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REPAIR HP 8018A
SERIAL DATA GENERATOR
SERIAL DATA GENERATOR
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January 2017
The HP 8018A Serial Data Generator is a complex item of test equipment with lots of inter-connecting coaxial & ribbon cables in between the pcb's and to the front panel. I have two of these Generators to repair and test.
The HP 8018A Serial Data Generator is a complex item of test equipment with lots of inter-connecting coaxial & ribbon cables in between the pcb's and to the front panel. I have two of these Generators to repair and test.
Power Supply testing
Initial testing identified a fault with the Power Supply. The -5.2V rail was not regulating correctly and oscillating badly. This fault was common to both units. The +25V rail and +5V rail were both ok.
Decided to strip down both units to assembly level.
Decided to strip down both units to assembly level.
Kit of Parts!
The 8018A stripped down for cleaning and inspecting. Easy to dismantle although notes and photos required to identify where everything fits.
I'm surprised how many different designs of linear power supplies HP came up with over the years. Some have been good, efficient and easy to manufacture. This one IMHO is not one of these! The circuit design is very complicated for the -5.2V rail with two operational amplifiers (LM307 obsolete) and three transistors, plus a poor pcb track layout, all of which I suspect is unstable and with the addition of a difficult mechanically assembly.
March 2017
After fault finding unsuccessfully for some time, I gave up and redesigned the circuit with a LM337 Voltage Regulator and a higher current bypass transistor. This is a definitely a first for me with HP designs! Maybe it is something to do with the 8018A being manufactured in West Germany back in the 1970's? One of my own engineering principles is for the design engineer to actually build the first ten production units, that way any manufacturing problems soon get resolved!
I'm surprised how many different designs of linear power supplies HP came up with over the years. Some have been good, efficient and easy to manufacture. This one IMHO is not one of these! The circuit design is very complicated for the -5.2V rail with two operational amplifiers (LM307 obsolete) and three transistors, plus a poor pcb track layout, all of which I suspect is unstable and with the addition of a difficult mechanically assembly.
March 2017
After fault finding unsuccessfully for some time, I gave up and redesigned the circuit with a LM337 Voltage Regulator and a higher current bypass transistor. This is a definitely a first for me with HP designs! Maybe it is something to do with the 8018A being manufactured in West Germany back in the 1970's? One of my own engineering principles is for the design engineer to actually build the first ten production units, that way any manufacturing problems soon get resolved!
Modified Power Supply Assembly
Now I have a functioning power supply which when fully loaded requires about 120W so the heatsink gets hot! I made sure that all the components fixed to the Rear Panel heatsink had fresh heatsink compound.
With all PCB's plugged in the current loads are: +25V rail 300mA; +5V rail 2.3A; -5.2V 6.5A; so probably a lot of ECL circuitry.
With the new complete Operating and Service manual from Artek I can start testing.
Adjustments on both units completed ok. Most of the Performance Tests on both units completed ok, didn't bother with PRBS tests as specific test equipment not available and PRBS will not be required anyway. Pleased that both units were fault free even after 40 years.
With all PCB's plugged in the current loads are: +25V rail 300mA; +5V rail 2.3A; -5.2V 6.5A; so probably a lot of ECL circuitry.
With the new complete Operating and Service manual from Artek I can start testing.
Adjustments on both units completed ok. Most of the Performance Tests on both units completed ok, didn't bother with PRBS tests as specific test equipment not available and PRBS will not be required anyway. Pleased that both units were fault free even after 40 years.
Completed Repair