Berkey Keystone 4030 renovation
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Patrick Souty
Jan 9, 2026, 3:34:54 PM (2 days ago) Jan 9
to OldCalculatorForum
Hi every one, I have just joined your Google group.
I am currently renovating that old Keystone 4030 calculator with a nice panaflex display.
I have removed some corrosion residuals, changed a dead tantalum capacitor and repaired some bad solder joints.
The calculator is now working fine excepted some digits are some time very faint or off.
After some warm up, the display gets better.
I suspect that the supply voltages are to low (exemple: +/21V instead of +/-25V found by Brent Hilbert on a similar Keystone 2050 calculator).
I intend to replace the high voltage Zener which is used for the power supply overall regulation but with +/-25V supply voltage, the capacitors will have 0% margin for their rated voltage.
Does some one know if this limited margin was usual for the calculators of the 70s ?
Patrick Souty
France - Jura
I am currently renovating that old Keystone 4030 calculator with a nice panaflex display.
I have removed some corrosion residuals, changed a dead tantalum capacitor and repaired some bad solder joints.
The calculator is now working fine excepted some digits are some time very faint or off.
After some warm up, the display gets better.
I suspect that the supply voltages are to low (exemple: +/21V instead of +/-25V found by Brent Hilbert on a similar Keystone 2050 calculator).
I intend to replace the high voltage Zener which is used for the power supply overall regulation but with +/-25V supply voltage, the capacitors will have 0% margin for their rated voltage.
Does some one know if this limited margin was usual for the calculators of the 70s ?
Patrick Souty
France - Jura
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