Electronics > Repair
TDS3014 adventures
Galen:
just a quick update for the crystal oscillator. The 75.7575MHz oscillator received today, drop in replaced the 75MHz one, the frequency measurement display right on 1.000KHz for the scope self cal output.
Now, the only left thing is to make the anchor assembly to hold the handle in place. The price is very expensive, like $80. So I plan to make it myself.
sicco:
A TDS3034 from eBay, and the DS1742W issue. Finally cracked it.
Pitfall #1: when Dremel-ing for the coin cell inside the 24 pin DIP Dallas RTC, the battery is not always in the same spot. So the first attempt failed, I cut through the 32 kHz crystal and then damaged too much. Start from the top on the right, near pins 12 and 13. That’s where DS1742 has its battery. Need to take all of the battery out, the + is the solder lip that remains. Battery - on pin 12.
Pitfall #2: when ordering a DS1742 on eBay, note that you must have the DS1742W. Only that is the 3.3V device. No -W means it is a 5V unit. And those enter the low power sleep / battery mode at below 4V or so on the VDD pin 24. So that’s always when we have only 3V3 on pin 24 as in the TDS3000.
Workaround if you’re stuck with a 5V unit: bend away pin 24 on the DS1742 (yes you do need a DIP 24 socket anyway) and then flying lead to a 5V line. I used the input of a 5 to 3.3 TO220 regulator IC elsewhere on the main board). Isolate the old VDD pin in the socket. That made my scope boot fully. Before it did only Tek logo, relay one click, floppy on second turning, and then nothing.
So that’s likely why many assumed that China was sending fake, counterfeit DS1742 units. I don’t think so.
The 75.7 MHz crystal module - I thought for a minute it also failed on mine as the 48 MHz unit did show up on the scope i used. But actually it was just that scope (/probe) not having the bandwidth needed here.
Now, I did go through the effort of reloading the DS1742 from eBay with the binary data shared elsewhere on this forum, but at hindsight maybe that was not really needed. Only when trying to program it, i noticed that my unit was a 5 volt type...
james_s:
You can locate the battery easily using a magnet, it is close to the surface, sometimes even a small bulge is visible.
The DS1742W is obsolete and out of production so if you bought one on ebay that has a recent date code it is one of two things. Either an old part that has been sanded off, blacktopped and re-marked, or a counterfeit part. I have bought Dallas parts from China sellers on multiple occasions and every one of them was one of those two things. The counterfeit ones are easily identified by xray, they are laid out completely differently inside, and in my experience they do not work properly either.
sicco:
James, thanks for your response. I would have much preferred your patch pcb with the DS1744W - but was afraid about delays in getting that and the DS1744W and the clip-on for it shipped to me in a timely fashion. You don't sell the patch boards do you?
One thing that I'm still in doubt about and what you must know for sure now: was there a need really to copy back the 2 kbytes of data or would it have booted up irrespectively with a blank chip, or a chip with random data, or 0xff or 0x00 in each byte? Some in this forum including me went through the hassle of copying and sharing hex dumps of what was in them when a unit works ok - but is that necessary? Or is the reason the scope doesn't finish booting up simply that it checks what it is writing back in the RAM, or in the RTC registers and then drops into an infinite loop of retrying and failing to read back. Or is it waiting maybe for a tick of the seconds counter which never happens?
My TDS3034 firmware was very old, 2.2, now upgraded that to 3.39.
voltsandjolts:
I used a blank chip, works fine. IIRC operating hours gets reset.
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