Transmation 1080 Calibrator Teardown and Repair

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I bought a Transmation 1080 some times ago. The unit was suppose to be working but was partially broken when it arrived. Ultimately my goal was to use this device as a precision (to some extend) voltage and amperage source.

The Device:
The unit look pretty old, with the fake wood on the front panel, but it was built in 1991.



The Transmation 1080 was originally used as a process calibrator. It can simultaneously mesure and produce dc volt and amp.

Here's the complete list of features and specs:






The Problems:
- The NiCad batteries in the battery pack are completely dead and they leaked a little bit.
- On the output, the Volt range is always at 0. Nevertheless, Milivolt and amp are working.
 

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I could not find the schematics for the 1080 but found the schematics for the 1045. The main difference between the 2 is that the 1045 only have 1 screen. Technically they should be a little bit similar inside.

So after studying the 1045 schematics, I realised that the output circuit was mostly built around one opamp and 2 transistors.



I started from the Volt output, trying to follow the signal path. I think I found the 2 transistors and started validating if they were powered or not. So power was fine but I eventually realised that the gate of Q2 was always 0v. That was really weird.



While I was looking for the opamp I ended up realising that the signal driving the gate there and working but before the relay. And just after the relay voltage was 0. So quickly I tried bypassing the relay and the Volt Ouput started working.


Next step, finding a suitable replacement for the broken relay.

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I was unable to find any information on the old relay. Nevertheless, from the drawing on the relay itself I realised it's a double coil with reset position. The coil voltage is 5V.



Since I could not find a relay with the same footprint I decided to go with a surface mount relay. I ended up choosing the  EE2-5TNU (https://api.kemet.com/component-edge/download/datasheet/EE2-5TNU.pdf). It offer the same features but with a footprint a little bit different.

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I had to improvise a little bit to fit the new relay on the board. Luckily the new one was smaller than the old one.

So on top I hooked up the diodes and the coil drivers. Apparently the wire I choose to do the jumpers is super low quality, the plastic melted almost entirely.



Then on the other side of the board I cut some traces and reconnected them to the right pins. The board was really hard and the traces really thick so I had some problems there. I used a tool designed specifically to cut trace but it didn't work really well. Next time I think I will try a Dremel.



 

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Disassembly Pictures

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Disassembly Pictures 2

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The original NiCad battery are still available but they are relatively expensive. I decided to replace the 2 big NiCad battery by 2 x 4 AA batteries in parallel. That should give the same voltage than the original batteries. I would now have to remove the batteries to charge them but AA nimh batteries are far more convivial.

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Input and Output Adjustments (Calibration)

Since I don't have the manual for the 1080, I had to play a little bit with the trimpot to understand what they are doing exactly. It's pretty straight forward, there is only 2 trimpots you can adjust, R12 and R25 (see picture).

R12 adjust the input and R25 the output of the device. In other models manuals they recommanded to only adjust the milivolt range.

So you need to start by connecting the input of the device to a known MV source. In my case I divided the output of a AD584 voltage reference. Then you need to adjust R12 until you can read the value of the source on the meter. Then by connecting another DMM (or simply the input of the 1080) you mesure the output on the MV range. You need to adjust R25 until the output is indicating what you are reading on your DMM.

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In the end, the 1080 was tracking pretty closely my Philips 2534.