Tek 7613 fault.
Posted: Sun Sep 24, 2023 8:18 am
The poor old 7613 has been sitting around for several years, quite literally "gathering dust", as when I gave up on it before, I didn't put the covers back on it, so it looks like one of those "back shed" acquisitions people show from time to time.
At the time, the CRO completely failed, & I tracked the fault down to the LV regulator board, which had lost its +15v output.
Q931 was dead, so I looked around for an equivalent.
One was referred to in various websites, but it turned out to be as much unobtainium as the real Tek one!
Digging around in my junk, I found a transistor of similar ratings to that equivalent, but in a different package, installed it, & turned everything on with high hopes.
No luck, still no operation!
At this point I started delving into the boards fed from the LV one, probably unnecessarily.
A whole lot of things came up of higher priority than 'scope finishing, so the poor old beastie has languished ever since.
Now that I have the BWD 845 useable, I decided to try again.
Firstly, I did what I should have done initially, pulling all the transistors out of the LV board, testing them, & checking that they are the correct one for that spot.
Most are, but I found that Q909 was missing, whilst Q908 & Q910 had been replaced with AT5058s by a previous Gorilla.
As it worked with those transistors before, the only problem transistor-wise was replacing Q909. (If, of course, my Q931 "bodge" was satisfactory).
The next trick might be checking every other component on the board, but the various repair blogs on the 'Net emphasised the possibility of a rectifier board fault, so I set out to look at that.
All the supplies had the expected DC voltages & hanging old "Dubya" across them showed pretty good levels of hum---nice having a CRO screen you don't have to squint to see!
In the process of doing this, I noticed a scrap of tape stuck on the 'scope frame with a bulge under it.
It turns out that it was Q909!
I now recall that while I was messing with the LV board, a transistor fell off it onto the floor.
I was just about to pack everything up for the night, so I taped it to the frame so as not to lose it in the chaos, fully intending to find where it was from when I got back to it, which I didn't due to various more important matters involved with what Zorba the Greek described as "The whole catastrophe!"
At the time, the CRO completely failed, & I tracked the fault down to the LV regulator board, which had lost its +15v output.
Q931 was dead, so I looked around for an equivalent.
One was referred to in various websites, but it turned out to be as much unobtainium as the real Tek one!
Digging around in my junk, I found a transistor of similar ratings to that equivalent, but in a different package, installed it, & turned everything on with high hopes.
No luck, still no operation!
At this point I started delving into the boards fed from the LV one, probably unnecessarily.
A whole lot of things came up of higher priority than 'scope finishing, so the poor old beastie has languished ever since.
Now that I have the BWD 845 useable, I decided to try again.
Firstly, I did what I should have done initially, pulling all the transistors out of the LV board, testing them, & checking that they are the correct one for that spot.
Most are, but I found that Q909 was missing, whilst Q908 & Q910 had been replaced with AT5058s by a previous Gorilla.
As it worked with those transistors before, the only problem transistor-wise was replacing Q909. (If, of course, my Q931 "bodge" was satisfactory).
The next trick might be checking every other component on the board, but the various repair blogs on the 'Net emphasised the possibility of a rectifier board fault, so I set out to look at that.
All the supplies had the expected DC voltages & hanging old "Dubya" across them showed pretty good levels of hum---nice having a CRO screen you don't have to squint to see!
In the process of doing this, I noticed a scrap of tape stuck on the 'scope frame with a bulge under it.
It turns out that it was Q909!
I now recall that while I was messing with the LV board, a transistor fell off it onto the floor.
I was just about to pack everything up for the night, so I taped it to the frame so as not to lose it in the chaos, fully intending to find where it was from when I got back to it, which I didn't due to various more important matters involved with what Zorba the Greek described as "The whole catastrophe!"
