Hi,
I have acquired a quite cheap Tektronix 1502 TDR, 1986 vintage, in very good condition, but sold as not working (not powering up).
A common fault is that the unit does not power-up when there is no battery, or battery completly dead.
Indeed the battery was there but it's small 2A fuse was open.
So I tried to power the instrument from a bench supply (set to 12V 0.8A) with banana plugs inside the battery compartment: no sign of life, 20mA drawn.
Does not turn on? Take it apart!
On visual examination of the power supply board, I immediately found the suspect, there is even a red arrow on the side pointing to it
![Grin ;D](https://www.eevblog.com/forum/Smileys/default/grin.gif)
:
![](https://www.eevblog.com/forum/repair/(fixed)-tektronix-1502-tdr-repair/?action=dlattach;attach=1013414;image)
The missing piece of the blown transistor was not in the unit, so somebody already went there...
Did he/she tried to fix with no success? Hum hum...
This power transistor Q6435, part number 151-0352-00 is a GE X44C282.
According to the "Tektronix Semiconductor Cross Reference" (
http://w140.com/tekwiki/wiki/Reference_material), it is from D44C6 family: 45V 4A 30W NPN transistor.
I found a D44H8 (60V 8A 60W NPN, same pinout) in my "stock" and managed to solder it from the component side, without removing the board!
I also reinstalled one of the spare fuses in place, instead of the small piece of wire somebody had soldered before as a "replacement".
![](https://www.eevblog.com/forum/repair/(fixed)-tektronix-1502-tdr-repair/?action=dlattach;attach=1013418;image)
I checked the power rails for shorts as there are some tantalum capacitors on the boards: no short.
First try, powered from the bench supply: the unit works!
Here with a 3.70m piece of coaxial cable:
![](https://www.eevblog.com/forum/repair/(fixed)-tektronix-1502-tdr-repair/?action=dlattach;attach=1013422;image)
Powered from mains, with a new battery fuse, the battery even takes some charge!
On first visual inspection, I was a bit worried by the small piece of unattached cable at the rear of the strip line:
![](https://www.eevblog.com/forum/repair/(fixed)-tektronix-1502-tdr-repair/?action=dlattach;attach=1013426;image)
I removed the shield to have a look:
![](https://www.eevblog.com/forum/repair/(fixed)-tektronix-1502-tdr-repair/?action=dlattach;attach=1013430;image)
According to figure 4-26 in the service manual, it seems normal, although I have not found any indications about its purpose.
Indeed this unit has been tested by real people:
![](https://www.eevblog.com/forum/repair/(fixed)-tektronix-1502-tdr-repair/?action=dlattach;attach=1013434;image)
![](https://www.eevblog.com/forum/repair/(fixed)-tektronix-1502-tdr-repair/?action=dlattach;attach=1013438;image)
Michel.