Tektronix TDS220 repair

[sbeube02]

Hello from France!
I am new to this forum. Found lot of great stuff and useful informations.
I would like to share with you my TDS220 fail search and repair procedure.

Someone given me a TDS 220 for free as it was not calibrated and not working.
Here is a picture of this tiny little scope:


I plugged it on the mains, it powered up but the screen stay white:


Decided to open it and look what I find!!


The power connector to the main board is no longer connected 
I plugged the connector and now the scope power up but display a strange message:


Acquisition CH1 and CH2 self test failled 
Anyway, if I press any button the scope display traces and works correctly.

If I go to the service menu, I can show lot of errors in the log:

At each later power up, the line trigger self test failled (error #6 DI).
The error appeared once at powerup #349 and at #508 and folowing.

I have no history of this scope but I can tell these things:

• The power supply board is from 96' and there is a ground modification
• One diode on the power supply seems to have already replaced (brillant solder joint with flux)
• All boards are dated from circa 96' except the main CPU board wich is the newer one from 2000 with firmware v2.03
• Serial number is early type B014XXX
• CH1 connector is broken at PCB side

Here are some random pictures:



So the next steps are to repair this broken CH1 BNC connector and repair the trigger line.

Any help will be appreciated 

[andy2000]

There should be a 50/60 cycle signal coming out of the power supply for line trigger.  I would start by verifying that.

[dr.diesel]

Someone given me a TDS 220 for free

I'm gonna get flamed for saying this, but you scored big my friend!  I still use my 220 to this day, completely silent and simple, a pleasure to use.

[sbeube02]

I will check the 50 Hz signal from the power supply board.
Anybody have a high res. picture of the PSU board? I suspect some components to have been changed previously.

For information here are some pictures of the main board with firmware v2.03.



The cpu is smaller than the previous version and the ROM is now stored in a tiny BGA flash chip.

The main chips on this board are:

• 2 x NAIS V214S -> input high voltage photo MOS relay
• NATIONAL SEMI ASIC ADG321D -> front end amplifier acquisition ASIC (amplifier, ADC and trigger logic)
• NATIONAL SEMI ASIC ADG422 -> display ASIC and front panel driver
• MOTOROLA MC68SEC000PB10 -> µ-processor
• XTAL 60.606 MHz
• OKI M54V16255A-45 -> 4 Mb DRAM ?
• IDT 74FST6800PG -> 10 bit bus switch
• AMD AM29DL800BB90 -> 8Mb CMOS Flash memory
• ELANTEC EL4581C -> Video Sync Separator
• 3 x unknown voltage regulator
• Various 74HCT chip and LM358

Now, the problem with the CH1 BNC input connector:

The center conductor is not broken but can move in the PCB. I don't know how to explain that, it's like the solder have shrinked.
The gold plate one the connector is oxydized :


You could see the BNC connector have four ground legs compared to the older one who have only 2 ground legs.

I have desoldered the bottom shield for better access. The BNC connector was cleaned and correctly resoldered:


That should work better now!
Next step is the line trigger signal investigation 

[vishaldotgupta]

hi

i also have this model with error messages of ADG and line trigger fail.  surprising after repeated on off the system some times work okay.
when it is working okay the probe output is 1khz and when failing about 3 khz. 

i suspect that some how the calibration constants are not loading into the system.  These are in flash memory.  I removed the flash
and powered up, the system works with same error message.  the calibration command doesnt function

a way could be to read the flash from working unit and reprogram another one with same constants or to do a fresh programming altogether

[vishaldotgupta]

further line trigger voltage for me is 1.6Vpp loaded when the system is working okay and when with error message

unloaded is also similar.  immediately after start up, the probe compensation signal is 5khz and then come to 3khz
thereafter the self test on the screen fails.

[sbeube02]

That's quite interesting.
I have replaced the Asic ADG321D with a new one from Alibaba.com
After that, I successfully performed a factory calibration with all the instruments needed (performed the 56 steps).
On power up, I still have the message "Line trigger diag fail" and the probe comp. signal is still at 3 kHz.

[vishaldotgupta]

i had also changed the ADG IC, so it sometimes work without error and many times not  so ADG is not the real problem

i also noticed that if go for self cal and interrupt it in between by powering off and then go again for self cal, it clears and work
okay.  i am pretty sure this has to do with flash memory contents

[vishaldotgupta]

hello, i did some reverse engineering for last 2 days and reached some conclusion.  Although you board is different than mine but should be of some help to you

i found that logic ic's are not getting +5v.  The supply has four outputs +5, -5, +23 for lcd bias and line trigger.  Although line trigger is reaching mother board but it is not getting processed by logic ics

i by passed and supplied externally +5V and -5V to these IC's and the error line trigger error vanished.

The probe compensator became 1Khz but self calibration failed.  now i need to find why and where this voltage to logic circuit is getting locked.  in mine case the VCC on logic iCs is 0.8 V which is way below operational point

i am not sure if there is texas 2274 opamp on your pcb.  if yes, please note down its voltages on all pins and share

you may also like to send email to me directly.  This post is quite old and not sure if other members would be interested to persue further

[sbeube02]

Thanks for the input.
I also have done some reverse engineering on the CPU board, mostly the regulators and filtering part.
Here is a detailed picture of the board.

U110 is a LM358

Here is the schematic.

Components numbers match the board, but not always the values. I didn't mind the value of the capacitors or resistor but just wanted to understand how this boar works.
I will check asap the voltages on the logic IC and on the LM358.

[vishaldotgupta]

in my board i have four transistors like q151, q141, q110  i could not see the fourth one on your board

please confirm the voltage on these three or four as the case may be.  also confirm the part nos and smd marks.  i could not verify from the pics

I found some fried smd resistors on my unit.  after replacing them, the logic ic's start to get some voltage of around 2.5V

The error signal vanished on start up, probe compensation starts from 5 khz and then becomes 1khz just before self test

however when attempting self cal, it fails, oscilloscope now shows waveform but voltage reading is not correct

need to do some more reverse engg,  but now i am very close to getting it fixed up

[sbeube02]

If I remember correctly, the 3 transistors are for +5V digital IC, +3.3V analog IC and -3.3V analog IC.
I will try to do the measurements as soon as I will be home and send you the piece of schematic I have drawn.

[vishaldotgupta]

yes, you are right.  The collector of these transistor are connected to the PSU.  let me have the voltage on base and emitter.
do you have a fourth transistor as well

Also check if ADG321 C/D is gets somewhat hot.  mine is getting hot and the measured signal is bit noisy.  keeping finger on the ic increases the noise.  as usual factory calibration during power up self test gets passed but self calibration fails

i am not sure if the noise is occurring because the sheild has been removed or it ADG321 ic has gone bad

[sbeube02]

Did some measurement today.
Pin 1 to 3 from left to right.
Q151 marking "CE" --> BCP69T1
1: -3.3V
2: -3.96V
3: -2.61V

Q141 marking "P1F" --> PZT2222
1: 3.52V
2: 4.92V
3: 2.78V

Q110 marking "P1F" --> PZT2222
1: 4.9V
2: 4.92V
3: 4.16V

I also checked voltage on U110 LM358:
1: 4.9V
2: 0V
3: 2.48V
4: 0V
5: 2.48V
6: 2.48V
7: 3.51V
8: 4.92V

Power supply on logic ICs:
U240: 4.92V
U360: 4.92V
U440: 4.32V

Negative power supply 5V rail is a little bit lower than expected with -4V instead of mini -4.35V

[JFJ]

I found this thread while searching, unsuccessfully, for a supplier of the 4-ground pin BNC connectors that are pictured in Reply #3, above. Can anybody tell me the name of the manufacturer of those connectors?

The 2-ground pin type that were used on earlier versions of the TDS220/210 main board, are made by AMP/TE Connectivity, but I can't find the type pictured above in their catalogue.


Hello sbeube02,

Did you have any success with the repair of your TDS220?

If not, then a way forward would be to replace the LMV358 dual op-amp (U110), as your voltage measurements indicate that one of its inverting inputs (pin 2) is shorted to GND:

I also checked voltage on U110 LM358:
1: 4.9V
2: 0V
3: 2.48V
4: 0V
5: 2.48V
6: 2.48V
7: 3.51V
8: 4.92V

That could be due to R224 being a short circuit. However, given the low voltage and extremely low current that R224 is subjected to, it's far more likely that it's the op-amp that has failed.

If the op-amp was functioning correctly, the voltage at the inverting input would be same as the reference voltage that's applied to the non-inverting input (pin 3). That makes it quite simple to calculate what the output voltage at the emitter of Q110 should be. I couldn't make out the values of R222 and R224 from your schematic, so I sketched out the relevant part of the circuit from my TDS210 main board:



Using the 2.48V reference voltage that you measured (at pins 3 and 5), and the resistor values from my rough sketch, the voltage at the emitter of Q110 should be:



The second op-amp in U110 controls the emitter voltage of Q141:



Your measured Q141 emitter voltage (2.78V) can be confirmed to be correct using the same calculation as above:

[tautech]

I found this thread while searching, unsuccessfully, for a supplier of the 4-ground pin BNC connectors that are pictured in Reply #3, above. Can anybody tell me the name of the manufacturer of those connectors?

The 2-ground pin type that are used on earlier versions of the TDS220/210 main board, are made by AMP/TE Connectivity, but I can't find the type pictured above in their catalogue.

On a 210 that I repaired some time ago I used the 2 leg sockets as replacements as they are "drop in".
Sure they are a weak point in these models if excessive stress is applied to the input connectors but there is another mod one can do to strengthen the BNC inputs. There is a good ground plane either side of the inputs, scrape away the coating and solder a 5mm wide copper strap up and over the input sockets. IIRC there was plenty of room to do this mod and it adds good strength to the connectors, the only tricky bit is you will need a soldering iron with a bit of grunt. Never took pics back then so sorry I have nothing more to share. 

[sbeube02]

First sorry for the late reply.
I put the oscilloscope on shelf and didn't use it since two years.
I decided to give it a try and followed your advice.
I first changed the OpAmp U110. I still had the same voltage reading, with 0V at U110 pin 2.
I made resistor measurements and R222 was 48.5kohm witch is really different from your board.
I desoldered R222 and it was open circuit, broken in two!
@JFJ, your resistance values were read directly on the resistor body or taken by measurement?
My resistors does not have any values marked on them.

[JFJ]

... @JFJ, your resistance values were read directly on the resistor body or taken by measurement?

The resistance values of R222 and R224 were read directly from the codes printed on their bodies. Those values are commensurate with the calculated output voltage of Q110, which is close to the measured emitter voltage on my board:

[sbeube02]

Thank you so much!
I replaced R222 with a 12 kohm because I don't have a 12.1 kohm.
I now have 3.25V at Q110 witch is close from yours.

But... I still have the Channel 1 and 2 acquisition failed message on boot screen... 

The probe comp signal goes from 5kHz to 4 kHz then 3 kHz and stays at 3 kHz. Anyone have information about this startup sequence?
I fear the ADG422 is shoot because of the over voltage from the bad resistor causing it to be powered with more than 4 V instead of 3.3 V.

[sbeube02]

When I check the error log, I always get a "Line trigger diag failled" message.

I started checking the voltages at J131 as per the service manual:

Everything is good, except pin 7 witch only gave me 1 Vpp:

I drawn the line trigger part of the power supply:

And when I desoldered R29 to R32 for measurement, R29 was broken in two!

I will replace this resistor and check if the error disappear.

[bd139]

Interesting. Wonder if that was on its way out on mine. I had a TDS210 that the line trigger diag failed occasionally on. It always worked however 

[sbeube02]

Ok, finally replaced R29.
Checked the voltage at J131 pin 7, I now have 1,8 Vppk (+1 V - 0.8 V) 50 Hz square.

I powered the oscilloscope and all self tests passed!


Probe comp is now 1 kHz!


Job done! 
Thank you all for helping me with this issue 

[bd139]

Nice work 

[LAB390]

Wow - what a score!
Great work (everyone) on getting this beauty back from the brink.
I'm going to bookmark this thread for future reference as an insurance policy!!!

[adriten]

was trying to get inspiration from this thread to try to repair my TDS210
I bought it cheap from a local auction ; the previous owner said the display suddenly froze and after rebooting display was blank and that's what I can see when I turn it on (CCFL works)
I checked the power supply connector :all ok
Not OK is the situation on the display connector : no activity on any of the 4 DATA wires, just steady 5V;   zero volt also on pin 1 and 2 (supposed to have -10V to -25V)
pin 7, 8 and 9 are OK (ground and +5V)
Pin 10, supposed to have square wave at 1.89MHz have instead it at 1.37MHz
Pin 11 supposed to have a pulse at 19.3kHz , pulses at 17kHz
Pin 12 has very narrow pulses whose frequency I was not able to measure (very low)

On the scope front panel, instead of the test signal at 1kHz I see a pseudo sinus at 3.3MHz (?) whose amplitude is 230mV, superimposed to 2.5VDC
Mobo is the newest one with small packaging CPU, and BGA flash memory (ouch!) pcb is clean, no visible cooked components
Any help to try to catch the culprit is welcome  Attached is a pic of the motherboard