First, Thanks to everyone for having this forum my 2445 is back from the dead.
A short recap of the last three decades:
I bought a 2445, SN B012772 back in 1984, It had been owned by a tek employee for less then a year before I bought it used.
It went back for warrantee service 4 times in 1985 to fix what were mostly listed as power supply problems, but it looks like it got a new U800 and the notes say it had a "Horiz mod Kit" and A9R1895 was changed from 12k to 3K.
We then worked together to pay for my first house until 1993 when I made a job shift from imbedded micro processor design to Agriculture. The scope was only used a few times to about 2002/3 when I turned it on and got a blank Tube, odd LED's with No switch response. I opened it up and there was too much "custom" at the time for me and Tek service had just ended so it went back into the closet.
In late 2012 a dog next door bit my wife and I needed a scope, so I pulled it out to look at again. Thanks to your forum I found a schematic and enough info to feel like it was a power supply problem that could be repaired. (little did I remember I had a schematic all along in the blue pouch in the closet)
Thinking I had a power supply problem, but was disappointed to find all the voltages dead on, with a 10.00V reference exactly.
I did not have a second scope to proceed and my wife was not smiling when she saw that Craigs listing in Auburn, but I did manage to make a few trips to other civilized locations with scopes (to be covered in later threads).
Oddly some time later I found out the same neighbors with the dog had a TAS465 scope sitting on a shelf in the garage they were going to get rid of that I could have for free. It was working.
So I proceeded to follow the best documentation I have ever used, to track the problem down to a bad CPU pin 17, Address line A8, which only goes to the Eproms, Ram and one decoding chip. I pulled the chip and bent the pin out to isolate it. It was floating at about 2.5V, it had a small pulse where the output should have switched. I would say it might have popped a bonding wire.
I went deep into some old boxes and pulled out a MC68B08 from a prototype I had built way back in 1985 (what are the odds of that) and I replaced the CPU and it powers up and is working, I do not see any loading on the A8 line that would cause failure.
Questions:
1. I don't want to miss a different cause then a popped bonding wire, Is there any history of CPU Address line failures and causes by other means I might have missed?
2. The CPU in the unit was a AMI S68A08P, Did Tek manufacturing use chips other then the Motorola 6802?
3. Given the U800 history, does any one know what a "Horiz mod Kit" was?
The scope now functions, but the CH1 input does not switch out of AC to DC and the horizontal position pot is not clean. So I have still have some work to do.
Thanks to everyone
John
