First, new to this forum. I am a scale model boat builder. I have two working submarines and a few surface boats. I have made a few of my own PCB's for these boats, mostly to power LED's. The PCB's I made were done on a freebie computer program, printed out on clear overheard transparent mylar, then transferred to a PCB using a clothes iron, then etched. I am not that adept and diagnosing electronic circuit problems.

I have a motor speed control kit which is a kit from our model boat club. The kit was designed by a member that recently passed away so I cannot go to him about this problem. I attached the schematics, parts list and a picture of the two speed controls. After inserting and soldering all the parts all I get during testing is the relays clicking. In his instructions, it says to not solder pin 8 and 10 of IC1 which is a ZN409CE. That IC is in a socket so I did not solder those pins. Pin 10 appears to be power for the IC. Pin 8 is an output which is also tied to pin 7. So I am asking here, shouldn't pin 10 be soldered so the IC gets power? Is that the cause of the speed control not working?

 

shouldn't pin 10 be soldered so the IC gets power?

It should connect to the 5V supply from IC2, so pin 10 of the socket should be soldered to the pcb.
Welcome to AAC!

 

Thanks for confirming that. Being that pins 7 & 8 appear to be the same output and are tied together in the schematic, does it matter if pin 8 is soldered or not?

 

Pins 7 and 8 of the socket should both be soldered to the pcb so that the load current is shared by the two outputs of the IC.

Edit:
Scrub that. See later posts.

 

In his instructions, it says to not solder pin 8 and 10 of IC1 which is a ZN409CE.

Welcome to AAC.

Could you show us the instructions that says this? It’s very hard to understand how he could have said that given that is simply could not work without +VE connected. Forgive me for suspecting you’ve misread something.

 

Perhaps the reference to not soldering those pins was within the context of testing some aspect of the circuit before the final connections were made to the IC?

 

Solder all the pins to be sure that it works.

 

Firstly, an interesting design, nicely laid out.

Secondly, I see that the ZN409CE is obsolete, maybe a decade ago, although they are still available but expensive. It took me a while to find the datasheet online. I wonder if a 555 could be used instead to get a similar result? And 10A is a big current, I wonder if that's necessary for a scale model, or whether an H bridge IC with 1.5A current would suffice?

Finally, I'm thinking the ZN409CE is obsolete because a small processor would happily do the same job, and for less money. And an ESP32 processor with bluetooth and WiFi would allow a lot of remote control lines!

Please don't see this as criticism - It sparked my interest, I hope the other suggestions here will help you get it working

 

pins 7 & 8 appear to be the same output

Looking again at the datasheet for the IC, pins 7 and 8 have separate driver stages. I can't find any Application Notes to indicate how they are intended to be used, and the datasheet itself is no help. If the stages operate in phase there should be no problem connecting pins 7 and 8 together. However, if they operate in anti-phase there could be an issue. Maybe your circuit designer was playing safe by leaving pin 8 unconnected?

 

I attached page 6 which is where it says not to solder those pins. And the full pages of instructions.

Yes this kit is a decade or so old. It sat in a drawer all that time until I finally needed to build it.

 

Given that we can only guess as to what the ZN 409 IC does, it is difficult to comment on how the circuit will function. AND, the rest of the circuit is an electrical schematic, except around that IC it is a wiring diagram. Not nearly as useful towards understanding what is happening.

 

40-odd years ago I built these small RC model servos from a kit :-



Unfortunately I no longer have them or the assembly instructions/schematic. Don't be misled by the 'digital' marking. These operated with the old-school 1-2mS pulse width system.
IIRC (at my age that may not be the case ) the IC used was different from yours but had two output pins for direct connection to the DC motor. I deduce that these pins were each driven by a push-pull stage to provide an H-bridge for reversing the motor. If your IC behaves in a similar way, then pins 7 and 8 would indeed be operating in anti-phase and shouldn't be shorted together.

 

40-odd years ago I built these small RC model servos from a kit :-

View attachment 304234

Unfortunately I no longer have them or the assembly instructions/schematic. Don't be misled by the 'digital' marking. These operated with the old-school 1-2mS pulse width system.
IIRC (at my age that may not be the case ) the IC used was different from yours but had two output pins for direct connection to the DC motor. I deduce that these pins were each driven by a push-pull stage to provide an H-bridge for reversing the motor. If your IC behaves in a similar way, then pins 7 and 8 would indeed be operating in anti-phase and shouldn't be shorted together.

I still have 3 of those Micron PL6D servo here intact, although they haven't been used in about 40 years either, and I've also lost the datasheet. I also have a pair of the slightly longer versions, unbuilt, but in their case the pcb's and components are missing, I'd guess scavenged as repair parts. Must hook one up to an Arduino and see how they've stood the test of time!

 

I deduce that these pins were each driven by a push-pull stage to provide an H-bridge for reversing the motor.

In this case I think the relays are changing the direction. Pin 4 of the ZN409CE which is shown on the datasheet as "direction" will energise the relays when low, not when high. It's being pulled high by R8 but how it goes low eludes me - the datasheet is pretty useless

EDIT: Stumbled across the attached application note which make things clearer. The IC is primarily intended for position control but pages 5 and 6 show how it can be used for motor speed control. Their example circuit is similar with a major difference that they are using "base drive" pins 5 and 9 and not using the "output" pins 7 and 8 at all. Not got my head around it completely but I'm getting there - sharing in case someone else can clarify.

Amusing that they are using 2 x 555 ICs to produce the input signal, makes me wonder if the ZN409 is necessary at all! Without an AC input presumably the relays "click" to change the direction (with pin 4 low) and somehow the position of VR1 determines the mark/space of the input at which 4 goes high to change the direction?

 

If it's any use, I've just come across this datasheet for the AA51880, which seems to be a clone (or nearly so) of the ZN409CE. It gives much more useful info on the circuit function. On this basis it looks as though the motor speed control PWM signal should be available at pin 7 or 8 of the ZN409CE, each of which is a half-bridge, so shorting those pins together would be bad.

 

There was one response so far saying that pin 10 should be soldered. Being that there is no power going to the IC sounds like that connection should be solder? Can we come to that conclusion?

And being that the ZN409CE is old tech, and it is questionable about joining pin 8 to the circuit, would it be feasable to solder pin 10 (Ve) and leave pin 8 unsoldered and test the speed control to see what happens? Can anything be damaged in this scenario?

I appreciate everyone's work looking into investigating this. So glad with having online access to such knowledgable people with these forum's!

 

There was one response so far saying that pin 10 should be soldered. Being that there is no power going to the IC sounds like that connection should be solder? Can we come to that conclusion?

And being that the ZN409CE is old tech, and it is questionable about joining pin 8 to the circuit, would it be feasable to solder pin 10 (Ve) and leave pin 8 unsoldered and test the speed control to see what happens? Can anything be damaged in this scenario?

I appreciate everyone's work looking into investigating this. So glad with having online access to such knowledgable people with these forum's!

The IC can’t operate without power and the only input for that is pin 10. Whatever reason the kit designer had for saying not to connect it must have included an “OK, now connect it” which was lost.

Pin 8 is still unclear.

 

Pin 10 is "Positive Supply Vcc". Surely that is how the IC is powered? Pins 7 and 8 are "Outputs". Although the schematic and the layout show them as joined together I'd recommend trying one and then the other separately. Even without solder they may be touching the track so I'd lift the IC out of the socket and gently spread-eagle bend them for testing purposes.

May I ask what signal you are using as an input on the white wire?

 

I'd recommend trying one and then the other separately. Even without solder they may be touching the track so I'd lift the IC out of the socket and gently spread-eagle bend them for testing purposes.

Agreed. Alternatively the pcb copper track around pin 7 or 8 could be drilled away.
BTW, Yaa'kov has pins 8 and 10 swapped (post #17). 10 is definitely for Vcc.

 

Hi Alec_t, did you see the app note I attached to my post #14? It’s much more informative than the data sheet and you may be more skilled than I am at working out exactly how it works?