Problem with CD4093BE

[aless2056]

Hello guys, I have some equipment that uses a control board in which the original HEF4093 ICs burned and in place I put a texas CD4093BE. However, the circuit does not work correctly. I don't know much about electronics, but someone can help me.

The CI is used in position U17, U12 and U1.

Just a note the pin 8 and 9 of the U17C is interconnected. The scheme is not without that connection.


Looking at the complete schematic does anyone tell me something that makes the Cd4093 from texas purchased from farnell not working properly?

[wraper]

On one side of the capacitor is gnd 0V, on the other is it if I had nothing connected to the U17 input?

That circuit is strange. You are not allowed to do that (unless you're an engineer with no brain). Maybe they simply forgot to draw connection between pins 8 and 9? Most likely you have another problem with the circuit, not with CD4093BE.

original HEF4093 ICs burned and in place

Burned means burned such with a magic smoke escaping? Of simply failing.

[Gyro]

I remember that the HEF4000 series was always significantly faster than the competitors' parts. If there is a hidden race condition in there somewhere, that could possibly be a factor.

[wraper]

I remember that the HEF4000 series was always significantly faster than the competitors' parts. If there is a hidden race condition in there somewhere, that could possibly be a factor.

It's somewhat faster, but not that much. Typical delay values for CD type do not exceed max delay values for HEF. Nor this looks like any sort of high speed circuit where this would matter even a tiny bit.

[Alex Eisenhut]

Where do you get polarized 200pF caps?

[aless2056]

A detail that may help to solve the problem:

The equipment even works, but when the power is increased the LD8 Q-up limit must light up and not allow the power to be increased.

With the old IC the led lights up and does not increase the power anymore, with the new IC the led also lights up but the power continues to increase.

[aless2056]

Problem update: The board uses the 4093 in position U1, U12 and U17. I did a test with some old ICs of the ST HCF4093BE, and that the CD4093BE of Texas does not give problem in the position U1 and U12, only in the position U17, in that position I left that of the ST and it is working.

However I have other cards and it is no longer manufactured in HCF4093BE in DPID-14

Where in U17 is the problem? No U17A, B, C or D?

Is changing the value of any component or making a change in the circuit with you a solution?

Remembering that pin 8 and 9 of U17 is physically interconnected, in the diagram no.

[aless2056]

Problem update: The board uses the 4093 in position U1, U12 and U17. I did a test with some old ICs of the ST HCF4093BE, and that the CD4093BE of Texas does not give problem in the position U1 and U12, only in the position U17, in that position I left that of the ST and it is working.

However I have other cards and it is no longer manufactured in HCF4093BE in DPID-14

Where in U17 is the problem? No U17A, B, C or D?

Is changing the value of any component or making a change in the circuit with you a solution?

Remembering that pin 8 and 9 of U17 is physically interconnected, in the diagram no.

[Gyro]

It depends how old those parts are. Despite what @wraper says, back in the '80s there were significant propagation delay and output drive current differences between HEF and CD parts, these differences have been lost over the years in company acquisitions and technology changes, but they used to be there.

If it is just U17 where the part type matters, then I see only 2 possibilities...

1. That there is an issue with the delay through U17A, B, and D paths. It would be difficult to fully analyse the circuit from just that schematic, there are too many signals going onto and off the page. It does contain latches though so I do not rule out the possibility of a data setup time issue somewhere (maybe the input timing of U13A or B).

2. Which I do consider most likely, the connection of C31 to the input of U17C. This is clearly 'wrong' design if the board is actually the same as the schematic. You can't simply attach a capacitor to a CMOS IC input (even Schmitt) and expect it to behave predictably.

As somebody mentioned previously, C31's symbol is wrong, you don't get 200pF electrolytics. If the board is as the schematic, then there may be some interaction with the input impedance of the Schmitt trigger input of the IC which is type specific. If the circuit is intended as some sort of power-up reset, then try fitting a 1M or 10M resistor between the capacitor - U17 pin 9 connection and its supply pin. This will give it a defined input state after C31 charges.


EDIT: I've just re-read and noticed your comment that the inputs of U17C are linked. That part of the circuit is correct then (assuming that the component values achieve the correct time constant). Can you confirm the identity of C31? Also, how old are the HEF parts?

EDIT1: I note that the signal defining the state of the inputs of U17C (via D23 and R81) is coming from the Q output of U13A, not VDD.

[aless2056]

EDIT: I've just re-read and noticed your comment that the inputs of U17C are linked. That part of the circuit is correct then (assuming that the component values achieve the correct time constant). Can you confirm the identity of C31? Also, how old are the HEF parts?

EDIT1: I note that the signal defining the state of the inputs of U17C (via D23 and R81) is coming from the Q output of U13A, not VDD.

HEF parts are from 3 years ago. Capacitor C31 is a 220pF ceramic disk

[dietert1]

U17 is meant to have a connection between pins 8 and  9 - otherwise circuit does not make sense. If this connection is missing in the schematic, it may be missing on the board, too. Maybe it got fixed in production by a hand made solder bridge that got lost during repair.

Regards, Dieter

[tooki]

Where do you get polarized 200pF caps?

It doesn't matter. Polarization in a capacitor is a bug, not a feature. It's a limitation we tolerate in some capacitor types (i.e. electrolytic and tantalum) in exchange for high capacitance in a small volume/at low cost. (There's never a situation in which polarization is advantageous: it's either a downside or irrelevant, but never desirable.)

In a nutshell: all other specs held equal, you can always use a non-polarized capacitor in place of a polarized one, but you can't always use a polarized one in place of a non-polarized one.

[Gyro]

EDIT: I've just re-read and noticed your comment that the inputs of U17C are linked. That part of the circuit is correct then (assuming that the component values achieve the correct time constant). Can you confirm the identity of C31? Also, how old are the HEF parts?

EDIT1: I note that the signal defining the state of the inputs of U17C (via D23 and R81) is coming from the Q output of U13A, not VDD.

HEF parts are from 3 years ago. Capacitor C31 is a 220pF ceramic disk

Sorry @aless2056, I've been trying to get my head around the schematics but without any luck. Unfortunately it is one of those hand drafted 1970s/80s designs which uses lots of R/C time constants and looping discrete logic. The original designer would have had it all clearly in his head, but unless any design documentation has survived, it is very difficult to follow.

The problem also is that the circuit does 'work', but it is marginal. Without a scope to carefully compare circuit timings between the HEF and CD 4093 ICs, any solution is going to be down to experimentation. The timing differences between the devices will be subtle.

I would suggest playing around with passive component values, as I said, there are a number or R/C time constants. The simplest way is probably by temporarily adding  'padding' components on top of existing passives rather than substituting them. eg. try adding a resistor of approx. 5 times the value of a resistor to speed up an R/C time constant by 20% or patching on a capacitor of 20% of the value of the existing capacitor to slow it down.

As a starting point, I would suggest the R/C delays directly related to U17, so R89/C55 on the input of U17A, R86/C54 on the input of U17B, R81/C31 on the input of U17C. Maybe try adjusting each one by 10-20% either way as I described above. Also try adjusting them with a working HEF4093 fitted to see if you can make the circuit fail in the same way, this may be a pointer to where things are marginal. If these don't have any effect, then it may be necessary to widen the area of search to parts of the circuit further from IC17 but still related to its inputs and outputs.

I'm sorry I can't offer a more 'scientific' solution, but without fully understanding the function of the circuit and having it in front of me, with appropriate test equipment, it's all I can think of. It's never easy to track down a marginal problem in a circuit like this.

I also notice that there are several adjustable pots on the board. I would be reluctant to touch these unless you understand their function, but mark their starting position carefully so that you can return them. Also check that the supply voltages are in spec - I can't see if the 4000 series logic is powered from +5 or +15V but if it is the latter, different manufacturers parts might behave differently if the supply exceeds the 18V absolute maximum limit.