Color Display failure - TDS500 TDS700 - Series C or D - Page 1
Forum section: electronics / repair

author: Tantratron
author_rank: Frequent Contributor
timestamp: January 17, 2021, 07:58:53 am
content: Hello All,I'm trying to repair a color display issue which could be a double failure (A30 color display driver) and A11 main board (video section).Symptoms: the TDS784C works fine (boot, SPC, self-test...) but the color CRT will stay kind of blueish with some bands flickering. However if connecting an external VGA screen, the video display works fine where in fact that was the only method to check self-test and usage.Preliminary testing: since I do have another TDS794D which works wonderful in color, I've swapped each main board A11 where the TDS794D has good CRT and driver. Installing the good A11 board into the TDS784C will kind of show the CRT with some faint flickering (no more blueish) but the external VGA output works fine. Same situation of the partial failed A11 board from TDS784C installed inside the TDS794D will not have CRT to work. So it seems a double failure issue somewhere of my TDS784C, video section of the A11 board and A30 display driver board.One option would be to purchase the LCD kit from USA made by SimComm Labs, it is a hacking of the A11 video section and using power supply rails from the J5 connector. One hypothesis being that if the external VGA display works then the LCD kit could work and offer less weight, less power consumption plus less failure in the future of the display.Unfortunately there are no detailed schematics on internet regarding the TDSxxx serie C and serie D, the only document found is the TDS320B component manual but it does not contains the color section.I did take some time to analyze or reverse the wirings of the J5 connector (video signals and power supplies) between A11 main board and CRT display driver. Since I do have as well a working TDS540C and TDS520D (Acquisition board failed only), I have compared the J5 signals between color versus mono:D1-D2: +26V (open load)D3-D4: +5V (open load)D5-D6-D7-D9-D11-D12-D15-D16: GNDD8, D10, D13 and D14:unknownThe A11 color main board has an additional connector J62 (Signal and GND) connected to A30 board plus of course more chips to manage the color generation including an additional 80MHz quartz (Y3) not found in the mono-A11 board.As for the D13-D14 pins of the J574 (mono), they are shorted whereas on the J390 they are not electrically linked.What is your opinion of what is wrong with this color display failure and do you think it could be solved by replacing the CRT unit and driver by the LCD kit ?By the way, does any of you have tried connecting the J5 output from a A11-Color board to a A30 Mono-CRT-driver where it seems most of the 16 pins are kind of same defined except few ones ?Thanks, Albert

author: capt bullshot
author_rank: Super Contributor
timestamp: January 17, 2021, 09:26:27 am
content: Quote from: Tantratron on January 17, 2021, 07:58:53 amThe NuColor display uses a different type of RAMDAC on the A11 board and higher horizontal refresh rate than the monochrome board, so connecting a A30 B/W CRT to A11-Color won't work. You'd have to modify the A11 board to monochrome (swap the RAMDAC, and some other components). You might have success by connecting the A30 monochrome to the VGA output, afair these use the same refresh rates.VGA output is generated through a different RAMDAC on both variants (color and mono), this is why you find two of the RAMDAC chip on the A11 board. So it's perfectly possible that the internal display fails on a color board while the VGA is still OK.You might find some useful information here:https://www.eevblog.com/forum/repair/conversion-tektronix-tds500-to-tds700-color-oscilloscope/

author: Tantratron
author_rank: Frequent Contributor
timestamp: January 17, 2021, 11:17:57 am
content: I've done an additional test this morning, namely to check the presence of 80MHz output from the S15R8 quartz (Y3 from Connor-Winfield). This chip has 4 pins with a 2x7 DIL layout, the pin 1 and pin 14 are properly reading +5V then pin 7 is properly GND but bad news, the output pin 8 has flat 5V with no 80MHz modulation. Then did same test on my working TDS794D using same tek probe, there is 80MHz from Y3.So no idea if other chips are failed on the A11 main board (video section) but for sure the S15R8 quartz is dead (actually its output pin-8 is flat 5Vdc).P.S. Probing the J62 connector shows no signal either

author: Jwalling
author_rank: Unknown
timestamp: January 17, 2021, 08:01:57 pm
content: Quote from: Tantratron on January 17, 2021, 11:17:57 amIt's probably the 80MHz oscillator. I've replaced more than a few of those...

author: Tantratron
author_rank: Frequent Contributor
timestamp: January 19, 2021, 04:34:14 pm
content: Quote from: Jwalling on January 17, 2021, 08:01:57 pmThe Y3 oscillator chip (S15R8 - 80MHz) now found as MXO45-3C-80M000000 is clearly dead.Only problem purchasing one or two MXO45-3C-80M000000 is not possible anymore at digikey or mouser.More generally do you know if this oscillator-chip tend to fail easy through time or is usually reliable ?One option would be that I purchase MXO45HS-3C-80M000000 but re-work its pins to fit the DIL14 form factor unless donation or scavenge Y3 from a TDSxxx no suffix, serie A or serie B failed color board due to capacitor plague ?Otherwise would you know any pin and 80MHz compatible crystal oscillator with HCMOS-TTL output level ?

author: CaptDon
author_rank: Super Contributor
timestamp: January 19, 2021, 07:56:50 pm
content: I had a bad can oscillator on mine also. Good VGA output, internal crt display was blank. I bought a replacement oscillator on Ebay for less than $6 total with shipping. Scope works great now!!

author: Jwalling
author_rank: Unknown
timestamp: January 19, 2021, 08:42:36 pm
content: Quote from: CaptDon on January 19, 2021, 07:56:50 pmThat's where I bought mine as well. 10 for about $40 total.

author: Jwalling
author_rank: Unknown
timestamp: January 19, 2021, 08:52:10 pm
content: Quote from: Tantratron on January 19, 2021, 04:34:14 pmhttps://www.ebay.com/itm/324245502292?Have some spares!I'd say I've seen about 7 fail in all, but I've repaired hundreds (probably500300+) of TDS500X, 600X and 700X scopes over about 14 years... I've never seen any of the other oscillators fail on the CPU or ACQ boards, so I guess you could call it a higher failure rate.

author: Jwalling
author_rank: Unknown
timestamp: January 20, 2021, 09:20:18 am
content: Quote from: Jwalling on January 19, 2021, 08:52:10 pmThere were 35 or 40 pieces yesterday. Someone bought them all!

author: Tantratron
author_rank: Frequent Contributor
timestamp: January 20, 2021, 10:31:28 am
content: Quote from: Jwalling on January 20, 2021, 09:20:18 amEarly this morning in France, there was only 7 left so I did purchase all of them... it will cost me an arm due to export-import taxes and shipping between USA-France but hey I really want to repair this TDS784C. Incredible 35-40 left yesterday, only one 7 left this morning so I'm lucky hereQuote from: Jwalling on January 19, 2021, 08:52:10 pmThat is interesting you have a consolidated return of experience on so many TDSxxx all series.Would you know the root cause or why specifically this 80MHz oscillator tend to fail whereas other Xtal seem immortal ?On a side note, I've ordered as well this morning from USA the LCD kit from Simmconn Labs because I'm curious to know if it would work when 80MHz (chip Y3) is dead.I still have a fear as mentioned few days ago on this thread that my TDS784C has a double failure: A11 logic board (video section) and A30 (CRT display driver). As a reminder when I did connect a good color A11 board from TDS794D to my failed TDS784C, the CRT would not work so my safety belt goes to LCD kit on the long run.If you know any testing method to really check my A30 color board, let's go for it even though my gut feelings suspect monochrome CRT's seems more reliable than color CRT's.

author: Jwalling
author_rank: Unknown
timestamp: January 20, 2021, 05:22:16 pm
content: If you bought 7, then you'll get 35 pieces! There are QTY 5 in each lot.Well, that explains that.Don't know why they fail. I suspect you'll get a display on the CRT when you replace the osc. Hopefully, it will be nice and bright.IIRC the Simmconn kit connects over thatTI video chip.No, the RAMDAC. It probably won't work either until you replace the osc.

author: Tantratron
author_rank: Frequent Contributor
timestamp: January 20, 2021, 05:32:03 pm
content: Quote from: Jwalling on January 20, 2021, 05:22:16 pmAgrrrr.... shoot you're right, I'm damned stupid

author: coromonadalix
author_rank: Super Contributor
timestamp: January 20, 2021, 08:15:36 pm
content: for the 34 osc left, re sell them ?? loll

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 06, 2021, 07:40:04 pm
content: Quote from: Jwalling on January 20, 2021, 05:22:16 pmQuick update where I've received from USA the 35 quartz-oscillator last wednesday and as predicted by some of you, changing the Y3 solved one failure (as a reminder there are 2 failures on this TDS784C). Do make a note that I've connected the A11 logic board with new Y3 quartz to a working color CRT board (A30) since I have two color TDS (one working and one failed). I still feel there is a double failure with my color TDS784C because 2 weeks ago when connecting a working color A11 board to its failed CRT, it would still not work.Anyway as mentioned before, I did order as well a LCD kit from Simmconn labs to see its value, performance and resilience to resist partial failure of A11 video section. Attached a picture of a temporary socket to try different quartz as well as see the reaction of the LCD kit with and without the Y3 quartz.If some of you would like some Y3 quartz, let me know since I made the mistake to order 35 instead of 7.

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 09, 2021, 09:14:09 am
content: I do have some time left this week but would like an advice from you guys in the know to repair CRT, the A30 board, the removal and shipment of the color screen unit including safety guidance.As a reminder, I do have two color TDS oscilloscope (one TDS784C and one TDS794D). The TDS794D works perfect, it was a great buy on eBay but the TDS784C had display failure except the VGA video output would work. So far so good, now changing the Y3 quartz oscillator and driver chip (80 MHz), the A11 works well when connected to the TDS794D display. However in the past, I did first try installing good A11 logic color board from the TDS794D into the TDS784C but there was still video failure. Unless I'm wrong, this is why I think whatever I do from now on, there was a double failure on the TDS784C (the Y3 quartz on logic board and some other failure inside the A30 board).Since I need both scopes for my RF testing lab, I did purchase the LCD kit to replace the CRT as a safety to keep both my color TDS operational. However my questions or need for advices are simple: say I decide to put more effort to repair the CRT-A30 unit, is it recommended or OK to remove it from the enclosure, what storage condition or shipment condition if I re-sell for parts ?I ask this because there is a main metal plate to screw covering the PSU and the CRT, then adding the A11 logic board. This can be tedious and not easy to verify, test signals of the CRT and its associated electronic in attempt of a repair. There is as well the safety issue of implosion and HV electrocution...Thank you in advance, Albert

author: andy2000
author_rank: Frequent Contributor
timestamp: February 09, 2021, 03:56:36 pm
content: Since you have a second scope, you can use that to power the display while you're working on it without having to reassemble it. You can run the display loose as long as you're careful to prevent anything from shorting the board. It's awkward, but doable. Also be absolutely sure to keep the outside coating of the CRT tied to chassis ground to avoid HV arcing.The first thing I would check for are leaking capacitors. I've seen them get so bad that enough carbon tracking forms that it causes the power supply to shut down.

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 09, 2021, 06:34:15 pm
content: Quote from: Tantratron on February 06, 2021, 07:40:04 pmHere is a picture where I’ve just connected the LCD kit from Simmconn labs to test it works plus see the influence of the 80 MHZ Y3 quartz. Wether Y3 is good, Y3 missing or Y3 failed (constant 5V output), the LCD kit works great.

author: madao
author_rank: Frequent Contributor
timestamp: February 10, 2021, 06:33:57 am
content: Hiyou wrote: You have succesfull repair CPU Board of TDS784C, it show correct colour with CRT & eletronic from TDS794D.miscolour/flickering on few segment with own CRT& Eletronic ? pleas take of Photo of failed colour pictures.I tell you: Shutter Eletronic on CRT assembly is possible dead/damaged. It is easy to repair, but, much work with mechanical (CRT, Electronic must be pulled out of case.)If you check CRT outside of case, very very important: Metal piece (frame) of CRT must be connect to ground -> otherwise: spark and risk with damaged eletronic.SimmConn LCD Kit run on DAC for external VGA Output.Internal CRT run on TLC4076 and 80Mhz xtal. -> it means: It doesn't matter, if this ciruit is dead/semi broken.A tipp with colour CRT schematic: Use schematic of TDS544A. I have compared with my TDS700D Schematic, it is same at most point. (Pleas don't ask me after this schematic, i have promised ! Sorry)Greetingsmatt

author: james_s
author_rank: Super Contributor
timestamp: February 10, 2021, 07:04:28 am
content: Quote from: Tantratron on January 20, 2021, 05:32:03 pmThe obvious solution is to buy 34 more broken scopes and hope that they all need oscillators

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 10, 2021, 11:08:51 am
content: Quote from: andy2000 on February 09, 2021, 03:56:36 pmQuote from: madao on February 10, 2021, 06:33:57 amOk just thought this idea, please see the picture where I put temporary side by side (opposite) the working TDS794D and the failed TDS784C. It seems doable stretch to connect the J62 and J5 from good TDS into the A30 module of the failed display TDS with respective fans partially air flow blocked.This way, I'll make a picture of the blueish failed screen symptoms, maybe via Front Panel adjust the Display intensity to estimate if the CRT is healthy plus the VGA connected to my external LG display... what do you think or recommend ?Albert

author: madao
author_rank: Frequent Contributor
timestamp: February 12, 2021, 10:34:12 am
content: HiYes, you can connecting flat cable and coaxial cable to good unit (TDS794D), it is enough for check of state of CRT. Because, CRT metal frame (& coating) is already grounded.But, if you pull CRT and electronic (A30 & A31) out of unit. -> CRT metal frame must be connect to ground. (Metal frame, see yellow arrow )(This pictures show: I have place a book on CPU Board and CRT & A30 & A31 sit on book. )I have forgot grounding of CRT coating/metalframe and learned on hard way. (big luck, only 1 74HC374 dies )Greetingsmatt

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 12, 2021, 10:56:52 am
content: Quote from: madao on February 12, 2021, 10:34:12 amMany thanks Matt so here are 4 pictures showing my test setup for later today or this week-end.For safety, I've left the PSU inside the failed TDS784C with AC grid cord connected at the same time the AC grid cord of the working TDS. Then kissing each other, video output (power, digital and analog) J5 and J62 from good A11 color board into stand alone failed CRT.Please instruct what testing, pictures of the failed CRT should be done in order to estimate if the CRT is bad dim, is it shutter failed or CRT power supply failed ?Cheers, AlbertAlbert

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 12, 2021, 05:59:45 pm
content: Ok there will be 2 posts since limitation of attached files.Forgive my bad quality picture, it was taken with my Samsung A40 (no flash), my room almost dark room when Sun going down.Now 10 pictures of initially failed CRT connected to repaired A11 logic board with new Y3 quartz (from boot to work). To my surprise, the CRT now displays whereas few weeks ago, when connected the other A11 color logic board it did not work at all. Not easy to see on the picture but there is whiteish or milkish, not contrast as opposed to next post showing the good CRT connected to the same A11 logic board

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 12, 2021, 06:01:55 pm
content: La suite... now the good CRT where it is really nice contrast black.Thanks, Albert

author: madao
author_rank: Frequent Contributor
timestamp: February 13, 2021, 06:31:27 am
content: CRT Color look good, but poor contrast, it look like failure in amplifier.try at first with adjustment of two pots.

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 13, 2021, 11:06:06 am
content: Quote from: madao on February 13, 2021, 06:31:27 amMany thanks, now playing quick and dirty with R403 (intensity) and R404 (contrast) potentiometer I can have disappear the whitish background, see attached some pictures taken with 80 (text) 80 (curve) intensity level. When decreasing say to 50-50 I still see the display but I need to study the optical calibration method from the Service Manual.Next step will be to re-install the A11 board (with repaired Y3 quartz) and A10 acquisition board into the same TDS784C with its own PSU. So it looks like I did purchase for nothing the LCD kit from Simmconn labs but that is the price to learn with hands on

author: madao
author_rank: Frequent Contributor
timestamp: February 13, 2021, 12:28:49 pm
content: It looks really good :-)No fault in amplifier of A30 Unit. Fine adjustment of two pots is enoughBut why is it deadjusted ? Proably: Preowner has playing with pots.

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 13, 2021, 12:48:57 pm
content: Quote from: madao on February 13, 2021, 12:28:49 pmWell I guess previous owner did not know the problem (display failure) was mainly the Y3 failed 80 MHz quartz so probably as you said, he twicked the two pots maybe other pots then gave up and sold unit to eBay for parts. He was happy with output VGA still working then he sold for whatever reason so I took the risk to purchase.Make a note on another thread there is an issue with its acquisition board where it is clearly a TDS754C but was sold as a TDS784C... very dishonest but hey that is the risk when distance buying on eBay or auctions. For those interested about this story and way to fraud, read my other threadhttps://www.eevblog.com/forum/repair/tds500-and-tds700-spc-and-fas-calibration-concept/

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 20, 2021, 05:49:24 pm
content: Quote from: madao on February 13, 2021, 06:31:27 amTwo days ago, I've run the adjustment pots of both my TDS794D and my repaired TDS784C. Only problem, I do not have a luminance meter so adjusting the contrast was not really doable, anyway here is attached the result after the procedure. If you know a method to properly adjust the contrast without luminance meter, thank you in advance.Today I've decided to redo the adjustment first on the TDS784C but using a magnifier in order to better distinguish the raster lines from the patches, everything seemed OK. However when redoing the adjustment on the TDS794D, not sure if it was during the brightness adjustment with patches or during the contrast adjustment with white display, suddenly my TDS794D abruptly turned OFF. After inspecting its fuse, it was blown so I've created a new thread dedicated on the PSU of these TDSxxx, please see herehttps://www.eevblog.com/forum/repair/psu-power-supply-unit-tds-500-700-failure-while-color-adjustment/Please make a note that in fact, I did install on my TDS794D the A11 logic board which was repaired with Y3 quartz change, in other words the A11 originating from the display failed TDS784C.Murphy's law

author: andy2000
author_rank: Frequent Contributor
timestamp: February 20, 2021, 11:47:15 pm
content: My TDS-784D started exhibiting an identical looking problem recently. I was looking right at the screen when the brightness of the CRT started slowly increasing until the background was far too bright. I've turned it on a few times since then, and it's still the same. I plan to investigate as soon as I have time. I'll post back if I find something that might be helpful.

author: james_s
author_rank: Super Contributor
timestamp: February 21, 2021, 05:45:03 am
content: I'm pretty sure I've seen that before, not with a TDS but with some other CRT display years ago. Seems like it was a bad connection to G2, the voltage on the grid would gradually drift up or down and cause the brightness to change.

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 21, 2021, 05:48:00 am
content: Quote from: james_s on February 21, 2021, 05:45:03 amCould this explain my TDS794D abruptly switch OFF from the grid, the main fuse blown up... all this happened while I was adjusting the brightness and contrast routine per the service manual ?What is G2 ?

author: james_s
author_rank: Super Contributor
timestamp: February 21, 2021, 05:58:12 am
content: Quote from: Tantratron on February 21, 2021, 05:48:00 amNo, that sounds like the power supply failed, that isn't anything related to the monitor.G2 is the 2nd accelerating grid, it's part of the electron gun and the potential on it controls the overall brightness. It is usually fed from a pot on or near the flyback which is often called the "Screen" control.

author: Tantratron
author_rank: Frequent Contributor
timestamp: February 23, 2021, 06:41:06 am
content: Quote from: james_s on February 21, 2021, 05:58:12 amYes you're right, here is on the other thread my findinghttps://www.eevblog.com/forum/repair/psu-power-supply-unit-tds-500-700-failure-while-color-adjustment/msg3477442/#msg3477442where I still do not understand why so many transistors, diodes died on the PFC section... it sucks really