Tektronix TDS 684C won't boot Front panel all LEDs Lit up only

[denimdragon]

And off we go again...

So during the last few days, I have been reducing my scope count. I'm currently working on a TDS 684C. When I first received the scope, it would not boot up and I set it aside. I would go back and try it again and see if I could get lucky and that never panned out for me. It would always come on with all the LEDs lit up with nothing on the screen.

Well today, I felt like getting down and dirty with it. I took it out of the cabinet to give it another good visual inspection, and still didn't see anything troubling. With the case off, I gave it a go again and it came on! Passed the start-up self test as well. So I turned it off to put the cabinet back on it and let it warm up so I could run SPC tests. Guess what, it went back to it's old ways again 

I have tried booting it with the #3 switch in the open position and still no boot. Initially all DIP switches were in the closed position. I can't remember the settings when I first recieved the scope. I've also tried plugging it into my external monitor (ASUS LCD), but that didn't work either. I'm not sure what to try next and I am looking for some advice.

I had a 694C, but I sold it when I found out how much the probes cost, so I would like to keep this one instead. I have a hacked DS1054Z for daily use and school but I still want a high BW scope in case I run into some projects that require it. From what I've read online, this one should be good until I can afford a newer high BW model. I'm also hoping I can add the 1M function to it once I get it working properly but I'm not sure if you can on this model.

Thanks in advance.

*It also has an optional hard drive. I'm not sure if that has anything to do with it or not.

Pardon the brightness on the one pictures...

[Jwalling]

When it doesn't boot, what's displayed on the seven segment LED?

[Armadillo]

Realm to the noisy world.
Hello, Noisy World!

[denimdragon]

When it doesn't boot, what's displayed on the seven segment LED?

GM Jay! When I saw that I had a reply a few minutes ago, I decided to turn the scope on again. Guess what, It boot! It must have known you were the one replying and you scared it into submission 

One thing stands out about this 684C and also a 544A I have that was doing the same exact thing. When I initially put them aside to work on them later, I stored them standing up with the front end pointing upwards. When I turned them on to check them again a couple of weeks later, they both worked.

Now earlier, this one wouldn't boot again, so I started the thread and made sure to store it front end up again until I received a reply. I had a hunch from reading on the Tek forum that someone else had a similar problem here https://forum.tek.com/viewtopic.php?t=138367  That's also where I read about the #3 dip switch, which didn't work. The OP of that thread changed out the display and the problem disappeared.

That got me to thinking that maybe the issue with this 684C is the same issue. I looked closer at the display after my attempts to boot it earlier and it looked like the CRT had a darker tinted blog under the top glass that receded after a minute or 2. Kind of like when you push an old calculator screen in with your finger and you could see the different colors until you took your finger off the screen and it reverts back to it's normal appearance. So now I'm wondering if the display is the culprit.

Right now the scope is still on with the cover off (strong fan blowing on it, I remembered  ) and I've let it warm up for about 30 minutes now. I was going to run SPC but I'm not sure if I should.

Here are the pics of the 7 seg and the scope:

[eKretz]

Go ahead and run it. It won't hurt anything. Have you checked the error log any of those times that you got it to boot?

[Jwalling]

Realm to the noisy world.
Hello, Noisy World!

?

Is it noon already?

[Jwalling]

If it boots, then there's not  much you can glean from the LED display. You have to catch it when it doesn't boot.

[denimdragon]

Go ahead and run it. It won't hurt anything. Have you checked the error log any of those times that you got it to boot?

Yes. But they are from 2007! I'm assuming it hasn't had any other errors and the initial error was a hard drive issue which was probably replaced. There is nothing recent on the log. That should be a good thing. I'm going to run SPC now. The scopes been on for quite a while because I didn't want to turn it off.

[denimdragon]

If it boots, then there's not  much you can glean from the LED display. You have to catch it when it doesn't boot.

I'm going to run the SPC and see what the results are. I'm curious. Do you think it could be the CRT?

[Jwalling]

Go ahead and run it. It won't hurt anything. Have you checked the error log any of those times that you got it to boot?

Yes. But they are are from 2007! I'm assuming it hasn't had and other errors and the initial error was a hard drive issue which was probably replaced. There is nothing recent on the log. That should be a good thing. I'm going to run SPC now. The scopes been on for quite a while because I didn't want to turn it off.

Now that I think about it, I have seen a TDS700C series scope with the HD option that would hang on the POST with a defective hard drive!

[denimdragon]

Go ahead and run it. It won't hurt anything. Have you checked the error log any of those times that you got it to boot?

Yes. But they are are from 2007! I'm assuming it hasn't had and other errors and the initial error was a hard drive issue which was probably replaced. There is nothing recent on the log. That should be a good thing. I'm going to run SPC now. The scopes been on for quite a while because I didn't want to turn it off.

Now that I think about it, I have seen a TDS700C series scope with the HD option that would hang on the POST with a defective hard drive!

That would be the Bee's Knees if the hard drive is the only issue! It passed SPC but I know it needs to be ran several times. It passed rather quickly relatively speaking (11:10). Also can't I set it up to test all the processes and loop it? I believe I read that somewhere and the only way to stop it is to turn it off.

Also how would I go about testing the HD? Thanks again for the help everyone!

OT - What is the difference in A,B,C,D Models. I assume the "D's" are Phosphorus.

[Armadillo]

Realm to the noisy world.
Hello, Noisy World!

?

Is it noon already?

OP was talking about 694 , 684 and going for higher BW, so if you cannot understand it, then you are not quite there yet, yeah!

There are many connectors, open it up and make sure all the connectors in particular the 2 vertical boards types are connected properly fully seated.
I would have a look at all the soldered joints and connectors joints for intermittent problems like this.
But the time keeper chip is also aging, I think already passed its time, could be a suspect. Swop one in if all else failed.

[Jwalling]

To eliminate the hard drive as a suspect, just remove the interconnect circuit board between the HD board and CPU. To test it, depends on what type of drive it is - PCMCIA or standard 2.5" PATA?

[denimdragon]

OP was talking about 694 , 684 and going for higher BW, so if you cannot understand it, then you are not quite there yet, yeah!

There are many connectors, open it up and make sure all the connectors in particular the 2 vertical boards types are connected properly fully seated.
I would have a look at all the soldered joints and connectors joints for intermittent problems like this.
But the time keeper chip is also aging, I think already passed its time, could be a suspect. Swop one in if all else failed.

LOL @ "Realm to the noisy world. Hello, Noisy World!"

I'm about to take the scope apart and inspect the boards but prior to that, I'm going to go with Jay's recommendation to see if it is , in fact, the HD causing the hangboot (new word ) issue. I finally had some good rest so I'm rarin' to go today (I'm a bit of an extremist when it comes to working with electronics and learning so 36-48 hour stints are the norm  ).

I also have some questions for you guys concerning this scope:

1. Is the memory upgradeable using the same process as used on the 7 series? Nevermind. I just found out that this model didn't have an option for more memory. That rained on my parade. Looks like I will be looking for a 784D or 794D.

2. Can I upgrade the HD to something larger (by conventional means) than it's current size? I think it's 2GB. Free space says 1.9GB? I'm contemplating on a SSD... yes I'm serious lol

3. How effective will the 520 schematic be as a reference for this C model?

4. Where to order the Dallas NVRAM Devices? I don't want something that's gonna die on me in 9 months like it did with TiN in his 7404 rebuild.

5. And lastly, does anyone have a working link to the Tektronix console build? I was looking yesterday but all the links were dead 


Ok, time to get after it! I will report back in a few...

*Is this ok to keep here since this repair will inevitably turn into a Frankenstein build thread, or should I make a new thread in "Projects" once this repair is done? Thanks again guys!

[denimdragon]

To eliminate the hard drive as a suspect, just remove the interconnect circuit board between the HD board and CPU. To test it, depends on what type of drive it is - PCMCIA or standard 2.5" PATA?

It's a standard 2.5" PATA. I have an 80GB 5400RPM Hitachi Travelstar. It would be cool to swap the 3.2GB out with that   

See Pics:

I was wondering about the formatting If I did use the Travelstar, but I think I saw something in the utilities for formatting the HD. I know it's there for floppy, but I'm not certain if it's there for the HD. Can anyone confirm? I'm putting it back together without the option board to see how it boots now.

[Jwalling]

2. Can I upgrade the HD to something larger (by conventional means) than it's current size? I think it's 2GB. Free space says 1.9GB? I'm contemplating on a SSD... yes I'm serious lol

3. How effective will the 520 schematic be as a reference for this C model?

4. Where to order the Dallas NVRAM Devices? I don't want something that's gonna die on me in 9 months like it did with TiN in his 7404 rebuild.

5. And lastly, does anyone have a working link to the Tektronix console build? I was looking yesterday but all the links were dead 


Ok, time to get after it! I will report back in a few...

*Is this ok to keep here since this repair will inevitably turn into a Frankenstein build thread, or should I make a new thread in "Projects" once this repair is done? Thanks again guys!

1. Right.

2. Don't bother. You'll never use up that much space! Older ones had 175MB PCMCIA, some flash based, some Viper rotating media drives. Even then you'd likely never get close to filling it.

3. Not really useful at all with regards to the ACQ board. The 600 series were completely different there.

4. Wouldn't worry about that either. Both have TWO batteries in them. On a dissected 20 year old one I have, one of the batteries is still @ 3.28V and the other is 2.97V
I suspect that the device switches over when is senses that the first battery falls below a certain threshold.
See picture where I've highlighted the 2 batteries on a DS1486.

5. The Tek console port adapter:  https://forum.tek.com/viewtopic.php?t=137307&start=20
When I made mine from that netlist, either power or GND was not getting to the board (can't remember which...)  One wire and I was up and running

[Jwalling]

Odd. The last time I measured the two batteries in March 2017, the one closest to pin 1 measured 3.01VDC, the one closest to Pin 16 measured 3.13VDC.
https://www.eevblog.com/forum/repair/tds-684c-nvram-backup/msg1173983/#msg1173983

Just double-checked them and they are definitely 3.28V and 2.97V. 

[denimdragon]

Well, I tried booting without the HD. No good. I checked all by voltages and everything was good. I also took a look at the front panel board and all I saw was a some flux remains around the 3 pins that connect the rotary encoders, but I also have a 744A dismantled and I look at the front panel encoders and they had  the same flux residue. Now that I think about, they came from the same source so they could have changed them out on both and did a shoddy job on this one. Initially, I just figured that was how the were from the factory.

I did see a solder joint at the base of one of the encoder legs that looked a tad suspicious, but I checked it's connection and it was good. I should have reflowed it but I have yet to solder on these PCBs, so I don't know their thermal characteristics. If this was a bad contact, would it cause the intermittent booting?

I'm kind of stuck now, and need some time to do a bit more research and think about it a bit more. I don't want to blindly start replacing components in hopes of "getting lucky", and worst, not knowing what the cause was/is and also risk upsetting the scopes balance. I've read that these scopes can act erratically if you do that.

Any suggestions at this point? 

[Jwalling]

The scope should boot fine if you disconnect the front panel board, although it will log the error. So I doubt that the front panel is the problem. What about the LED display?

[denimdragon]

The scope should boot fine if you disconnect the front panel board, although it will log the error. So I doubt that the front panel is the problem. What about the LED display?

I'm about to take a look at that. Between changing out the thermostat on my car, waiting for my little voltage reference to come in, and troubleshooting this scope, I'm about to go stir crazy    (Not to mention this 99° weather). Talk about a full days work. But the bad part is I'm having fun lol.

I'm also going to take a look at the display driver board. Something just isn't connecting right. Well at least that's what I think. I have another question. I'm assuming that the boot process checks all boards before the scope will fire up. Am I correct in assuming this?

[andy2000]

It's unlikely, but check the cal protection switch.  If it detects that it's in the unprotected position, the scope won't boot.  Also, if your NVRAM has been put in a socket make sure it's making good contact.

[denimdragon]

It's unlikely, but check the cal protection switch.  If it detects that it's in the unprotected position, the scope won't boot.  Also, if your NVRAM has been put in a socket make sure it's making good contact.

NVRAM is still in factory configurations. These scopes came from HP (old Compaq actually) so they are pretty much stock. The memory protect was the first thing I checked. I also checked the DIP switch to see if it could have failed open on me but it all looks good.

I ordered my kelvin wires for my Extech 380560 Milliohm meter and I'm hoping FedEx get's it to me soon. Trk info says it's out for delivery so my fingers are crossed. I want to use it to check for continuity. I strongly believe that something is just not connected properly or there is a cold joint somewhere. I'm consider throwing the boards in the oven to see if I can a bit of bit of reflow (I've confirmed some soldering state temps, but there's still a margin of error based on the many variables that exist). The couple of times it booted properly, the dang thing ran like it was brand new. 

You have any other trouble shooting ideas? Your help is greatly appreciated my friends.

I've actually started documenting these repairs in Excel spreadsheets. That's going to be a tremendous help in the future and from now on I'm logging all repairs I do. I have to take the scientific approach to this. The machines are just too complicated to not have logged data as an aid for these uncommon phantom issues.

[Jwalling]

The scope should boot fine if you disconnect the front panel board, although it will log the error. So I doubt that the front panel is the problem. What about the LED display?

I'm about to take a look at that. Between changing out the thermostat on my car, waiting for my little voltage reference to come in, and troubleshooting this scope, I'm about to go stir crazy    (Not to mention this 99° weather). Talk about a full days work. But the bad part is I'm having fun lol.

I'm also going to take a look at the display driver board. Something just isn't connecting right. Well at least that's what I think. I have another question. I'm assuming that the boot process checks all boards before the scope will fire up. Am I correct in assuming this?

Depending on how the dip switch #3 is set, yes. If off, it skips a lot of the testing. There is no test for the HV CRT driver board, though.

[denimdragon]

I'm just doing a visual inspection on everything and reconnecting connections. I'm hoping to see something out of the ordinary.

[denimdragon]

The scope should boot fine if you disconnect the front panel board, although it will log the error. So I doubt that the front panel is the problem. What about the LED display?

LED display was showing "_" then "8,6(?)" alternating.