Noritake display dead ???

[KD0CAC John]

Helping a friend to get a display repaired is possible .
Noritake itron GU128X64-800A
It was in a commercial convection oven , I check the 2 wire connector for power - it had about 4.97 volts but on light anywhere on display .
Removed from oven and checked the surfacemount fuse & it was good .
I tried to use one of the data sheet sites for one of the chips for pinout , and when I got to a listing for the PDF I clicked on it and then ended up with nothing except contact supplier to buy IC .
So I am starting from scratch to see if I can find a fault & fix ?
Thanks John

[macboy]

You need to look up the 800 series at Noritake:
http://www.noritake-elec.com/800.htm
Click on the download link at the footer of the page, and you can get all datasheets, but you need an account. I've attached it. The datasheet is a poor quality scanned pdf, so I attached the 800B one too, which is a "proper" text based pdf.

if there is no display, check the filament voltage. On the display glass, you will see two sets of 3 pins at either end. These supply the filament with a low voltage. Check for around 3 VAC between the two sets of pins (each set of 3 is in parallel). Be careful when poking around on the board, VFDs use high voltages for grid & anode.

You can also check the current draw when powered up. The nominal current with all dots off is 0.55 A. That sounds like a lot but VFDs are power hungry. If the current is much lower, then maybe one the DC-DC converters is not working (either the low voltage one for the filament or the high voltage one for grid/anode).

Another option is to simply replace the module. You are lucky that this is an off-the-shelf part and not custom like most appliances have. Not so lucky: Cost. Expect to pay at least $100 USD.

[KD0CAC John]

IK thanks , I was able to download the B version of PDF , but did not find the A vs.
My friend has at least 3 of these CV ovens , one display went out a couple yrs ago , I found a defect with the pins at the right angle bend coming out of the display tube , a bunch were cracked , so I soldered wires overlaying the pins and that fixed that one .
Now a couple yrs late the other went dead , looked for the same issue and not an issue .
One of the black diodes had what looked like the solder heated up and looked questionable , so going to remove to make sure testing is leaving out any other circuit results , then resolder to see if it works - I like to solve observable questions before looking for deeper issues .
I tried to find a wiring diagram / schematic to fallow it through , but they say they will not let it out .
Will check your suggestions .
Digi-key local here , or at least in state , there online quote was $145.49 , the local sales guy for Noritake [ the one that hand delivered a couple of free samples { different ;( } quoted $175.16 ] .
I get free BBQ for partial payment and also get to learn more on repair , so I feel like get paid a couple of times , Kansas City style BBQ .
Thanks , will give result later . 

[KD0CAC John]

With the bench power supply set at 5.14 v , one side of the 3 pins shows 2.865 the other 3 pins show 2.245 .
I removed the diode and check as no continuity in one direction and .925 in the other direction .
Soldered back in place and still no light up , this is all all my place - not connected to anything but the PS .