Got today my latest “for parts only” purchase from the US, the famous Tektronix 2336YA and had a first look inside just to make sure it doesn’t show any obvious damage and will blow my breaker on the first try. This is my 3rd one of this series which I all got from a surplus sale on eBay.
Some would say it is not only too risky to buy such “sold as-is” and untested parts and when considering the customs tax and horrendous shipping costs, I doubt I will do it once more. This specific model however is mostly unknown and unavailable in Germany and I like it not just because of its rarity but also because I’m kind of attracted to the old analog CRO’s and had always luck to be able to repair this particular type. This one is working fine OOTB, the Caps seem to have been replaced already and it only shows some small flickering on the inserted signal from my SG.
However, the point of this post is to show what I found inside and have never seen bevor: Right next to the fan in the back rear and connected to the 5V rail which supplies power to the adjustment for the A and B slope offset is a additional PCB with a part I’ve never seen.
The PCB shown on the attached picture has the following numbers written on: “+5”, “G-8533-01” and “G70-8368” underneath the tube. Someone also scratched “409/2780” as far as I can read it bevor the green coating came on top of the PCB. On the back of the PCB is nothing as it is a single layer type.
Beside the “0”, “2500” and “5000 hrs” markings on the scale of the tube there is, I guess the manufacturer of the tube device named: “The fredericks company” “P/N 8005”. The top and thicker connector is also marked as “+” while the lower one is marked “-“, accordingly the device was connected to the 5 volts rail. Beside of the hours marking this all is hard to see as it is basically underneath the tube thing and facing the PCB.
The little resistor reads 353 KOhms (357 according to the color code), the tube itself reads 2.7 (on my PeakTech 2170) or 5.6 KOhms (on my Fluke 45), don’t know why.
As you can see on the second and third picture inside the tube is a kind of a pipe which holds a little copper wire like piece which is now stuck at the bottom and on the “0 hrs” scale. The tube thing looks like being filled with something but there is no bubbles to see when I move it. I can’t neither shake the copper thing away or move it when I turn the part around or hit it on the table.
What is this tube-like device?
Is this a kind of usage hours meter and is it now showing the device was used more the 5000 hours?
If I read the IC’s right in this scope, it was built around 1988.
My first Tektronix 2335 which I easily repaired and sold to a colleague had nothing like this inside and the other 2336 waiting for repair neither. Was this “bodge” thing put it by some service provider who wanted to know the total usage time for this oscilloscope? Should I try to put 5V in reverse order of what is shown on its marking? Has anyone ever seen this particular part or a similar one?
The scope as I said is working and obviously this part has nothing to do with its intended capabilities. I wonder if this is a known thing and why it was put inside this machine. Anyone any idea?
Cheers,
Geronimo