• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

WP-775B power supply repair

Status
Not open for further replies.

gray5596

New Member
I am trying to repair a WP-775B, 0 to 30 volt power supply, made by Vector-VID. My main problem is IC2 (14 pin DIP) is missing. The circuit board layout strongly suggests it is a quad op amp, but I can’t find a schematic to identify which op amp it is. This IC feeds the analog current and voltage meters, so I’d like to be reasonably sure which op amp to use so I won’t ‘smoke’ the meters.

My 1st guess is a LM324 because 24 VDC is on pins 7 and 11 and the unit appears to be built around the 90s. Also IC1 is a LM723.

Any ideas or suggestions would be greatly appreciated.
 

spec

Well-Known Member
Most Helpful Member
Hy gray5596,

The Vector-VID WP 755 Power Supply Unit (PSU) manual, including schematic and parts list, is attached below.

The component nomenclature appears to be different to your PSU, but I would think that the circuit principle is similar. At a guess I would think that there are two versions of this PSU: one with an LM723 voltage controller and one with an LM324. So it could be that the missing chip on your board is intentional.

Note that this PSU has a pre regulator using a phase angle controlled (I think) Silicon Controlled Rectifier (SCR) (SCR1) to maintain a roughly constant voltage drop across the linear series pass element (FET1) and thus limit the dissipation in the serial pass element.
 

Attachments

Last edited:

gray5596

New Member
Thanks!

My model is the 775B and doesn't have a SCR pre regulator. However your schematic shows a LM324 op amp and so it would be a safe guess that my model would also use the same op amp.

This information is what I was looking for, thanks again!
 

spec

Well-Known Member
Most Helpful Member
Glad to help gray. Hope you get your PSU working.:)

spec
 

gray5596

New Member
The missing IC was a LM324. After installing this op amp, repairing a burn trace and a few other components, it is working.

Instead of a SCR pre regulator, this has a high and low voltage output on the transformer that is controlled by a relay. A neat idea to keep the pass transistors from dissipating too much power.

Spec, thanks again for the schematic.
 

spec

Well-Known Member
Most Helpful Member
No probs Gray.

Glad to hear that you fixed the PSU.:cool:

spec
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top