BA11 power supply

Parent Category: How-to's Category: DEC hardware errors, and how to repair them Written by Administrator

Line power fuse pops out

Error: When switching ON a 11/34, about half the time the 16A 220V power fuse pops out.

Repair: Replace your fast "B16" fuse with a slower "C16" type.


Explanation: at power OFF, the 11/34's transformer iron stays magnetized in a certain flow direction.

If at "power ON" the electric phase is the same as at "power OFF", the iron is already magnetized in the same direction and strength, and there is no induction limiting the current flow through the copper coils. So there's a short overcurrent.
Slower "C" type fuses are made for inductive transformer or motor loads.

Contact: Jörg Hoppe

861 Power controller

Error: An electrolytic condensator inside the power controller blows up.

Detection: The power switch inside the power controller makes terrible noise, line power fuse comes out.

Explanation: Power switch is driven bei DC, but since condensator is dead, it gets driven by 50 Hz semi wave and switches on and off with 50 Hz.

Repair: replace condensator.

Contact: Jörg Hoppe

AC input assy in BA11 box power supply (H765)

Error: the solid state relais (SSR) in the "AC input box" is damaged.





Detection: power supply can not be powered on by front switch, or by remote control. Or line power fuse pops out, if BA11 is connected to line power.

Explanation: the big main power switch relais is driven by 220V 50Hz AC. This control current is switched by an solid state relais. If this SSR is damaged, control current may be always off, always On, or may be a 50 Hz half-wave.
If power supply is switched on and off with 50 Hz, high induction currents of the transformater let the line power fuse come out.

Repair: replace with a modern SSR. Foot print is DIL 16 (or 14), DC control current is at pins 1 and 16, AC load switch is between pins 7/8 and 9/10. Control voltage should be 3 - 10VDC, with about 250 ohm resistance, load current is surely less than 1 A. I used a CRYDOM SDV2415.

Documents: 1134A Power Supply Assy Field Maintenance Print Set (Jan 1977, MP00270)

Contact: Jörg Hoppe