| Electronics > Repair |
| TDS3014 adventures |
| << < (12/34) > >> |
| james_s:
Sync separator ICs do exactly what the name implies, they take a composite analog video signal and separate out the horizontal and vertical sync signals. In the scope it will be used for the video triggering option, not hugely useful for most people anymore but it was very handy in a former job where I often used a TDS3000 to look at the Macrovision analog copy protection pulses on the analog video outputs of the settop boxes we made. Macrovision used a series of pulses in the blanking interval of several specific video lines to upset the AGC in VCRs to prevent recording protected content and the TDS3000 with that option could trigger on a specific video line. We also had a few Tek VM700's that were much more capable in terms of measuring analog video signals however they were limited to 480i standard definition. Not that any of this helps you fix your scope. I see nothing particularly suspicious about that resistor and 39k is not an unreasonable value for a resistor but I suppose it can't hurt to compare it. I really think the problem is going to be with the address decoding logic that enables the DACs or whatever those are. How that is actually implemented in these I have no idea, it would be fantastic to fully reverse engineer these scopes at some point. |
| giosif:
Thank you for the info and apologies for not responding up to now! I've been waiting for a replacement oscillator I ordered to show up, but over a month later and still no joy. In the meantime, I've tested the non-working oscillator and it behaved exactly like in your case: it won't do anything for supply voltages above 3.3V but, at about 1.7-2.0V, it would start oscillating at 25.25 MHz. Afterwards, I decided to have a look inside (see attached pictures). |
| james_s:
That's interesting that they both failed in exactly the same way. While you're waiting, I suspect an oscillator that is approximately the right frequency would probably work ok at least temporarily. Can you find anything in the 70-80MHz range locally? My scope actually booted up with a 27 MHz oscillator, it wasn't usable but something that is at least in the right ballpark might work. I actually have a spare oscillator as I bought two at the time I ordered it, but as I'm in the US I doubt I could get it to you any faster than the one you already ordered. Some mail is very slow these days, I ordered some small parts from Australia that took over 2 months to arrive. |
| giosif:
I have already fitted an oscillator that I had - it is running at 50 MHz. Maybe trying something closer to the 75.75 MHz would be a good test to see if channel 4 would start working properly then. However, I am not that keen to swap oscillators on the board, in fear I may damage something else. So, I think I'll wait for the right part to arrive. Hopefully sooner than 2 months... |
| giosif:
Just a quick update: the oscillators I've been waiting for all this time have finally arrived (would have one to spare, in case someone UK/EU-based needs it). :-+ Installed one in the scope, fired it up and checked channel 4 - the problem persists (signal from channel 3 input replicated on channel 4, no signal from the actual channel 4 input). :-- Another issue I had noticed before, but wasn't sure whether it may be due to the wrong frequency of the oscillator (the temporary one was running at 50 MHz) - Ethernet connectivity was not working. This problem continues to be present even after installing the correct type of oscillator. :-- Some details: when connecting the Ethernet cable, the link on the switch port comes up (at 10 Mbps, half-duplex), but there is no traffic coming in from the scope (used static IP config on the scope). I even tried manually entering the MAC address into the switch MAC address table, as well as a manual ARP entry for the IP of the scope, but still no joy. I checked connectivity between the board with the Ethernet connector and the main board and all seems to be in place. I'm stating to think whether the main CPU might have some issues... |
| Navigation |
| Message Index |
| Next page |
| Previous page |