TDS-420A power supply repair


Brendan
 

Brian
Jan 18 #153753

I have a bad psu in my TDS-420A , it burned a track on the pcb bur I cannot find the cause , the switching transistor os it seems . I have had it suggested that the hybrid device is probably the fault , does anyone know what the device consists of , or better still does anyone actually have one that they would part with .

Thanks in advance for any help you can give


On Sat, Jan 19, 2019 at 08:22 AM, Bob Koller wrote:


Where is the burn? Can you post a picture?

I just finished two of these PSU's, I think you need to replace ALL of the
small electrolytic caps, don't bother testing, etc, just replace, they are all
past it.
One of the problem areas in this unit is the black potted mains switching
circuit in the primary. It controls the input doubler configuration by
automatically sensing 120 vs 240 mains input. It can be removed and jumped
across.
The other issue is the regulator board mounted vertically near the output
connector. These can get dirty from the fan, causing leakage paths, and
subsequent erroneous shutdown signals.
That is identical to the power supply I just fixed. Every single capacitor on the power supply board was bad. Either in the process of leaking or already leaked out and dried out. After replacing those and the all know SMD caps issue all seems well. You may want to check that the output connector joints are solid as well,just in case.


Bob Koller <testtech@...>
 

Where is the burn? Can you post a picture?

I just finished two of these PSU's, I think you need to replace ALL of the small electrolytic caps, don't bother testing, etc, just replace, they are all past it.
One of the problem areas in this unit is the black potted mains switching circuit in the primary. It controls the input doubler configuration by automatically sensing 120 vs 240 mains input. It can be removed and jumped across.
The other issue is the regulator board mounted vertically near the output connector. These can get dirty from the fan, causing leakage paths, and subsequent erroneous shutdown signals.


Brian
 

Hi , I checked for that sort of thing last night . I removed several of the caps and found no tell-tale liquids on the pcb and having checked them for shorts , as I had no replacements I put them back for now . Them mains fuse had blown and when I looked at the psu there was a burned track which I have repaired . As I have no Variac I have not dared to try turning it on again without a load even in case the cause of the burned track only makes more damage ,

On Friday, 18 January 2019, 17:24:56 GMT, lop pol via Groups.Io <the_infinite_penguin=yahoo.com@groups.io> wrote:

On Fri, Jan 18, 2019 at 10:12 AM, Brian wrote:


I have a bad psu in my TDS-420A , it burned a track on the pcb  bur I cannot
find the cause , the switching transistor os it seems . I have had it
suggested that the hybrid device is probably the fault , does anyone know what
the device consists of , or better still does anyone actually have one that
they would part with .

Thanks in advance for any help you can give
I know the TDS420 NON A  that i just repaired the power supply on every single capacitor had failed. They mostly looked fine but when you removed them there were puddles of liquid underneath them.


Brendan
 

On Fri, Jan 18, 2019 at 10:12 AM, Brian wrote:


I have a bad psu in my TDS-420A , it burned a track on the pcb bur I cannot
find the cause , the switching transistor os it seems . I have had it
suggested that the hybrid device is probably the fault , does anyone know what
the device consists of , or better still does anyone actually have one that
they would part with .

Thanks in advance for any help you can give
I know the TDS420 NON A that i just repaired the power supply on every single capacitor had failed. They mostly looked fine but when you removed them there were puddles of liquid underneath them.


Brian
 

I have a bad psu in my TDS-420A , it burned a track on the pcb bur I cannot find the cause , the switching transistor os it seems . I have had it suggested that the hybrid device is probably the fault , does anyone know what the device consists of , or better still does anyone actually have one that they would part with .

Thanks in advance for any help you can give