CRT Resistor Array U21ΒΆ
On the CRT board there is a resistor array U21. This device is a custom film resistor array in a ceramic 14 pin DIP. It implements 9 resistors. The HP part number is 1810-0416 and it is used in HP85A/B, HP87A/XM
As I have extensively documented testing of this device both in and out of circuit in the Series80 forum, all we need is a link to the forum article: