Keithley 2612 teardown and repair

[dzseki]

Anyone here on eevblog that has a 2612 or similar?

At work we have a few depending on their age we have 2612 no suffix, A and B, we even have 2635B and 2536B.
Ocassionaly they fail a channel...

[MegaVolt]

Let's continue the repair

I could not save the PCB Unfortunately, there was a short circuit inside and all the burnt part had to be removed
Here are photos of the result. And the circuit of the primary winding itself.

I have to restore it.

[MegaVolt]

I restored the primary winding of the transformer and the device started working !!!! It turns on without a single error. It was already late and I did not test it further. Plus you need to disable interlock.

But I found that two LM2940C LDO stabilizers are very hot. (you can't hold your finger.). And I don't understand yet, is it another kind of error on the board, or it was so laid down during development. It feels like they have 24V at the input ) And at the output 5V. And 50mA current causes 1W loss .... Maybe someone knows more?

[razvan784]

They may rely on airflow from the fan for additional cooling. With the case open I imagine the airflow is significantly lower.

[MegaVolt]

They may rely on airflow from the fan for additional cooling. With the case open I imagine the airflow is significantly lower.

The fan has been turned off. Perhaps with the lid closed, the temperature will rise and it will work ... But it seems to me that the fan monitors the temperature of the radiators of powerful transistors.

[MegaVolt]

It feels like they have 24V at the input )

I checked the input voltage. At the input 9V. The output is 5 volts. The voltage is in the isolated area to power one SMU channel.

It looks like it was intended. And I'm really thinking about radiators for these LDOs.

[Kleinstein]

Some 4 V drop at 50 mA is not that bad, to really need a radiator. The regulator closer to the edge of the board has an extra isolating cover - so the radiator might need isolation too.

The special very loose wound isolation transformer looks funny. It it would be about low capacitance they should have added another spacer on top of the core.

[MegaVolt]

Some 4 V drop at 50 mA is not that bad, to really need a radiator.

50 mA was my guess based on the estimated power. In reality, the voltage is less. The current means more. I am assuming 250 mA. But I did not measure this figure. And I don't know what consumption should be.

The regulator closer to the edge of the board has an extra isolating cover - so the radiator might need isolation too.

To be honest, I do not understand why there is additional insulation that worsens convection. The body of the device is far enough away.

The special very loose wound isolation transformer looks funny. It it would be about low capacitance they should have added another spacer on top of the core.

Maybe there is a picture of how it should be?

[MegaVolt]

Cables have come. Here's what they are inside:

[Nebulex]

Hello I think I have the same device with a different error. If you like I could take some pictures of the part you want.

[MegaVolt]

But I found that two LM2940C LDO stabilizers are very hot.

I am finally back and can continue
Add radiators for very hot stabilizers:

[Davidwasalreadytaken]

I stumbled over this thread and I wonder if you ever got this device working again

[MegaVolt]

I stumbled over this thread and I wonder if you ever got this device working again

Yes, sure. The device is working. Here I wrote about it.

https://www.eevblog.com/forum/metrology/keythley-2612-teardown-and-repair/msg3236456/#msg3236456

Once I used it all day as a bipolar power source )))) and by the end of the day there was a bad smell You need to disassemble and carefully study where it still heats up more than necessary.

[ch_scr]

One has to add, even fully working, these devices (K2600 series SMU) don't get warm, they get hot. Even doing nothing, just sitting turned on. If you have one, observe the (quite wild IMHO) warmup drift (i.e. measuring an external stable voltage). I got the impression, they use the idle power dissipation as a heater with the whole device as an oven so to speak, and the fan to regulate it, to stay at an (constant) elevated temperature.