Here's an example of a ghosting VFD, and the cause was mainly a cap in it's supply rail
https://www.eevblog.com/forum/repair/vfd-unwanted-segments-glowing/
Hugo
https://www.eevblog.com/forum/repair/vfd-unwanted-segments-glowing/
Hugo
Checking supplies is always the first rule of fault finding. Never assume. There may be a ripple component that is interacting with the multiplexing of the digits. It would very unlikely for both drive chips to have some kind of issue whereas it is far more likely for the VFD's as they are thermionic in operation. The supplies are common to both.
Never assume, but also use common sense 😎
The drive system surely is common to both too; there are standard ICs for that purpose.
Anyway, I still am not convinced that there is a problem.
What I see is the familar dual indication of peak level and slowly decreasing 'history' level in the same display.
Common use of such displays.
This unit can be switched between spectrum analyzer and eq display. Did the OP try that, and what were the results?
But we'll see.
Jan
The drive system surely is common to both too; there are standard ICs for that purpose.
Anyway, I still am not convinced that there is a problem.
What I see is the familar dual indication of peak level and slowly decreasing 'history' level in the same display.
Common use of such displays.
This unit can be switched between spectrum analyzer and eq display. Did the OP try that, and what were the results?
But we'll see.
Jan
To me the short clip is definitely ghosting. Like Mooly said, this was quite common in old VCR's, and I had enough of these machines on my bench in the past to recognise the phenomenon.
The description at eevblog appears to match.
Let's see what OP comes up with. Like I always say: It ain't fixed till it works. 🙂
The description at eevblog appears to match.
Let's see what OP comes up with. Like I always say: It ain't fixed till it works. 🙂
C29 is a capacitor 470µF / 50V, not a diode
It's hard to imagine you swapped a cap for a diode. 🙂
You should read -34V at the indicated point. Can you confirm?
It's hard to imagine you swapped a cap for a diode. 🙂
You should read -34V at the indicated point. Can you confirm?
Sorry, I was wrong to write😴
Yes, I measured that point and I read -34.5V
I think you have to point the finger at the displays although it might be worth looking at Zener D43 which looks as though it holds the filaments at a few volts below the -34 volt rail. These are typically around the 4.7v region... you are probably down to experimenting now to see if you can improve the situation. A small change here might improve the ghosting as might slightly lowering the -34 volt rail but that is easier said than done without adding a regulator. Series dropping with a resistor won't work due to the varying current draw as each segment lights..
I still have a suspicion this is going to be down to the VFD's themselves but it would still be worth looking further... but as I mentioned earlier it is down to experimenting and trying and seeing what altering the supplies and their relative value to each other might do.
A scope check is always worthwhile (essential really) as it shows issues simple voltage checks miss.