BK Precision 9130 Triple Power Supply repair. - Page 1
Forum section: electronics / repair

author: jchw4
author_rank: Regular Contributor
timestamp: October 13, 2021, 11:56:39 am
content: I got BK Precision 9130 with dead temperature sensor, so fan never turns on.I believe that IC 2U27 is a temperature sensor. It is SOT-23-3 chip marked "NS7A". I desoldered it and found that fan is turned on when out=3V and turned off when out=2V.I cannot find anything like this. Comon 10mV/C or 19mV/C sensors will give 3V at \$T=\frac{(3V-0.5V)}{0.010V}=250C^o\$ or \$T=\frac{(3V-0.4V)}{0.0195V}=133C^o\$ which does not seem right.What could it be?Upd: Component was identified as voltage monitor, seehttps://www.eevblog.com/forum/repair/bk-precision-9130-triple-power-supply-(identify-component)/msg3752309/#msg3752309.But fan still does not start, so this is now "fix the temperature monitoring" thread.

author: Fraser
author_rank: Super Contributor
timestamp: October 13, 2021, 12:19:54 pm
content: Just a quick sanity check….have you tested the original IC for behaviour ? Is it truly dead/faulty or is the circuit monitoring its output at fault with incorrect on/off thresholds ?

author: jchw4
author_rank: Regular Contributor
timestamp: October 13, 2021, 06:54:32 pm
content: Quote from: Fraser on October 13, 2021, 12:19:54 pmThis was the only component that was marked IC and was not a voltage regulator. Output was stuck at 16mV. Fan was always off.I desoldered it and tried applying external power to the output. At 3V (measured 2.92V) fan turned on, at 2V (measured 2.0224V) fan turned off.I did not check the component on itself (will do it later today), but my guess is still that it is temperature sensor.Hmm. Now I started thinking that it could be 3V regulator that was used as a source of a threshold. But why whould 5V-powered MC use an external 3V source for it? (And where is the temperature sensor?)On the other hand, putting 3V regulator there will kind of solve the problem, though only 2 levels of PWM (0.4% and 100%) is not great. But may be it is by design? I don't have another unit to compare.

author: floobydust
author_rank: Super Contributor
timestamp: October 13, 2021, 07:15:11 pm
content: You can ask BK for the service manual, the product is discontinued.It might just be the voltage reference IC for the MCU A/D. I would see if other analogs move as the voltage is changed.The temp sensor is usually right at the power semiconductors, on the heatsink- I would look there.

author: MSchalk
author_rank: Newbie
timestamp: October 13, 2021, 08:12:17 pm
content: I wonder if anybody knows what what chip that is with the markings scratched out. I agree with floobydust that it is likely an analog reference. If you look at the pinouts on TO-23 smd linear regualtors they match the inputs/outputs on the picture. I took a look at some temperature sensors in TO-23 packages, none of them that I found would make sense for their input/outputs.EDIT: Also why would you need a capacitor on a temperature sensor?

author: jchw4
author_rank: Regular Contributor
timestamp: October 14, 2021, 06:03:51 am
content: Here is a panoramic photo of the digital board without capacitors (these were bulged and needed replacement as suggested on this forum).Ignore some panoramic artifacts. The board stiched correctly, higher parts do not always look good

author: jchw4
author_rank: Regular Contributor
timestamp: October 14, 2021, 06:11:24 am
content: The three sanded chips near the main IC look like [2U11.jpg], which I believe are MSP430F1101Ahttps://www.ti.com/lit/ds/symlink/msp430f1101a.pdf.The three sanded chips along the left side look like [2U5.jpg, 2U6.jpg], which I believe are CS5550-ISZhttps://statics.cirrus.com/pubs/proDatasheet/CS5550_F1.pdfThe main chip looks like the [main_IC.jpg] below. I could not read its markingsWe need more photos from different devices to identify it.

author: jchw4
author_rank: Regular Contributor
timestamp: October 14, 2021, 06:17:52 am
content: Here is power domains map with test points for those trying to diagnose it.This time on top of the original board photo

author: jchw4
author_rank: Regular Contributor
timestamp: October 14, 2021, 06:31:23 am
content: Quote from: floobydust on October 13, 2021, 07:15:11 pmAs it has not yet leaked (could not find it anywhere), I guess they won't part with it.QuoteI don't know how to find these, becase I don't think main IC has any analog input/output (maybe one for the temperature sensor if I can find it).The three CS5550-ISZ seem to use analog refs in SOT-23 package marked R30C. Which I guess are REF3025 from TIhttps://www.ti.com/lit/ds/symlink/ref3025.pdf.Why would they use another part for the main IC?But maybe it's really a 3V regulator. But is it 3V or 3.3V ? If we have another owners of these devices, could somebody check the voltage on this part?QuoteI looked all around the analog board and did not find anything. I don't think there is one on the main heatsink either...I'll try to make photo of the analog board later, it's large and the process is somewhat complicated.Quote from: MSchalk on October 13, 2021, 08:12:17 pmThis is good point. If it is indeed a voltage regulator, what voltage does it provide?

author: jchw4
author_rank: Regular Contributor
timestamp: October 16, 2021, 08:39:54 am
content: Here is panoramic photo of the analog board.

author: fzabkar
author_rank: Super Contributor
timestamp: October 16, 2021, 09:48:03 pm
content: Quote from: jchw4 on October 13, 2021, 11:56:39 amThis behaviour is consistent with a power supply supervisor, or a uP reset monitor.I expect that "7A" is a Year/Something" date/batch code.Those "NR78" ICs may also be power supply supervisors, albeit with a different voltage setting. Maybe the date code is "Year/Month".Edit:http://file2.dzsc.com/product/17/10/14/1129211_101248570.pdfhttps://www.onsemi.com/pdf/datasheet/cat810-d.pdfNRYM -> CAT809xNSYM -> CAT810xNote: the two datasheets have different marking codes for the same devices.

author: floobydust
author_rank: Super Contributor
timestamp: October 17, 2021, 02:35:06 am
content: I think they'd use a low cost bead thermistor but can't see anything at the heatsink (unless under it). They might be using a diode or diode string to sense temperarture.SMD marking code NS7A might be old Fairchild N-ch mosfet NDS7002A (2N7002) but I can't confirm it, yet it makes no sense for the gate to be grounded.

author: fzabkar
author_rank: Super Contributor
timestamp: October 17, 2021, 03:03:08 am
content: Quote from: floobydust on October 17, 2021, 02:35:06 amIf it were a MOSFET, then its circuit reference would be 2Q27, not 2U27, just like the BR parts nearby. Moreover, it wouldn't make any sense to have a capacitor between gate and source.Edit:2U14 could be an 8-bit uC.80C51/87C51/80C52/87C52 - 80C51 8-bit microcontroller family:https://www.nxp.com/docs/en/data-sheet/8XC51_8XC52.pdfPage 6 has the QFP-44 pinout.Pin 4 is Reset, which connects to the supervisor IC's output.Pins 14 and 15 are the crystal inputs.Pin 38 is Vcc, and pin 16 is ground.

author: floobydust
author_rank: Super Contributor
timestamp: October 17, 2021, 04:22:37 am
content: That makes more sense, because the mystery SOT23 has a pullup resistor on the output pin which you don' t need with an analog temp sensor IC.A temperature sensor is best located next to parts that heat up, so it can see their temperature. Usually it's independent circuit not using two pins on the MCU (temp in , fan on/off out). Does the fan power transistor trace go back to the MCU then?Another approach would be to look at other BK Precision power supplies in the family - for schematics or board pics etc. 9129, 9100 etc.

author: jchw4
author_rank: Regular Contributor
timestamp: October 17, 2021, 07:42:58 am
content: Quote from: floobydust on October 17, 2021, 02:35:06 amThere is nothing that looks like thermistor, I spent quite some time looking for it. There is nothing under the heatsink too.

author: jchw4
author_rank: Regular Contributor
timestamp: October 17, 2021, 07:45:04 am
content: I'll check the power monitor idea and report back.Fan does trace to the main MC, I'll try to draw some schematics.

author: Fraser
author_rank: Super Contributor
timestamp: October 17, 2021, 10:23:45 am
content: This may be of no relevance to this power supply but one of mine uses the calculated wattage to set the fan speed. There is no heatsink temperature sensor for the fan. The lab power supply knows how much voltage and current is being produced and calculates the wattage. This is then used by the microprocessor to determine how much cooling is needed from the fan and the fan speed is set. I was surprised to see such a cooling routine but it certainly appears to work. There is a safety circuit monitoring the heatsink for over temperature in case the fan port becomes blocked. For those doubting this approach, as I did, I tested my power supply response to load and sure enough, the fan has a stepped speed response and each step comes in at a set wattage. At low wattages the fan is off and the next step is cyclic fan on / fan off. Once higher wattages are reached the fan is constantly on and running fast.As I say, this may have no relevance to the particular power supply that is the subject of this thread, but I thought I would highlight that some power supplies use unconventional fan control systems.Fraser

author: Kean
author_rank: Unknown
timestamp: October 17, 2021, 11:34:01 am
content: I have a BK 9130 on the round tuit bench which I've recapped in the past but is now reporting wrong readings.Happy to take a look at any readings you are after, but I agree with fzabkar that the component is most likely a power supply supervisor/reset chip.

author: fzabkar
author_rank: Super Contributor
timestamp: October 17, 2021, 06:26:58 pm
content: Quote from: jchw4 on October 13, 2021, 06:54:32 pmWhen you removed this IC, the output pad should have risen to +5V via the resistor and capacitor. AISI, if the capacitor doesn't charge, then it must be leaky, or the resistor must be open.

author: jchw4
author_rank: Regular Contributor
timestamp: October 18, 2021, 02:04:12 pm
content: Quote from: fzabkar on October 17, 2021, 06:26:58 pmYour idea was right, it's likely a supervisor.I cheked that it's output goes low when input is more than 4.7V.When I removed the IC device did not boot until I pu some low voltage on the IC output pin, so yes, it's voltage supervisor.Thank you! I soldered it back.Now, back to the fan problem.Quote from: Fraser on October 17, 2021, 10:23:45 amThis is an interesting idea, but after I recapped the device I set it to load test. With 30V 3A constant output device significantly heats up, but I did not see fan spinning.If they calculate wattage, it's definitely broken.Fan only spins in the very beginning when device performs tests. Actually, as I noticed that resetting main IC spins up the fan, it might be just a side affect that FAN PWM was not initialized while booting.Quote from: Kean on October 17, 2021, 11:34:01 amDoes it spin the fan? Could you check when it starts the fan? I think just one scenario that I could reproduce would be very useful!The fan is controlled by the 1Q25 (TIP41C) transistor next to to it. Which is controlled by 1IC12 (TL082CN) that you can find on my analog board photo above the transistor along the left board edge.Here is quick schematics:Fan (+) goes to unregulated CH1 12V (before the 7812 regulator).1R39 input goes directly to the pin 3 of the main IC (measured about 0.4 Ohm between them). So I am pretty sure this fan is directly controlled by the main IC.But I still don't know the soure for the temperature. I don't see any analog inputs of the main IC (so far all I traced were digital lines). It has a few digital output lines to the analog board, but I haven't traced them yet. Maybe it has digital inputs too? I did not get to the analog board yet, so I don't know.Upd: If you want to monitor fan PWM there are two convenient vias in the top right corner of the digital board to probe:

author: Kean
author_rank: Unknown
timestamp: October 18, 2021, 03:31:30 pm
content: Quote from: jchw4 on October 18, 2021, 02:04:12 pmI ran it for a couple of minutes with 100W+ load across Ch1 & Ch2 and the fan didn't come on. The heatsink was getting pretty warm.There is a good chance I have a similar fault. I will have a quick poke around, but I need to head home for the evening soon.

author: Kean
author_rank: Unknown
timestamp: October 18, 2021, 04:21:17 pm
content: I can confirm my fan spins for a few seconds if I power off and on again, but not if I leave it off for a few minutes. Then it just moves a few degrees. Fan PWM stays low even when the heatsink gets hot under load.All my power rails seem fine, but the regulators run quite warm - which is why the caps fail I guess.The weird problem on mine is that Ch2 voltage readout follows Ch1, and Ch2 current readout follows Ch3. But the channel outputs do work correctly as programmed.It is such a painful unit to work on I ended up putting it aside, but I did quite like it.

author: fzabkar
author_rank: Super Contributor
timestamp: October 18, 2021, 05:25:53 pm
content: Why not just run the PSU at a very low load and use a hair dryer to warm up the components? If there is a temperature sensor, that should find it, assuming it is working.

author: jchw4
author_rank: Regular Contributor
timestamp: October 20, 2021, 12:29:43 pm
content: The digital parts for the three channels are not symmetric. The per-channel microcontroller MSP430F1101A for the channel 1 has additional circuitry that I believe could be used for the temperature measurement.Assuming the SOT-23-3 parts with "BR" and "15" marks are NPN 2SC2412 (as suggested by Google) I traced it to:I haven't looked at the analog board yet.Hopefully somebody could suggest a suitable part number for the main IC 2U14.Upd:Added pullup resistor to pin 37.

author: jchw4
author_rank: Regular Contributor
timestamp: October 20, 2021, 12:39:26 pm
content: Quote from: fzabkar on October 18, 2021, 05:25:53 pmI tried it, but never succeeded. Either my heating was not enough (analog board is too deep and has too many components and wires), or I did something wrong.

author: Kean
author_rank: Unknown
timestamp: October 20, 2021, 01:31:05 pm
content: Potential candidate for 2U14 is something like AT89S51, S52, or C55 - these use an 8051 core.These match the pin layout you've drawn up for power, reset, and crystal. No I2C on pins 12 & 13, but that could be handled via GPIOs in software.These apparently require access to almost all GPIOs for flash programming, so it probably wasn't programmed in circuit.A pic of mine is attached in case you can decipher anything from it.

author: Kean
author_rank: Unknown
timestamp: October 20, 2021, 02:13:20 pm
content: OK, I traced out the circuit from pin 18 of J1 on the analog board. It appears that bridge rectifier 1D28 is used for temperature sensing of the heatsink. It has no connections on the AC pins.Edit: Schematic isn't quite right - see update below by jchw4

author: fzabkar
author_rank: Super Contributor
timestamp: October 20, 2021, 07:19:17 pm
content: 1D28 is reverse biased, so how does it do anything? :-?

author: Kean
author_rank: Unknown
timestamp: October 21, 2021, 07:17:58 am
content: Quote from: fzabkar on October 20, 2021, 07:19:17 pmI traced the circuit late at night, but pretty sure I got it right. Hopefully jchw4 can double check.Reverse biasleakagesaturation current of a diode can certainly be used for temperature sensing although typically only used when power consumption is an issue, but it also has a benefit in being non linear. We don't need much in the way of accuracy here, just want to know when cooling is needed.https://thecavepearlproject.org/2019/11/04/single-diode-temperature-sensor-with-arduino-icu-via-reverse-bias-leakage/Edit:I apparently should have said reverse saturation current, not reverse leakage current.See page 4 ofhttps://www.kennethkuhn.com/students/ee351/diode_characteristics.pdfStill this seems a strange technique to use in a potentially electrically noisy environment...

author: jchw4
author_rank: Regular Contributor
timestamp: October 21, 2021, 09:40:17 am
content: Quote from: Kean on October 21, 2021, 07:17:58 amI actually put it in exactly the same orientation as you did. But then there is fzabkar's comment.... Which seems reasonable. I double-checked everything but found nothing.And only then I looked at the labels on the bridge rectifier itselfLook at the photo, "+" is on the right and the key is on the right too. And KiCad's model has "+" on the first pinWhich means that pins are counted from the rightAs you can see on the photos, it traced to "GND" and +12V.So this is what I got:Here is my schematics:

author: Kean
author_rank: Unknown
timestamp: October 21, 2021, 10:34:36 am
content: Oops, I missed that GND trace dissapearing under the heatsink. I used some backlighting on the PCB and still missed it, but I can see it now I know it is there!I traced the 1R5 pull up to 1IC12 pin 8, which I was thinking was going to be 5V but I now realise I didn't verify that.Thanks for your work in drawing up the schematics. Hopefully my hints for 2U14 will help.

author: fzabkar
author_rank: Super Contributor
timestamp: October 21, 2021, 04:26:50 pm
content: That makes sense.The tempco of each diode pair is -4mV/C (-2mV per diode), so you should see the diode voltage drop as you heat it up.Edit:Would it be worth shorting the + and - terminals of the bridge rectifier to simulate a high temperature condition? Would the firmware see this is as a genuine high temperature event, in which case it should turn on the fan at full RPM, or would it detect the temperature reading as being out of bounds, ie a sensor fault?According to the manual ...https://bkpmedia.s3.amazonaws.com/downloads/manuals/en-us/9130_manual.pdf... "If the internal temperature of the power supply exceeds 80 °C, the instrument will protect itself by automatically turning power OFF. When this happens you will hear a buzzer and the display will indicate the following: Over Temp".

author: jchw4
author_rank: Regular Contributor
timestamp: October 22, 2021, 02:17:20 pm
content: Quote from: Kean on October 21, 2021, 10:34:36 amSorry, I did not have time to dig into it. Let's solve the fan issue first

author: jchw4
author_rank: Regular Contributor
timestamp: October 22, 2021, 02:19:24 pm
content: I don't understand how this circuit is supposed to work.(I verified that pulling up base of 2Q2 to +5V turns on the fan though.)2U8 has no way of talking to 2U14 except through the pin 10.(It has 3 incoming digital lines thath seem to be CS/CLK/DATA but all of them come from the outputs of the level shifter 2U13 (SN74LVC07A), so these cannot be used for output).Upd: this might not be true, see next message.2Q2 controls the fan. It is attached to the pin 10 of the 2U8 (MSP430F1101A,https://www.ti.com/lit/ds/symlink/msp430f1101a.pdf) which can be used as comparator output.So it's reasonable to assume that it is indeed wired to the comparator output.MSP430 has two comparator inputs: 11,12 which both could also be used for GPIO.Pin 13 could be either auxilary clock output or GPIO.Comparator is explained in the chaptor 16 of the user guidehttps://www.ti.com/lit/ug/slau049f/slau049f.pdf.It can compare either its two external inputs, or compare one of them to the internal reference (selectable [0.25 x Vcc], [0.5 x Vcc], or "or a fixed transistor threshold voltage of ~ 0.55 V").Vcc in our case is 2.5V, so it should be 0.625V, 1.25V, and 0.55V.I tried to simulate the circuit for the temperatures 25C and 85C as two possible edge cases:For all pins 11,12,13 input voltages decreases when temperature rises.Threshold 0.5 x Vcc = 1.25V is too large for any simulated input.Threshold 0.25 x Vcc = 625mV is barely crossed by pin 13 input around 25C (which is not a comparator input anyway) and pin 12 input, but now close to 85C.I think this does not work, because by the time this sensor reaches 85C other parts will be cooked.Another question is "why make that complicated circuit to start the fan only at about 80C"?MSP430 manual suggests doing "precision slope analog-to-digital conversions".There is actually a ceramic capacitor 2C31 which potentially could be used for that purpose.Playing with random pulses in the LTspice I could make it cross 550mV threshold at about 35C:I used 10uF capacitor for simulation, but I later measured it in-circuit 100nF. (by DE5000 at 100kHz)It is also possible to make it work with the 100nF cap:But it looks weird. Pulse width 0.0002ms suggests system clock at least 5Mhz, but this MC has only 4.096MHz crystal.Also I ccould not see any change in behavior when setting pin 13 to either 2.5V or 0V. It does not seem to affect anything.Ok. I powered the device that I am repairing and measured:- Pin 11: 816mV- Pin 12: 685mV- Pin 13: 570mVwhich is very close to the static simulation above of 900mV, 755mV, 624mV.I did no see any activity on these pins.Could somebody help me understand how this sensor circuit is supposed to work?

author: jchw4
author_rank: Regular Contributor
timestamp: October 22, 2021, 02:29:38 pm
content: Quote from: fzabkar on October 21, 2021, 04:26:50 pmThis is a very nice idea! Yes, it beeps and starts the fanHm, I wonder how it detects simple "start the fan" vs "overheating, beep"? I am probably missing something in my tracing, because I thought that MSP430 has only one way of sending data to the CPU and its via 2Q2. Which only starts the fan but does not beep....

author: Kean
author_rank: Unknown
timestamp: October 22, 2021, 03:36:30 pm
content: I won't have time to look at this again for the next few days, but another thing you can try is shorting out just one of the diodes instead of both, i.e. one AC pin to one DC pin instead of both DC pins.

author: fzabkar
author_rank: Super Contributor
timestamp: October 22, 2021, 05:51:55 pm
content: I'm wondering about the function of 2Q1.When 2Q1 is switched on, the voltage at pin 12 is 685mV. When it is switched off, the voltage rises to 695mV. I thought this may be some kind of hysteresis, but that doesn't make sense because hysteresis could easily be implemented in the firmware, could it not? It might be instructive to see whether 2Q1 switches off after the diodes are shorted.What is your ambient temperature?As I see it, the tempco at the diodes is -4mV/C, so the tempco at pins 11 and 12 would be -3mV/C and -2.5mV/C, respectively.You are currently seeing 685mV at pin 12. Your two reference voltages are 550mV and 625mV. The differences are 135mV and 60mV. These represent temperature differentials of 45C and 20C above ambient.Edit:I see some sources which state that the tempco at low currents can be typically -2.4mV/K.

author: jchw4
author_rank: Regular Contributor
timestamp: October 25, 2021, 01:51:30 pm
content: I attached my HP 66311B in parallel with the diode. This old HP can sink current, which is very handy here.So when device boots at my ambient 26C, sensor output sits at about 1.116V.Pin voltages:- 2U8(11) 832mV- 2U8(12) 699mV- 2U8(13) 580mVFan starts to spin (PWM 25%) when sensor output is about ~982mV.Fan goes full speed when thansitioning from 953.6mV to 949.5mV (the discrete step of my 66311).It beeps when sensor reaches ~805mV.

author: jchw4
author_rank: Regular Contributor
timestamp: October 25, 2021, 01:58:31 pm
content: To really investigate how it works I had to go find a real scopeThe first screenshot shows the fan start sequence:Zooming in to the beginning:The right part (fan still runs at 25% PWM):Pin 13 seems to have software control:When pin 12 fully goes under 650mV threshold fan goes full speed:Overheating signal:Overheating still puzzles me. Screenshots have all the noise filtered out, so it probably detects overheating when comparator "significantly agrees that PIN 11 is below Vcc x 0.25.

author: jchw4
author_rank: Regular Contributor
timestamp: October 25, 2021, 02:03:41 pm
content: I attached thermocouple next to the temperature sensor and loaded the device with 90W.Ambient 27C. While device was heating I wrote down some measurements:Sensor temperature 29.8C gives 1.1425V sensor voltage.33C 1.132V34C 1.129V35C 1.125V36C 1.121V38C 1.111V - Stable tmperature (Here I switched the load off for some time and waited for the temperature to stabilize.)40C 1.104V40.6C 1.100V - Stable temperature45.3C 1.082V - Stable temperature50.1C 1.062V - Stable temperatureI did not risk heating it more because my thermocouple does not have good thermal connection to the heatsink.So it seems to match the simulation above. Which means that all the parts function correctly.I still don't understand the designers intention for chosing these thresholds.

author: jchw4
author_rank: Regular Contributor
timestamp: October 25, 2021, 02:07:54 pm
content: Now we need to do something to make it work.Simulation says that changing 2R10 to something about 1.8k should bring down start temperature to about 31C.It would be nice to add some resistor in parallel instead of replacing this SMD resistor.(There is a very handy unpopulated 2C32 in parallel to the 2R10 that could be replaced with a resistor.)Resulting 1.8k would require 5.4k. I had 6.8k and tried it.And it did not work. Double-checking eberything revealed that Pin 11 is very close to Vcc.In fact Pin 11 to Vcc measures 10Ohm for me now (when power is shut off).So I probably killed this pin somehow.Still don't know how I did it.Ok, I cut the trace to this pin and it is alive!Putting load on the device showed that fan started at about 27C (thermocouple losely attached to the heatsink next to the sensor), and it went full speed at 31C.Putting 176W load on the device thermocouple temperature stabilized at 49.6 (26.1 ambient). Which is probably good enough.Adding my 66311B as a sensor revealed that "overheating" never occurs, so it is indeed Pin 11 resiponsible for this

author: jchw4
author_rank: Regular Contributor
timestamp: October 25, 2021, 02:09:14 pm
content: Well, I don't really know what to do next. On the one hand it works fine and probably will never overheat.On the other hand it would be nice to fully restore it.Maybe I should check whether the two other MSP430 controllers have this feature, so I could just exchange the fautly MSP with the one from another channel.But this will require good soldering tools that I don't have.It would also be nice to dump the firmware and replace this chip with the new one.Both of these options are probably too much work for me now, so I will probably leave it as it is.

author: fzabkar
author_rank: Super Contributor
timestamp: October 25, 2021, 05:18:57 pm
content: I was going to suggest connecting a pot across the diodes to vary the voltage. It probably would have been a safer approach. :-(

author: Kean
author_rank: Unknown
timestamp: October 26, 2021, 02:27:09 am
content: Thanks for all the research into the fan control jchw4. I'll try a similar mod on the fan temperature control.Apart from this PSU being a pain to work from, the big problem people seem to have with it is the caps prematurely failing - presumably a factor of poor cooling.Now I just need to work out why I now get mixed readout between channels on mine

author: jchw4
author_rank: Regular Contributor
timestamp: October 26, 2021, 04:40:31 am
content: Quote from: fzabkar on October 25, 2021, 05:18:57 pmThe MSP430 input is protected by 1k resistor from the sensor. So I doubt it was an issue. I think I probably shorted the test wire that I soldered to the pin11 itself after I disconnected the scope.But I did not notice anything.Well, it happens

author: jchw4
author_rank: Regular Contributor
timestamp: October 26, 2021, 05:39:13 am
content: Quote from: Kean on October 26, 2021, 02:27:09 amI cannot promice to make a schematics of it, but it is connected like this:ADC 2U5, 2U6, 2U7 are connected to the main IC 2U14. They share the same serial bus.ADC pins are connected like this:(5) - Serial clock in (shared)(6) - Serial data out (shared)(7) - ~CS (not shared)(19) - ~RESET (shared)(20) - ~INTERRUPT out (shared)(23) - Serial data in (shared)2U13 controls communications with all MSP430 and RS232 TX.2U14 controls communications with ADCs.So in your case something could be broken in these CS lines.I did not trace it too far (as this part works for me), but I hope my tracing image will help you.

author: Kean
author_rank: Unknown
timestamp: October 26, 2021, 06:00:38 am
content: Quote from: jchw4 on October 26, 2021, 05:39:13 amYes, maybe a damaged CS signal for channel 2. Great suggestion! I hadn't really studied how it was all connected, so that info is much appreciated.