Vintage Calculator Repair - 1972 Hitachi KK561 - Part 1

We have another vintage electronic calculator for repair - this time round it's a 1972 (or thereabouts) Hitachi KK561, sibling to the KK562 which had 2 memories and not that dissimilar to the Friden EC1117 and EC1118 calculators which were also made by Hitachi.

As is fairly normal, the calculator didn't work, the vacuum fluorescent display tubes just showed a load of decimal points and the three warning lights were illuminated. After much testing, we discovered that the calculator was actually running - when you entered 17 digits the calculator would overflow, requiring the clear key to be pressed. After that we discovered that you could read the contents of the main register and memory using an oscilloscope, it was in binary coded decimal or BCD format, but it was there all the same. So the problem lies with the display driver section, from what we can tell, the issue is with the HD3233P chip - I have a random PCB on order containing some of those chips, so hopefully the problem will be solved when we replace said chip. If however the problem is actually the HD3253P chip, then that's not so good, because I can't find any of those anywhere......yet.

The follow up video with the calculator repaired is now available to watch here:
   • Vintage Calculator Repair - 1972 Hitachi K...  

If you wanted to see the two videos looking at the HP97 and Elektronika MC1103 calculators, there are links below:
HP97 & Elektronika MC1103    • Epic Fail - HP 97  &  Elektronika MC 1103 ...  
HP97 Part 2    • HP-97 - More Tests - Still Not Working - V...  

Start 00:00
Disassembly 01:02
Cleaning the PCB 02:11
Keyboard 02:48
Voltages 03:10
Capacitors 03:38
Oscilloscope 05:09
Overflow 05:28
BCD 06:28
Display Driver 08:45
Faulty Chip 10:47
Outro 11:33

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Outro Music
"As Yet Untitled"
by GrumpyTim (available to download from GrumpyTim's Bandcamp page)
https://grumpytim.bandcamp.com/

http://www.grumpytim.com