Dear friends,
The first HP5065A were produced around the late years 60. Over time some flaws,
related to engineering and the choice of components, are highlighted.
The main ones are the following:
- The capacitors used primarily on power lines of +20 Volts tend to lose
the liquid inside and in the worst cases can corrode the copper circuit boards.
- The power rectifier diodes heat up too much and tend to burn the
fiberglass boards where they are mounted.
Only one of these two issues has been partially resolved in more recent sn.
The Capacitors
These capacitors need to be replaced even if not visually appear to leak, this
is to ensure the safety and reliability of your standard. Their characteristics
are: 100uF 30 volts. You can also use higher voltages.
The capacitors are mounted on the following boards and modules:
- A3 C37
- A4 C1
- A6 C2
- A7 C3
- A8 C9,C10,C20
- A15 C8,C9,C10
Note: 001 option is not included in this list. Check on site.
The problem of these capacitors has never been solved at the factory, even in
more recent sn.
It is however well check, especially with older sn, the capacitors C2 and C3
mounted on the chassis. These capacitors are connected to the rectifiers for
leveling.
A good way to test it without disconnecting them, is to measure, using a
multimeter, the residual AC voltage in parallel to the capacitors. If the
measured value is higher than 1 Volt probably the capacitors have lost their
original characteristics.
A symptom of this problem may be an off of the green light despite all
measurements of “circuit check” appear correct.
The Rectifier Diode
The board A15, A18 or A2 in case of option 002 installed, uses some power
diodes as AC rectifier and Power summing.
These mushroom-shaped diode, heat lot and tend to burn the printed circuit on
which are mounted. More recent versions, HP have replaced CR1-4 with a bridge
rectifier mounted on the chassis.
The update is very simple and for wiring, just disconnect the four-wire from
A15 and attack them on the new chassis-mounted rectifier bridge (300V 5A).
The other two diodes, of the same type are mounted on A18 or A2 if the option
002 is installed.
The current will go through one of two diodes depending on whether the HP5065A
will be powered by AC or DC and the heat generated will burn the card as in the
case of the bridge rectifier.
For standard A18 board see: CR1,CR2.
For option 002 board A2 see: CR12,CR13.
The easiest solution in this case is to install a star shape heat-sink on each
diode.
The service manual is an excellent tool to facilitate these simple actions.
All these steps will help keep fit for a long time your HP5065A.
Luciano
www.timeok.it
tim...@timeok.it
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