Display driver issue

Thread Starter

Earl Wright

Joined Jul 18, 2021
36
Good morning!
I have an older 70's pinball with 7400's series ics. (look at old posts), anyway I've made good progress with this over the last 6 months thanks to the wonderful people on this forum and dusting off 20+ years of neglect in my head. I've changed out several ics with success but now it looks like one of the display drivers (BCD to 7 segment) might be bad. I'm getting letters instead of numbers for the 3 and 4 for example. It's displaying c and d, Ive checked the outputs from my 7490,and the inputs to the 8880, they are okay. The display is good, other numbers display fine. Here is the issue, the chip that drives this is an DD8880. I cant find this anywhere...is there a secret source or can I substitute another 7 seg driver as long as the pins match? Its the 100s display.Capture3.PNG
 

Thread Starter

Earl Wright

Joined Jul 18, 2021
36

JohnInTX

Joined Jun 26, 2012
4,596
I ordered it and will try it, thank you
@Earl Wright
Don't do that. It is easy to miss on the schematic but with an anode voltage of 180V I suspect these are gas-discharge displays, each segment is like a little neon lamp. Orange segments. Very popular back then to get a bright display. The chip you bought will fry at those voltages. As @ericgibbs says, measure the switching voltage on the segment pins but I suspect it will be much higher than the DM9374 will handle.

EDIT: a quick search for gas discharge display driver found this outfit. There may be more. That 180V anode is problematic. The DI-220 would work as the HV driver, you would have to add a BCD-7segment decoder.
http://www.dionics-usa.com/hv-display-drivers.html

FWIW: here's the original datasheet for the DS8880N. There's one listed on eBay from China... roll the dice?
https://www.ebay.com/itm/221947141356

Are you sure the display itself is good?

Good luck!
 

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Thread Starter

Earl Wright

Joined Jul 18, 2021
36
Yes they are the orange segments and they are all working fine at this point. ericgibbs- what are you refering to by switching voltage? The ic supply or the output? please explain, im a little dim in this area. I ordered the DS8880N. I'll try it.
 

Ian0

Joined Aug 7, 2020
3,754
Are these Nixie tubes or something similar?
Texas makes a whole load of high voltage drivers with part numbers starting TPIC6A and TPIC6B
https://www.ti.com/product/TPIC6A595?keyMatch=&tisearch=search-everything&usecase=partmatches
You don’t need the output to withstand the power supply voltage, because the neon is effectively a zener diode. For example, look at the original 74141 Nixie tube driver. It will drive Nixie tubes on a 180V supply although its output voltage is limited to 55V.

Microchip has also recently introduced some high- voltage drivers
https://www.microchip.com/en-us/parametric-search.html/441
I can’t think why, unless they are planning to reintroduce the Nixie tube.
 

Thread Starter

Earl Wright

Joined Jul 18, 2021
36
These were made in mid 70's and not anymore, so I'm told and unable to find, only used available now and very scarce. The player 1 display is in good shape, all segments are working, player 2 is not, looks like multiple segs out but maybe other board issues. going to fix 1 first then move to 2. The segments are orange in color like was noted. There are no names on the display except "Allied Leisure". ( pinball brand). I have little work in displays. I just need something to replace the 8880 and get it working. (if it is the issue). Ive ordered 3 ics so far, price isn't that bad and delivery time lets me do other home projects. I'll look at the nixie tube driver, 74141 and if not to expensive all order that too.
 

Thread Starter

Earl Wright

Joined Jul 18, 2021
36
Here's the latest update. I've dug into the circuit more, removed the pcb to clean better and take a closer look. On the schematic, the driver for the displays are written as DD8880. On the actual boards however they are SN75480N, all of them, and appear to be original. All other ics are the same as schematic. After more investigation, it was found that the BCD counter for the driver (7490) was outputting an incorrect code for the number 4 and 5. When counted to 4, the output should be (1,2,4,8) HHLH on the output lines, but instead was giving me HHLL which is 12. Now 12 is 3 steps past 9, Which is C (10,A, 11,B, 12,C, or so i'm thinking?) and that is what I'm seeing on the display. When counted to 5, the output should be LHLH. But instead I'm getting LHLL, which is 13, and that gives the next letter D, which is what I'm seeing. At this point it looks like the BCD 7490 is the culprit. Any thoughts here? I also swapped the 2 displays from 1 to 2nd player, and the good display from 1 lights up perfect in 2's spot, so the 2nd player display is sour at this point, its spotty. Time to scour the countryside for a new display, or something that will work.
 
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