Great Bill!! Glad I could help.
I have 2 working 468s, and 2 parts units. The first working unit had bad PROMs when I got it, and several bad big electrolytic caps in the main power supply. The other working unit had a bad TTL clock oscillator in the microprocessor section, a bad U571 (if I remember correctly), and lots of minor problems like bad pots, broken knobs, etc. They both work and look great now.
When I get time, I enjoy fixing up old classic Tek and HP scopes. I use them from time-to-time. Last time I used the storage function on one of the 468s was troubleshooting on a PC's motherboard that had blown MOSFETs in the CPU power supply per bad electrolytics one the core supply's output.
Jimmy
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--- In TekScopes@..., "maninashed1" <bill.valvetechnology@...> wrote:
Hi Jimmy, and thank you for that information. Checked U571 - no problem, checked U558 op-amp faulty waveform present. In between is U352, a LF351 op-amp, this proved to be faulty and the source of the oscillation. New LF351 and scope now working fine again. Just needs a good service and thorough clean. Im going to keep this one, its a lovely bit of kit and is so useable for the things Im interested in. Thanks to everyone who took time to read this thread.
Bill
--- In TekScopes@..., "jtjewell83" <jtjewell83@> wrote:
Bill,
I'm wondering if that's noise from the D-to-A converter circuit, maybe because a low-pass filter cap is open. I'd suggest to check on the Storage Display Logic Board (A16), which is the top-most board. Check around op-amps U571A, U352 and U558. See if you've got that noise on the signals on pin 6 of those last 2 op-amps, and pin 1 of U571A. Oh, In between, there's a 250 kHz switching pulse on U523D. Hhhhuuummmm????
Jimmy
--- In TekScopes@..., "maninashed1" <bill.valvetechnology@> wrote:
Ive added some photos of the scope displaying the fault. These are in my photo folder under bill.valvetechnology.
Ive checked the waveforms and ripple from both power supplies against the manual and both the analogue and digital power supplies look fine.
Can anyone identify this fault? It has been suggested that it could be the clock signal being imposed on the waveform and the cursors in digital mode.
Thanks
Bill
