[SOLVED] TDS754D Won't boot, Load Buzzing, and leds lit  - Page 1
Forum section: electronics / repair

author: denimdragon
author_rank: Regular Contributor
timestamp: October 04, 2017, 09:09:28 pm
content: I decided to start a new thread on this. I thing Jay_Walling had an issue like this as well but I'm not sure. I have attached the console port to the scope and I get this:RUNNING FROM DRAM.DRAM test passed.{Tab}Bootrom Header Checksum passed.{Tab}Bootrom Total Checksum passed.{Tab}BootRom Check Sum passed.{Tab}Bus Error Timeout test passed.Kernel Diagnostics Complete.Calling SDM (monitor) Routine.{Tab}Enabling Bus Control register. Value = 0x67{Tab}IMR 1 Register test passed.{Tab}Misc. Register test passed.{Tab}Timer Interrupt test (Auto-Vector) passed.{Tab}NVRam DSACK test passed.{Tab}NVRam Write protected.{Tab}Flashrom DSACK and JumpCode test passed.{Tab}Flashrom Checksums passed.Bootrom Diagnostics Complete.DipSwitchValue: 0Skipping boot loader.Transferring control to FlashROM.No PCMCIA option board detected.FLOPPY: DetectedAdding 7165 symbols for standalone.CPU: 68EC040. Processor #0.Memory Size: 0x1000000. BSP version 1.0.Executing Diagnostics->Bus ErrorProgram Counter: 0x052dc8e0Status Register: 0x3710Access Address : 0x072c09f2Special Status : 0x0145Task: 0x5fffe80 "tRootTask"{BEL}And that's about it. I'm going to go and check all my voltages to see if there are any that are out of whack. Here's the video if you haven't seen it in the other 754D repair thread. Hold your nose

author: Jwalling
author_rank: Unknown
timestamp: October 05, 2017, 09:56:24 am
content: Keep in mind that this killed the video portion of the CPU board on mine! Don't run it anymore like that.Run it with the ribbon cable disconnected from the HV assembly.

author: denimdragon
author_rank: Regular Contributor
timestamp: October 05, 2017, 04:28:11 pm
content: Quote from: Jwalling on October 05, 2017, 09:56:24 amThat's good to know! I just had it on to get some data via console port.That ribbon cable runs to the TI video chip I'm assuming (How can I test the chip to see if it isn't toasted already)? I'm going to pull up the data sheet on the video chip for a pinout. Also where is a good place to get an LCD to replace the Tube? eBay? I think I'm just going to go that route. I have 2 TDS5054B I need to start on that don't have hard drivesSame as the TDS7154B we worked on.

author: Jwalling
author_rank: Unknown
timestamp: October 05, 2017, 05:27:20 pm
content: Quote from: denimdragon on October 05, 2017, 04:28:11 pmI had a known good HV assy. and tube, so it was easy. In the service manual, there are some waveforms shown for the CRT driver. And you could use your 684C display to test. Which, BTW - would you be interested in selling the front panel sticker from your 684C?

author: denimdragon
author_rank: Regular Contributor
timestamp: October 06, 2017, 01:04:05 am
content: Quote from: Jwalling on October 05, 2017, 09:56:24 amFor you Jay, no problem brother. You, ekertz (sp?), andy2000, and others have help me learn a lot about these old scopes. How do I remove it, with a heat gun?This 754D isn't going to be a keeper. I'm just trying to get it in excellent shape for resell locally. I might be getting rid of the 684C as is because in addition to this 754D, I have another fully working 754D, 2 784Ds (one with a 1M option, It's ugly but it works like a hot knife through butter so that will be my new HBW scope. I'm hoping to be able to upgrade them both to 2M. Any tips? ), and the 2 5054B with no HDDs.I've actually put the 754D on the back burner until Sunday. I'm researching how to enable options on the 784Ds. Also one off topic question. I have a prologix GPIB to LAN adapter i received last week. Could I use it to get into these scopes and change the options? I'm green to GPIB, so any clues would be great. Thanks again.

author: Jwalling
author_rank: Unknown
timestamp: October 06, 2017, 09:59:04 am
content: Quote from: denimdragon on October 06, 2017, 01:04:05 amThe TDS700D scopes with serial prefix B030 and up all come with the right memory installed for option 2M to be enabled. All serial prefixes are capable of 1M. Do a search for "password pitbull" and you should find the answer; if not let me know. And yes, the commands can be sent via GPIB or through the console port. You need to set the rocker switch to enable writes after the scope boots up, then set it back when done sending the commands, then power cycle.To remove the sticker, an x-acto knife works well. Pull up a corner, then lift right off the bezel. Keep the angle shallow to avoid creasing the sticker. Let me know what you want for it via PM and I'll send a paypal payment. Thanks!

author: denimdragon
author_rank: Regular Contributor
timestamp: October 07, 2017, 12:38:44 am
content: Quote from: Jwalling on October 06, 2017, 09:59:04 amI'm using the console port. I type:libManagerWordAtPut(0x5000f, 1)Rebooted the scope and option 2M showed but I went to the horizontal menu and the 250000 and above is still greyed out. It also failed SPC but I ran it right after reboot. I'm going to let it sit and then rerun it (SPC). I didn't type PASSWORD PITBULL because I only read people using this for GPIB. When I did attempt to type it in, the scope said it was invalid

author: Jwalling
author_rank: Unknown
timestamp: October 07, 2017, 10:07:04 am
content: Quote from: denimdragon on October 07, 2017, 12:38:44 amTwo things about 2M1. You can only get 8 million points on a single channel.2. Press "Ext Acq Setup" menu button to get there.It sounds like you got it right if you see the option 2M on boot. I've always used GPIB to enable so can't comment on using the console port - I just read about others who've done it that way.

author: denimdragon
author_rank: Regular Contributor
timestamp: October 07, 2017, 02:54:02 pm
content: After letting it warm up, all is well with SPC

author: denimdragon
author_rank: Regular Contributor
timestamp: May 15, 2018, 06:50:03 am
content: I managed to fix the TDS 754D. The flyback transformer had a hole in the top of the casing. I wonder how it got thereI swapped the display assembly from my 684C and it works like a charm. I still need to check the rest of the system and connect to the scope to see what it's doing on boot-up. This thing still had the correct time and date on the screen. It's the first time I've brought one back and the time was correct. That has to be a good sign. Pics of the FB transformer and the display assembly for both units below.Thanks everyone for the input!

author: andy2000
author_rank: Frequent Contributor
timestamp: May 16, 2018, 01:45:57 am
content: Since it's in an isolated location, you can probably patch that hole with silicone rubber, or epoxy (at least a temporary fix). Scrape away as much carbon as you can first. I'm sure it started as a microscopic crack, or hole and was enlarged by the arcing.

author: denimdragon
author_rank: Regular Contributor
timestamp: May 16, 2018, 10:06:34 am
content: Quote from: andy2000 on May 16, 2018, 01:45:57 amYeah, that's exactly what I was thinking about doing but I wasn't sure. I'll have to do some research and see where I can get some epoxy that will suit that purpose well. I have some here, but I'm not sure how well it will work.... Well one is for metal which is Loctite brand, but the other (Surehold) says that it works with plastic as well as metal, ceramic, glass, and rubber. I'm going to see if I can find some industrial grade epoxy. Thanks for the help as always

author: PartialDischarge
author_rank: Super Contributor
timestamp: May 16, 2018, 10:41:45 am
content: That was probably caused by a small bublle inside the casing causing partial discharges that in turn generate ozone and destroy insulating material around it, its a slow process.Slowly drill a hole with a small flat head end mill, not with a normal drill, and fill with a epoxy that does not contain metal particles

author: denimdragon
author_rank: Regular Contributor
timestamp: May 16, 2018, 04:45:08 pm
content: Quote from: MasterTech on May 16, 2018, 10:41:45 amHow deep do you think I should go though? I know I can't go too far but would you say maybe 3 mm, or more? I have plenty of end mills as well (Ex-CNC programmer/Machinist) and one of my friends has a desktop CNC.

author: PartialDischarge
author_rank: Super Contributor
timestamp: May 16, 2018, 05:40:59 pm
content: Can't know a priori, I'd do it manually, slowly until area is clean. Problem is the fault may have reached the winding, and repairing that kind of thin wire in a potted transformer is quite a task...

author: andy2000
author_rank: Frequent Contributor
timestamp: May 16, 2018, 07:31:15 pm
content: It looks like the hole is near where the HV cable exits the flyback. If that's the case, then it's arcing from the HV multiplier rather than the windings. If it was arcing from the windings, then it wouldn't be fixable. I would carefully cut away the burned plastic with an xacto knife until the area is clean.

author: denimdragon
author_rank: Regular Contributor
timestamp: May 17, 2018, 09:35:22 am
content: Quote from: andy2000 on May 16, 2018, 07:31:15 pmI have this boy running now so the flyback will have to go on the back burner, especially since my 684C was in pieces anyways as I was trying to troubleshoot the original issue with it not being able to boot unless it's connected to the console port. Now I'm having an issue with the 754D not wanting to write to the NVRAM via console port. I'm trying to enable the 2M function on it but it won't stick. I'm going to use my Prologix GPIB to Ethernet and try it that way.Anyone ever had this happen?

author: Arnie
author_rank: Newbie
timestamp: December 20, 2020, 09:05:19 pm
content: Hello, All,I know this is an old thread, but today, I just found the same issue with my 754D. 3 minutes after powering it on, I could hear a loud buzzing. Didn't have time to notice the display, as immediately pulled the power-cord.At first I thought the hole in the flyback transformer was just a scratch as it was smaller than a needle point. However, I could not find any other issues and so I removed the CRT in case that was arcing from the HT connection due to dirt or dust. Anyway, cleaned everything and I put it all back, and again the arcing noise. This time, though, the hole has become quite visible.Should I try repair with epoxy, as suggested above?Thanks in advance.

author: madao
author_rank: Frequent Contributor
timestamp: December 21, 2020, 04:52:13 am
content: Yes, you can try repair with epoxy. But you must drill hole , careful.. Then fill it with epoxy and cover it with plastic plate.

author: snoopy
author_rank: Frequent Contributor
timestamp: December 21, 2020, 09:28:52 am
content: Quote from: Arnie on December 20, 2020, 09:05:19 pmYou can also use a non acidic silastic and cover up the hole with a decent size amount. This is how we used to repair EHT triplers and LOT's on color TV sets if they were arcing like that.cheers

author: Arnie
author_rank: Newbie
timestamp: December 21, 2020, 09:48:53 am
content: Thank you for the tips. I will give it a go. I can get the black, 2-part electrical epoxy in small amount, within a couple of days' time. It seems more than a coincidence to find the issue in precisely the same spot on the transformer as the first poster,Dnimdragon. I guess it must be a weak spot in this unit. I'm just a little concerned that it doesn't have an internal winding failure, which may cause it to explode after the repair, with collateral damage. Anyway, I'll try the repair and fit some insulation sheets around and above it, where it was arcing to the top metal cover plate.Incidentally, has anyone fitted the LCD 'upgrade kit' and if so, does it look OK in practice ? I really like the original display - mine is still bright - and that it has fine lines without 'pixels'My Dallas ROM will probably require attention sooner rather than later. Is there a workable replacement for these and if so, what EPROM reader can be used to copy the code? The last time I had to use such a device was with the BBC micro, 35 years ago.thanks again

author: CJay
author_rank: Super Contributor
timestamp: December 21, 2020, 10:04:45 am
content: I'd stay with neutral cure clear silicone intended for high voltages, that way if you miss a bit of carbonised material you can remove it easily and have another goOther than that, the bit of the FBT with the hole looks like it's the rectifier/tripler section (most likely just rectifier if it's monochrome, likely tripler if it's colour)

author: Arnie
author_rank: Newbie
timestamp: December 21, 2020, 10:48:58 am
content: Thank you for the reply. That's a good point about the silicon. Yes, it's a monochrome CRT, so I take it that it should be repairable and worth a go.