Tektronix TDS210 repair - oscillator help needed - Page 1
Forum section: electronics / repair

author: Burner_357
author_rank: Newbie
timestamp: June 01, 2017, 03:16:14 pm
content: Hello community,after being a passive member of the forum for a while, mostly reading and looking for interesting and helpful stuff...the time has finally come...I need your helpI bought a defective Tektronix TDS210 on eBay. The seller said, the display wouldn't show anything. So i got it for 50€, hoping it would be an easy fix (like pluging back in the powersupply to the main board).After unboxing and taking the unit apart, I saw that the previous owner has already changed an exploded electrolytic cap. He was even so kind to include the defective one into the packageUnfordunately the power connector was plugged in correctly, so there vanished my easy fix. So I powered the powersupply up, without connectin anything -> the voltages were within specs. After that I connected the other PCBs and testet it:The backlight of the display works fine, but the display stays black. So I checked the oscillator and bingo, the output is continuously on 3.3V and no signs of life from the oscillator.The oscillator is a 60.606 MHz type (see photo) but finding a replacement part seems difficult. I found a possible replacement (see attached datasheet) but these guys cost 15€ plus 18€ shipping on DigiKey.Here comes my question:Is it possible to replace the defective oscillator with a 60MHz type? At least for further testing.Has anyone located in Europe one of these 60.606MHz oscillators at hand and could send me one (to Germany)? This may be cheaper than the DigiKey costsThanks,Alex

author: Samogon
author_rank: Frequent Contributor
timestamp: June 01, 2017, 07:29:02 pm
content: They are not available at Digi-Key and mouser

author: John_ITIC
author_rank: Frequent Contributor
timestamp: June 06, 2017, 03:32:44 am
content: Is that an oscillator or just the XTAL? If the latter, then the oscillator is in the chip, which may be bad?

author: ArcticGeek
author_rank: Regular Contributor
timestamp: June 06, 2017, 08:43:24 pm
content: Assuming this really is an oscillator, you can get a programmable oscillator from Digikey in that frequency. Go to the digikey website and search on "programmable oscillator". Digikey will program that part to whatever frequency you want, in this case 60.606MHz. They are pretty reasonable in price, but I don't know if the package is correct for what you are looking for. Good luck!

author: rmm
author_rank: Newbie
timestamp: November 19, 2019, 08:55:51 am
content: Hi Alex and all,I too have a scope with the same simptoms as yours.I power it on, only blacklight goes on, no screen activity whatsoever.I need to mention it worked ok, before I started changing the PS caps and the bnc connectors on the MCU board.I am more than sure my repairs (new low-ESR caps on the PS rails and BNCs) have 0 contribution to this, however I do think that perhaps stress due taking the mcu board out contributed to this non-start behaviour?I really don't know, measured the voltages on PS, everything checks out (+5V, -5V, -24V, line trigger). Even the 1kHz probe compensation signal is there.Did you manage to get yours up and running eventually? And bw do you have a check/repair list I could use and probe for voltages on the MCU board? I looked inhttp://w140.com/tekwiki/wiki/TDS210, but this applies mostly to powering units.Thanks,Rob

author: george.b
author_rank: Frequent Contributor
timestamp: November 19, 2019, 11:00:26 am
content: Quote from: rmm on November 19, 2019, 08:55:51 amRob, you might want to check whether you have -24V on the LCD connector. I've seen two TDS220s (sister model, same main board, 100MHz bandwidth - the TDS210 can be modded into a TDS220, even, but I digress) that didn't, and the screen would be blank as a result.I bodged a straight connection from the PSU connector to the LCD connector and that seemed to fix it.I reported my repair of one of the units here:https://www.eevblog.com/forum/repair/tds220-repair-report/The presence of the 1kHz probe comp signal, in principle, indicates everything is okay with the logic and that the board passed its POST, so I would think you needn't worry about the other power rails. In any case, if memory serves, there are 4 LDOs on the main board, regulating down to +3.3, +2.5, +1.8 and -2.5 volts.

author: rmm
author_rank: Newbie
timestamp: November 22, 2019, 10:41:15 am
content: Hi George,You were right!!! Thanks!!!!I traced down the issues caused by the absence of pin1 connection, on that display connector. When restored, that measured eventually around -18V on that display flex. The raw -24V coming off the PS isnotdirectly applied to the pin1, it passes through some scaling resistors, maybe some const. current circuitry, etc.I noticed that another pin (#11) inside the connector suffered, from inserting/retrieving the flex a few times into the display connector, here's a pic attached showing the initial situation.All with all, I am very happy with the outcome. The new low-ESR panasonic caps installed perform very well, I measured ripple lower than 20mV pp on the loaded PS rails.I can move further now and try to source a TDS2CM module (since they're cheaper than TDS2MM); I've read you can mod (changing EPROM and RAM) these into TDS2MM and get FFT and rise/fall time measurements.

author: JFJ
author_rank: Regular Contributor
timestamp: November 22, 2019, 12:36:13 pm
content: Quote from: rmm on November 22, 2019, 10:41:15 amOver time, the connector pins do appear to adhere to the ribbon cable (perhaps, a lubricant dries out and sets hard), causing the pins to distort or break when the cable is pulled out. Tektronix, presumably, became aware of the problem, as they changed the connector to a zero insertion force type:Molex "Easy-On"

author: george.b
author_rank: Frequent Contributor
timestamp: November 22, 2019, 02:54:31 pm
content: Glad to be of help!Quote from: rmm on November 22, 2019, 10:41:15 amOh yes, you're absolutely right. On mine, the problem was with pin 2 (which also doesn't seem to be originally connected straight to the -24V rail from the PSU); the connector was okay - mine has the ZIF connector JFJ mentions - but it was actually the circuit that had malfunctioned somewhere. Having found nothing obviously damaged, I thought "what the heck" and connected it directly. According to the service manual, -24V on pin 2 is within spec. I've left it continuously on for over a week and nothing bad happened, so the bodge remains there.Pin 1 is contrast and pin 2 is Vbias, IIRC.Quote from: rmm on November 22, 2019, 10:41:15 amHeh, that's exactly what I'm doing. I have acquired a TDS2CM, the RAM of which I've already replaced, and now I'm trying to source the adequate (E)EPROM locally. I'm curious to see what FFT looks like on that old scope

author: james_s
author_rank: Super Contributor
timestamp: November 22, 2019, 04:39:54 pm
content: Funny, I recently fixed a TDS3014 that had exactly this symptom and mine was a bad oscillator. It too was a somewhat odd frequency however a bit different than yours, I was able to find a replacement and that fixed the scope. For testing you should be able to use any similar oscillator you have around, I initially tried a much lower frequency part I pulled from a scrap board and my scope booted up. It was not usable like that but it verified the fault.

author: rmm
author_rank: Newbie
timestamp: November 22, 2019, 05:25:42 pm
content: QuoteNice!Let us try in parallel then.Let me get one of those TDS2CM modules first.I will go the easy way, choose an Eprom (1 time programmable, 27C040, still to get via Ebay) instead of the 29F040 flash some people are also trying. When using the flash one needs to modify how A17 and A18 are connected as well, while for the 27C040 is directly a drop-in.As for RAM, I am thinking of IS62C1024AL-35QLI, as someone suggested in one of the online posts.As for programming the hex in the 27C I was thinking of Willem? Saw these around 25$ for sale.What's your approach for this mod?

author: rmm
author_rank: Newbie
timestamp: November 22, 2019, 05:33:56 pm
content: QuoteYou are right. When I pulled the flex for the first time, it felt like it was welded in there.In one of the pics you see debris from the flex pcba deposit hanging loose in that connector compartment, I suppose since it was literally scrapped off during one of the connect/disconnect actions of mine.Thanks for the ZIF pno. I will try to get one of these and install it next time I open it again.

author: george.b
author_rank: Frequent Contributor
timestamp: November 22, 2019, 07:37:41 pm
content: Quote from: rmm on November 22, 2019, 05:25:42 pmThe IS62C1024AL should work just fine, but any standard 32-pin SOP 128k x 8 SRAM will probably do. I found a Sony CXK581001M-85 in my scrap bin, and that's what I went with. I know, it's 15ns slower than the original chip, but meh, it's what I had at hand, and it's working so far. If it gives me headaches later - maybe once FFT is enabled it craps out? - then I'll replace it.I feel more inclined towards getting the original 27C040 (or the pin-compatible 27C4001), both because I would rather not modify the board and because the programmer I have available is an old Leap SU-1 that won't program 29F040 EEPROMs.I actually had some trouble acquiring the EPROMs locally. I bought a lot of 5, the ad said they were blank, but when I went to program one of them... "Device is not blank". What the?I tried another one from the lot, same thing. I dumped the contents and it was full of crap, including some plain readable strings. It seems the seller, in their infinite wisdom, pulled the parts from some old scrap and thought they could be erased...at least they accepted to give me my money back. Still, time I would rather not have wasted.

author: rmm
author_rank: Newbie
timestamp: November 22, 2019, 08:30:50 pm
content: I see AT27C040-70JU-T from Microchip, available on Mouser.This could work.

author: george.b
author_rank: Frequent Contributor
timestamp: November 24, 2019, 03:30:26 pm
content: Quote from: rmm on November 22, 2019, 08:30:50 pmIt will workunfortunately for me, it's not economical to order from Mouser, or any of those other, nice stores. Shipping would cost a few times the price of the EPROMs themselves.

author: james_s
author_rank: Super Contributor
timestamp: November 24, 2019, 05:59:40 pm
content: It shouldn't cost much to stick a few parts in an envelope and send them on to you. For small stuff like that you could order them to a member in the US who can forward them on to you, just another option. Otherwise you should be able to find something suitable from China.

author: george.b
author_rank: Frequent Contributor
timestamp: November 24, 2019, 07:36:39 pm
content: No worries, Icanfind them locally, just not as conveniently or professionally, as we don't have any large, online component store like Mouser, Digikey and the like. We used to have Farnell-Newark, but it closedso it's either small online stores that don't have much stuff, or individuals on our ebay equivalent.Our post service is crap anyways. I've been waiting for some parts from China for a couple of months now.

author: george.b
author_rank: Frequent Contributor
timestamp: December 08, 2019, 09:23:49 pm
content: Success!I bought some 27C040-150. Those didn't work - too slow.Then a friend brought me a 29F040-70 and we hotflashed the image using a Pentium III motherboard. I had to do the bodge wire mod as described elsewhere on the forum due to the swapped pins 1 and 31 on the EEPROM. Results attached belowEdit: you might notice I've replaced the RAM as well - I wasn't sure whether the fact it wasn't working was due to the 85ns RAM or the 150ns ROM. I replaced it with a 70ns part from a HP48G+, which works just fine with the 85ns RAM.

author: Nprod
author_rank: Contributor
timestamp: February 10, 2020, 09:00:07 pm
content: Hey, george.b ! I see your scope has version 2.03 of the main firmware, is it possible for you to dump it here? I had asked for it awhile back in the other thread discussing the TDS2CM to MM conversion, but nobody had it.

author: george.b
author_rank: Frequent Contributor
timestamp: February 10, 2020, 09:44:44 pm
content: Hey Nprod, can the firmware be dumped through RS232/GPIB? If so, please tell me how it's done and I'll do it. The EEPROM on mine is BGA, so I can't dump it directly.

author: Nprod
author_rank: Contributor
timestamp: February 11, 2020, 11:26:37 am
content: I wasn't aware they had versions with a BGA EPROM, that's unfortunate... If there is a way to dump it through RS232 it's not officially documented, i can't find anything about it in the programmer manual.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 11, 2020, 05:13:47 pm
content: Quote from: george.b on November 19, 2019, 11:00:26 amDo tell!

author: george.b
author_rank: Frequent Contributor
timestamp: February 11, 2020, 06:55:50 pm
content: Quote from: TERRA Operative on February 11, 2020, 05:13:47 pmYou mean the TDS210/220 mod? It will change its ID with the usual "pitbull" hack. Seemingly (I read this after writing the post you quoted) that doesn't change the actual bandwidth; I suspect the input filter is hardwired. I will probably get to compare TDS210 and TDS220 boards side by side in the near future and will report back.The TDS210 is my friend's; he bought a non-functioning unit. The capacitors on the PSU were oozing electrolyte, and the TL2274 on the mainboard was dead. I might do a repair report once it's done (we're waiting for him to get a replacement TL2274). When he brings it back, I'll see about comparing the frontends.

author: 2lostkiwis
author_rank: Newbie
timestamp: March 09, 2020, 07:12:05 pm
content: Quote from: JFJ on November 22, 2019, 12:36:13 pmFor what it's worth, I had the same issue of the connector "welding" to the LCD FPC cable, causing damage to one of the connector contacts. I ordered one of the linked Molex easy-on connectors - only to find the pinout pitch mirrored. See attached photos...

author: george.b
author_rank: Frequent Contributor
timestamp: March 09, 2020, 07:34:17 pm
content: Quote from: 2lostkiwis on March 09, 2020, 07:12:05 pmOh wow, that's good to know. Thanks for the heads-up.

author: al_m
author_rank: Contributor
timestamp: January 16, 2021, 05:59:05 pm
content: Hello all,I found this topic after searching for TDS210 repairs, and thought i'd see if anyone has any advice for my next move in repairing a TDS210 i picked up with the blank display issue.I have verified all the power rails are good, but the LCD flex connector was missing the two negative voltages on pins 1+2. The data lines also appear to be pinned high, but i can't verify this as i don't have another scope to check with! The upper 4 read 5.1VDC, or ~10VAC on my meter, which seems odd. Anyway, i went ahead and stuck in a bodge wire connecting pin 2 on the LCD connector straight to the -24V off the power connector, and pin 1 to the same rail, through a 100k resistor. Powering up after that gave me -22V on LCD pin 1, and -24V on pin 2, so within spec for the LCD according to the service manual. After plugging in the display i now get a black border around the screen! Some progress, but nothing more happens.Is it likely then to be a fault in the main oscillator, as the first poster reported with his unit? Is there some way the circuitry is switching in the voltages for the LCD after boot, which isn't happening cos the osc is buggered?Any tips would be much appreciated. I'm pretty limited in my tool set here, my main scope is about 120 miles away and we're in lockdown, so no go. Thinking of picking up a second unit just to be able to probe this one but am a bit skint at the mo.

author: george.b
author_rank: Frequent Contributor
timestamp: January 16, 2021, 06:33:54 pm
content: Quote from: al_m on January 16, 2021, 05:59:05 pmCould you post a picture of what you're getting on the display?

author: al_m
author_rank: Contributor
timestamp: January 17, 2021, 03:26:54 pm
content: Quote from: george.b on January 16, 2021, 06:33:54 pmHi George, yes, here's a picture.There's definitely life compared to what it was like before (totally blank). Now when i turn the unit off i can see the scan line die out, and it's in a different position every time. So there is probably a clock running somewhere. But, having read more into it i realised i was setting the contrast by putting a voltage on pin 1, so i removed my bodge resistor and it made no difference. There does seem to be a signal on the probe comp lug, i get ~2.5VDC or ~6VAC when i stick my meter across the terminals, which sounds about right for a 5V 1kz square wave. Hmm.

author: george.b
author_rank: Frequent Contributor
timestamp: January 17, 2021, 06:56:35 pm
content: Alright, so, the black border is normal. I wasn't entirely sure what you meant, I thought it was a black border inside the display area, but that's outside it, so there's nothing wrong with that.Ideally you'd check the probe comp signal at least with a frequency meter, since you don't have a second scope handy. Maybe you could cobble one up with a microcontroller if you have access to any. The TDS200 series will output a square wave of different frequencies during the progress of its POST, so checking for the average signal value won't help you much other than "there'ssomesignal present". It will output 1 kHz when it passes POST; it will output, IIRC, 4, 2, and 1 kHz depending on which step of the POST it's executing.Failing that, I would suggest you check the voltage rails on the logic board. There is a triple semi-discrete (I mean, there's an opamp, TLC2274 or some such, so not fully discrete I suppose?) regulator providing 3.3, 2.8 and -2.6V. See pic - not mine, but from another user, JFJ. If there's a problem with those rails, the board will, of course, not pass POST.Edit: you could also try setting the contrast - push "Display", and then the bottommost soft buttons to increase/decrease contrast. It's conceivable that the contrast is so completely out of whack that you don't see anything. Admittedly, it's a bit of a long shot, but hey, if it works, then it works

author: al_m
author_rank: Contributor
timestamp: January 18, 2021, 12:20:05 am
content: Hi George, thanks for the pointers. You are of course right about the frequency being opaque just using a meter on the probe comp lugs. At least we know something is going on! I have a frequency counter sitting on top of my scope actually, only they're both inaccessible... Sigh. Anyway just checked and the voltages at the regulators seem ok. 3.3V rail reads slightly low at 3.23V, but the other two are pretty much spot on. I'm in one of those catch 22 situations where i need a scope to really be able to diagnose this scope! Where next? I'm wondering whether the caps on the display board may not be worn out or something like that? There's a lot of small electrolytics on there pushing 20+ years of service...

author: al_m
author_rank: Contributor
timestamp: January 18, 2021, 12:21:17 am
content: Oh, the contrast buttons don't work btw. Sadly. That would have made my day!

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 18, 2021, 01:04:12 am
content: I have heard that the capacitors in the PSU in these units can fail.My TDS210 is still working fine without a recap (ex university scope, so decent hours on it) though so I guess it's pot-luck if you got a good or bad PSU.I would suggest checking ripple on the PSU output as a sanity check, but you need another scope for that. Do the voltages all look ok from the PSU?Also, if you don't have it already, here's the service manual:https://www.tek.com/oscilloscope/tds210-manual/tds200-series-service-manual

author: george.b
author_rank: Frequent Contributor
timestamp: January 18, 2021, 06:43:45 am
content: Quote from: al_m on January 18, 2021, 12:20:05 amYup -completelydead it ain't; whether that's a good thing or not remains to be seen, thoughQuote from: al_m on January 18, 2021, 12:20:05 am3.23 is most likely fine. I don't think the 3.3V rail is critical.Quote from: al_m on January 18, 2021, 12:20:05 amBad caps on the display board was one of the many problems my own TDS220 had. The symptoms were different from just showing nothing, however:Then again, symptoms could certainly be different from what I experienced.Quote from: al_m on January 18, 2021, 12:20:05 amIndeed you are. Measuring the frequency of the probe comp output would immediately give you an idea where (not) to focus your troubleshooting. Couldn't you order an el cheapo Arduino thingy online and use it to measure the frequency? Plenty of Arduino frequency meter projects floating around the 'net that you could use. Other than that, I think you will need proper instruments indeed.Quote from: al_m on January 18, 2021, 12:20:05 amIf not a power supply issue of some sort - TERRA Operative is right, by the way, the capacitors on the PSU may leak, I fixed a friend's TDS210 where, again, among other problems, most of the capacitors there had leaked, so you could check that, but you'd probably be able to smell it when you opened the scope already - that would make it likely to be a logic issue of some sort. A bad ASIC is possible, although I haven't seen it happen yet. This would mean very bad news.Something that happened on mine is that it wouldn't even give out a probe comp output. I decided to check whether the processor was even running - lo and behold, it wasn't; the /HALT line was asserted. With another scope, I determined that it happened soon after /RESET was deasserted. I made an educated guess that if the processor were reading garbage on the data bus, it would throw an exception, and if it read garbage again when trying to handle the exception, it would halt. The explanation I could come up with is that there should be a bad solder joint on the EEPROM containing the firmware - in my case, a BGA chip - and it was seemingly a correct guess, because reflowing the chip brought the board back to life.Now, I'm not saying your case is the same - mine wouldn't even output a probe comp signal, so something is different there - but checking for bus activity etc could reveal something. You'll need a scope for that, though.

author: al_m
author_rank: Contributor
timestamp: January 18, 2021, 04:00:37 pm
content: Hi,Thanks again for all your help chaps. I decided to order one of those cheap chinese hand-held scopes (FNIRSI 1C15) from eBay. Hopefully it will be good enough to shed some light on what's going on here plus be useful to have around in case i can't get this Tek 210 back on its feet. Will report back once it's arrived.

author: al_m
author_rank: Contributor
timestamp: January 22, 2021, 12:18:47 pm
content: Hello again. My Fnirsi scope arrived today and first thing i did was measure the probe comp output of the 210. It's giving a ~117khz wave. I'm guessing it's a proper square waveform, but the probe that came with the Fnirsi is absolute rubbish and doesn't appear to have a trimmer anywhere to sort out the compensation so what i see looks a bit like a shark fin. Will have to go digging around inside the unit later and see what other signals i can find.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 22, 2021, 01:56:40 pm
content: Sharkfin shape means you probably have AC input coupling, can you switch to DC input coupling?

author: george.b
author_rank: Frequent Contributor
timestamp: January 22, 2021, 07:38:54 pm
content: Quote from: al_m on January 22, 2021, 12:18:47 pmSomething's not right here. It shouldn't output 117 kHz. Measure the frequency "manually" (using the reticle), see if it makes sense. Try other horizontal ranges.I wouldn't trust that Fnirsi too much - not just the probes.

author: al_m
author_rank: Contributor
timestamp: January 22, 2021, 07:57:06 pm
content: Hi both of you, the Fnirsi is set to the following:1v per div1us per divAC couplingnormal trigThis is what it shows meSorry for the poor quality iphone photo, but it's all i had to hand. Measurements look right to me if the scope is doing what it should. I will try and get a better probe, but in the meantime i have to work with what's here now...

author: al_m
author_rank: Contributor
timestamp: January 22, 2021, 08:31:46 pm
content: Ok, a bit further. The power supply rails all read within spec. Ripple doesn't seem to be too bad. The square wave on pin 7 is there and within spec. Main oscillator seems to read ok, comes up 1v pk-pk with a triangle wave in the region of 60.6mhz. Might have a bit of DC offset, is that normal?Where things get fishy is on the display lines. The four data pins all stuck at 5v no activity even when power cycling the scope. The clock signals are there but all read too slow compared to the expected freqs, and the last one on pin 12 is totally weird. It phases in and out over a long period, like theres some very slow AM on the signal. Really strange...

author: andy3055
author_rank: Super Contributor
timestamp: January 22, 2021, 09:28:17 pm
content: Quote from: Burner_357 on June 01, 2017, 03:16:14 pmOP: UK RS has a 60 MHz crystal:https://uk.rs-online.com/web/p/crystal-oscillators/4785317/Not sure if it will work anyway!

author: george.b
author_rank: Frequent Contributor
timestamp: January 22, 2021, 11:36:37 pm
content: Well, it sure does seem like it's outputting a 117kHz wave. Very weird.The display lines not showing activity is to be expected if it's hanging before the display comes up. Check for activity on the main processor bus. Check whether the processor has a clock (IIRC it's derived from the ASIC). Check whether the ASICs are giving out any signs of life (communication between themselves, communication with the CPU/RAM, etc).

author: al_m
author_rank: Contributor
timestamp: January 23, 2021, 01:11:42 am
content: Hi george, yes it does seem pretty weird!I've done some probing around the exposed chips, which i assume are the processors and some memory. Story gets even stranger from here. There's quite a lot going on but it's hard to tell with the crappy Fnirsi exactly what, as the triggering is horrendous. Anyway, i'm finding a 140khz clock on a lot of pins. Also the 60mhz oscillator looks like it's reaching the National chip ok. Then there is the TI HT244 buffer which i've marked on the picture. I think all the signals on the display pins are present on this chip, which i assume is being fed from the National ADG422 near it. Also, very odd, but the 117khz wave is there, and it comes up as a really sharp square signal.Honestly, this is a bit beyond my skill level. Without a schematic i'd have to get the shields off and try to reverse engineer it to find where things might be going wrong, but i don't have the time. I wish Tektronix were more forthcoming in the service manual, but it just says 'replace the main board' for nearly any problem i might be facing, so i assume it was really just meant to be used by registered Tek service engineers who could order spare parts.Really appreciate your time and help so far. Thanks for trying to figure this one out with me..

author: george.b
author_rank: Frequent Contributor
timestamp: January 23, 2021, 01:24:51 am
content: The 68SEC000 (main CPU) should get a 7.something MHz clock, IIRC from one of the ASICs. It should be present on pin 6 of the CPU. Also check the status of /HALT (9) and /RESET (10).If the clock is present, and my recollection of the clock coming from one of the ASICs is correct, that means at least that ASIC is working to some degree.The service manual for the TDS200 series is almost uselessit comes nowhere near the quality of older manuals.It's not like I know totally what I'm doing - I'm looking for clues

author: al_m
author_rank: Contributor
timestamp: January 23, 2021, 02:44:59 am
content: Hi, just checked and the CPU does indeed have a 7.58 mhz clock on pin 6. Waveform looks a bit funky, but it's there. Pins 9 & 10 are both high (~3.2V). I've also tracked down those signals that i said in my last post were at the HT244 buffer. Looks like they're coming from the National ADG422. Except the 117khz signal at the probe comp. No idea where that's coming from yet. I'm going to remove my bodge wires sending power direct to the display connector tomorrow and see where that gets things. Hopefully i'll discover something obvious, otherwise the likelihood is this will have to go on ebay as a spares or repairs. Bit of a pity. I was hoping it would be more clear what was wrong with it, but as the power rails seem within spec, it's getting into mystery territory. The fact it's a teeny weeny surface mount double sided board with thousands of vias definitely isn't helping. Tracking down a something like a cracked 2mm long capacitor isnt my idea of fun!

author: george.b
author_rank: Frequent Contributor
timestamp: January 23, 2021, 03:28:24 am
content: Quote from: al_m on January 23, 2021, 02:44:59 amYou could also check /BERR (pin 12). It should be high as well. An unresponsive device on the bus (like a faulty ASIC) could cause it to be asserted. Is there activity on the data/address lines, like, say, on lines D0 (pin 61) or A0 (pin 19)?Quote from: al_m on January 23, 2021, 02:44:59 amIf memory serves, it comes from one of the ASICs. I want to say it's from the same one that controls the display, but I'm not sure. It shouldn't be outputting that, which makes me suspect a bad ASIC. I've never seen this before, and a cursory internet search reveals nothing.Quote from: al_m on January 23, 2021, 02:44:59 amThat would be a pity indeed, as it's a nice little scope, even if it's quite old. Maybe you could find a replacement logic board?

author: al_m
author_rank: Contributor
timestamp: January 23, 2021, 07:27:46 pm
content: Hi george,Well, after getting a datasheet for the 68000 series and checking all the pins on the CPU, it looks like it's working, or at least doing something. I realised i've probably been shorting pins out and then the halt signal gets fired or something, as by probing in the vias i can access some of the pins without risk of touching other ones and there's a lot of activity on the D and A pins. I took out the display and probed around the circuit there, it's getting all the signals which are present at the connector on the main board. So, my last step is going to be to remove my bodge wires sending power to the display, do some more checking of signals, and then if i can't find anything really obvious then it's going on ebay, which is a shame, but that's life, i only have limited resources to dedicate to something like this, plus i find it a bit like trying to read war and peace one letter at a time, backwards, and in russian...

author: al_m
author_rank: Contributor
timestamp: February 09, 2021, 08:42:35 am
content: The sad end to this tale is that my TDS210 is now on eBay for spares or repairs.Taking off my bodge wires put it back to where it was when i got it, with no power going to the display connector, and the data lines just held at 5V.I got a Tek 2225 for a decent price, so will have to make do with that, but it's not nearly as portable!

author: blade
author_rank: Newbie
timestamp: September 29, 2023, 01:13:03 pm
content: Hi all,Came across this post while trying to bring back to life an old TDS220, so i thought it would be worthwhile to post here how far i got. I got the scope off eBay, had a damaged display, lose BNC connector, lose rotary encoders and a broken power button. I replaced the screen and fixed everything else and when I powered it on, the display was black and nothing else. So I took the service manual and started from there.All power signals are ok, but there was no -24V on pin 2 of J302 display connector. I did not want to put a jumper wire to force power, so I did a bit of multimeter probing and figured out the circuit. I attached it for reference. The signal comes from U310 (ADG422) pin 97. This pin is always low. At this point, I believe that the ASIC is waiting for some OK signal from the processor to enable display power. I manually grounded the base of Q130 to simulate the ASIC enabling -24V line. The display turns white so everything is fine.Moving my attention the the processor (Motorola MC6800), I checked /RESET, /HALT, /BERR. They are all at 3.3V. By the way, on this board revision, /BERR is directly tied to +3.3V, so I guess it is not used anymore. So the processor is in a running state, it has the a clock signal from the ASIC as well, both chips are fine, I would say. In the MC6800 datasheet, I found that there are 3 pins that output the processor state. These are FC2,FC1 and FC0 (Pin 16, 17 & 18). These pins read 110, which means the processor is in Supervisor program. According to an old scanned book found online, the Supervisor state can control an external memory management device and system software. I believe the processor is trying to read from flash and it can't.Checking flash memory this is a AM29DL800B in BGA form. Not good since you can't probe BGA pins. Luckily the mainboard has a second footprint U430A for the same chip in standard 48 pin TSOP. First I reflowed the flash chip thinking the solder must have cracked over the years. No change in the scope status. I then began to check all pins if they have a connection with the address and data bus. The flash is set into byte mode (pin 47 BYTE# is tied to GND), so there are only 7 data pins (DQ0->DQ7) and 20 address pins (A-1,A0->A18) connected. They all have connection with the processor and ASIC. I then checked control pins (WE#, RESET#, RY/BY#, CE#, OE#. The CE# is tied toGNDpin 29 on ADG422,meaning the flash chip is always selected. All control pins are connected to MC6800except one[TL;DR]OE# is not going anywhere. So basically, the processor can not enable the output on the flash to read the data. I suspect a broken PCB trace here. The board is 6 layers and 20+ years old, so it is kind of a given situation. Since I do not have another board of the same type, can someone here with a TDS220/210 that knows or can probe for me where OE# is connected to? I attached a picture where the OE# is located on the PCB.

author: PwrElectronics
author_rank: Regular Contributor
timestamp: September 29, 2023, 08:54:27 pm
content: RE: blade....Thought I could help here but apparently the TDS220 I have access to is older and the board is different...I powered this one up and it was working before I opened it up for the pictures. Don't match yours unfortunately.

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 30, 2023, 03:33:53 am
content: I checked my scope, that pin doesn't seem to go anywhere obvious that I can see with a continuity test all over the PCB, besides 616ohms to ground.

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 30, 2023, 03:35:48 am
content: Quote from: PwrElectronics on September 29, 2023, 08:54:27 pmAs an aside, if you were wanting to update your firmware, you can program a new PROM chip with v1.19 from this link and just plug it straight in there in place of 163-0792-02https://w140.com/tekwiki/wiki/TDS220

author: blade
author_rank: Newbie
timestamp: September 30, 2023, 07:40:11 pm
content: Thanks for all the help. I check my OE# pin and it has 10.8K resistance to ground and 3.5k to VCC(3.3). Very different than your results. In diode mode I measure 0.56V to GND and 0.71V to VCC(3.3V). The multimeter negative terminal is tapping the OE# pin in diode mode. Based on these values I think I'm measuring the flash internal resistance and some diode junction (clamping diodes most likely)So, I probed the back of the board for continuity test and quick enough found a 100Ohm resistor in series connected to the OE# and a via on the other end going under the ADG422 ASIC. I probed the new found via with the ASIC pins and no contact. This could be the broken via. I put a picture where this resistor is located and the new via i tested. Can you safely verify the continuity to the ASIC? If not I will have to remove the ADG422 and take a look underneath.PS: thank you PwrElectronics for your effort, even though your board is different. These new mainboards with BGA flash have V2.x firmware and I believe is the last update by Tektronix. The flash chip is an EEPROM with JEDEC CFI interface. Program and calibration data are on a single chip. I ordered some 24pin 0.5mm flex connectors and cable from Aliexpress. I plan to read the chip memory and dump it here. A few people were asking for it years ago, but no one seemed to have it.PPS: I mentioned in my previous post that CE# is tied to ground. This is wrong. CE# is connected to pin 29 on ADG422. I powered on the scope and used a frequency counter to see what the flash is doing. There is a 1.3Mhz signal on the CE# pin and all data pins have 300~700Khz on them. So the chip is working. Someone with the same board as PwrElectronics had the same issue as mine, and the problem was that his flash got corrupted and the scope could not write incremented power cycle counter to flash. In my case the OE# pin has to go HIGH to write to flash. Instead it is always at 20mV.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 01, 2023, 05:28:30 am
content: Ok, I get 4.6K when probing between that BGA pin and ground whilenotusing the continuity beeper on my multimeter. Red herring...Also, probing the two points you show in your latest pic gives me continuity, and 100R resistor. Flipping over the PCB has the via to just outside the chip, and the trace visible to the pin, as per the attached image.

author: blade
author_rank: Newbie
timestamp: October 02, 2023, 07:42:42 am
content: That would be pin 23 on AGD422. I can confirm I also have connectivity from ASIC to OE# via 100R resistor. My continuity checker might have missed it in the first place, thanks for pointing it out. The flash chip connectivity is OK. I also probed DRAM chip. I figured that since there is activity on the flash, the boot process might have moved further. Pin 16 (/RAS) is held HIGH. According to the function table in the datasheet, that corresponds to DRAM being in Standby mode.At this point, it can be assumed that the flash chip is corrupted and it is in a continuous read loop(maybe scope was shut off in the middle of a write process and got corrupted, who knows). There is not much, I can do at this point, but wait for the parts to arrive and build a simple JEDEC CFI logic analyzer to probe what happens in the data bus. that will probably take a few weeks. The U430A footprint will be my tapping point to the chip. To read the flash, I will probably have to remove R305 to suppress clock signals to ASIC and halt it so to avoid any digital interference.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 02, 2023, 11:03:44 am
content: Let me know if you need more probing done, I can open up my scope again.

author: Mr Lurpak
author_rank: Contributor
timestamp: September 07, 2025, 09:44:34 pm
content: I know this is YEARS ago but I just had a similar issue and the HINT about the -24 Volt solved the issue on my TDS210.It was a transistor Q144 (on my board) marked 1AM - replaced it with BC848 NPN SMD (just general use transistor I had in stock) and it solved the problem. I THOUGHT I had checked all voltages but for reason missed the NO -24V.Anyway I hope this info can help others if similar problem.