Fluke 5440A repair

[Rax]

Alright, we have good working extender cards. Yeah!

Now, as I'm going ahead with the SM steps, a couple of confusing points I would appreciate some thinking along with me:

• What should be the default state of the troubleshooting switches? I am referring specifically to those on A2 and A16. Mine were all in the OFF position (which seems to be tagged as "1" by the troubleshooting switches schedules notes, which is quite counterintuitive). See pic for how I found them.
• At p.4-31, section 4-28, step 3 calls for S1 to be switched to "0." I assume this to be the Controller S1 (A16). This though has four different sections. Does this mean it needs to be closed circuit ("0") on all four sections?...
• Step 5 is clearer, where I guess all sections need to be in the way they spec - first, second and fourth closed circuit, third open.

Am I reading the above correctly?

[Rax]

My working hypothesis is all four sections of the switches need to close.

If I do this on the Controller/A16, and then dial S1 to 0010 (after the unit fully starts), the Guard Crossing/A14 LED starts flashing - like there's data being transmitted to it every second or so (which seems to match Table 4-4). All four LEDs on A16 stay lit.

But I've been unable this far to find any consistent logic pulses on P80:24/25 and 2/22, as per 4-28 steps 6 and 7.

No progress whatsoever. I'll try to pull A2 tomorrow and see if there's anything visible that needs addressing.

A question for Megavolt - given the interruptions in data we've seen prior, what sort of failure you'd think could trigger that? Maybe I should try to work back on the signal path and see where it gets corrupted - though I frankly do not understand the circuitry enough to think this through.

BTW - does anyone have any good tips on removing and reinserting large DIP ICs? Such as 40 pin. I have a Radioshack inserter that is pretty good, and recently purchased one of those Jonard EX-2s for pulling, which is a complete POS. A well thought through puller would have large jaws locking on the IC body (not the typical, 1/8" or whatever all these crappy tools have), and rails that would mechanically push against the socket as one engages some lever or whatever. Anything else puts the PCB at risk. I still have to see a toold that's designed this way. Maybe I should model and 3D print it...

[alm]

BTW - does anyone have any good tips on removing and reinserting large DIP ICs? Such as 40 pin. I have a Radioshack inserter that is pretty good, and recently purchased one of those Jonard EX-2s, which is a complete POS. A well thought through puller would have large jaws locking on the IC body (not the typical, 1/8" or whatever all these crappy tools have), and rails that would mechanically push against the socket as one engages some lever or whatever. Anything else puts the PCB at risk. I still have to see a toold that's designed this way. Maybe I should model and 3D print it...

I find that using a large ish screwdriver as a lever between socket and chip works better since it's more controlled and puts stress on the socket instead of on the board like with the cheap and nasty IC puller. I think I might have seen a tool like you describe in a catalog back when DIP was more common. Just make sure you work gradually and from both sides to prevent bending the pins on one side/corner.

[Tony_G]

I bought the previous version of this and it does a good job - You have to be careful to ensure that you keep moving it under the IC otherwise you'll bend pins at the other end from the lifter.

https://www.digikey.com/en/products/detail/wiha/27922/11585736

TonyG

[Rax]

I bought the previous version of this and it does a good job - You have to be careful to ensure that you keep moving it under the IC otherwise you'll bend pins at the other end from the lifter.

https://www.digikey.com/en/products/detail/wiha/27922/11585736

TonyG

That's very interesting... I actually have a similar tool, from a larger set for desoldering. I had no idea it's (also?...) intended for extracting ICs. Good to know!

[MegaVolt]

Let's go in order.

Read my previous answer and recommendation to start with the A2 board. board A16, judging by the LEDs, is more or less working, which means that the switch for testing A16 was in the correct state 1111 this is the position for work.
This means that all switches must be open (high resistance). You can check with a multimeter.

Here are two tables. Several lines are of interest.
For A2
1. display test
2. Exchange test with A16 board. The same byte is continuously transmitted. Can be observed with an oscilloscope or analyzer.

For A16
1. Exchange test with A2 board. The same byte is continuously transmitted. Can be observed with an oscilloscope or analyzer.

Accordingly, I propose to get A16 and put it aside. And only work with A2. The monitor test should show some changes on the screen. The exchange test will show the health of the communication channel.

Until this is passed, there is no point in touching the A16.

[Rax]

On a relatively different track, if anyone in this thread is interested in a pair of extenders (short version at this time), please PM me.

[Rax]

For A2
1. display test
2. Exchange test with A16 board. The same byte is continuously transmitted. Can be observed with an oscilloscope or analyzer.

[...]

The monitor test should show some changes on the screen. The exchange test will show the health of the communication channel.

Until this is passed, there is no point in touching the A16.

If I'm starting the unit with A2 S1 switch all closed/on (0000) - A16 S1 switch stay 1111 - I see some minimal changes to the screens (see image below). Unless anyone can read something relevant on this screen state, I remain of the mind that this is essentially random. BTW, it may change next time I do this. But some changes seem to occur when doing this, though they may just be random changes between consecutive unit startups which would happen anyway.

Under the switch state above, RINT (which I measure with a Fluke 8840A on pin 7 of A2/U1) is low (around 150mV). If then I switch S1-2 to 1 (open/off), RINT stays low. I assume RINT needs to switch to high (5V?) for the "0100" switch mode troubleshooting mode to be active. BTW - I'm not sure how to check the presence of the "ASCII character, ACK, [being] continuously sent to the front panel interface circuit."

[MegaVolt]

I advise you to remove the A16 board from the device.  It may interfere with the operation of A2.  Communication between the boards is described in the link.  with waveforms.

https://www.eevblog.com/forum/metrology/fluke-5440a-repair/msg3616353/#msg3616353

[Rax]

I advise you to remove the A16 board from the device.  It may interfere with the operation of A2.

 

Sorry, but I am not following... If I remove A16, how would they communicate? I think I need to be assessing their capability to exchange data and I'm not sure how that'd occur if one of them is removed.

Communication between the boards is described in the link.  with waveforms.
https://www.eevblog.com/forum/metrology/fluke-5440a-repair/msg3616353/#msg3616353

Thank you, MegaVolt, but your quoted post makes no mention of where and how you measure those waveforms. Where did you connect your scope/LA (by far the biggest question here), and what were the measurement settings? Trigger (y/n, if y on which channel?), ground, etc. I can't tell what I'm looking at without that context.

So I went back to the SM and spent some additional time with 4-28 and 4-29 from p. 4-31 and 4-32. I am not sure how this is possible, but I am not seeing any "pulses" or "logic activity" on P80-2, 20, 24 and 25, regardless of the troubleshooting switches (or instrument collecting data) settings.  .

I tried my 54522A scope (including on the two logic modes available, ECL and TTL), and the "toss a coin to know if it'll work this time" KeeYees (WTF?...) logic analyzer. I collected ground from the A16/Controller TP1 (GND). 

The universe has just decided this project will stay stuck on me regardless of how much work I put in it.

 

[Rax]

One thing I just realized, is that jumpering E6 to E5 instead (on A16) - which means flipping the A16 jumper to the other possible position - disables the watchdog reset, which in turn stops the restart loop my unit's been since day one. This I think is intended to allow for further troubleshooting of A2.

I'm not sure if very useful, but I'll be trying to see if this allows me to collect more information on A2.

[MegaVolt]

Sorry, but I am not following... If I remove A16, how would they communicate? I think I need to be assessing their capability to exchange data and I'm not sure how that'd occur if one of them is removed.

Checking the exchange is the next step. First you need to check that everyone is trying to say something to the other. The fact that there is no other is not a problem.

The A16 board works for you and stops on the exchange with A2.
So the problem is A2. She needs to be dealt with. A16 can be put aside. You can leave )))

Thank you, MegaVolt, but your quoted post makes no mention of where and how you measure those waveforms. Where did you connect your scope/LA (by far the biggest question here), and what were the measurement settings? Trigger (y/n, if y on which channel?), ground, etc. I can't tell what I'm looking at without that context.

So I went back to the SM and spent some additional time with 4-28 and 4-29 from p. 4-31 and 4-32. I am not sure how this is possible, but I am not seeing any "pulses" or "logic activity" on P80-2, 20, 24 and 25, regardless of the troubleshooting switches (or instrument collecting data) settings.  .

You are interested in pin 25 of the UART chip (A2 U5). This is the data output to the A16 board.

Data can be transferred once when the power is turned on. You need to put one probe of the analyzer on a 5V supply and set it to trigger once when this signal appears. And put the second on 25 pin. And connect the ground. then, when the power is turned on, the analyzer will write data among which it will be possible to find one byte that was transmitted.

If it is not there, something is possible with the A2 board. You need to be busy troubleshooting on it.
1. Check the reset.
2. Check clock.
3. View other signals on the processor - WR, RD, MREQ, IOREQ, M1, A0...A15, D0...D7
4. Check the content of the memory chips
5. And then look for a microcircuit that does not do what it is supposed to.

You can record signals with the analyzer in different places of the circuit, and I will say if they are similar to what they should be. The recording conditions are the same as above for UART. 7 signals can be recorded at one time.

This can be a long-term activity. Perhaps it makes sense to open a separate topic for this. I think there are a lot of people here who can customize the Z80

[MegaVolt]

Here is the waveform.
The first data transfer starts about 1.5 s after power is applied. This means that the analyzer must record more than 2 seconds from the start of power up to see the data.

[Rax]

Thank you very much, MegaVolt. This provides very welcome clarity.

[Rax]

MegaVolt - thanks again, I will hop on that route you point out relatively shortly.

In the meantime, I probed some more some of the data lines at A16 (those pertaining to troubleshooting steps 4-28 and 4-29). Posting this data here for analysis and hoping it may provide some clues.

I collected this with the watchdog suspended by switching the jumper on A16 from E6 to E5. In this situation, the restart/reset loop is being broken and the unit stops on the state where the FPC and the CR4/FAULT on A2 stay lit.

1. All troubleshooting switches in "operational," default state (1)

• P80-2: there's a bunch of states' changes (high/low switching visible on scope), until the circuit stabilizes high (about 3.2V)
• P80-22: same, around 3.5V. The circuit stabilizes low.
• P80-24: nothing going on past maybe 220mV of fluctuations. This one's dead.
• P80-25: this one has some high/low events, until it seems to stabilize high at around 3.5V

2. Troubleshooting switches per 4-28. Note I'm keeping A2 switches on operational, open/1 state for this step. A16 is 0010.

• P80-2: steady high state (3.5V)
• P80-22: about 500mV of flatlining
• P80-24: about 200mV of flatlining
• P80-25: comes high at 3.5V immediately

3. Troubleshooting switches per 4-29. Note I'm keeping A16 switches on operational, open/1 state for this step. A2 is 0100.

• P80-2: goes high immediately (3.5V), then low (about 500mV) a second or so later.
• P80-22: initially low (about 500mV of flatlining), then goes high at 3.5V and stays there. I think this sequencing/timeline mirrors the state of the fault indicator LEDs.
• P80-24: about 200mV of flatlining
• P80-25: comes high at 3.5V immediately

[MegaVolt]

MegaVolt - thanks again, I will hop on that route you point out relatively shortly.

In the meantime, I probed some more some of the data lines at A16 (those pertaining to troubleshooting steps 4-28 and 4-29). Posting this data here for analysis and hoping it may provide some clues.

I collected this with the watchdog suspended by switching the jumper on A16 from E6 to E5. In this situation, the restart/reset loop is being broken and the unit stops on the state where the FPC and the CR4/FAULT on A2 stay lit.

The FPC error is a communication error with the front panel. Those. this error will always be there until A2 answers.

By signals. It is very difficult to say something in words. It is better to watch them all at the same time with an analyzer.

On the P80, many signals are differential. Those. two wires. One is set to 1 and the other to 0 and vice versa.

[Rax]

By signals. It is very difficult to say something in words. It is better to watch them all at the same time with an analyzer.

I'd like to, but my "logic analyzer" works about a third of the time. It's so frustrating it makes it very hard to collect any data.

On the P80, many signals are differential. Those. two wires. One is set to 1 and the other to 0 and vice versa.

One thing that's been pointed out to me is that 24/25 are complementary, while 24 stays dead. I wonder if I should suspect U28 having at least one dead driver.

[MegaVolt]

One thing that's been pointed out to me is that 24/25 are complementary, while 24 stays dead. I wonder if I should suspect U28 having at least one dead driver.

I would disconnect the cable from A2 and check again. A2 can make corrections. If one signal changes value and the second does not change at the same time, this may mean that U28 needs to be changed.

[Rax]

I would disconnect the cable from A2 and check again.

Great point. A2 could clamp that line to ground. Will give this a shot.

[Rax]

A very quick, rushed check with the ribbon cable pulled from A2 (mostly looking at 24) seems to return similar results. Maybe U28 is the culprit.

One thing I don't feel I quite digested is where signals originate, which I think is important in this case. For instance

• 4-28, A16 being on 0010, the main MP "continuously updates the watchdog circuit." Now, I currently have the watchdog disabled, so maybe I need to retry with it enabled. It shouldn't change the weirdness I'm seeing with U28, 24 and 25 should just be complementary, period.
• 4-29 has A2 sending ACK "to the FP interface circuit" (is that out of A2 and to A16 via the ribbon cable?).

Anyway, a bit of thinking out loud here.

[MegaVolt]

A very quick, rushed check with the ribbon cable pulled from A2 (mostly looking at 24) seems to return similar results. Maybe U28 is the culprit.

Yes. It doesn't work according to your description.

One thing I don't feel I quite digested is where signals originate, which I think is important in this case. For instance

• 4-28, A16 being on 0010, the main MP "continuously updates the watchdog circuit." Now, I currently have the watchdog disabled, so maybe I need to retry with it enabled. It shouldn't change the weirdness I'm seeing with U28, 24 and 25 should just be complementary, period.
• 4-29 has A2 sending ACK "to the FP interface circuit" (is that out of A2 and to A16 via the ribbon cable?).

1. The exchange goes on a flexible cable.
2. In normal mode, the boards communicate for real.
3. In test mode, the boards simply transmit data and do NOT listen to data from the other side. This is done for ease of debugging. Data is sent periodically and can be conveniently checked with an oscilloscope.
4. The watchdog timer is turned off only when the block is fully operational. Those. passed all checks.

[Rax]

4. The watchdog timer is turned off only when the block is fully operational. Those. passed all checks.

With the "watchdog disabled," I meant A16 is jumpered to E5 instead of E6. I think this effectively disables the watchdog circuit (p.2-22 of the 5440A SM). Are we on the same page on this?

[MegaVolt]

With the "watchdog disabled," I meant A16 is jumpered to E5 instead of E6. I think this effectively disables the watchdog circuit (p.2-22 of the 5440A SM). Are we on the same page on this?

Yes I understand. Hardware disable watchdog timer. I described normal operation.

[Rax]

Yes I understand. Hardware disable watchdog timer. I described normal operation.

Great! Just making sure, for our consistency and clarity.

Also, there are some relatively minor differences between the SMs for the "5440 series" vs "5440A," but honestly a bit larger than I initially imagined. I don't think anywhere nearly as radical as concerning A2, but still, same things are on different pages, etc. I didn't quite get a chance earlier today to find the E5/E6 operation in the "5440 series" SM and wasn't quite sure what to make of that until just now.

[Rax]

Well, MegaVolt and the entire chunk of the whole internet interested in Fluke instruments and maybe just calibration stuff generally speaking... I think we have a living Fluke 5440A!!!

After many other investigations offline and the sweat and work associated with that, it seems the U23/704114 EPROM was corrupt. Once I got that reimaged (and a giant bunch of thanks to MegaVolt for making that available!!), the whole thing is back online. I am looking at a 9.9999997V right now on my Prema 6048 after a shorter than required warmup.

Happy camper doesn't describe it.