diode, so the voltage on Q522 collector should be about -33~-34 volts.
Check the zener diode (covered by arrow) and make sure it is not shorted. If you have a scope check the ripple on the B-. If C521 and C522 or C003 are bad that will cause a dim display. I would try bridging them with another 47µf and see if it helps
I see part of the display is bright [1 ~ 10], it could be that the display is bad, if it was a problem with the voltage it should effect the whole display not just part of it.

[slayernn]

Re: DHC-EX77MD problem with display

Yes, sorry forgot to add that..and, sony_mds_ex77_full_sm.pdf exceed forum upload size :/
I think i'm close to problem solution.
Voltages that come from main board and feed front board/display do not match service manual. First thing strange is that VFL pin on display ic driver show 32.3v and not 29v. 3.3V pin reading is normal. Somewhere i read that AC probe between filaments end should draw few volts (ac) and i have 0v. Still, in dc mode, end of filaments to ground show normal voltage.
On main board section (pic included) i have removed and check all resistors, diodes and transistors, everything seems to be normal. Im not sure where im wrong.. maybe problem is Q521/Q522 transistor. Any ideas? Thanx in advance!

[R_J]

Re: DHC-EX77MD problem with display

Upload the service manual/schematic, Listing pin numbers and voltages etc. without referece has no meaning

[slayernn]

Re: DHC-EX77MD problem with display

Update monologue On MD (MDS-EX77) i check voltage on ribbon that connect main board and front board (display), pin 18,19 (ACF1,ACF2) show ~30v and pin 13 - 3.3v. So i assume main board is good and the problem is in front board/display as it is getting enough power. Hm.

[slayernn]

Re: DHC-EX77MD problem with display

To add more details, cd display heaters are visible, here is pic. Overvoltage?

[slayernn]

Hello! Got used hifi system which work great except few things. Display vfd on minidisc is blank, not working, other then that, MD work. Also display on cd work partially ~75% (lower brightness, especially lower bottom). So far i opened md to see any visual damage and check ribbon cable etc, which done nothing as resoult. On MD mainboard i see some burn mark under set of resistors which tells me something bad happend before and probably fixed. Is it posible that cause of problem is in amp (TA-EX77) which controls other elements via system control cable? Its strange that 2 components have fail with display (1 partially), only tuner display is working perfect. Anyone experienced in subject? Where to start, how to troubleshot? I have feeling that display is working and btw, visual inspection on MD display after i disassemble unit, looks fine, good. Im electronic hobbyist, not pro but i'm willing to understand Thanx in advance guys!