Hi everybody
I've got a few days ago a heavily smashed up Technics SL-P520, good cosmetic state, dirty as hell, and just turning on the LEDs on the tray mirror.
Removing the cover exposed me that the main PCB was plain broken, a full crack broking more than 30 traces near the CPU, observing the damage smoke started to come out of the power supply part.
removing, rebiulding traces and replaced the smoked components got the player working but:
-32v Power supply burned out and was replaced completely, meanwhile the CPU received -37v...
Remote control IC got completely shorted and had to be removed.
So... the problem now, if i connect completely the front PCB, machine goes crazy... not starting up, motors runing crazy, lens coil going nuts... if i isolate 5v supply or pin marked as "50" of that PCB everything goes fine...but... that's really wrong.
And the most concerning problem... display is so dim that is unreadable if i go to a dark room i can see that is displaying the correct information.
Measuring tensions on pin 36 of CPU i got the -32v perfectly (from the former blowed up power supply), but on every other point that says that it has to have -27,6 or -27.5v i still got -32 or -31... Grid display tension and anode tension is the same on my CDP, i think here relies the problem... but still no clue why tensions are off, tryed replacing the transistors marked as FL Drive and got same reading...
From what i see it seems like it's been missing some ground or reference inside the regulators supply but still can't find where...
i hope i can make it work with your help.
Thanks a lot!
I've got a few days ago a heavily smashed up Technics SL-P520, good cosmetic state, dirty as hell, and just turning on the LEDs on the tray mirror.
Removing the cover exposed me that the main PCB was plain broken, a full crack broking more than 30 traces near the CPU, observing the damage smoke started to come out of the power supply part.
removing, rebiulding traces and replaced the smoked components got the player working but:
-32v Power supply burned out and was replaced completely, meanwhile the CPU received -37v...
Remote control IC got completely shorted and had to be removed.
So... the problem now, if i connect completely the front PCB, machine goes crazy... not starting up, motors runing crazy, lens coil going nuts... if i isolate 5v supply or pin marked as "50" of that PCB everything goes fine...but... that's really wrong.
And the most concerning problem... display is so dim that is unreadable if i go to a dark room i can see that is displaying the correct information.
Measuring tensions on pin 36 of CPU i got the -32v perfectly (from the former blowed up power supply), but on every other point that says that it has to have -27,6 or -27.5v i still got -32 or -31... Grid display tension and anode tension is the same on my CDP, i think here relies the problem... but still no clue why tensions are off, tryed replacing the transistors marked as FL Drive and got same reading...
From what i see it seems like it's been missing some ground or reference inside the regulators supply but still can't find where...
i hope i can make it work with your help.
Thanks a lot!
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Dim VFD's are a common issue generally. Some are just low emission (worn out) while others have problems with the supplied voltages. You need to measure the voltages on a scope to make sure that the segments are seeing the proper drive voltage required. The segment drive will be multiplexed but the voltage on a segment should be 'clean' and constant during the 'on' time.
The filament voltage should be checked and also the voltage the filament is 'floated' at. This is typically done via a zener.
Most real faults related to displays are caused by failed caps in the negative rail generator/regulator. That and the tube itself.
The filament voltage should be checked and also the voltage the filament is 'floated' at. This is typically done via a zener.
Most real faults related to displays are caused by failed caps in the negative rail generator/regulator. That and the tube itself.
Interesting... in this case i don't think that is low emission with a multimeter even i get strange readings... on the display regulators there are two zeners one capacitor a diode some resistors and a transistor, everything except the diode and resistors were replaced... they were toasted.
Still... how can i measure the signals of the vfd with OSC,? i tried but voltages are too high and my scope can't draw the signal
Still... how can i measure the signals of the vfd with OSC,? i tried but voltages are too high and my scope can't draw the signal
Also, is there a way of easy testing the vfd? like grounding a pin or connecting to 5v or whatever tension? Thanks!
I think from memory, if you 'ground' (well use a resistor such as 2k2) any of the cathodes (so that's most of the pins on a display) the appropriate segments should light brilliantly but its only a rough test because in use the display is multiplexed meaning each segment is only active for a small percentage of the time.
The relationship of all the voltages, particularly the filament, is very important.
Marantz CD5000 - display very dull - help?
The relationship of all the voltages, particularly the filament, is very important.
Marantz CD5000 - display very dull - help?
perfect, i try like that, i want to make sure the tube is not busted, since the power supply was heavily damaged the vfd could have suffered overvoltage for a loooong time.
As for the relationship of voltages..i'm pretty sure there is a faoult over there since i have almost same tension on grid and anode... as far as i understand, if voltages are the same there are no flux of electrons
As for the relationship of voltages..i'm pretty sure there is a faoult over there since i have almost same tension on grid and anode... as far as i understand, if voltages are the same there are no flux of electrons
wellll.... grounding the pins did light the display but in the same dim state.... it might be busted... any other test?... if i measure across the display pins, between filament and any other pin i have 5.8 v... isn't that a low voltage?
Hmmm. Grounding the pins normally lights the segments brilliantly (super bright, many times more than normal brightness).
So it doesn't sound good. The filament is typically 5 volts AC and the filiament is usually 'floated' and offset to the negative supply with a bias of around 5 volts.
Look at the image in post #11
Marantz CD5000 - display very dull - help?
The zener at the top of the image is the way the filament is tied with an offset to the negative supply. Here it is a 4v7 zener.
So it doesn't sound good. The filament is typically 5 volts AC and the filiament is usually 'floated' and offset to the negative supply with a bias of around 5 volts.
Look at the image in post #11
Marantz CD5000 - display very dull - help?
The zener at the top of the image is the way the filament is tied with an offset to the negative supply. Here it is a 4v7 zener.
Display outer pins, the Filament should have, as Mooly says, around 2 to 5 Volts AC across them and around negative 32 Volts DC with reference to 0 Volts.
You need to check these and get back to us with the findings.
If the -32V is low check around Regulator Q12.
Also a favourite in these circuits is the Cap supplying the AC in series to the Rectification from the Mains TX. C12 in this instance. This may have drifted in value and is not passing the requisite AC to the -32 V supply circuit.
What voltages have you around the regulator Q12?
With reference to 0V what have you on the Data Pins on the Display?
P.
You need to check these and get back to us with the findings.
If the -32V is low check around Regulator Q12.
Also a favourite in these circuits is the Cap supplying the AC in series to the Rectification from the Mains TX. C12 in this instance. This may have drifted in value and is not passing the requisite AC to the -32 V supply circuit.
What voltages have you around the regulator Q12?
With reference to 0V what have you on the Data Pins on the Display?
P.
The outer pins have the correct voltage according to the SM, haven't checked recently against 0 but i guess is not even close to -32...
-32v PSU was rebuilt almost completely... replaced Q13 C18 D13 and D14 since they were all shorted and C18 preventive, since because of this the PSU was delivering -37v
about the data pins i have -31.5/31.6 in every other pin of the vfd...on the SM is stated that it should be -26.5 and -27.6, replaced the FL drive transistors with the same result. i'm pretty sure it is a power supply fault.
Thanks
If all the voltages are correct then it sounds more like display trouble to me. Have you looked on YouTube ? Several videos on there showing displays being tested.
SO, are you saying you have, or have not got -32v (-37V wouldn't be bad) with reference to 0 Volts on either/both of the end pins of the Display?
P.
P.S. My mistake about the component Ref's. I was looking at the 250 Manual !! (I'm an idiot !!)
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when i got the machine the cpu instead or receive -32v was receiving -37v because of the faulty psu, now i checked and filament to zero and i have -24.9v which seems fine... only thing by now that seems wrong is that i dont have the exact voltages on the vfd data pins, i have -30.8 on all grid and segment pins, even the output pins of the cpu that say -27.6v has -30.8v... is my cpu toasted?
I would doubt the chip is zapped. You mentioned it shows the correct info on the display, just that it is dim. The chip outputs are normally just open FET switches to pull each display line down when active. The multiplexing means that the duty cycle is low and that in turn means any readings with a normal meter are meaningless. You have to use a scope.
i think i'm gonna end up with the mistery and just wire another random vfd of similar characteristics to see if it works...
Okay, game over... i soldered another random VFD and it works fine... i'm going to order a new one...thanks everybody!
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