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Old 20th Oct 2021, 12:53 pm   #21
jjl
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Default Re: Trouble at Mill, Bridgeport Interact 2

That machine has surprisingly unsophisticated encoders for something built in the '80s. When I first encountered rotary and linear encoders around '84 they were all of the the type that had digital squarewave A, B and Z outputs and I believe that they all had photographically processed glass disks.

Re mechanical damage to semiconductor devices - I've heard that some power devices in TO220 packages are very sensitive to bending forces and / or mechanical shock applied to the mounting tab causing breakage of the bonding wires to the device's chip.

John
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Old 21st Oct 2021, 1:16 am   #22
beery
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Default Re: Trouble at Mill, Bridgeport Interact 2

Quote:
Originally Posted by Radio Wrangler View Post
Sometimes, when the legs of ICs and transistors are sheared off, the shearing process can create a pressure transient shock-wave which travels into the device up the leg and does damage resulting in later failure.

That sharp snap when sidecutters cut a leg is actually quite risky. Trimming the legs of a device once it's soldered in a through-hole board is OK because the solder damps the transient.
Hi David, that would explain it. I've attached a couple of photos of the earlier type of thick film unit. One shows the soldering of the IC and the SMT caps. The other shows the underside, with the thick film resistors and low value printed capacitors.

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Originally Posted by Radio Wrangler View Post
Is that grinder a nice Jones and Shipman? I spent a lot of time with their internal, external and surface machines at Rolls.
Sadly not. If it had been, then motor replacement might have been easier. The machine is an Elliott 921 and the motor has a custom body casting that incorporates a mounting flange that forms the belt tensioner. I have a plan...

Quote:
Originally Posted by jjl View Post
That machine has surprisingly unsophisticated encoders for something built in the '80s. When I first encountered rotary and linear encoders around '84 they were all of the the type that had digital squarewave A, B and Z outputs and I believe that they all had photographically processed glass disks.
Hi John. Later versions of these encoders were indeed made with printed glass disks and that is what I found in the Interact 412 that I worked on (from about 1990 with the Heidenhain TNC355). The outputs were still sine waves though.
For some reason Heidenhain persisted for some time with analogue encoder inputs on their CNC control systems. Perhaps it was to force the use their own encoders with their control systems.
They did however offer encoders with digital A, B and Z outputs for use with control systems made by their rivals. An example of this can be found in the turret press that I electronically overhauled. It used a proprietry control system with Heidenhain digital encoders that were external to the servo motors. This machine is also from the 80s I think.

Cheers
Andy
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Old 21st Oct 2021, 7:25 am   #23
beery
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Default Re: Trouble at Mill, Bridgeport Interact 2

Hi all,
I've just noticed that pin 1 of the IC shown in my last post is dry jointed. Soldering on these thick film units is incredibly difficult because the ceramic just conducts away the heat. It is at least satisfying to have spotted a potential fault that may have been the cause of all the trouble.

Cheers
Andy
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