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vac gauge4-wire tube http://www.televac.com/downloads/datasheets/2A_Thermocouple.pdf













MISC. LINKS

  • 128543 Quiktip thermocouple crimps hex $152.00/100
  • nickle "TC pressure connectors" 128543 leeds betts honeywell $100.00/100
  • (or if you have the tool, just use gold crimp pins from a DB9 connector!)
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    EPPENDORF MINISPIN CENTRIFUGE: DOOR STICKING STUCK

    The mini-spin centrifuge is vulnerable to tiny amounts of spilled buffer contamination it its door latch interlock section. The latch needs to return very quickly when the door comes down, otherwise the motorized wheel will catch it in a between state and bind permanently. (Permaently! Sometimes temporarily fixed by giving it a thump, or by using a paperclip to rotate the interlock wheel via the bottom slot, rotate it one complete turn in either direction.)

    Unfortunately any dried solution down in the shaft/latch will slow its return motion and let the motorized nylon wheel crash. Quick fix: remove the lid shaft, open the case (note the position of the lid-lifter and heavy spring.) Then bend the wire spring which returns the moving latch, bent to greatly increase the return force. That way it pops rapidly into place after deflection, regardless of built-up crust. Better fix: take a photo for ref of spring positions, then remove snap-ring, springs, and disassemble the whole latch part. Don't lose the tiny snap-ring! I cleaned everything and heavily greased those rot/slide parts, so perhaps future spilled fluids will be excluded, and any dried crust will have no effect.

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    LASER PRINTER ERROR/INCOMPATIBLITIY ON PERKIN-ELMER RX-1 FTIR SPECTROMETERS

    This FTIR spectrophotometer is only compatible with certain laser printers. At first we thought this involved an issue with the printer's PCL command set, and the HP-GL/2 plotter language. Nope. Intstead I find that the instrument has an apparent design problem on its parallel port: it ignores the "BUSY" pin and just keeps sending data to the printer. The printer then freezes up, leaving the "BUSY" pin high. All of our RX-1 units do it. This doesn't cause problems when using the old HP-1200 laserjet. But on the modern printer HP P2035 equipped with a parallel port, this behavior causes the printer to lock up and require a power-off to reset.

    We'll try adding an LPT-to-USB smart cable, then try other modern USB laserprinters. It might only be the HP P2035 which has the "BUSY pin" compatibility issue. See LPT2USB for a $70 converter to allow modern printers to be used with Centronics parallel LPT port found on old instruments.

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    SIPEX DAC CHIP 9377-16-4 NO LONGER SOLD, BUILT A REPLACEMENT USING TI DAC712

    Our old Leybold e-beam controller acts weird: its 24-pin DAC chip is corrupted and no longer gives trustworthy output voltages. No DAC 9733s to be bought anywhere. I find that the T.I. DAC712 (digi-key) is fairly close, but different pinout. I can build a little hand-wired adapter board that carries the DAC712 and plugs into the 9377 socket. Differences: the /CLR pin needs to pull up to +5, so I add a 4.7V zener and 33K on pin-5 10-volt ref. out of the DAC712. I ground A0 and A1 to make it behave as a transparent latch. The MSB pin has to be inverted to map the negative values to positive, so I make a simple inverter for A15 using a 2N3904 transistor. The gain and offset trimmers go on this little board (the original ones on the main PCB are now unused.)

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    EDWARDS THERMOCOUPLE VACUUM GAUGE TYPE 507, D35501000 GAUGE TUBE FRIED, NO LONGER SOLD

    The gauge-tube finally died on one lab's Edwards 507 tabletop vacuum gauge. Sensor part no. D35501000 (actually D355-01-000,) with a 5-pin DIN audio connector. Obsolete product, no longer sold by Edwards, and the last one on eBay was back in 2010. It's a 4-wire type gauge not the popular 3-wire thermopile Teledyne Hastings DV-6. At full scale (hard vacuum) it puts out 10mV to the 507 meter, and the meter's drive current to the blown out heater filament is 5.0Vdc through a 470ohm resistor and a 200ohm trim pot set to 80ohms.

    Maybe the Hastings DV-23 or KJL-1518 would work? Might need a custom paper face for the meter-needle. I have a similar 4-wire tube available: the old Televac "2A" gauge tube, 2-2100-10, from a Fredericks gauge. It's a 10mV fullscale tube, and this one has a 6-ohm heater which needs 0.57Vdc and 89mA. The Edwards 507 gauge CAN ONLY SUPPLY 10mA FOR THE HEATER. Rats. For the heater supply I'll need to add a little AC stepdown transformer, 120 : 6.3VAC, a Zener to give stable AC volts (two 3.3V zeners back to back in series, with 30ohm series resistor.) Then connect this to the gauge tube pins 1,8 with series resistors 22ohm and a 50-ohm trimpot. With the sensor pumped down to 10e-3 Torr vacuum, I can set the trimmer to give zero reading on the meter. Works fine, no other modifications needed.

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    INEXPENSIVE REPLACEMENT FANS FOR BRUKER NMR AMPS, BLAX300RS, ETC.

    The three 3-wire 80mm fans in the rack inside various Bruker NMR amplifiers are no longer available from online suppliers or from the manufacturer NMB. If your web search finds an NMB 3110NL-05W-B59, it won't be any twelve bucks each!! Must you buy them from Bruker?

    Inspecting the NMB catalog, we find that "N" fans are gone, and are replaced by identical "K" fans which have a mirror-image rotor blade shape. The max DC drive current is also 6% higher. The closest match which is widely available is NMB 3110KL-05W-B69-D00, on Digi-key as P13491, $11 each. That's what we've been using in all our amps. Note that the "B69" means ballbearing, speed-6, and 3-wires. Don't buy "B60," it's 2-wires.

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    BAD "ELBA ARTESYN" POWER SUPPLY, BLAX AMPLIFIER, BLARH, BRUKER NMR, MAGNETIC RESONANCE


    Bill Beaty (beaty atsign chem washington e d u)
    Mon, 10 May 2004 16:07:47 -0700
    
    
    Rather than paying the $1500, I've managed to repair a bunch of these power 
    supplies in Bruker BLAX.  Want some info?
    
    First note that these Artesyn or "Elba" 220VAC supplies WILL RUN ON 120VAC.  
    This makes testing easier.  But I wouldn't recommend drawing a high-wattage 
    load when the line voltage is so low.
    
    Also note that you need to place a small load on the +15v, -15v, +5v 
    supplies, and a 10-watt load on the +28V.  If you run them with no load 
    at all, the switching-supply starts up, but then halts.  Without a load,
    the output voltages start out briefly correct, then start falling.  Load
    the +28V output with a 47-ohm 10w resistor.  Put 91-ohm 3W on each of 
    the + and - 15V, and a pair of 15-ohm 2W resistors paralleled on the +5V 
    line.
    
    On the first supply I repaired, the main bridge rectifier and the big 
    APT5025 FETs for the 365VDC Power Factor regulation were fried.  These 
    components sit right on the 220VAC line, so any major surge can kill 
    them.  The diode bridge is a weird thin little thing under the main PCB, 
    part number D20XB60, availible from Mouser Electronics, (600V 35amp bridge.)  
    The MOSFETs were APT5025BN from Advanced Power Technology, advancedpower.com/ 
    http://www.dz98.com/wjj-pdf/apt5025.pdf
    I found an actual APT5025BN, but probably a similar transistor would 
    work, if you can find a TO-247 package for 500V 23A 0.25ohm 300watt,
    N-channel, gate threshold max 4v (such as IXFH24N50 or IRFP360
    from DigiKey.)
    
    The second dead unit also had a bad NPN transistor from ZETEX which, if 
    I recall right, drove the gates of the main switching MOSFETS driving the 
    220AC to 365VDC switcher.  The big MOSFETS were dead, as was the UC3854N 
    power-factor IC on the soldered-in daughter board next to the 270uF 400V 
    capacitors. (See below for a schematic that's similar to the 
    daughter board PF-correction circuit.) There was a fried 22-ohm resistor 
    below the big ferrite transformer, and a shorted 1N6284A zener across the 
    28VDC output (located near the middle of three UC3524 chips near the 
    output terminals.) No doubt a surge on the 220VAC line shorted out one 
    component, and the large current destroyed everything else.  Be sure to 
    check the value of that 22-ohm resistor, because if its value becomes far 
    more than 22 ohms, the regulated 28VDC output voltage can rise greatly.
    
    A third unit had a stalled fan.  The heat had killed the two big 270uF
    400V electrolytics.  Also, the values of tiny electrolytics were all wrong
    on the soldered-in PF daughter board (the board next to the 270uF 400v 
    caps.)  I found I could replace all these tiny capacitors without having 
    to unsolder the many pins of the daughter board.  Be sure to mark the 
    polarity, since there's no silkscreen plus-signs on that PCB.  These
    capacitors are part of a tiny high-freq switching power supply that runs 
    components on that board, so high temperatures will bake out these capacitors 
    and make the supply fail during a power-up.  (Apparently the Elba supply can
    run almost forever when its fan is dead, but the extra heat slowly ruins
    the capacitors critical for power-up sequence.)  I replaced the two 47uF 50v 
    (a volt doubler) that runs the power factor chip, the 100uF 50V cap on the 
    corner next to the power transistor, and the two 22uF 35V caps next to 
    the fan connector (they're essential for the fan's power supply.)
    
    
    Now our fourth dead unit was very interesting.
    
    There is an apparent design weakness in the 30V section of the "Elba" power 
    supply used in some versions of the BLAX 300 and similar amps.  When the supply 
    first comes up, the 30VDC switching regulator chip (UC3825) on the second
    daughter board needs at least 9V to wake up and start making DC.  In normal 
    operation it creates its own supply voltage from its own 30VDC regulated 
    output... it pulls itself into the sky by its own bootstraps!  But during 
    startup, it temporarily needs another supply.  It gets this from a little 
    "bootstrap power supply winding" on that big iron tapewound inductor in the 
    center of the PCB which is part of the power-factor switching circuit.  
    This winding is voltage-doubled with two diodes and three capacitors (two 10uF, 
    one 220uF, partly hidden under a transformer,) making 20VDC, which supplies 
    a LM7812 regulator, which supposedly puts out 12VDC for the UC3825 chip.  But 
    the UC3825 draws 33mA, which can drag the 12v supply voltage of the 
    bootstrap/LM7812 down to 8.9V...   and sometimes the UC3825 goes into continuous 
    repeating reset and never starts.  It's waiting for its bootstrap-supply to rise 
    up above 9.0V.  This all depends on temperature and on many component values.   
    This is possibly bad design?  They should have given plenty of leeway (like 
    designing it to actually put out 12VDC, even when it draws 33mA as it does.)
    
    Regarding the idea that heat can kill these supplies...  yep, if any of the
    three small electrolytic capacitors next to the LM7812 regulator in the voltage-
    doubler bootstrap supply should get baked out, so their capacitance value 
    drops, or their internal leakage gets large...   then these changes will 
    push things over the edge.  The UC3825 on the pluggable daughter board at
    the edge of the main board never gets its 12VDC, and the supply cannot wake 
    itself up anymore.
    
          The usual symptom: your system was running for many days or weeks, 
          but then after being switched off, or after a building power failure, 
          it won't wake back up again.
    
    (But sometimes, if you switch it off and back on more than once, it will 
    "catch," and start running.)  Our dead supply had a 220uF 50V electrolytic 
    capacitor (next to the LM7812) which had changed itself to 20uF over the years.  
    When replaced, the supply worked fine again.  But replace all three caps
    in that cluster, since they all are exposed to high temp.
    
    So note well that these Bruker amps often die after a power failure, but very
    often THIS ISN'T CAUSED BY A SURGE.   Instead, the power supply malfunctioned
    weeks before, but the problem remained invisible as long as the amp remained
    in operation.  If the AC power should drop for a second or two, then the power
    supply goes to sleep and will never wake up until the capacitors are replaced.
    
    
    
    Also about ELBA power supply schematic:
    
    I discovered that the schematic for the front end, the 220VAC input section,
    is very similar to the schematic shown in the following app. note for the 
    UC3854 chip used in the supply's power-factor correction daughter-board.  
    It uses a big MOSFET and an inductor to massage any line input voltage (50VAC - 
    270VAC,) and it supplies 400 volts DC (365V) to the rest of the board.   The 
    400Vdc is later switched as a 200KHz squarewave and applied to the ferrite 
    stepdown transformer to make 28VDC.  Schematic:
    
      Advanced Power Factor Correction Control ICs (n.b. schematic on page 4)
      http://focus.ti.com/lit/an/slua177a/slua177a.pdf
    
    Note that this power supply ***WILL RUN*** on 120vac, at least for testing.
    Supposedly it up-converts any AC line voltage between approx. 60VAC and 
    250VAC.   However, I wouldn't leave the whole NMR amp running on 120VAC, 
    since the supply is probably out of spec for power factor, and might
    overheat during a 600Watts load.
    
    Other schematics for your reference:
    
      THE UC3823A,B AND UC3825A,B 
      ENHANCED GENERATION OF PWM CONTROLLERS
      http://focus.ti.com/lit/an/slua125/slua125.pdf
    
      UC3854 Controlled Power Factor Correction Circuit Design
      http://focus.ti.com/lit/an/slua144/slua144.pdf
    
      UC3854 provides power limiting with sinusoidal line current
      http://focus.ti.com/lit/an/slua196a/slua196a.pdf
    
      Optimizing UC3854 performance
      http://focus.ti.com/lit/an/slua172/slua172.pdf
    
    
    Also see messages (need password from AMMRL nmr forum ):
    
    
      question about Bruker amps and their power supply modules
      http://www.ammrl.org/archives/February-2004/13.html
    
      question about Bruker amps and their power supply modules--Summary
      http://www.ammrl.org/archives/February-2004/17.html
    
      Bruker BLAX/H Power Supply Cooling Fan
      http://www.ammrl.org/archives/June-2001/7.html
    
    
    
    Bill Beaty (beaty atsign chem washington e d u)
    Mon, 10 May 2004 16:07:47 -0700
    
    More news!
    
    The design weakness in the BLAX Elba power supply is NOT in the designed
    capacitor values as I thought.  But the problem is nearby:  the LM7812 
    overheats the capacitors, causing them to slowly decrease in value over time, 
    so the supply fails early.  There's a 10V Zener diode which seems to be the 
    origin of the problem, and it might help things if we change it to a smaller 
    value ( such as 4.3V 1N4731.)  This is not essential.  Instead just replace 
    the three bad capacitors to get things up and running again.)
    
    The overheating of the three capacitors occurs because the little voltage 
    doubler on the big series inductor winding (the two diodes and three 
    capacitors) is only supposed to supply its 22Vdc to the LM7812 for a couple 
    of seconds; during power-up until the main +30Vdc comes on line.  The output 
    from this voltage doubler is passed through a diode, as is the main 28Vdc 
    output.  Both are applied to the LM7812 regulator input pin, and whichever 
    is higher, that one powers the regulator.  This lets the bootstrap supply 
    send current to the LM7812 during power up, then after a couple of seconds 
    the main +28V takes over from the volt-doubler when it later wakes up.
    
    But unfortunately Elba has put a 10Vdc Zener diode in series with the 30Vdc 
    output to drop it down to 20V (no doubt because the LM7812 without 
    heat sink gets quite hot when given 30V input, so the series zener is 
    there to share some of the thermal wattage.)
    
    So the little volt-doubler AND the main 30V are BOTH set to approx. 20V, and 
    if you happen to be unlucky and have just the wrong circuit values, then 
    BOTH ARE ALWAYS POWERING THE LM7812.  Or perhaps the voltage doubler "wins" 
    and becomes the main supply for the UC3285 on that daughter board.   This is 
    bad news for the three capacitors in the voltage doubler, since they normally 
    see two-ampere pulses at around 50KHz, and they will run fairly hot.  Over 
    the months and years they get baked out, their values decrease, their 20Vdc 
    output voltage decreases, and finally the voltage falls below the 9.0Vdc 
    required by the UC3825 main 30Vdc regulator chip on the second daughter board.  
    
    It also doesn't help that the capacitors are right up against the very hot 
    LM7812 regulator; and that might even be the real trouble here after all.  But 
    regardless, the temporary bootstrap power supply voltage gets too low, and the 
    system gets flakey during power-up and can't wake up every time.  However, if 
    it's ALREADY running, the bootstrap supply is not critical for operation, and 
    the system will run fine...  as long as you never turn it off!
    
    :)
    
    Or, if your BLAX or BLARH apparently dies right after a power-off, be aware 
    that in some cases the bootstrap supply is still VERY close to the correct 
    voltage.  Try perhaps turning it off and on a couple of times (with luck 
    it may "catch" and start working.)
    
    The cure we used (your milage may vary!):  replace the two 10uF and the one 
    220uF capacitors (they're all glued together, positioned next to that 
    LM7812 voltage regulator approximately in the middle of the main board,
    near one edge of the pluggable daughter board.)  Replace them with low-ESR, 
    105degC electrolytic caps.   But that doesn't fix the real problem.  So also 
    look for a chain of resistors right at the edge of the main board (labeled 
    DZ1, DZ2, DZ3.)  One is a 10V zener diode, the others are zero-ohm jumpers.  
    I replaced the 10V zener diode with a one-watt 4.3V zener.   This lets the 
    poor little voltage-doubler circuit turn off when it's not needed.   But 
    it makes the LM7812 regulator run even hotter than before during boot up.  
    If I see another one of these dead supplies, I think I'll also be putting 
    a couple of little bitty TO-220 heatsinks on the LM7812 regulator (HS214-ND 
    from digikey.)
    
    
    See also (passworded):
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    Bad resistor in BLAX 300RS, BLMX001

    T. Pratum (pratum@u.washington.edu) Tue, 21 Jul 1998 16:58:54 -0700 (PDT) We have had 2 blax300rs failures in the past 6 months, and one of our electronics engineers has found the same problem in both cases- the MSA1023 amplifier in the blmx001 failed due to a failure of the bias resistors R16,17,and R9 (150 ohm 2 watt composition). Their resistance appeared to have decreased over time (in at least one case down to 10 ohms). I have checked 2 other blax300rs units that were delivered at the same time (approx June 1995) and found the same problem in each of them (although the MSA1023 hadn't failed yet). I also checked 2 other blax300rs units which were delivered earlier (in 1994) and found no such problems. So, my warning is that if you have a blax300rs that was delivered in 1995 it might have some bad resistors in it which will eventually stress the MSA1023 into failure. You can check them in-situ with an ohm meter after opening the unit up- they are quite obvious and the 3 in parallel should have a resistance of 50 ohms (approx.). If anyone is interested in any further information, please let me know. Tom Pratum Dept of Chemistry Box 351700 Univ of Washington pratum@u.washington.edu (old addr, No longer at UW NMR) List archive: Bruker Users Mail (BUM), for 1998 Archive

    Strange explosion inside Spectra Physics 2018-RM Laser power supply


    The UV Laser in our mass-spectrometer department had a strange failure: blown supply fuses, and a huge splotch of golden mirror coating on the PCB connected to all the large power components. Somewhere there was a direct short across the main power line on the DC side. Two metal terminals had touched together between PCBs in the supply, and the point of contact was explosively vaporised, coating everything around it with metallic copper!

    The failure apparently came from a MOV device which had been crushed between two circuit boards, where a big screw with DC main power on it had pushed through the epoxy coating on the MOV. This placed a short on the output of the main 3-phase bridge rectifier, which blew out one of its diodes before the 50-amp cartridge fuses blew.

    I found that Spectra Physics apparently was expecting this failure, since they sell a repair kit: the bridge module plus cables, along with screws which are shorter than the original ones. The 50-amp cartridge fuses can be had from Mouser. (and if Spectra Physics should discontinue their kit, the three-phase bridge is similar to a known part available elsewhere):

    Bridge Rectifier Upgrade Kit, 4801-1108UPG, Spectra Physics
    Bridge Rectifier, 3-phase, EH80, EH100, Microsemi.com
    NON-50 cartridge fuse, 504-NON-50 mouser.com
    After replacing the bridge, the laser still didn't work: it ran at full power (50 amps,) and the current-adjust pot on the remote console box had no effect. Occasionally it went into overcurrent shutdown. I traced this to a shorted zener. Besides killing the bridge module, the transient had shorted out CR-23 on the logic/driver board, a 1N4735 6.2V zener associated with the main series regulator (it's on a transistor driving the base pin on one of the big darlingtons in series with the main 50amp supply.)

    One last note. I had one of the big darlingtons removed from the water-cooling heat sink and noticed that the heat sink has large holes allowing direct water contact with the bottom plates of the transistor bricks. If you should try removing one of the bricks while the cooling water pump is running, you might get a big wet suprise!

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    Applied Kilovolts K9174 supply w/too low voltage, noisy output


    I've now seen two of these supply modules with the same problem. One side of the dual HV supply has an incorrect voltage with large noise signal. Is the noise from 60Hz, or from switching-freq leakage? Nope, it's a varying-frequency spike signal ...caused by arcing!

    Unfortunately the pinout is unlike any of the others on the http://www.appliedkilovolts.com website. To operate the supply I traced through the circuitry to find the +24v and ground pins on the connector. The four linked pins at one end of the 32-pin connector are ground, while the two linked pins near the other end (one position in from that end) are the +24v input. There is also an Enable pin which normally has +5 while floating, and needs to be grounded to run the supply. If pins 16 and 15 are the supply ground, while pin 2 is +24, then Enable is pin 7. Apply a +24DC supply at about 1/3 amp, ground the enable pin, and HV will be present on the two output cables.

    The failure I observed was from arcing caused by a weak point in their design. It's located right where the ground braid of the HV cable is twisted around the center conductor in the cable (right near where the cables dive into the silicone-embedded HV section.) Apparently the voltage rating of their HV cable is too low, so the strong e-field caused by the edge of the tightly-twisted ground braid will create corona discharge which eventually eats its way through the thick polyethelene insulation of the center conductor. Eventually a continuous arc punches through and burns a slot in the insulation.

    The cure is easy: Unscrew the single screw which holds the HV cables' ground braid lugs, carefully cut off about an inch of the black outer jacket of the HV cable, then untwist the ground braid and open it out so it's not bound tightly around the center conductor. You'll find a black-edged hole burned through the white polyethelene insulation there. I ran a drop of cyanoacrylate crazy glue to fill the hole, let it harden, then ladled in lots of RTV silicone caulk around the failure point and between the ground braid and the center conductor. (Avoid making bubbles which trigger arcing!) This keeps air away, and keeps the ground braid smoothly flared out so no high-field spots exist. I didn't even have to cut the ground lugs off, just screwed them back into position.

    . Even though only one cable shorted out, you might want to give the same treatment to both cables to prevent a future recurrance.

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    Edwards Vacuum Valve PV25EK, IV25EK, blows fuse


    More than one of these high-vacuum solenoid valves has now had the same problem. These valve contain two DC coils: one connects to points numbered 1 and 2, and is pulsed at high current to trigger the valve coil. The other is connected to points 1 and 3, and is continuous at low current to hold the iron core in position.

    Rather than pulsing on for 50mS as designed, the malfunctioning driver turns the pulse coil on full blast, which instantly blows the internal fuse. In both dead units the problem was the same: the small NPN transistor in TO-92 case was shorted, and the 220K resistor in series with the 22V zener diode was open. I replaced the transistor with a 2N2222A, and replaced the 220K with an old half-watt carbon resistor. Since these valves spend their whole lives in the turned-on state, probably the failure was caused by line spikes on the 220VAC supply. But the 220K was a film type resistance element, and the high 220V might have slowly degraded the film and lowered the resistance until it fried the transistor and itself.

    Notes: the coil driver is a fullwave bridge with two SCRs as the diodes on the positive side of the bridge. A second pair of diodes supplies the +310VDC for the holding coil and for the rest of the driver circuit. A diac in series with a 120K resistor with .047uF capacitor is used to trigger the SCR gates, and the NPN transistor pulls the diac signal down in order to turn off the coil after the pulse time has completed. When power is first applied, the NPN transistor is off, so the SCRs turn the coil on. Then the tantalum capacitor charges up through the 220K towards 31VDC, until the 22V zener diode turns on and raises the NPN base voltage, turning on the transistor and pulling down the SCR gates to zero. The coil in the smaller unit sees 400 watts, and 1000 watts in the larger unit. Obviously the driver needs to turn these coils off after just a few AC cycles have passed.

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    Early failure, source filament coil in Perkin-Elmer FTIR spectrometer, "Spectrum RX1"


    We have several identical Spectrum RX1 spectrometers, but only one has a problem: the hot source coil degrades after several months and finally burns out. These are $290 each, part# N017-1386 (replacing the old obsolete 17-0179.) Hmm, maybe try the one here

    Perhaps voltage too high? There's no controller, just a constant-volts supply

    Notes:


    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    455A746 Gearmotor on "Maxi Rotator" Shaker Table, Thermo-Scientific Model 4631

    I found an Allied Electronics replacement for the failed 455A746 motor in Thermo-Fischer 4631 shaker table (called 3D rotator.) These motors are no longer available from Thermo or from Globe Motor. Globe Motor catalog no longer lists 48V spur-gear motors. Neither does Pittman. However, a quick measurement showed that this 48V motor is only being driven at 16VDC at maximum, and has 64:1 stepdown ratio on the motor gearbox. If instead we use a 24VDC gearmotor, it will run at twice the speed ...so just use a 128:1 gearbox. If internal friction is small compared to the motor work done in lifting off-balance sample tubes ...then a 48V 64:1 motor draws the same current as a 24V 128:1 motor (if both are being run at 16VDC.) Globe Motor 455A105-3, avaliable Allied Electronics: 70217722 $135

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    Bad jacks in Texas Instruments TI-83 calculators with Vernier LabPro
    ( bad plugs, bad connectors, graphing calculators, communication jack, GRAPHLINK, GRAPH LINK, comm cable, communication cable, link cable, worn out, link port )

    Fairly old Texas Instruments graphing calculators give a communication error when linked together to transfer programs, or in classroom use with Vernier LabPro. This happens because the internal jack in the TI-83 wears out over time (especially it wears out with heavy student use.) The tiny gold leaf-springs get crushed out of the way so they no longer make contact. Sometimes you can open the case and use a needle to bend them back again, but this doesn't always work. And in an education lab environment, they will quickly go bad again.


    For those skilled with electronics, the 2.5mm connector is not that difficult to solder in on your own. However, only a somewhat-similar part is available. I've never found a source for the original gold-plated surface-mount 2.5mm stereo sub-miniature jack. Digi-key sells a useable replacement, their number CP-2523SJCT-ND, but one pad is in the wrong place, and the tiny alignment posts on the bottom will not match the holes in the calculator circuit board.

    WARNING: TEXAS INSTRUMENTS WANTS YOU TO SHIP THESE BACK TO THE FACTORY FOR FREE REPAIR!!! If you want to break into these yourself, you take responsibility for possibly messing up the electronics.

    WARNING: OPENING THE CASE WILL DISCONNECT THE MEMORY BACKUP BATTERY AND WIPE OUT ALL STORED SOFTWARE.

    To get inside many TI calculators, the screws require a #6 spline screwdriver such as Xcelite 99-62. Fortunately a 1.5mm hex (allen) screwdriver works great, and probably you can even use a 0.050" hex wrench if you tilt it so the points grip the inside of the screw. (And older TI calculators just use normal philips head screws.)

    Before soldering in the new jack, slice the *rear* tiny pin off the bottom. The front pin still provides some alignment. You might wish to affix the jack to the board with a bit of cyanoacrylate glue before soldering. The rear terminal on the new jack does not match the PCB pad, and it also touches against the PCB ground. I bend these rear terminals upwards out of contact with the PCB, then solder a piece of bare-wire resistor-lead between the PCB's pad and the bent terminal. Note: when reassembling the calculator, make sure all the calculator keys line up with the keypad holes in the case before replacing all the screws.

    Note that these calculators will "forget" their LCD brightness setting. Don't panic if the display seems blank when you reassemble the unit. Hit the ON switch, and look for the phrase "Mem Cleared" on the display. Then type [2ND][UPARROW][2ND][UPARROW] over and over to find the correct LCD brightness setting.

    Vernier LabPro, bad jack

    The same Digi-Key part CP-2523SJCT-ND can be used to repair bad TI calculator jacks in Vernier LabPro units, but the larger height of the new jack makes the fit even more of a problem. If you really want to repair your own LabPro using the Digi-key part, you'll have to take a chance and do some slight case-modifications where the blue plastic walls in the rectangular well are pushing against the top of the new jack. And as above, slice off the tiny rear alignment pin on the bottom of the jack, use a tiny bit of crazy-glue to bond the jack to the PCB, and solder some bare wire to connect the rear terminal pad to the PCB pad.

    See also:
    Created and maintained by Bill Beaty.



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