Marantz 6009 no front display

[frankusb]

Hi,

I recently took this receiver out of storage and the front display shows no signs of life. Everything else is working fine. I have not worked with VFDs before so I am not sure how to approach debugging. Are there any good pointers to how VFDs work or typical failure modes?

It seems that the NJM2887 should be Vo = Vref x (1 + R2 / R1). R1 is 100k, R2 is 225k, Vref is 1.29, so F+ should be 4.19DC (as marked).

VH (the heater?) has 42VDC marked on the schematic.

F- is GND.

[R_J]

Re: Marantz 6009 no front display

VH is not the heater, the heater (filament) on this display is F- and F+ check the voltage between the two pins. what is the voltage on F+ ? Check for poor solder connections and check C6118

[frankusb]

Re: Marantz 6009 no front display

F- to F+ measures 0.001. F+ to DGND measures 4.19VDC, F- to DGND measures 4.19VDC. C118 in circuit measures 12.6uF on a Fluke 12. R6083 to DGND measures 40.37.

I reflowed the pins on FL601, they looked fine but I did them anyway.

[budwich]

Re: Marantz 6009 no front display

check the resistance between +/- F

[frankusb]

Re: Marantz 6009 no front display

3.1 ohms in circuit.

[R_J]

Re: Marantz 6009 no front display

I suspect one or more of the D6005~D6007 diodes are open. check the voltage at each diode.

[stj]

Re: Marantz 6009 no front display

the heater really should be AC

[frankusb]

Re: Marantz 6009 no front display

the heater really should be AC

Unless I am mistaken, there are no AC sources connected.

[frankusb]

Re: Marantz 6009 no front display

I suspect one or more of the D6005~D6007 diodes are open. check the voltage at each diode.

No power at the house at the moment (since 2am, winter storm) but diode test mode shows similar forward and reverse values for all 3. I will test voltages when we get power back.

[frankusb]

Re: Marantz 6009 no front display

Problem solved! I tried to get the measurements on the diodes and they looked reasonable and lo and behold the display was working. But after I power cycled, it was not. So i reflowed the diodes and C6118 and now the display is working.

I still don't have a firm grasp of how VFDs work but my receiver is back online so I thank all the people with suggestions.

[R_J]

Re: Marantz 6009 no front display

Good to here it's working, here is one explanation, there are others on the internet https://www.noritake-elec.com/techno.../vfd-operation

[frankusb]

Re: Marantz 6009 no front display

Well, the display stopped working again. After some measuring, I found that D6007 appears to be conducting in both directions and the voltages are not proportional as I would expect.

4.19V, 1.06V and 0.54V.

What is the function of the diodes? If I am looking at the correct data sheet, it's a 1000V 1A rectifier. https://cdn.badcaps-static.com/pdfs/...a80cb05ad4.pdf. It's also marked obsolete.

Would this be an acceptable substitute?
https://www.mouser.com/ProductDetail...MdIHKbxA%3D%3D

[R_J]

Re: Marantz 6009 no front display

Yes the diode is a 1A/1kv D6007, along with D6005 & DD6006 are in the return for the filament voltage of the display, but rather than connect direct to ground they lift it by 3 diode drops about 1.8 volts. I would replace all three diodes along with C6118.

[frankusb]

Re: Marantz 6009 no front display

Thanks R_J. Is the substitute I linked appropriate?

I am curious why they use a 1000V 1A diode. It's 4.2V and 163mA if the schematic is to be believed.

I will replace C6118 as well.

In use, 4.2V to 1.8V would be the voltage drop across the filament. NJM2887 is adjustable, why would one not just adjust it to 4.2-1.8 and skip the diodes?

[frankusb]

Re: Marantz 6009 no front display

Actually, https://www.mouser.com/ProductDetail...TF3Syt3w%3D%3D matches one more parameters.

[R_J]

Re: Marantz 6009 no front display

Thanks R_J. Is the substitute I linked appropriate?

I am curious why they use a 1000V 1A diode. It's 4.2V and 163mA if the schematic is to be believed.

I will replace C6118 as well.

In use, 4.2V to 1.8V would be the voltage drop across the filament. NJM2887 is adjustable, why would one not just adjust it to 4.2-1.8 and skip the diodes?

The diodes provide a bias voltage to the display filament to prevent "ghost illumination"

They don't need to be 1kv but it is likely what they had in stock so they used them.
The model SR7005 uses three 1SR35-400 diodes (1A/400V)

[frankusb]

Re: Marantz 6009 no front display

I replaced the diodes and capacitors today and the display is working again. The diodes measured 0.8V, 1.6V and 2.4V. Thank you for the help.

Curiously the diodes and capacitor measure fine out of circuit.