Tektronix DM5120 - a Keitley 196 brother - Page 1
Forum section: electronics / testgear

author: coromonadalix
author_rank: Super Contributor
timestamp: April 06, 2019, 11:27:59 am
content: here's my latest pick on FleaBayTek Wiki - Photos and schematicshttp://w140.com/tekwiki/wiki/DM5120I registred and updated some of the Wiki infos and put a firmware dump there too.Im gonna hack the meter casing to reduce it in size, but not touch the DM5520 frame who holds it, it's a 3 slot chassis.The problems are :No direct ac (120-230-240v) supply in it, the small x-former receive from the DM5520 frame a 25v ac for it's primary, gives the +15, -15, -5v dc analog sections.The main 5vdc 1 amp supply come from the DM5520 frame.And some small front panel switches with leds who get stuck once in a while. Keithley pn : 260-2454-01 SU-475( cant find anything on them, obsolete )-----------------------------------------The meter was never repaired or tampled, will do a recap very soonThe analog section has 2 chemical caps and 2 tantalums caps, they will be changed too.-----------------------------------------There's a part called rt1 who intrigues me, you see this part in the Keithley 196 service manual, it goes from the s1 switch thru rt1 to the Q9 and Q16 mosfets ... and the switch goes to U25 "B" pin 7 ??-----------------------------------------I had a Keithley 196 for sale here, but changed my mind, gonna keep it for the meter case hack / mod, mostly the digital section, i wont touch the analog board, but keep it safely.I dont think i'll keep the DM5520 frame, its a looooong frame (17 inches)-----------------------------------------Eeprom dump of the v1.0 ...attached here, the calibration memory ic is not socketedCalibration dump in case of ...attached here, your meter may need to be re-calibrated-----------------------------------------Next photosThe RT1

author: coromonadalix
author_rank: Super Contributor
timestamp: April 06, 2019, 11:31:27 am
content: next photosAnalog boards similarities 196 vs Dm5120

author: coromonadalix
author_rank: Super Contributor
timestamp: April 06, 2019, 11:33:03 am
content: next photos

author: coromonadalix
author_rank: Super Contributor
timestamp: April 06, 2019, 11:33:58 am
content: next photos and the 1988 print on the shieldTime travel loll

author: coromonadalix
author_rank: Super Contributor
timestamp: April 06, 2019, 11:35:35 am
content: next photosYou see the massive shield board and the aluminum cageThe problem is : when you try to remove the top panel section, it is composed of 3 sections slotted together, the analog section will fall inside the meter, be careful.You see the main input pcb adapter, as i wrote on the first opYou cannot power up the meter directly, it need an 5vdc at 1 amp for the digital section and a 25vac voltage ... for the small xformer inside the meter.And the second one is the gpib adapter board.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 06, 2019, 11:36:22 am
content: And the last photosThe case panels, the 3 parts top casing section ?Back in the days the meter was sold around 1890$ usd ??

author: coromonadalix
author_rank: Super Contributor
timestamp: April 06, 2019, 11:54:04 am
content: Length comparaisonThe DM5120 is 3 inchs shorter than the 196

author: lowimpedance
author_rank: Super Contributor
timestamp: April 11, 2019, 11:45:54 pm
content: Fascinating, never heard of the DM5120 till now. Much nicer front panel than the 196.Should be a fun 'hack'.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 12, 2019, 12:28:24 am
content: Fun ? yes and no lollTaken out the xformer of my 196, the xformer is bigger than the 5120, but the mounting holes on the pcb will fit, just need to add an ac socket w emi rfi filter, an 10000uf / 25 volt capacitor, a small 2 to 4 amps bridge rectifier, and fit them nicely between the logic pcb and the analog cage.On the photos near the two fuses, you have the 14 pins idc connector, it receives the 25vac and a main dc voltage for the 5v digital regulator (the one with the big heat sink), gonna use this header to fit the parts and hold them ...The xformer will be hold against the pcb, but flipped 180 degree with wirings, one footing side pins doesn't fit in the pcb (around 1/4 inch larger)BUT i'm gonna check if i can put it on the right side by drilling the footing pins ?? i have some room to play on the pcb ??For the power switch, the "measurement done" signal bnc plug will go on the rear, or simply removed.I found a nice car switch, 12vdc at 8 amps, it should tolerate the 120vac ... with a pull (stay pulled) push (stay pushed) lever, it act like the old sencore power switches ... i'll fit and bend a long rod who will go at the rear small pcb i'll craft to hold the main 10000uf capacitor and rectifier bridge, the black switch knob is m3 threaded.I did manage to desolder the calibration ic, made 3x "read" binary dumps of it and put it back on a socket, even with the right tools, the traces are very small and fragile, they can break easily ... link in the first thread.

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: April 12, 2019, 12:38:49 am
content: Quote from: coromonadalix on April 06, 2019, 11:27:59 amAccording to the ANSI reference designators, RT is a Thermistor (NTC or PTC).

author: coromonadalix
author_rank: Super Contributor
timestamp: April 12, 2019, 12:41:47 am
content: The RT1According to the ANSI reference designators, RT is a Thermistor (NTC or PTC).I just dont understand it's purpose in the circuit ??

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: April 12, 2019, 01:11:26 am
content: I did not see whether it is a PTC or a NTC. If it is a PTC, it is probably a sort of overload protection, while a NTC might be used as a temperature compensation for other parts.

author: texaspyro
author_rank: Super Contributor
timestamp: April 12, 2019, 03:45:12 am
content: I've seen several of these with a bad AC input channel. The problem was a blown resistor... I don't remember which one or the value. It was around 2W size and brown in color.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 12, 2019, 10:08:06 am
content: thks for the tipIll try to fit the two bottom tektronix frame locks into a switch leverI could keep the look intact ?? the hardests parts to find would be the keypad switches if they break.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 17, 2019, 10:01:59 am
content: It liiiiives !!! outside the frame, some photosThe 196 xformer secondary is almost a perfect fit, you have to cut a small top portion of the white mta156 connector (the analog meter section plug)You have to cut and remove some pcb traces on the component side after drilling new holes for the primary section of the xformer, i used a twist drill wth 1mm bit for the holes, the xformers pins are very short in lenght, i had to put wires on the primary side.Build a small rectifier board with the 10000uf capacitor for the 5vdc digital section (cpu rom sram etc..), i use the idc connector to hold it and thru it transfert the xformer rectified 10vdc to the main 5vdc regulator (huge heatsink)All the patchs i've made must not exceed the height of the main 5vdc regulator heatsink, because the analog meter will go over it, it will have around 1/2 inch of clearance, the regulator get warm.I've kept the 5vdc reulator 1 amp pcb fuse and socket (photo), removed the ac fuse pcb socketAdded an 115v 230vac selector switch, and a ac socket with 2 included fuses, I changed ideas for the Emi rfi filter due to space contraints.I'll simply use a main ac powerbar with included protections, the Keithley 196 did not have emi rfi protections ...My only problems left are the power switch, i'll try to keep the vintage look, or remove a bnc connector on the frontThe two Tektronix levers frame locks aren't easy to adapt ... and make a new rear aluminum plate with the needed holes for the voltage selector switch and ac socket.I dont think i'll ever use the gpib port on the board.For the keen eyes you see a green wire going into the xformer, i replicated the Keithley 196 wiring for the earth ground, the xformer seems to have a ground shield inside it,and i'll add the final green wire to the metal casingonce the project is completed.EDIT: the case is at ground supply level already, the front panel and the logic panel give it thru the metal mounting spacers.

author: Smokey
author_rank: Super Contributor
timestamp: December 23, 2023, 08:58:11 am
content: What was the deal with Tek and Keithley back in they day that they shared technology like this? Were they that friendly? Funny they ended up both being part of the Danaher empire eventually.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 23, 2023, 01:28:57 pm
content: with time i had / have a problem, i think around the eeprom a pcb trace or many have gone defective, the meter displays some inconsistanciesput it aside for a long time, never got time to play once again in it