|Schematic: ||RE|| ||
|Max. Rate: ||12.5 MHz|
An early all-IC counter.
The main ICs used in this counter are MSI TTL decade counters and NIXIE drivers.
They are proprietary HP devices having some additional functionality not found
in the standard 7490 / 7441 devices.
The additional functionality of the ICs is for leading-zero blanking in the display.
The decade counter ICs have an 11th state (decimal 15) to represent blanked-zero.
The NIXIE driver IC blanks the NIXIE upon input of 15.
Upon reset the decade counters are set to the blanked-zero state.
Any clock activity on a given decade (digit) unblanks that decade.
At the end of the gate/count period leading zeroes are still blanked while lower-order zeroes have been unblanked.
This scheme can result in some briefly idiosyncratic displays when changing the function mode.
Unfortunately the special ICs seem to fail somewhat frequently, especially the NIXIE drivers,
making it difficult to keep units of this model or series functional.
- Unit Log -
|Serial Number: ||716-00361|
|Year of Manufacture: ||1967 (IC date stamps 6711 to 6752, one cap 6539).|
|Other Identification: ||HP service sticker dated 8 July 69.|
|Date of Receipt: ||2005 Aug|
|State upon Receipt: ||Non-functional.|
Problems with display.
U1 (7400) had previously been replaced.
U18 and U21 (1820-0093 decade counters) had previously been replaced with 1820-0119.
U32 (NIXIE driver) had previously been replaced.
|Date: ||1996 Aug|
|Procedure: ||MSD NIXIE driver IC (U35) bad, replaced with IC removed from other HP counter.|
|Procedure: ||Checked against 10MHz GPS by Peter:
unstable@0min, -76Hz@1min, -36@30min, -4@60min, +5@100min, +4@210min.|
|Date: ||2005 Aug 26|
|Procedure: ||MSD is blank. U35 replaced again with IC removed from other HP counter.
NIXIE is functional, but also replaced in case problem is with it.|
|Date: ||2006 May 5|
Old-style power connector replaced with IEC standard.
TI/FP switch on back panel sticky, replaced.|
|Date: ||2006 May 5|
|Procedure: ||100 ohm resistor on input circuit partially burned (overdriven through clamping diodes).
Replaced with film resistor, original was 1/4 W carbon composition.|