The onset of YALBOA!

Oh no!

I have more oscilloscopes.

Test Equipment Anonymous

Well,

My name is Mark and I suffer with Test Equipment Acquisition Syndrome (TEAS).

It starts quite mildly but soon creeps up on you; symptoms are said include:

1. Buy some broken test gear cheap
2. Buy service manuals for the broken test gear (often costing more than the gear)
3. Troubleshoot broken test gear
4. Seek obsolete components to repair the broken test gear
5. Buy more test gear to help with the repair of the test gear you are working on
6. Build shelving and storage for test gear
7. Buy second and third same items as "spares" and find they are better condition than that you already have
8. Go to 1 and repeat

You get the idea.

There is help available here, but the condition is quite hopeless.

My latest acquisition is a Tek 466 "storage" scope.

Its in very good condition for its age and notably has "LEDs" instead of "indicator lamps" so is a more recent one of these models:

I've fiddled about with it and given it a good clean, replaced some caps and transistors in the PSU and also a (socketed - thanks Tek) IC regulator and bingo:

There seems to be very little wrong with this. Now all I need is another for spares....

Miss Luna cat is become slightly less timid, but not much:

A complete waste of time?

Well,

I decided it would be a good idea to buy this from eBay:

Its an old HP DVM and Frequency counter; with a glorious Nixie display.

Initial testing revealed some issues with the frequency counter part of the functionality which I traced to an IC that was basically a set of NOT gates, so I removed it and replaced it with a good old 7404:

So, now the frequency counter is working, but the digit in the image below shouldn't be a 4 but a 0:

It works when the digit is supposed to be displaying a 4, 5, 6, 7 or blank:

So the rules of BCD tell me that the line that represents "4" is always stuck LOW no matter what the actual signals tell it to do.

There's a bunch of logic in the system, but there's basically a 4-bit latch that seems to have appropriate signals coming into it for this digit, but the "4" line is just stuck low.

The part is labeled a HP  1820-0116, and I think it's one of these:

So I've ordered some - the "2" on the end of the display also seems to be a similar problem so more to investigate.

So, I removed the suspect chip and fitted a DIL socket in its place:

I then swapped the chip in the "option 001" which is also socketed and bingo:

Now, I will need to do the same to the "2" digit chip as that is also stuck with a line low. Having investigated further, the 7475 I mentioned above doesn't seem to be a direct replacement for the HP device - I suspect the logic is the same, but the pin out isn't. I think the HP device is like this:

So, to try one of these I will have to make an adapter board of some kind. But maybe.....

Is it normal to buy test gear, to fix the test gear you just bought on eBay? I could always find another one of these for "spares or repair" and get some bits from there.....

I think I've got a bad case of GAS. I'm told there is no hope or indeed cure.