Tek 2213 from ebay

Discussion in 'General Electronics Chat' started by drobe011, Sep 10, 2013.

  1. drobe011

    Thread Starter Member

    Dec 28, 2012
    33
    2
    Quote:
    Originally Posted by drobe011 [​IMG]
    FWIW, I won that Tek 2213 for $47.00.

    Channel 1 is off the grid and will not adjust position.

    Channel 2 works ok, but image not good.

    Had mold all over (which cleaned off easy).

    If I can't fix it cheaply, at least I have an electron gun to play with...

    -Dave


    My father gave me his scope 26+ years ago along with a Simpson analog meter. Crazy as it sounds, I recently have not been able to locate the scope anywhere. A whole scope (heavy) just vanished. It was only single channel, but did it well enough for my use. I do suspect my wife as a culprit in the disappearance.

    I decided, well I should just buy a MSO or DSO but decided to hold that thought as I am in the process of retiring and couldn't justify that expense right now. So I opted to try ebay for a cheap analog. This was my first attempt at ebay as well.

    Electronics has just been a hobby for the past 30 or so years, so I'm not loosing money on not having a scope. Although for some things it's a PITA for not having one.

    I do have several DVMs.

    Short description of issue:

    Channel 1 displays noisy horizontal trace in upper quadrant of display (approx 5-7mm from top). Adjusting vertical position from min to max only displaces the horizontal trace approx 1mm.

    Displacement is the same no matter the V/Div setting.

    Applying signal to channel 1 does not alter the trace in either of the three coupling modes.

    Intensity and focus work, however, not smooth and sometimes change significantly with little movement.

    The trace will sometimes disappear, but a very light tap sideways on the beam find will bring it back (or make it disappear).

    Channel 2 works good enough to calculate rough voltage, duty cycle, frequency. I have tested up to 500Hz; trace not crisp enough to use waveform any faster than that.

    Trace is so unclear that selecting an intensified zone has no visual effect.

    The crest (esp horizontal portion) is more distorted (thicker) than the rest of the waveform.

    I do have the user and service manual for it.

    From the mold and spilt paint on the unit, it looks like it was just sitting in a pile for several years if not decades. All the wipers in the pots are sure to be very dirty as well as worn from years of use.

    I will post a pic of the display shortly. Not sore at the purchase, couldn't really expect much for $47.00.

    I will also try to borrow a scope to diagnose the test points from the service manual, but it may take a while to track one down.

    Any other help in troubleshooting or advise on whether its actually feasible to continue any further on this venture would be appreciated.

    -Dave

    __________________
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,421
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    Not a problem. I have the service manual and will get back to you on what to look for with your DMM.

    Sounds like you have some dirty pots as well but we will tackle that when the time comes.
    In the meantime you may want to look for a spray can of control cleaner.
     
  3. drobe011

    Thread Starter Member

    Dec 28, 2012
    33
    2
    Some slightly different behaviour on this mornings power-up.

    I could not get a trace to show without holding down beam find. After tapping it several times it would come on then slowly fade to black. Several more taps and the trace stayed on.

    Channel 1 trace is now smooth where it had been noisier. However, it does not move position at all now.

    Channel 2 trace used to only show crest and trough on square wave, but as you can see in the second pic, it now shows the waveform in between the crest and trough.

    Pic 1:
    -Channel 1
    -1X probe on Probe Adj connector (0.5V negative going 1kHz square wave)
    -DC coupling
    -.2 V/Div
    -.2ms S/Div

    SDC10330.JPG

    Pic 2:
    -Channel 2
    -1X probe on Probe Adj connector (0.5V negative going 1kHz square wave)
    -DC coupling
    -.2 V/Div
    -.2ms S/Div

    SDC10332.JPG

    I will pick up some contact cleaner today. The pots on the front panel board are fully enclosed.

    Thanks, Dave
     
  4. drobe011

    Thread Starter Member

    Dec 28, 2012
    33
    2
    Even more different behaviour after rebooting:

    Now waveform in Pic 2 above is sharper. I do believe that intensify horizontal mode was stuck somehow.

    Now I can switch to intensify and highlight the waveform using the multiplier. If I highlight the whole displayed waveform, it appears as it did earlier.

    Could not do that before.

    I do let it warm up for at least 30 minutes before using/testing. Manual says 20. Going to leave it on for a while and observe.
     
  5. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,227
    If the scope had mold all over, then it likely was in a moist environment, such as a basement, and some of the parts may have absorbed moisture. Just leaving the scope on continuously for a day or two may help bake out some of the moisture. You might also trying baking it out in an oven at a low temperature (say 120°F) for a day or so.
     
    Last edited: Sep 10, 2013
  6. MrChips

    Moderator

    Oct 2, 2009
    12,421
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    I assume you have already removed the cover to the TEK 2213.
    To do so you will need a T15 Torx screwdriver.
    There are three screws to remove, two on the back plastic panel and one on the right side.

    Let's begin with CH1 position control.

    Locate pot R190 and R191 on the front panel PCB.
    Using a DVM on 200VDC range measure the voltage at the top of R191 with respect to GND.

    The voltage reading should change from +3.5V to +1.4V to +3.5V as you turn the VERT POSITION pot (R190) from CCW to CW.
     
  7. drobe011

    Thread Starter Member

    Dec 28, 2012
    33
    2
    Yes sir,

    Voltage measures CCW to CW:
    +3.48 to +1.1 to +3.12

    Compared to Ch2:
    +3.47 to +1.26 to +3.48

    A point I realize I left out; and probably pretty important, Channel 1 doesn't seem to be triggering on any signal. Ie., the TRIG'D LED never comes on (only briefly when I change the ch1 V/Div selector).

    I picked up some control cleaner/lubricant but have not applied it yet.

    Thanks.
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    What happens when you set VERT MODE settings to BOTH, ADD,
    and trying to adjust VERT POSITION, CH1 and CH2?
     
  9. drobe011

    Thread Starter Member

    Dec 28, 2012
    33
    2
    Awesome new behaviour now.

    Ch1 trace no longer displays unless I hold BEAM FIND.

    Ch2 however, is looking better and better.

    BOTH, ADD:
    No trace displayed
    If i press BEAM FIND, I get the typical Ch1 trace

    BOTH, ALT:
    Ch2 trace displayed
    Ch1 trace displayed also if BEAM FIND pressed
    Ch1 VERT POSITION - nothing
    Ch2 VERT POSITION - moves trace as expected

    BOTH, CHOP:
    Ch2 trace displayed
    Ch1 trace displayed also if BEAM FIND pressed
    Ch1 VERT POSITION - moves ch2 trace ~2mm
    Ch2 VERT POSITION - moves trace as expected

    I cleaned what contacts I could get to, but no change. More time though will undoubtedly result in something new.

    -Dave
     
  10. MrChips

    Moderator

    Oct 2, 2009
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    I don't have the service manual here with me now. I will check tomorrow.
     
  11. MrChips

    Moderator

    Oct 2, 2009
    12,421
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    Now comes the tricky part.

    You are going to measure the DC voltages on the output transistors of CH1 Vertical Preamps.

    I am looking at Q177 and Q187 on schematic 2.
    You will need to turn the scope on to its left side or over upside down.
    Q177 and Q187 are located at the bottom left corner of the PCB about 1" from the bottom.

    CAUTION

    There are some high voltages on the PCB. You want to exercise extreme caution.
    Also you don't want to make the unit worse than what you already have.
    Make sure all measurements you make are taken with proper probes and with extra caution.

    Your +ve meter probe (red) should have a sharp point to avoid shorting to adjacent solder points.

    Your -ve meter probe (black) should be an alligator clip securely attached to the metal case.

    Measure the DC voltages at the three terminals of Q177 and Q187 for the CH1 VERT POSITION at CCW and CW.

    Nominal voltages are shown on the schematics:

    base +4.3V
    emitter +5.0V
    collector +2.8V
     
  12. drobe011

    Thread Starter Member

    Dec 28, 2012
    33
    2
    Thanks again sir, for your help.

    I couldn't tell from a visual of the board or on the schematic CBE of the two transistors. I probably could have if I looked up their datasheets......

    Q177 does exhibit some odd behaviour. When I say it varies, it constantly changes the highest I can tell on my DMM is +1.2

    Q177-Q187.png

    Again, thanks for your valuable time and patience.

    -Dave
     
  13. MrChips

    Moderator

    Oct 2, 2009
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    What voltages did you measure at Q177 and Q187? I should be able to figure out which is CEB.

    Edit: Sorry, I am only now looking at your attachment.

    Again, don't have the manual here. I will have to remember to carry the manual with me.
     
    Last edited: Sep 11, 2013
  14. drobe011

    Thread Starter Member

    Dec 28, 2012
    33
    2
    Figure 9.2 of the service manual shows the layout of the transistors.

    But to me, it doesn't coincide with what is marked on the board (from the angle I can see).

    sec9.png

    I am trying to make sense of this paragraph and attempting to determine what influences the vertical preamp.

    ch1_vert.png

    Only thing my feeble mind can come up with right now is the possibility of CR177 or CR187 being shot. But would probably lead to bigger problems if it were so..
     
  15. MrChips

    Moderator

    Oct 2, 2009
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    I am going from memory now. There is a possibility that something is wrong with CR177.
    You said there was mold on the scope. Does the PCB look clean on both sides of the board around CR177?

    If not, take some clear well focused photos before we have a go at cleaning it.
    You will need some isopropyl alcohol and Q-tips to clean the board. Make sure you unplug the power cord before doing this.
     
  16. drobe011

    Thread Starter Member

    Dec 28, 2012
    33
    2
    There does not appear to be any mold or anything unusual in its appearance or in the components appearance on the inside. I will take some pics soon just in case.

    I tested CR177, CR178, CR187 and CR188 in circuit with power off.

    They all had 580mV Vf in forward bias and 0V in reverse bias.

    Looking at the datasheet (TI 1N4152R) that is the normal Vf for If = 0.25mA


    Not sure how to test C179 (if I even need to) without a scope or removing it from circuit.

    I have noticed when ch1 trace does move vertically when adj the ch1 VERT POS knob, its ~2mm movement is paradoxical: that it is moving the trace opposite of what it should.

    This mornings behaviour is consistent with yesterday. Leaving it running for a while as recommended above hopefully has stopped all the anomalies.

    -Dave
     
  17. MrChips

    Moderator

    Oct 2, 2009
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    Looking at the schematic, transistors Q341 and Q331 will affect both channels.
    If you set the channel select switch to CH1, only the signals from Q177 into CR178
    and Q187 into CR188 come into play.

    Set the CH1 VERT POSITION to midrange and measure the voltages at Q177 and Q187 again, and also at Q341 and Q331.

    Seems like CR178 is suspect.

    (CR178 is not labelled.)
     
  18. drobe011

    Thread Starter Member

    Dec 28, 2012
    33
    2
    CH1 VERT POSITION midrange:

    Q177
    B: +2.26
    E: +4.84
    C: +4.25

    Q187
    B: +2.66
    E: +5.00
    C: +4.25

    Q341
    B: +2.13
    E: +1.84
    C: +2.68

    Q331
    B: -3.00
    E: +1.96
    C: +2.68

    I cannot find Q331 and Q341 on the schematic. The lookup table says it's on 4H, but i can't see it. I may need to look for a better service manual. A few of the pages are out of order, and I have noticed some are missing. I am using a digital copy of REV NOV 1981.

    I checked the base of Q331 numerous times and got the same result.
     
  19. drobe011

    Thread Starter Member

    Dec 28, 2012
    33
    2
    Finally found a service manual that wasn't missing schematic #3.

    I don't see how the bases of Q331 and Q341 can have different readings as noted above.

    The base of Q331 is driven from Q187 via CR188.

    To me, it's not making sense with the readings I have taken. I will attempt to ensure I tested properly at first light.
     
  20. MrChips

    Moderator

    Oct 2, 2009
    12,421
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    A couple of possibilities.
    From the symptoms you have described sometimes the problem is simply a deteriorating solder connection. You can try going over the solder joints of Q177 and CR178 with a soldering iron.

    I believe you have base and collector interchanged on Q177 and Q187. The base is not the middle lead.

    The voltage readings you show for Q341 and Q331 are way out of whack. The voltages in the schematic indicate

    B +2.1
    C -0.7
    E +2.9

    But we know CH2 displays ok so there is some inconsistency with those readings.

    Make sure that the channel selector switch is set to CH1.

    We might be looking at replacing Q177, Motorola SPS8223
    If we are going to replace Q177 we should replace the pair Q177/Q187.

    btw, here is a service manual on line as pdf if anyone is interested:

    http://www.diagramasde.com/diagramas/otros2/Tektronix_2213.pdf
     
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