Keithley 2306 Dual Battery Simulator Repair (maybe) - Page 1
Forum section: electronics / testgear

author: Smokey
author_rank: Super Contributor
timestamp: July 10, 2022, 04:04:22 am
content: I just scored a battery simulator from the ebays. Advertised as "powers up, no display".https://www.tek.com/en/products/keithley/dc-power-supplies/2300-serieshttps://download.tek.com/manual/2306-901-01%20(F%20-%20Apr%202008)(Ins).pdfDave did a teardown of the one channel model here:https://www.eevblog.com/forum/blog/eevblog-1005-keithley-2302-battery-simulator-teardown/I don't think there is a repair manual available.Got it on the bench and turned it on. The fan comes on, and as described there is nothing on the screen. The corner of the VFD looks like it arc'd inside. That may be the only issue, but I'm still waiting for the GPIB adapter to ship so I decided to poke around inside and see what I can see.(The lighting in the pictures I took sucked, so I'm using screen shots from Dave's teardown)There are some test points for the output voltages of the transformer.+/-15V, +/-5V, +25VThe +/-15V and the +5V are regulated, and measure good.The -5V and +25V both appear to be unregulated and measure high:+25V Testpoint measures +40V-5V Testpoint measures -9VThe transformer primary is a regulated 12V chopped into a 60kHz square wave by those two devices on the left of the transformer. There are +/-40V, +/-25, and +/-9V square wave secondaries.The strange thing in this case is that there are two nearly identical channels (both populated on the 2306 model I have here) and BOTH of them measure the same high voltages for the +25V and -5V rails.Does this make any sense? I don't see anything obviously wrong with the diodes or caps doing the unregulated filtering. Since both channels are acting identically, I would be surprised if there was a transformer drive or secondary issue.If these rails are supposed to be +40V and -9V, why label the test points +25V and -5V?

author: edpalmer42
author_rank: Super Contributor
timestamp: July 10, 2022, 05:00:49 am
content: I can't find a service manual, but here's a 367 page Instruction Manual that includes parts lists, component placement drawings aaannnndddd no schematics.https://images-na.ssl-images-amazon.com/images/I/B1fzKhl8h3S.pdfAlso, lots of info & documents here for you to wade through. There's bound to be some treasures.http://electronicsandbooks.com/edt/manual/index.php?dir=Hardware/K/Keithley+www.keithley.com/Ed

author: Smokey
author_rank: Super Contributor
timestamp: July 10, 2022, 06:51:32 am
content: Ya, I've done a bit of digging and I haven't heard anyone talk about those voltages. I know there is another repair thread with a different problem here:https://www.eevblog.com/forum/repair/keithley-2306-dual-psu-battery-simulator-repair/So there are a few people with these simulators. I would have thought someone would have measured the +25V test point and said something about that voltage being +40V if it was supposed to be like that.

author: Smokey
author_rank: Super Contributor
timestamp: July 10, 2022, 06:57:39 pm
content: Sunday afternoon Keithley bump....

author: picburner
author_rank: Frequent Contributor
timestamp: July 12, 2022, 08:39:16 am
content: I am one of those who wrote in the other tread.I still have the K2306 and should do some maintenance on it.If you have patience, as soon as I can, I open it and take the measurements in the points indicated.

author: gamalot
author_rank: Super Contributor
timestamp: July 12, 2022, 10:32:13 am
content: Quote from: Smokey on July 10, 2022, 04:04:22 amI just opened my 2306 and measured those voltages, they were pretty close to yours, measuring 36V at +25A/B and -9V at -5VA/B.

author: gamalot
author_rank: Super Contributor
timestamp: July 12, 2022, 10:52:13 am
content: I put the upper PCBA back and connected it to the lower one, the voltage of +25VA measured at this time is 28V.---In order to verify the guess of that the +25V rail voltage will decrease when the load is increased, I connected my 2306 to the electronic load. Sure enough, when the channel #1 source 8V/5A, the test point +25VA voltage drops to 25.2V.

author: picburner
author_rank: Frequent Contributor
timestamp: July 12, 2022, 11:16:00 am
content: Measurements made with respect to TP102:TP100 = +4,97VTP101 = +14,90VTP103 = -15,06VTP104 = -6,64VTP111 = +28,20VIf you need other measurements just let me know.Can you take a picture of your display?If there is a problem on the main cpu side on the display you can read "INITIALIZING" a sign that the display controller is unable to communicate with the main cpu.If, on the other hand, the display is completely dark the display pcb may be missing 5V, the display is broken, the display controller's xtal is broken or there are other problems on the display pcb.

author: Smokey
author_rank: Super Contributor
timestamp: July 13, 2022, 07:27:37 am
content: You guys are the best! Thank you for checking that. Gives me new hope it's just the display, which shows no activity at all.The remote display should be here soon. I saw another thread somewhere where some dude replaced the vfd with an lcd module and minimal hacks.

author: Smokey
author_rank: Super Contributor
timestamp: July 15, 2022, 06:05:58 pm
content: Thanks again for checking on those voltages. Well this may be the easiest repair of all time.I couldn't find a 2306-DISP remote display, but there are some 2304-DISP modules on ebay and I picked one up for $15USD.Just got here, plugged it in with a standard RJ45 ethernet cable, and it works!. Simulator is alive. Outputs looking good. I'm not sure if I'm missing anything by using the 2304-DISP instead of the 2306-DISP but it looks like all the menus are available.Still waiting for the GPIB adapter for full tests, but looking really promising.

author: Smokey
author_rank: Super Contributor
timestamp: July 18, 2022, 11:13:00 am
content: Update..... Not out of the woods yet.The supply only successfully powers up intermittently. Especially if it's been sitting for a while and is cold, it will just hang at the "initializing" part of the remote display routine (as mentioned in the other repair thread, the display has it's own processor and is responsible for that "initializing" text). The remote display actually doesn't show the word "initializing", it just shows two flashing boxes in the middle, but I think it's the same thing.Power cycling sometimes results in the supply powering up successfully, and once it does it seems to power up consistently until I let it sit again. I confirmed the output is good when it's working and I can talk to it over GPIB.There is also one more piece to the puzzle, which is while the unit is working, sometimes the front panel display will actually come alive for a few seconds and show "Initializing", then die again. It never actually displays anything else even when I unplug the remote display while it's running, still just "Initializing" randomly flashing on the front.I had the thought that maybe something on the front panel display is shorting a supply rail or something, but having it completely unplugged has no apparent effect on the intermittent power up issue.I can also confirm that the issue looks like it's in the bottom processor/supply board (not the top output board). Even with the top board off, it still only powers up intermittently with the remote display showing the flashing boxes when it fails, and an error code when it does power up without the top board.A few people replaced the SRAM (R1LP0408CSB-5SC) in the other thread, but they are presently out of stock unless I want to buy a minimum of like 20 pieces at $15-$20 each. I'm still unsure why that would be causing an issue like this though.

author: picburner
author_rank: Frequent Contributor
timestamp: July 19, 2022, 07:12:30 am
content: The two vertical flashing boxes you noticed on the display are normal and are shown just before the final splash screen appears.It should do this when everything is working normally.I had to replace the SRAM because the VFD display was stuck on 'initializing', this is not necessarily your case because at least sometimes your instrument starts up......Unless this is a symptom of an upcoming demise.

author: Smokey
author_rank: Super Contributor
timestamp: July 19, 2022, 10:36:16 am
content: When the unit fails to power up, the two vertical boxes on the remote screen never go away. They just keep flashing until I power cycle.When it does power up, they are only there for a second or two before it kicks into operational mode.

author: Smokey
author_rank: Super Contributor
timestamp: July 20, 2022, 02:22:09 am
content: Ok. New update.First a confession... The unit I'm working on is actually a 2308, which is the updated version of the 2306:https://forum.tek.com/viewtopic.php?t=94760#p153847But... The bottom board that is giving me trouble is shared with the 2306, just with a different firmware build (it actually has the 2306 check mark on the silk screen for the board model). I haven't seen anyone here with a 2308 and I didn't want to scare everyone off since the board that's having issues appears to be the same.Update:I hooked a logic analyzer up to the serial lines on the display connector and captured the messages on Pin4 and Pin5: [UART decoding at 9600 8n1]. Pin4 is coming from the main processor because it gets traffic even when the cable to the display is unplugged.During successful power up without the top board installed:Pin4 has the following messages:\x0C\x01\x06\0 2308 ADDR 6 A01 00000 60HZ\x05\xFF\x06\0 start response model INVALID\x05\xFF\x06\0 start response rev INVALID\x05\xFF\x06\0 start response key INVALID\05\0\06\0 0.000 V #1 OFFOVERFLOW\05\0\06\0 0.000 V #1 OFFOVERFLOW...Pin5 has the following messages:2304 B02 \x80The overflow message is because the top board isn't installed. That doesn't happen when the top board is installed.When the unit doesn't power up correctly I get these messages, then nothing...Pin4 has the following messages:\x07\t\x17\x07\x0C\x01\x06\0\x20Pin5 has the following messages:2304 B02 \x802304 B02 \x80With the remote display plugged in, I get the following message on Pin4:\x0C\x01\x03 REMOTE PANEL ENABLEDDoes any of that set off any alarms for anyone?Any more ideas on ways to troubleshoot this? I haven't see any other diagnostic interfaces.

author: Smokey
author_rank: Super Contributor
timestamp: July 20, 2022, 07:35:36 am
content: I'm not sure if this is relevant, but it is interesting.I took the front panel off of the unit and powered the unreliable internal VFD display from a 5.00V bench supply. When I power up the display this way, it pulls about 230mA and powers up every time. Right into "INITIALIZING". Nice and bright. This is very different from the random intermittent flashing that happens when it's being powered while connected to the unit.So I figured I would see what minimum voltage would turn on the display. And... It starts to operate unreliably at about... 4.95V. It won't turn on under 4.94.Well when I measure the +5VD rail at the display cable, it measures..... +4.95V. So that appears to be the (an?) issue with the display.Is this a design flaw where they used some parts in the display board without sufficient minimum voltage margin? Or has something aged to where it's unreliable now? Is this related to the system not powering up somehow (like whatever components won't power up in the display are also refusing to consistently power up on the rest of the digital section?).::Update 7-24:: See msg bellow:https://www.eevblog.com/forum/testgear/keithley-2306-dual-battery-simulator-repair-(maybe)/msg4319182/#msg4319182It looks like the undervoltage monitor IC on the display board is not working correctly....

author: Smokey
author_rank: Super Contributor
timestamp: July 20, 2022, 08:57:43 am
content: Plot thickens....The +5VD rail is powered by an LM2940CT:https://www.ti.com/lit/ds/symlink/lm2940-n.pdfThe input to that regulator is +6.5VD, which measures about 6.40V at the input to the LM2940CT.As I said in the last post, the +5VD rail is measuring about 4.95V. Normally I would say this is pretty damn good.Test = power the 5V rail from an external supply:So far, when I power the whole system +5VD rail from an external supply, and confirm with measurement that the voltage of the +5VD rail at the display connector is the full 5.00V, the supply powers up consistently every time as confirmed by the external display. When installed in the system, the internal VFD display only powers up every time consistently when I boost the +5VD rail to 5.13V. With the whole system running, the +5VD rail pulls about 575mA.It just seems insane that having the +5VD rail be only 50mV low would make the whole system unreliable.Any ideas?::NOTE:: I should add that I have looked at the 5V rail on the scope and it is really solid. No excessive ripple or noise or anything nasty.

author: Smokey
author_rank: Super Contributor
timestamp: July 20, 2022, 05:54:25 pm
content: I'm thinking I can replace the LM2940CT with something that has a variable output and just bump it up to about 5.1V, but that seems like a band aid for some underlying issues.This looks like it might be viable:https://www.digikey.com/en/products/detail/microchip-technology/MIC29302WT/771593I can probably hack this in the same footprint without needing a carrier board since they are both through hole. I can solder the new part into the IN,OUT,GND pads of the existing TO-220 footprint, and just air wire the adjust and enable pins.

author: Smokey
author_rank: Super Contributor
timestamp: July 21, 2022, 03:40:37 am
content: Looking at the LM2940CT 5V part datasheet, the recommended input voltage range is 6.25V to 26V. This is surprisingly close to the 6.4V that is actually on the input to the regulator (even through the dropout plot does say it's rated at 0.5V dropout at 1A).The output voltage range, depending on the current level, can be anywhere from 4.75V to 5.25V. So the normal operating range extends way into the non-functional zone at the low end of the regulator output tolerance.There has to be something else going on.

author: AVGresponding
author_rank: Super Contributor
timestamp: July 21, 2022, 05:36:56 am
content: I take it you have checked for dry caps on the output side of the regulator, and the display board, which could easily cause such symptoms? What is the ripple voltage?

author: Smokey
author_rank: Super Contributor
timestamp: July 21, 2022, 06:23:44 am
content: The LM2940CT has maybe 50mv of high frequency ripple at about 200kHz, which I would think is coming from the square wave drive into the transformer primaries for the output voltages. I don't think it looks that bad at all really. When I power the unit from the bench 5V supply, the character of the voltage rail doesn't change at all, it just increases the voltage a little.That's what so strange to me. The voltage rail looks solid at 4.95V. It's not like its dipping whenever there is a current demand.I actually don't think there are any electrolytic caps on the 5V rail... but there are a ton of tantalums.With that said, the in circuit resistance across the 5V rail is about 750ohms, but that's in circuit. The total current on that rail is under 600mA, which is well within range for the regulator. It's not even getting very hot.While the display board and the system board are both showing what looks like essentially the same symptom (extreme sensitivity to under voltage on the 5V rail), the main board has the problem even when the display board is completely disconnected.

author: mnementh
author_rank: Super Contributor
timestamp: July 21, 2022, 01:00:26 pm
content: Have you tried isolating the input to the LM2940CT and powering it with a slightly higher voltage; like 8-12V? What you're describing sounds to me like it may be right on the verge and dropping out.mnem

author: Smokey
author_rank: Super Contributor
timestamp: July 22, 2022, 03:55:47 am
content: Quote from: mnementh on July 21, 2022, 01:00:26 pmThat's a good test. I'll set that up.One thing I don't understand is that the LM2940CT datasheet lists this part as 0.5V dropout, and the dropout plots clearly show 0.5V at 1A as the dropout.....But the electrical characteristics for the 5V version clearly show the input voltage as:Input voltage : 5 mA ≤ IOUT ≤ 1 A: Min=6.25, Max=26https://www.ti.com/lit/ds/symlink/lm2940-n.pdf(page5)I don't necessarily just want to start replacing parts that aren't showing failure symptoms, but the LM2940CT is probably going to be the first to go.

author: AVGresponding
author_rank: Super Contributor
timestamp: July 22, 2022, 05:41:49 am
content: Quote from: Smokey on July 22, 2022, 03:55:47 amHave you checked the input ripple voltage? If it's reading close on DC, it might be falling under the dropout voltage at the bottom of ripple voltage. Though the output you measured looks good to me; I'd be surprised for anything designed to work using a standard 5V linear regulator like this to stop working at 4.94V if it's not faulty in some way.

author: Smokey
author_rank: Super Contributor
timestamp: July 22, 2022, 05:56:50 am
content: I've been out all day. I'll check the input soon.But I agree 4.95v is usually pretty stellar for an ldo.I had this idea that there may be some adc or comparator somewhere that is confirming rail voltages before enabling the system and a voltage divider resistor is out of spec causing the thing to never turn on even though the actual voltage is fine.But there is no schematic....

author: Smokey
author_rank: Super Contributor
timestamp: July 22, 2022, 11:22:27 pm
content: Considering that both the +25V and -9V test points are expected to have unloaded voltages much higher than what is listed on the silk screen.......I wonder if the +6.4VD testpoint that feeds the 5V regulator is actually supposed to have much higher voltage than that as well.::Update::... its' not.I know you guys probably already put your supplies back together, but if you could measure one more voltage, it would be interesting to know what a good unit measures at the +6.4VD testpoint on the board right next to the fan.::Update::No need for this. It's just the output of a switching regulator is that is programmed for 6.4V. It's doing what its supposed to.

author: Smokey
author_rank: Super Contributor
timestamp: July 23, 2022, 02:53:43 am
content: Quote from: AVGresponding on July 22, 2022, 05:41:49 amAbout 15mv ripple on the +6.5VD rail. There is some +/- 50mV high frequency stuff coming from the switching regulator frequency that's generating the voltage, but I wouldn't say it's excessive.U112 is the switching regulator that's driving the +6.5VD rail. It's listed as "ADJ VOLTAGE REG STEP DOWN" in the component list on the data sheet. Thanks Keithley.The part is actually a LM2675:https://www.ti.com/product/LM2675https://www.ti.com/lit/ds/symlink/lm2675.pdfThe output from the regulator is essentially a 260kHz 0-12V square wave into the inductor/cap.R124 = 2.55KR125 = 11KSo assuming R124=R1 and R125=R2, The output voltage is set to:(((R2/R1) + 1) * 1.21) = 6.429V, which is pretty much right on.NOTE: Since this looks good, no need to get any other measurements on this. It is what it is.

author: Smokey
author_rank: Super Contributor
timestamp: July 23, 2022, 03:30:03 am
content: As a test, I bumped R124 to 2.4k....Which increased the measured input voltage of the LM2940CT to 6.68V.The measured output of the LM2940CT is still super solid at 4.95V, and the 2308 supply still won't consistently power up with just the internal regulators.So... It's not looking like it's an issue with the input to the LDO powering the +5VD rail.

author: AVGresponding
author_rank: Super Contributor
timestamp: July 23, 2022, 09:01:37 am
content: Time to start looking at the control logic then... IC decoupling caps, reset signals etc...

author: Smokey
author_rank: Super Contributor
timestamp: July 24, 2022, 07:09:21 pm
content: Filling in some part numbers for "Model 2306 digital board":U132 = "INTEGRATED CIRCUIT " = LM2937 = "500-mA, 26-V, high-PSRR, low-dropout voltage regulator"https://www.ti.com/lit/ds/symlink/lm2937.pdfU135,U136,U235,U236 = "INTEGRATED CIRCUIT" = LM7121 = "235-MHz Tiny Low Power Voltage Feedback Amplifier"https://www.ti.com/lit/ds/symlink/lm7121.pdfOn the "Model 2306 display board parts list"U601 = "UNDERVOLTAGE SENSE CIRCUIT" = MC34064https://www.onsemi.com/pdf/datasheet/mc34064-d.pdf

author: Smokey
author_rank: Super Contributor
timestamp: July 24, 2022, 07:55:18 pm
content: Checking some processor lines:This is all in the "failed to power up" state.{Checking (not)RESET, (not)HALT, and (not)BERR line on the MC68331CPV16 Main processor...Reset line goes high about 525ms after 5V rail comes up. Stays high.HALT line goes high at the same time as 5V rail. Stays high.BERR (bus error) is also high at power up. Stays high.Clock out looks good at 25MHzFreeze line stays low.}Nothing strange here.Powering the system with an external 5V (successful power up){Same behavior. No changes to the above signals}That all looks good.

author: Smokey
author_rank: Super Contributor
timestamp: July 24, 2022, 08:45:55 pm
content: Note: As I said above, the main digital board does not consistently power up regardless of whether the display board is plugged in or not. Also I have captures of the display board's serial communications in both working and not working conditions, so I'm not saying this is causing the issues with the digital board... or is it?.....The MC34064 undervoltage sensing circuit on the display board is acting strangely..From this plot in the datasheet...The output is supposed to snap on around 4.5V input. It's not exactly doing that.At about 4.4V input it starts to turn on the output, but it's output is only 1.5V.4.5V in = 2.2V out.4.6V in = 2.75V out.4.7V in = 3.3V out4.8V in = 4.0V out4.9V in = 4.9V out5.0V in = 5.0V out.That isn't even close to what the plot says it should be doing. The IC itself doesn't look damaged and it's not getting super hot or anything.So that may explain why the display only turns on at the full 5V input....but... at least according to the parts list, there is no voltage monitor IC on the digital board and the main digital board does not appear to rely on the display board for anything since it will power up when it's totally disconnected.....

author: Kean
author_rank: Unknown
timestamp: July 24, 2022, 09:47:50 pm
content: The MC34064 has an open collector output and so depends on a pull up resistor.Maybe the MC34064 is damaged, or more likely something else is loading down the reset line.

author: Smokey
author_rank: Super Contributor
timestamp: July 24, 2022, 10:05:33 pm
content: The pullup on the "Model 2306 display board parts list"R612 = RES, 4.75K, 1%, 100MW, THICK FILMIf the comparator in the MC34064 was acting correctly, I would expect the open collector to pull hard to ground until it hits the threshold and the output snaps on. But its got this strange ramp that's under spec before the turn on. Once the input gets to 4.9V it's full on like it's supposed to. If there was excessive load, I would expect a voltage droop here too, but it's solid above 4.9V.But even at the top range of the input specifications in the data sheet, the highest it should get before it snaps on is 4.8V. So even if we ignore the ramp voltage, it is turning full on too high.

author: Kean
author_rank: Unknown
timestamp: July 25, 2022, 03:25:45 am
content: So two possibilities I see1. The MC34064 output is not changing state cleanly at 4.5V, which seems unlikely as it has a simple comparator driven output with hysteresis2. The MC34064 output is changing state at around 4.5V, but between 4.5V and 4.9V other circuitry loads the signal more than the pull-up resistor can handleThe fact you see a change at around 4.4-4.5V makes me think the latter is the case. You could isolate the output pin of the MC34064 and see what happens to the reset signal voltage with just the 4k75 pull-up as you vary the supply from 4V to 5V. Or just swap out the MC34064 to eliminate that as the cause.

author: Smokey
author_rank: Super Contributor
timestamp: July 26, 2022, 07:45:46 pm
content: Success. (so far.....)I ended up doing the mod I described above, where I replaced the original LM2940CT generating the +5VD rail with a MIC29302WT adjustable regulator.I set the MIC29302WT output to 5.10V, and the whole supply works fine now. (The original LM2940CT had an output spec of +4.85 to +5.15, so I don't see this causing any issues with the other parts of the system).External VFD display turns on with good brightness (The 5.1V pushes the display MC34064 voltage monitor into the region that's full on, so that problem goes away as well).Digital board powers up every time. I tested the output of channel1 and it's still accurate. It's been put back together running in it's home on the bench all morning with no issues.In my desire to be done with this project, I didn't run some additional experiments that I probably should have:1) I didn't use the pot to drop the output voltage down to the 4.95V that the original LM2940CT supply was making when the unit wouldn't turn on consistently.2) I didn't just replace the LM2940CT with another LM2940CT and see if that fixed it as well.3) I didn't replace the MC34064 on the display board (even though I'm suspecting that the 5V reg was causing this strange issues as well somehow).If I had to guess, I think the problem was most likely just a faulty LM2940CT (even though the output looked fine on the scope). If anyone else has a 2302/2306/2308 that isn't powering up, I would start by just replacing the LM2940CT. (Update: See posts below. It's probably not the reg)

author: Smokey
author_rank: Super Contributor
timestamp: July 27, 2022, 05:41:53 am
content: One more post here to thank everyone that posted ideas, and helped troubleshoot. You guys are the best!

author: Smokey
author_rank: Super Contributor
timestamp: October 15, 2022, 02:49:30 am
content: Grrr..... Saga continues... This power supply has been acting up again.It's been need to warm up for a couple minutes for the internal display to work. Once it's warm it will work fine when you power cycle it... at least it was doing that.Now the internal display won't come on even after it's been running..... The external display still works though so I know the unit is powered up and working.I'm going to replace the MC34064 voltage monitor chip on the internal display board, and I'll see if that fixes it.Parts ordered.

author: ottobad
author_rank: Newbie
timestamp: July 14, 2023, 01:50:47 pm
content: Hello, I have a Keithley 2306 and it suddenly appeared INITIALIZING ... and that's all it does. I took it apart and measured internal source , its source outputs 12VDC, after that the LM2940 outputs 5VDC, and then if I measure TP 101,102,103...nothing. On the CR102, rectifier bridge, I have nothing on the alternative and nothing on the DC, as well as the next module. I measured on SRAM and 2.5VDC comes in... what should I measure or where should I start?Thank you and sorry if I disturbed you.

author: Kean
author_rank: Unknown
timestamp: July 14, 2023, 02:23:12 pm
content: Quote from: ottobad on July 14, 2023, 01:50:47 pmI think you need to enable the channel before voltages will appear on those test points. If it is stuck on INITIALIZING then I guess you cannot do that.If the main 5V voltage looks OK, then per the above post #10 the SRAM chip could be the culprit. You mention 2.5V on the SRAM, but I think it should be powered from 5V rail. What pin did you measure 2.5V?I bought mine on eBay knowing it may have similar issues, but so far it has been fine after I recalibrated it.

author: ottobad
author_rank: Newbie
timestamp: July 14, 2023, 04:59:55 pm
content: It stuck on INITIALIZING, also no service manual on internet, anyone have it here? I measure SRAM chip on pin 32Vcc and pin 16, i have around 2.5Vdc. Do you know who supply voltage to sram chip?I will order from Ebay the SRAM chip....Being a RAM, does something need to be written, copied from the old one?Thank you for reply.

author: Kean
author_rank: Unknown
timestamp: July 14, 2023, 05:23:50 pm
content: On the SRAM pins 16 and 32 are GND and Vcc and my unit reads 4.95V. There is a capacitor C186 across the SRAM supply rails near pin 32.The SRAM is not battery backed in the K2306 - no battery I can see and no voltage to the SRAM when powered off, so no need to copy any data.The R1LP0408C SRAM needs 5V +/-10% so 2.5V is bad. If you really have 2.5V then I suspect that may not be caused by a RAM chip fault if you measure 5V elsewhere.There are a couple of different voltages in the digital section, and a bunch more isolated supplies in the analog area. I will make notes of some measurements for you to compare.

author: Kean
author_rank: Unknown
timestamp: July 14, 2023, 05:45:49 pm
content: OK there are three isolated supply sections on the K2306 main PCB.I've listed them below along with measurements from my K2306 with the top PCB removed (so no load on analog supplies).Digital supply "D" (test points near fan) - referenced to GNDDTP105 Vin = +11.97VTP106 GNDDTP109 +6.5VD = +6.47VTP110 +5VD = +4.96V (this connects to the SRAM Vdd pin 32)Also there is a second 5V regulator in the digital section at U132 with pin 1 = +6.42V (from +6.5VD via filter) and pin 3 = +4.96V. Not sure what this supplies.Analog supply "A" - referenced to GNDATP100 +5VA = +4.96VTP101 +15VA = +14.87VTP102 GNDATP103 -15VA = -15.01VTP104 -5VA = -9.50VTP111 +25VA = +37.18VAnalog supply "B" - referenced to GNDBTP200 +5VB = +4.97VTP201 +15VB = +14.96VTP202 GNDBTP203 -15VB = -15.08VTP204 -5VB = -9.52VTP112 +25VB = +37.42V* I was wrong about needing to enable channels to read all measurements - you just need to use the correct GND pin as they are isolated supplies.

author: Kean
author_rank: Unknown
timestamp: July 14, 2023, 06:15:13 pm
content: Before putting my K2306 back together, I took a little look around the main CPU (MC68331)U129 and U133 are 24LC16B I2C EEPROMs which probably store the calibration data - much better than battery backed SRAM, but not infallible. When I got my unit the calibration was messed up, but that could have been someone playing around before me rather than any kind of failure.U132 might be a separate 5V regulator for the remote display connector so if it is shorted it doesn't take out the main 5V rail. Or it could be a clean supply for the nearby analog components: 2 x LM393, MAX391, AD706. I don't know what they are used for.There are 2 x ADM232 which will be for the remote display comms, a ULN2003 for the relay outputs, and some opto-isolators for comms to each of the isolated analog channels on the top PCB.

author: ottobad
author_rank: Newbie
timestamp: July 18, 2023, 07:48:40 am
content: Hello,I have the :TP105 Vin = +11.8VTP106 GNDDTP109 +6.5VD = +6.47VTP110 +5VD = +5VOn U132 in 6.4V out 5VDC but on SRAM pin 16-32 IS still 2.5VDC...Is ok If I take out the memory and mesure again if 5 Vdc is present on pin16-32...maybe is a faulty memory?On this...I have 0 insted of value you putAnalog supply "A" - referenced to GNDATP100 +5VA = +0VTP101 +15VA = +0VTP102 GNDATP103 -15VA = -0VTP104 -5VA = -0VTP111 +25VA = +0VAnalog supply "B" - referenced to GNDBTP200 +5VB = +0VTP201 +15VB = +0VTP202 GNDBTP203 -15VB = -0VTP204 -5VB = -0VTP112 +25VB = +0VThank you

author: Kean
author_rank: Unknown
timestamp: July 18, 2023, 08:25:20 am
content: Quote from: ottobad on July 18, 2023, 07:48:40 amAs you measured 5V OK at TP110, then I suggest measuring the supply pins of a few other components in the digital section other than the SRAM.Did you try measuring across capacitor C186? Other points to try measure would be between GNDD and VCC on the various 74-series logic ICs, or ther I2C EEPROMs U129, U133.You could also measure the resistance between the supply pins on various ICs in the digital section and pin 32 of the SRAM (with the power off of course) to see if there is some broken connection.I don't believe there is a service manual or schematic available. One user here (picburner) created a partial schematic of the digital to analog opto-isolation section athttps://www.eevblog.com/forum/repair/keithley-2306-dual-psu-battery-simulator-repair/msg632229/#msg632229and three people in that thread fixed (or partly fixed) their unit by replacing the SRAM IC.Quote from: ottobad on July 18, 2023, 07:48:40 amJust to make sure... when you measure these analog section supplies... you do have your DMM black probe on GNDA or GNDB and not GNDD?I will open mine up again and see if I can identify any other suggestions.

author: ottobad
author_rank: Newbie
timestamp: July 18, 2023, 09:04:25 am
content: So, C186 ( shorted ) is 4.98Vdc and now SRMA is at 5V BUT STILL IN INITIALISING ( don't know the value of C186 so is out from the board )TP110 is ok, 5Vdc.I will buy the SRAm and after recieve, will try again.

author: Kean
author_rank: Unknown
timestamp: July 18, 2023, 09:40:15 am
content: OK. C186 is 100nF 20% 50V Ceramic per the list of parts in the manual. I don't think the exact specifications are critical.Let us know how you go after replacing the SRAM. i hope that fixes it.For your two isolated analog power supplies that read 0V on the outputs, check the input fuses F100 (marked FH100/FH101) and F200 (marked FH200/FH201)They should read approx 12V (relative to the non-isolated digital GNDD) on both sides of the fuses, or should at least not be open circuit.

author: Smokey
author_rank: Super Contributor
timestamp: July 18, 2023, 09:18:54 pm
content: Hey guys. Sorry for not getting back sooner on this. I actually never fully updated what I discovered on my unit.Firstly I have about 10 of the SRAM chips that I bought when I was first doing my investigation, but never used because that wasn't a problem I actually had.https://www.eevblog.com/forum/buysellwanted/fs-r1lp0408csb-5sc-4mb-sram/Before you go swapping that, here is what I did that actually fixed my unit (at least made it reliable enough that it appears to work without any of the errors I was originally having).Firstly, if I remember correctly, the "Initializing" on the display is actually coming from the display board. So it's not some informative error message that the main processor is trying to tell you, it's just what the display board shows at power up when nothing else is talking to it.Ok, so what I determined was the actual problem with my unit was a bad cap on the DISPLAY BOARD that was pulling down 5V for the rest of the system. Unfortunately, the cap is between the display and the PCB which are soldered together with a lot of pins. So instead of disassembling that, I just stuck a TON of extra capacitance on the top side of the display board 5V rails. There are at least two unpopulated 5V cap footprints on that display board, so I stuck two 100uF 5V tantalums which I had around on those pads. That gave the board enough capacitance that it no longer pulled down the 5V rail, and everything was happy after that.Hopefully that helps.

author: ottobad
author_rank: Newbie
timestamp: July 19, 2023, 09:55:38 am
content: H :-//ello, thanks for the advice, I disassembled the display module, checked all the capacitors, they are good. I checked 5Vdc, all good. All that remains is to get the SRAM and change it... maybe that will fix it