Check the voltage across the zener diode at VR1. If it's lower than 7.8 volts, replace it.

Yes, if I measure 7.8V or less across that zener diode I replace it. The voltage across that zener is kind of used to determine if power is good at startup.
Measure the voltage directly across the zener diode (one meter lead on each zener leg).

On.
Your measurements said there's 7.76V across it (12.9 - 5.14).
I was just saying to measure directly across the zener to see how much voltage is across it.

There's plenty of online info about zener diodes. Essentially when they're connected in reverse, at a certain voltage (spec of the specific zener diode) they conduct. This makes them suitable in simple voltage regulator circuits - remember that 13V zener in your bench power-supply you were building at the start of the year?

The spec of the VR1 zener on the Bally/Stern MPU board is 8.2 volts. But I've seen plenty of them running around 7.8 volts and at that voltage, the boards don't like booting from some bench power-supplies.
To be honest if you leave that zener on the board it will probably work fine in game due to the rate that the supply rails reach steady levels - different rate to bench power-supplies.

What happens if you pull out the 5101 RAM? Do you get the flicker every power-on?

When the board doesn't boot, what voltage do you read at the reset pin of the CPU (Pin 40 of U9)? If you then very briefly short pin 40 to pin 39 on the CPU, does the board boot?

Is that replacement Q1 the right transistor?

Looks like you'll have to test the resistors/transistors/diodes in that "valid power detection" circuit.
The schematics have a couple of voltages in that circuit listed.

Also, temporarily disconnect capacitor C13 and see what happens.

Yes, it's a 50nf capacitor. The original value is 10nf.

Did it seem to make much difference?

Have you got a 2N3904 to replace Q1 with?
Does R138 and R140 measure good?
How about the diodes at CR5 and CR7?
Is the big R11 resistor good?

Check them in circuit. If they measure out of spec then investigate further.

Change that C13 capacitor to original spec. Its larger value isn't helping because it's delaying the 5V reference state used for the reset.

If you feel like delving in, pull out the oscilloscope and enable dual channel mode.
Connect one of the scope input leads to the banded side of zener diode VR1
Connect the other scope input lead to the banded side of diode CR5
Take a snapshot of the signals the moment you power up. Lets see the relationship between the rise time of the 12V line and whether the 5V reference state used for reset has stabilised.

Compare the result to your working Stern board.

Adjust the vertical position of the traces so that zero volts is on the first grid line at the bottom of the screen. Since you're measuring positive DC voltages the trace shouldn't go downwards so this gives you the full screen for better resolution.
When you're measuring AC voltages, then have the zero volt traces running in the centre of the grid.
See how you go about getting the vertical controls working again.

Someone has changed R12 to a blocking diode for an external battery. Actually I do the same thing but use a 1N5817 diode which has very low voltage drop. Since there's no battery currently on your board, the other end of that diode is going to an open circuit.

Yes, give it a quick try tomorrow.

It doesn't have a store settings button that's stuck?
Is there anything in the menus about restoring factory defaults?

If you press the Utility button and go to the System Info menu, what firmware version do you have loaded?

The latest Hantek firmware appears to be dated 25-Jan-2019

Carefully pry the plastic IC socket cover off. It will expose all the socket pins pins and you'll be able to see what condition they're in. Lever your screw driver off U15. Don't twist screw drivers under the socket against the PCB because it will damage traces. Lever off a close by IC.

Do the same with the socket at U8 and U11 and inspect their pins for corrosion.

Sorry, I meant U7 where the 6810 RAM is.

Actually that's how I remove those sockets when I replace them. Pry off the plastic cover then heat each pin one at a time and pull them out with my fingernails
Pretty much no risk of damaging traces provided you only start pulling the pins when you feel them moving in the molten solder. It takes me about 20 minutes to remove all the sockets on a board like that.

Good luck with the oscilloscope - I hope the supplier resolves the issue.

Heh, sometimes they bite for a split second but it's not that bad. It's not for everyone..

I always remove the components in the corroded area, clean the corroded copper traces with acid and tin them with solder to put some "meat on the bones" and protect the copper. Replace all IC sockets and pin headers - very rarely do those boards need any follow up diagnosis, they usually work first go.

I see in your picture above some of the components in the "valid power" section have stale solder and tarnished copper pads. The components previously replaced before you got the board weren't cleanly solder attached to the copper pads.
Shine a bright light from behind the board and closely inspect the pin area between the U8 socket and the board to get some idea of the work previously done and the current condition.

Look at the solder joint on the right leg of the big R11 resistor. Is it making contact?

To be honest, I'd remove those components in that area and clean then resolder tin the copper pads the components should be soldered to and install new components. If you feel this is too much work then at least reflow all those components for now (both top side and bottom side of the board) to see if it resolves.

Pop the socket covers off and look at the state of the pin receptors.

Don't worry about the solder pads falling off the copper pads - it seems common for those late 70's Bally MPU boards. Just clean the copper pads and flux/retin with solder.

You might have had some solder still attaching that pad to the header you were removing, so the pad pulled when you removed the header. Or if it was the other side, maybe too much heat for too long as Mark said or too much aggression with the solder sucker.

If you're going to replace the components in that valid power area of the board, just cut them out and remove the leftovers like you did with the CPU socket.

I feel your pain. The Stern boards were better chemically treated before they were solder bathed.
Sometimes I'll try to desolder pin headers on a particular MPU board and the solder just doesn't want to clear effectively. In those cases I'll switch to using an iron to heat the pin and pull the pin out from the other side with pliers when the solder and plastic melt.

The problem you may experience with this board is getting new solder to attach to the tarnished copper pads which might need to be cleaned beforehand - more work..

You're not using a desoldering gun to clear the holes? It helps to add a touch of solder to the pads before sucking.

No way to get the pin out with tweezers?
If you have a faulty chip, cut one of the legs where it comes out of the plastic and solder it onto the broken pin stub on that Stern ROM.

Question is also whether reseating the ROMs essentially got it working - i.e. one of the ROM sockets suspect?

Essentially what we were trying to see is whether the board was releasing the /RESET signal to the CPU (so it could wake up and start to boot process) when in fact power was detected as "valid" or not.
The waveform snapshots you took the other day showed the same initial behavior between this Bally board and the Stern board. But we need to go further.

Note you're getting a hell of a lot of noise on the blue signal (banded side of diode CR5). Maybe a grounding issue with the scopes probe?

Hook up one of the scope probes to pin 40 of the CPU which is the /RESET line. Hook up the other scope probe to test point TP5 on the MPU board which is the 5 volt rail. What we want to see is when the /RESET line is released and goes from zero to 5 volts, that the 5 volt power rail is already steady at 5 volts. In other words, when the CPU is told to wake up and start running it must occur after power is stable. Otherwise the CPU will startup unpredictably and could cause solid LEDs on power-ups.

If you want to be creative, desolder that pin receptor, pull it out of the socket, reshape it and put it back in. Yes I've done this before...

See pic below: The chip was a bit rough but you get the idea.

I always add a spot of new solder then suck it out with the desoldering gun.

Sounds good. Sometimes those test point are so tarnished, getting a good connection can be tricky.

Yes if that's easier, hook up the probe there to R139.

Score!
IMG_0056a.jpg

Ha! too late, been sniffing too much solder flux and acid fumes from these boards

Phew, that's a relief that you got to the bottom of the problem. Looks like those suspect ROMs are Lectronamo/Nugent PROMs.

Did you accidentally flick the x10 switch on the scopes probe? Or do you have some other setting on the oscilloscope for amplitude division/correction?
When you connect both the blue and yellow probes to TP5 on the MPU board, they should obviously read the same voltage.

The scope pics are interesting. I wonder if it was just a glitch or if there's something relevant about that blue skinny line spike on the Bally /RESET line.

Well, the snapshot images don't tell you the moment you powered on the system. You probably need another snapshot of the 12V rail vs the R139 /RESET line. The moment the 12V rail starts to rise tells you when you applied power and then see how long it takes for the /RESET line to release and go high.

By the way, incase you don't know, when you see signals on the schematics with a line over them, the line indicates those signals are logically active low, ie. they are active when at zero volts. So when I type a forward slash "/" in front of RESET, I'm indicating that reset signal is active low. When the reset signal goes to logic high (5 volts) the system is no longer in reset mode.

Oh dear, I thought I was the only one still using a CRO (Cathode Ray Oscilloscope)!

I think you already have

I just looked up the Motorola 6800 CPU datasheet. With respect to the speed that this CPU runs on these boards, the calculation says the CPU must stay in reset a minimum of 16us (micro seconds) after 5 volts has stabilised, so the 8ms you're measuring is plenty of time.

If all the potentiometers are the only front panel items not working then look for common signals to them all and back trace.

Might be worth disconnecting the flat ribbon cable to the front panel board and reconnecting it.
To do so lift one side of the black cloth tape holding the cable to the female receptor.
On each side the receptor there are brown tabs. Push the brown tabs outwards (towards the cable) about 1/16" and then the flat cable will be free to remove. Resinsert the cable and push the brown tabs back into position to lock the cable in.

So the common signals from the pots go to the chip at location UF2 which is a 74HC4051. Google the 74HC4051 datasheet and look up what the pin functions are to try and get some sort of idea what its purpose in this circuit is.
Note, UF2 on that diagram is split into two parts. You've highlighted "UF2A" and if you look above it one of the four yellow blocks is "UF2B".

Do you remember whether the other switches connected to U2 still worked? i.e. is anything hooked up to U2 working?

There's a function table in this datasheet for the 74HC4051 which can give you an idea what it does and if there's anything common to the signals not working.
https://www.onsemi.com/pub/Collateral/MC74HC4051-D.PDF

Thanks for that Mark, you saved me some typing
Bob, now with that info and the fact that X4, X5 and X6 at U2 are having problems (X7 isn't connected), do you see anything that's common to them based on the function table in Marks picture?

Do you remember if any of those push button switches on the pots still worked? because they have U2 X5 connected to them.
Actually they are not pots (potentiometers) at all. You'll notice you can freewheel them 360 degrees so they're not variable resistors with a start and end position. Those things are what's called "incremental encoders". Put simply, their pins digitally indicate which direction you're turning the rotary control.

In that case, U3 is probably ok.

Correct, U1 controls both U2 and U3. Your next mission is to download the datasheet for U1 "74HC393" and see what it does

Pin 9 being held low could be U1 pin 5, BUT U1 pin 5 also goes to U1 pin 13 which then controls U3. Since we presume U3 is working ok, the problem might potentially be the input pin 9 of U2.

In this circuit, pin 6 of U2 and U3 never go high. The circuit is designed so those two chips are always enabled by tying their active low "enable" pins to ground.

Nope, the terms LO and HI refer to logic levels. The red clip is just the logic probes power lead so connect it to the power rail of the logic circuit.
Have a read of the below link which explains logic levels (OFF or ON, 0 or 1, Low or High) and how voltages levels translate to logic levels for TTL and CMOS devices. Because logic levels are a little different between TTL vs CMOS chips in the middle voltage range, this is the reason for the switch on the logic probe so it can better determine what's "LO" or "HI" (low or high).

https://learn.sparkfun.com/tutorials/logic-levels/all

In the old days it was easy. Logic chips with part number starting with "74" (74 series) were TTL chips. Logic chips starting the "40" or "45" (4000 or 4500 series) were CMOS chips.
The funny thing is the part number for the U2 chip is a 74HC4051. This part number is an amalgamation of both 74 and 4000 series chips. The function of this part was originally sold as a "4051" back in the day.

https://en.wikipedia.org/wiki/List_of_7400-series_integrated_circuits
https://en.wikipedia.org/wiki/List_of_4000-series_integrated_circuits

Sorry for the information overload..

Looking at the front panel schematic basically indicates the oscilloscope panel switches and incremental encoders are all hooked up to U2 and U3 in a switch matrix scenario. I'm not sure how familiar you are with the switch matrix on the early Bally/Stern games?

U3 sends the "Strobe" signals to the panel switches, U2 receives the state of the switches being strobed. The difference between the switch matrix on this panel and the switch matrix in those early pinballs is the oscilloscope panel reports one switch at a time (serial data) meanwhile the pinballs report 8 switches at a time (parallel data).
Besides power to U1, U2 and U3, only 3 other signals are used to interface all those switches/encoders to the main processor board in the oscilloscope.
The three signals are:
FPCLR to pin 2 and 12 of U1 which indicates to start reading from the beginning of the switch matrix.
FPCLK to pin 1 of U1 which moves to the next switch/encoder to read.
FPMUX from pin 3 of U2 goes back to the processor board with the state of the panel switch/encoder just read.

I don't think the logic probe will work on 3.3 volt logic circuits anyway. If you have one of the common 610 logic probes, minimum voltage is 4 volts.
You might need to use your other oscilloscope.

See if you analyse pin 3 of U2
Also pick one of the three rotary encoders and analyse the three pins near each other. Do the outer pins voltages change when you rotate its knob? I suspect you should see activity on the middle pin pulsing low which should be the strobe pin.

If it comes to attempting repairs, are you in any position to be able to replace U2? before shipping costs, 74HC4051 are less than a dollar.
Having said that, I think it might be too early to be attempting repairs in terms of replacing parts - what if they ask for the faulty unit back?

I'm impressed! that's pretty good.

I've drawn the switches in the matrix setup below:

The CLR signal from the mainboard forces the A, B, C signals to U2 and U3 to go low (zero volts) which switches X0 to the X pin on both chips.
At U3, this causes X0 pin to connect to ground via the "X" pin.
If the first switch is closed (top left corner), the X0 pin at U2 will be connected to ground so the mainboard will read logic low (zero volts) on the U2 X pin (FPMUX signal). If the switch is open the mainboard will read a logic high (the FPMUX signal has pull-up resistor (10k ohms) to 3.3 volts on the main board).

The mainboard then activates the CLK signal to switch U2 to the X1 pin (via the A, B, C pins) so it can read the state of the next switch. After a few CLK ratchets when U2 is at X7, the next CLK signal activation rolls U2 back to selecting the X0 pin. At the rollover, U3 then moves to the next pin which is X1.
So in the matrix, the top left switch is read at the beginning of the process and each CLK then goes down the column. At the end of the whole process which is 63 CLK signals later, the last switch on the bottom right has been read.

This process probably happens hundreds of times a second. FYI relating this to the Bally/Stern MPU boards they perform this process 120 times per second. Difference is they read eight switches at a time.

Do you have a soldering hot air gun? You'd be surprised how easy it is.

Oscilloscope_FrontPanelSwitches.png

Cue Pink Floyd?

U2 pin 4 (X7) isn't connected to anything that I can see on the schematic. So that waveform is probably residue you're seeing coming from the U2 pin 3 "X" pin back from the main board.

Can you take a snapshot of the CLK signal at U1 pin 1 showing the full cycle of 63 odd ratchet clicks?
Essentially what you need to do is use the CLK signal as your trigger reference, then with the other oscilloscope channel record the U2 pin 3 (FPMUX) signal.
At the 5th and 7th CLK ticks, the FPMUX signal will indicate the state of the two "Volts/Div CH2" encoder bits. Rotating this encoder should change the state of those bits during the read switch process.

However I understand this is going to be difficult to achieve with only 2 hands and limited access..

Please jump in if you have some extra insight or need to correct me

What we're looking for is the CLK signal being idle, then it pulses 63 times then goes idle again. That's the full cycle. This is the theory.
So you may have to adjust the Sec/Div to fit all those CLK pulses in on the screen.

I count 50 CLK ticks. Try taking the recording another few times. If there is no idle, then as soon as it finishes reading the last switch it goes straight back to read the first switch.
Can the scope go down to 4.00us SEC/Div? That should fit it all in - will be difficult to see the transitions though.

If there's no idle time then the only way to know when the read process is at the beginning is when the CLR signal pulses high (U1 pin 2).

Thanks Mark, I actually don't have a digital scope so that info helps. I presume Bob will be able to zoom in time wise on the recording?

BTW, change the time base to 4.0us, not 400us.

At 4.0us Sec/Div, how many "screen fulls" of data could it record?

Is the recording long enough to determine how many CLK ticks are occurring before it goes idle again?

The purpose of capturing the CLK signal was to be able to determine exactly when the scope wanted to read the incremental encoders.
If we can't do this effectively then maybe need to try another crude approach.

We know that when the "C" control signal at U2 pin 9 goes high, the scope is in the phase of reading the incremental encoders. So using U2 pin 9 going high as the trigger, what happens on the FPMUX signal at U2 pin 3?
You're going to need to connect both oscilloscope probes. Ch1 on U2 pin 9 and Ch2 on U2 pin 3.

The problem with this approach is we don't know which encoders data we're looking at.

Yes both at the same time, because when U2 pin 9 goes high that's when one of the encoders are being read (with this approach we don't know which encoder). So we're looking at what info is coming out of U2 at that time. The encoders should be reporting a mixture of open and closed switches going into U2.

What about a third probe? (I'm not kidding ). How gymnastic are your fingers?

Ext Trigger input connected to the FPCLR pin 2 of U1. This tells the scope and us when the read process is beginning and to start tracing.
Ch1 input connected to the FPCLK pin 1 of U1 which we can use to tell us which switch is being read at a certain point in time.
Ch2 input connected to the FPMUX pin 3 of U2 which tells us the state of the switch (or encoder we are interested in) being read.
Somebody rotates the first encoder (Volts/Div CH2) and we watch if the switch state out of U2 is changing.

Getting complicated huh?

Answering your previous question, voltage on channel 2 make it the same as channel 1, time base probably around 24us.

Let me book a super jet now and I might make it in time..

Hey,
Have a look at the diagram I drew on the following post which shows all the switches configured in the matrix. I left off the U1 chip that controls both 74HC4051 chips.
https://pinside.com/pinball/forum/topic/mpu-100-don-t-boot-on-first-try/page/3#post-5284901

If you download the schematics Bob linked and mentally put U1 from page 7 onto my diagram, you should get an idea how the switches are read and that it takes 63 clock pulses to go through the matrix.

https://www.mikrocontroller.net/articles/Datei:Hantek_Tekway_DSO_MSO_hw1007.pdf

The assumption has been that the CLK signal we're trying to measure, pauses at the end of each 63 cycles which may or may not be true.
If yes we have some way of knowing when the process starts and when each switch is being read.
If not we need to trigger the scope on the "CLR" signal going to U1 to know when the circuit is being reset to read the first switch state.

Bob needs more hands to hold all the probes in place or find a way to connect them to the board by soldering wires to the pins being probed.

At the end of the day, there's 3 surface mount chips controlling these switches/encoders and U2 on the board is the first suspect with its "C" input pin potentially not working.
One way or another Bob probably needs to replace it and if unsuccessful maybe the other chips. If replacing the 3 chips doesn't fix it then it's potentially an issue at the FPGA 1 chip on the main board which could mean it's game over.

Kind of, you're getting external activity on U2 pin 9 coming in, but internally, U2 pin 9 might be open circuit - this is the assumption since U2 pin 9 needs to go high to pass the rotary encoder signals through.

The waveforms you posted for U2 pins 11, 10 and 9 all look good to me. You should notice that pin 11 is switching twice as fast as pin 10 who is also switching twice as fast as pin 9.

Essentially, the way U1 is wired yes. But your U3 pin 11, 10 and 9 pin waveforms don't look right. They're not uniform like those from U2. Now the U3 pins 11, 10 and 9 are controlled by the same U1 signal (pin 5) driving the suspect pin on U2 pin 9.

Download the U1 "74HC393" datasheet. Have a quick read of the description and then look at the function table which will tell you what happens on the outputs with each active CLK signal change. This chip is designed to change outputs on the falling voltage edge of the CLK signal. We call this a falling edge triggered clock. A logic high voltage on the CLR signal on this chip resets all outputs to logic low voltage state. i.e. when this happens both U3 and U2 are connected to the very first switch in the matrix.

https://www.ti.com/lit/gpn/sn74hc393

Hot air guns aren't that expensive but you can do this with a soldering iron. My method back in the early 90's was to solder the corner pins so the chip is held in place, then flood solder over all other pins. Using the thinest solder wick, remove any solder bridging the pins. It actually worked quite well with nice results. Flux helps a lot with this because it makes the solder less likely to bridge when you're cleaning up excess with the solder wick.

Of course you need to remove the chip first, probably cutting each pin with a sharp pointy nose cutter then remove the remaining pin debris with your soldering iron and solder wick.

Pins 1 and 2 of U2 connect to the rotary encoders which are reporting their bit positions. While the activity looks unusual, they should be changing.
Pin 5 goes to all the push button switches on the encoders. Since you're not pressing any of them, they are all responding with open circuit. Press a few of the encoders push button switches while analysing pin 5. Does the waveform change?

Bob, see the two diagrams below.
I've configured both the U3 and U2 A,B,C input pins - refer to the function table.

First picture shows U3 C,B,A pins configured as Lo, Hi, Lo respectively. This makes U3 internally switch the X2 pin to the X pin which is grounded. So in the switch matrix, you can see the column of switches on X2 are now connected to ground.

U2 C,B,A pins are configured as Hi, Hi, Lo respectively. This makes U2 internally switch the X1 pin to the X pin which is then sent to the mainboard via the FPMUX signal. So in the switch matrix you can see the row of switches which are now connected to U2 X1.

The junction point of these two selected column and row lines is the front panel switch "F0" (Function 0).
If the F0 switch is being pressed, then the FPMUX signal reports logic low zero volts to the mainboard that the switch is closed.
If the F0 switch is NOT being pressed, then the FPMUX signal reports logic high 3.3 volts (via the 10k pullup resistor) to the mainboard that the switch is open.

U1 controls the state of the A,B,C input pins to both the U3 and U2 chips. U1 is controlled by the mainboard which via the CLK signal steps through the switch matrix.

The second picture I've configured the U3 and U2 A,B,C input pins to look at one of the rotary encoder lines of the "V0" control.

Oscilloscope_FrontPanelSwitches_1.png
Oscilloscope_FrontPanelSwitches_2.jpg

Can you post a more closeup clear picture of U2? It almost looks like some of the pins on the left side aren't soldered properly.

When you're not sure of the package type, download the datasheet - you'll find details there:
Your dimensions roughly match the "TSSOP-16" package.

.
74HC4051.jpg

It's a TSSOP-14 package. The "PW" letters is Texas Instruments way of including TSSOP-14 to their part number which for them becomes 74HC393PW.

On a quick look I like the Nexperia brand parts which have low capacitance. You should be fine with the two Texas Instruments parts you linked from Mouser.

But gee they're pretty small. I hope you've got a decent magnifying glass.

I'm listing these 4051 grouped by type:

These two are 74HCT where the 'T' indicates they are TTL version and only run at 5 volts - you don't want these.
https://www.mouser.com/ProductDetail/771-74HCT4051PW
https://www.mouser.com/ProductDetail/771-74HCT4051PW-T

These two are 74LV where the 'LV' indicates they are low voltage version (between 1 and 6 volts) you don't want these.
https://www.mouser.com/ProductDetail/771-LV4051PW112
https://www.mouser.com/ProductDetail/771-74LV4051PW-T

These two are 74HC (same spec your board has) which is what you want. They are identical, the only difference is how they come packaged from the supplier. The first one comes in tubes and the second one '-T' comes in tape reels. Choose whichever. The tube ones will probably be easier to store away.
https://www.mouser.com/ProductDetail/771-74HC4051PW
https://www.mouser.com/ProductDetail/771-74HC4051PW-T
.
.
Ditto for the 393 parts, you want 74HC only - first one is tube, second one is tape reel.

https://www.mouser.com/ProductDetail/771-HC393PW112
https://www.mouser.com/ProductDetail/771-HC393PW118

Since their cost is peanuts get some Texas Instrument ones too.

Funny I was looking at buying those a month ago but got something else and not sure I made the right decision. If you get them I'll be interested on your thoughts. It's got more than enough zoom I think.

By the way, I find soldering these small things outdoors in daylight helps a lot with visibility - best light conditions..

ChipQuik seems to be a brand of a range of products. Which one are you referring to?

If it's not too late get the thinnest solder wick you can. My personal experience is I always found it performed better for dealing with surface mount stuff - it robs less heat from the iron and is easier to manage. The wick I've always used is about 1mm thick.

I put the chip into position, push down on the chip say with a screw driver so it doesn't move, put some solder on the iron and then iron onto a corner leg so it attaches to the board. Inspect the chip positioning to the PCB pads and once I'm 100% happy it's centered, do the opposite corner leg. If positioning is still good then solder the rest. Otherwise adjust if necessary til it's right before doing all pins.

Great idea!

Interesting.
You'll be an expert in no time

Yeah, this is the problem with some of them.

Yes! Flux is your friend with surface mounts.

Well at least it looks like you got the same brand 4051 as the original.

Beautiful! Easier than pulling pin headers off Bally MPU boards?

I bought a pair like this:
ebay.com link: itm
You can install one or two lenses (they're large) to get more zoom options, but they get a little heavy so you have to tighten everything to stop them drooping:

This ones very similar to yours but also includes lower zoom lenses - they're harder to find in online stores though:
ebay.com link: itm

Use the same method with the small caps/resistors. Add flux. Add some solder to the iron tip, hold the component in place with tweezers then touch the joint with the iron tip.

The chip soldering looks great!

I'm hoping you're giving others watching the confidence to try surface mount and not be intimidated.

If you're having trouble, I'd let it go since they're electrically the same connection. Last thing you want to do is overcook the chip with the iron.

Are you ready to turn this thing on? Clean up the flux and verify there's no solder whisker shorts across any other pins first.

There is one way to find out... That is if you're prepared to swap boards with your new scope..

We never quite got into that detail to see what those lines were doing when we were hooking up your scope to those lines.

Test them all in circuit with your multi-meter.

Just out of curiosity, (scope off) if you measure the resistance on one of the encoders between the middle leg and either side leg, does the reading change between open circuit and closed circuit as you rotate the encoder?

I count 7 transistors and they're all located on the back side of where the LEDs are.
[EDIT] Oops, there are 8 transistors.

Set your multi-meter to low resistance mode.
Put a meter lead on the middle encoder pin "C", put the other meter lead on the "A" pin. You should measure either short or open circuit. Rotate the encoder slowly and you should see the state of those two pins alternate between short and open circuit.
Do the same between pins "C" and "B" - should get similar behavior.

Oscilloscope_FrontPanelSwitches_3a.jpg

Schematic might be a previous model, the transistors are probably MOSFETs switching the LEDs.

No, see the animation showing how the outputs change as the encoder is turning here:
https://en.wikipedia.org/wiki/Incremental_encoder

Imagine a "1" is when the pin is shorted/connected to the "C" pin, and a "0" is when the pin is disconnected from the "C" pin.

If you rotate these two encoders, does the OL reading go away?

The encoders click as you turn them right? These are 12 position encoders according to that schematic you linked.
Data sheet says closed circuit resistance is maximum of 3 ohms. So you should be seeing closed circuits as you slowly rotate the encoder.

Datasheet for the encoder is here - there's no mention of how the switching occurs as you rotate other than it's not optical - presume it may be magnetic/reed?:
https://www.mouser.com/datasheet/2/54/bourns_pec12-1159230.pdf

Hmm, well do you feel like hooking it back up and powering on. Then toggle a short with a screw driver a few times between pin A to pin C on one of the encoders while watching the display to see if there's any reaction? Choose an encoder that would normally make an obvious change.

BTW, have you ended up replacing all 3 SMT chips or is there still one not done yet?

Wow that's cheap. Might be worth asking for the flat ribbon cable too.

Since you're invested in your current board, you may as well swap the last SMD.

When you pay via paypay, the receivers account is based on their email address registered with paypal. To be honest them using a hotmail account doesn't surprise me much.
They probably have cheaper shipping options so long as you don't mind waiting a little longer.

Boo!

It's been a valuable thread. Even I've learnt from it.

Bought yourself one of those practice surface mount kits yet?