There is this collector of stereos in Melbourne who tried to replace belts in his Marantz CD-95 and failed.
He then sent it to me with a note saying that other than the belts, he wanted me to fix the display which "used to work fine, but with all this handling of the player during the belt replacement attempt - it no longer does. All the segments are now lit". He does not recall doing anything specific that might have caused it.
it looks like this:
I have replaced the belts and the player now works OK but the display is still stuffed.
I am afraid to keep the player on for too long, because I have no idea if I will not blow it completely, given it has 30% more voltage supply than it should.
In addition, it is very hard to work on, because there is this "Feature Board" in front of the display and all the cables are short, so it is hard to measure anything.
Anyone has any experience with this or any ideas what went wrong?
The only manual for it I could find was CD-95DR which only shows differences between it, and the Marantz CD-12.
The display circuits in both CD-95DR and CD-12 are similar to what is inside of this player, but marginally different nonetheless.
I soldered some wires and have been able to measure some voltages.
The 3.2V AC heater is OK (connector JF10 pin 3 & 5 on the bottom of pic)
The 20V AC is on the pins 1 & 2 of the same connector.
The negative -20V is in fact -27.
The 5V and the 12V rails are both OK.
Resistor RF-51 measures as it should - 6.8k
DF-50 is IN-4002, DF-51 is a 5.6V Zener and the 1 Ohm resistor RF-50 are all OK.
I know, because I managed to blow the last two trying to measure voltages, so they are brand new and the display still behaves as it was before.
Any ideas why I have the -27V instead of -20V supply?
The service manual warns about the display issues and suggests... resetting it by turning it on and off and checking oscillator frequencies (all appear to be OK).
He then sent it to me with a note saying that other than the belts, he wanted me to fix the display which "used to work fine, but with all this handling of the player during the belt replacement attempt - it no longer does. All the segments are now lit". He does not recall doing anything specific that might have caused it.
it looks like this:
I have replaced the belts and the player now works OK but the display is still stuffed.
I am afraid to keep the player on for too long, because I have no idea if I will not blow it completely, given it has 30% more voltage supply than it should.
In addition, it is very hard to work on, because there is this "Feature Board" in front of the display and all the cables are short, so it is hard to measure anything.
Anyone has any experience with this or any ideas what went wrong?
The only manual for it I could find was CD-95DR which only shows differences between it, and the Marantz CD-12.
The display circuits in both CD-95DR and CD-12 are similar to what is inside of this player, but marginally different nonetheless.
I soldered some wires and have been able to measure some voltages.
The 3.2V AC heater is OK (connector JF10 pin 3 & 5 on the bottom of pic)
The 20V AC is on the pins 1 & 2 of the same connector.
The negative -20V is in fact -27.
The 5V and the 12V rails are both OK.
Resistor RF-51 measures as it should - 6.8k
DF-50 is IN-4002, DF-51 is a 5.6V Zener and the 1 Ohm resistor RF-50 are all OK.
I know, because I managed to blow the last two trying to measure voltages, so they are brand new and the display still behaves as it was before.
Any ideas why I have the -27V instead of -20V supply?
The service manual warns about the display issues and suggests... resetting it by turning it on and off and checking oscillator frequencies (all appear to be OK).
Well, I did think about it and I did see the -27V on the other part of the diagram which you added.
But I could not find this C880 100µF / 50V capacitor anywhere on the main board. This is one of those differences between the diagrams and the unit I have.
From the (disconnected) transformer, I get 20V AC and it ends up to be -27V after rectification and with the help of smoothing capacitor.
But if the supply voltages are good (-27V and 3.2V AC) the problem then would have to be... grounding?
I did confirm that there is ground connection between the display board and the main board and chassis.
I will re-examine the Display and the Feature boards for broken off components. This is something that the owner could have inadvertently do when handling this pretty heavy unit.
It is pretty unlikely I think to expect static caused damage to the display driver IC. Although who knows how the front panel was handled. I'll ask him if he removed it from the chassis.
Cheers and thanks for you reply.
Sounds like the -27v is unregulated, so the actual voltage will very somewhat from nominal. Depends on the power transformer, the primary taps, the line voltage, the power supply load, how much filtering, etc.
Depending on what type of display the unit has, LCD, Fluorescent, LED, etc., the display may be fully lit or full dark if it is not being actively strobed/driven. For example, IIRC it takes a bias signal present/asserted to darken an LCD pixel. The default then would be lit up in the absence of a control voltage (assuming the back light is on).
Anyway, looks like QF01 is the MCU, then there are some connections between boards, and the data lines go into QY01 (which I assume is some like of character generators and or display strobe generator - something more or less like that). The output signals on the left side of QY01 may normally have some digital switching waveforms on them to strobe the rows and columns of the display matrix - again, something more or less like that.
First thing to check might be the connections between boards. Something might have gotten loose, unplugged, damaged, etc.
If that looks okay, I would probably take a look around with a scope to see if there are digital signals on the data lines on the right side of QY01, and or on the output lines to the display and the strobe driver transistors, QY02 thought QY06. There should also be +5v present on Pin-64 of QY01.
Depending on what type of display the unit has, LCD, Fluorescent, LED, etc., the display may be fully lit or full dark if it is not being actively strobed/driven. For example, IIRC it takes a bias signal present/asserted to darken an LCD pixel. The default then would be lit up in the absence of a control voltage (assuming the back light is on).
Anyway, looks like QF01 is the MCU, then there are some connections between boards, and the data lines go into QY01 (which I assume is some like of character generators and or display strobe generator - something more or less like that). The output signals on the left side of QY01 may normally have some digital switching waveforms on them to strobe the rows and columns of the display matrix - again, something more or less like that.
First thing to check might be the connections between boards. Something might have gotten loose, unplugged, damaged, etc.
If that looks okay, I would probably take a look around with a scope to see if there are digital signals on the data lines on the right side of QY01, and or on the output lines to the display and the strobe driver transistors, QY02 thought QY06. There should also be +5v present on Pin-64 of QY01.
It looks like a fluorescent display, these were common in VCRs at one time.
The problem could be dust between contacts, give it a good clean.
And do read up, those parts are simply not made any more.
It could also be loss of vacuum, there is a characteristic gray color at the wires and glass seal point, read up on that as well. That is very hard to fix...if at all.
I would make a new display using a large LCD, and a Raspberry / Arduino / similar device, taking the signals from the unit, and showing on display.
Costly, but effective.
The problem could be dust between contacts, give it a good clean.
And do read up, those parts are simply not made any more.
It could also be loss of vacuum, there is a characteristic gray color at the wires and glass seal point, read up on that as well. That is very hard to fix...if at all.
I would make a new display using a large LCD, and a Raspberry / Arduino / similar device, taking the signals from the unit, and showing on display.
Costly, but effective.
I've only quickly skimmed through this but it does all sound like a man made fault. It's hard to make out in a picture but your display looks to have a possible valid info present such as '14' showing at the right. The other segments look to all be lit because of incorrect biasing... but pictures can be deceiving I know,
Make sure that the filament is floated correctly to the negative 27v supply, that is done by the Zener and resistor at the lower bottom right in your first image. Make sure the Zener and that other diode are OK. They are typically around 4.5 to 6 volts apart (the Zener voltage) if my memory is correct.
The segments on a VFD normally light when the appropriate pins are pulled toward ground (zero volts) and they are off when taken to the same voltage as the negative supply.
Make sure that the filament is floated correctly to the negative 27v supply, that is done by the Zener and resistor at the lower bottom right in your first image. Make sure the Zener and that other diode are OK. They are typically around 4.5 to 6 volts apart (the Zener voltage) if my memory is correct.
The segments on a VFD normally light when the appropriate pins are pulled toward ground (zero volts) and they are off when taken to the same voltage as the negative supply.
Hi, I've seen the same fault on a Marantz CD94 a few years ago, The problem was a faulty display driver IC QY01, sadly it never got repaired as the QY01 - HC10212030LC6554D that was available at the time, needs to be programmed to function correctly... made from unobtainium
Not exactly help, but may stop any hair being pulled out like I started doing after a few days of chasing the fault on mine.
Hopefully you've had better luck than me
Not exactly help, but may stop any hair being pulled out like I started doing after a few days of chasing the fault on mine.
Hopefully you've had better luck than me
have a look here , same issue after replacing belts
https://forum-mfbfreaks.nl/viewtopic.php?t=18392
https://forum-mfbfreaks.nl/viewtopic.php?t=18392
