开云体育

Hi all,

My new project is the repair of a THS710 I bought broken at a Dutch secondhand website.
So far I found three problems:

The screen has a 1/2" black bar at the bottom of the screen and it is quite dim.
After removing the screen from the unit and opening the screen by undoing the small metal clips I found some cracks in the glass of the screen where the connections are.
So I know it has to be replaced when the time comes.
Since the screen is the most expensive part of the scope, I will wait ordering it until I managed to fix the other 2 problems.

The second problem is the Channel-1 attenuator.
When I connect a test signal to both channels, the Channel-2 does respond properly to the input sensitivity setting, but Channel-1 however, seems to skip some settings.
After taking the board from the scope and removing both metal covers from the input ceramics I found the following:
There are 3 relays per attenuator, the first one is the AC/DC selector, the second one is a 10x attenuator, and the third one is a 100x attenuator.
These two, in combination with a change of the amplifier gain, provide the 1-2-5 etc. attenuation of the input.

The relays used are the type who are Bi-Stable, double coil latch type, so they have two coils to change the position from 'Set' to "Reset', they are only energized for a short period to change the position of the relay, this to safe energy from the batteries.
A datasheet can be found here:

As it turned out, the second relay of Channel-1 was stuck in one position. (contacts burned together ??)
I removed the relay from the ceramic (again I used a bit of QuikChip) to avoid damage to the ceramic.
A test of the relay free from the scope showed that this was the case, both coils still OK (143 Ohm) , but the relay stuck in one position.
I ordered these:

Third problem: the battery is dead.
Not so weird for NiCad cells from 1996.
I found the scope only has a trickle charger circuit inside, so I found it more-or-less safe to change to NiMh replacements.
I do not have the external charger.

So for now I ordered the replacement relays and the battery cells.
Mouser no longer stock the original brand relays, but there are several brands that make the same voltage, layout, size and contact type relays, I ordered them from the Zettler brand. but also Panasonic does make them.

After I manage to fix these two problems I will order the screen.
On AliExpress they are quite expensive, but on eBay the prices are more reasonable. (though not cheap!)

Some pictures about the progress are here: /g/TekScopes/album?id=41029

To be continued, un saludo,

Leo