Re: [neonixie-l] Re: IN-18 Blue Dream PWB

[Dekatron42]

Thanks for the link on the TI document.

I agree that in this particular circumstance it is probably not a latchup 
condition.

In one specific case I came across recently I never dug deep enough to 
check if it was a proper latchup or not but it certainly looked like it as 
it pulled the 5V line low. The case was with a TI PCF8574 which was hooked 
up to the same 5V line as a PIC processor, the PIC processor started to 
communicate with the PCF8574 on the I2C bus at some 1.8V and then the TI 
PCF8574 went bonkers, pulling the 5V line to some 2.5V. If I replaced the 
TI part with an NXP PCF8574 everything was just fine (the design had used 
the NXP parts for many years without a problem but as soon as the TI parts 
were used the problem started to pop up intermittently). It was also fine 
if I let the processor wait until the voltage had reached some 4.85V with a 
POR ic. I didn't dig further into problem after I added the POR ic to the 
circuit. Instead of using the TI PCF8574s I made SOIC to DIP adapters and 
continued to use the NXP PCF8574, but I still use the POR ic as a 
precaution if NXP change their design in the future and also as a good 
measure.

/Martin

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Re: [neonixie-l] Re: IN-18 Blue Dream PWB

[gregebert]

On second thought, the resistor value I stated is still too low because the 
worst-case scenario is when the 3.3V supply is off (zero volts), and the 5V 
supply is fully on. That would make the minimum resistance around 175 ohms 
= (5.0 - 0.7)/25mA .

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Re: [neonixie-l] Re: IN-18 Blue Dream PWB

[gregebert]

I'm doubtful that latch-up is happening here, because it usually results in 
a short-circuit across the supply. Also, the problem as described happens 
after a few hours of operation, and not during power-up. I'm suspecting a 
hold-time marginality.

--
>From my experience in chip design, latch-up is initiated when excess 
current is forced thru a pin. For most IC's, the only way to do this is by 
applying a voltage greater than Vcc or less than GND (ie, a negative 
voltage) to a signal pin. Usually, currents well-above 100mA are required 
to induce latch-up; not many datasheets spec the latch-up current, but you 
can use the short-circuit current as a guideline for your design. Latch-up 
can happen on input, output, and inout pins under the right circumstances.

So, what can you do to prevent latch-up ? The highest-risk areas are 
mixed-voltage designs, where the supplies are not sequenced in a specific 
manner. If you have a +5V and +3.3V design, a diode forward-biased from the 
3.3V supply to the 5V supply will provide a lot of protection as long as 
the 3.3V supply is brought-up first, and brought-down last. Also, the 3.3V 
supply must be able to provide sufficient current to hold-up the 5V rail 
until that supply comes up. Years ago we used this on desktop PCs that had 
a mix of 3.3V and 5.0V devices; we also had a string of 3 diodes from the 
5V supply to the 3.3V supply, and that allowed supplies to come-up in any 
order. There were millions of PCs built with this approach back in the 90's 
and I'm not aware of any field returns root-caused to latch-up.

If that wont work, you can add series resistors on signals between power 
domains to limit the current. Suppose you need to protect signals between 
3.3V and 5V domains, and the current needs to be limited to 25mA (the 
output short-circuit current of an LM348 OP-amp). Be aware it takes at 
least a 'diode-drop' voltage difference (about 0.7V) to start forcing more 
current thru a CMOS pin. Knowing this, the series resistance should be at 
least R= (5 - 3.3 - 0.7)/25mA, or 40 ohms. This will affect circuit timing 
somewhat; if load-capacitance is around 25pF the signal-delay from the 
RC-network will be around 1 time-constant, which is 40*25 = 1000psec 
(1nsec) in this case. This assumes a 2.0V threshold for a 3.3V supply.

Here is a brief paper from TI that discusses latch-up: 
http://www.ti.com/lit/wp/scaa124/scaa124.pdf

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Re: [neonixie-l] Re: IN-18 Blue Dream PWB

[Dekatron42]

I don't know anything about this clock in particular but I have come across 
several other designs where a mix of TTL ic's, CMOS ic's and other ic's 
with different VCC capabilities has been used, some starting to operate 
from as low as 1.8V and some like TTL above 4.75V, but all capable of 
running at 5V as the main VCC voltage.

The problem with these designs have all been that the microprocessor has 
started at the lowest voltage of all ic's which has then led to latchups in 
some of the external ic's as they weren't ready to work until the voltage 
had risen above their minimum operating voltages. The microprocessor 
started to run its program and communicated with them right away when it 
was ready as it used its internal power on reset and thought that 
everything was green to go. Now some of these designs worked for years 
until they failed due to different reasons, possibly ageing components, 
some only worked for a short while and some were problematic 
intermittently. All of these problems were due to not waiting for the 
voltage to rise above the minimum voltage for the type of ic used with the 
highest minimum voltage requirement - this I feel can only be blamed on bad 
design, or poor knowledge on how things should be designed.

In some cases there has been differences between different manufacturers 
producing the same ic, one under license from the other, and even within 
different runs from the same 2nd source manufacturer. Even if different 
manufacturers produced the same ic they didn't work equally under the 
startup conditions when voltages where rising to their operating levels 
(and in some cases when the voltages were being removed), in some cases it 
resulted in lockups or strange behaviours later when the ic in question was 
being used.

Fortunately most of the problems I have come across could be remedied by 
adding a POR (Power On Reset) ic to the microprocessor halting it until 
power had risen to the required level for the TTL ic's that were the most 
problematic.

Trying to locate this kind of problem is very time consuming but when you 
know about it is one of the first things I check in a mixed ic environment.

/Martin

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Re: [neonixie-l] Re: IN-18 Blue Dream PWB

[gregebert]

Those ICs should last forever, because they are not exposed to anything 
hazardous (high-voltage, high-temp, high current).
My hunch is that there is a design marginality somewhere, and that as the 
part itself ages, or it's surrounding parts, the marginality becomes a 
defect.

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Re: [neonixie-l] Re: IN-18 Blue Dream PWB

[Nicholas Stock]

I also replaced one of those on a friends blue dream clock for exactly the same 
issue. 

Nick

Sent from my iPhone

> On Dec 27, 2017, at 11:29, MichaelB  wrote:
> 
> Sounds like the same exact issue I had. Replaced 2 of the 74HC595D's. Problem 
> vanished
> 
>> On Wednesday, December 27, 2017 at 11:17:45 AM UTC-8, dixter wrote:
>> working with Dieter on the issue now...
>> 
>> Note:  Blue Dream Nixie Clock
>> 
>> Symptom is flickering of the two hour nixie tubes.  for example when a 0 is 
>> displayed you also see a 1 flicker on at the same time for both nixie tubes 
>> in the 
>> hour slots...  schematic reference is Valve 1 and Valve 2
>> 
>> strange item is that if you pull the power plug from the clock and let the 
>> clock sit for a few minutes and re-power the clock, then the flickering goes 
>> away for several hours and then it shows up again...   shouldn't be a heat 
>> issue as its not hot at all where the clock is located...  
>> 
>> I also didn't have a schematic... but I do now and should be able to scope 
>> the actual part when I get it apart... 
>> 
>> for reference suspect part 
>> 
>> 74HC595D, SOIC-16/SO-16, SMD
>> mouser part no. 771-74HC595D-T
>> 
>> On order... maybe get this all fixed next week ..  :-)
>>> 
>>> 
>>> 
> 
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[neonixie-l] Re: IN-18 Blue Dream PWB

[MichaelB]

Sounds like the same exact issue I had. Replaced 2 of the 74HC595D's. 
Problem vanished

On Wednesday, December 27, 2017 at 11:17:45 AM UTC-8, dixter wrote:
>
> working with Dieter on the issue now...
>
> Note:  Blue Dream Nixie Clock
>
> Symptom is flickering of the two hour nixie tubes.  for example when a 0 
> is displayed you also see a 1 flicker on at the same time for both nixie 
> tubes in the 
> hour slots...  schematic reference is Valve 1 and Valve 2
>
> strange item is that if you pull the power plug from the clock and let the 
> clock sit for a few minutes and re-power the clock, then the flickering 
> goes away for several hours and then it shows up again...   shouldn't be a 
> heat issue as its not hot at all where the clock is located...  
>
> I also didn't have a schematic... but I do now and should be able to scope 
> the actual part when I get it apart... 
>
> for reference suspect part 
>
> 74HC595D, SOIC-16/SO-16, SMD
> mouser part no. 771-74HC595D-T
>
> On order... maybe get this all fixed next week ..  :-)
>
>>
>>
>>
>>

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[neonixie-l] Re: IN-18 Blue Dream PWB

[dixter]

working with Dieter on the issue now...

Note:  Blue Dream Nixie Clock

Symptom is flickering of the two hour nixie tubes.  for example when a 0 is 
displayed you also see a 1 flicker on at the same time for both nixie tubes 
in the 
hour slots...  schematic reference is Valve 1 and Valve 2

strange item is that if you pull the power plug from the clock and let the 
clock sit for a few minutes and re-power the clock, then the flickering 
goes away for several hours and then it shows up again...   shouldn't be a 
heat issue as its not hot at all where the clock is located...  

I also didn't have a schematic... but I do now and should be able to scope 
the actual part when I get it apart... 

for reference suspect part 

74HC595D, SOIC-16/SO-16, SMD
mouser part no. 771-74HC595D-T

On order... maybe get this all fixed next week ..  :-)

>
>
>
>

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[neonixie-l] Re: IN-18 Blue Dream PWB

[gregebert]

When you find the cause of the failure, please share. It helps us design 
better clocks.


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[neonixie-l] Re: IN-18 Blue Dream PWB

[MichaelB]

Yep, I recently had an issue with that clock and it ended up being a shift 
register. Easy fix. Ping Dieter and tell him what the issue is. He may be 
able to advise you on a fix.
On Tuesday, December 26, 2017 at 4:17:39 PM UTC-8, Greg P wrote:
>
> Thanks for the clarification.  That's a new one on me, never heard that 
> term.
>
> What exactly is the issue with your clock?  I'm sure the folks here can 
> help troubleshoot the issue or failing components.  Might not be necessary 
> to source a new PCB.
>
> Have you reached out to the Nocrotec/Dieter for help?
>
>
>
> On Tuesday, December 26, 2017 at 2:48:54 PM UTC-5, dixter wrote:
>>
>> PWB = Printed wire board or PCB= Printed circuit board   
>>
>> On Tuesday, December 26, 2017 at 11:37:50 AM UTC-6, Greg P wrote:
>>>
>>> What is a PWB kit? 
>>>
>>>
>>>
>>> On Tuesday, December 26, 2017 at 10:35:46 AM UTC-5, dixter wrote:

 Any one have a source for a PWB for the IN-18 Blue Dream Clock  
 mine is acting up and I am wondering how long it will last  so I am 
 going to try and purchase a new PWB kit to fix it

 thanks
 Dixter

>>>

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[neonixie-l] Re: IN-18 Blue Dream PWB

[Greg P]

Thanks for the clarification.  That's a new one on me, never heard that 
term.

What exactly is the issue with your clock?  I'm sure the folks here can 
help troubleshoot the issue or failing components.  Might not be necessary 
to source a new PCB.

Have you reached out to the Nocrotec/Dieter for help?



On Tuesday, December 26, 2017 at 2:48:54 PM UTC-5, dixter wrote:
>
> PWB = Printed wire board or PCB= Printed circuit board   
>
> On Tuesday, December 26, 2017 at 11:37:50 AM UTC-6, Greg P wrote:
>>
>> What is a PWB kit? 
>>
>>
>>
>> On Tuesday, December 26, 2017 at 10:35:46 AM UTC-5, dixter wrote:
>>>
>>> Any one have a source for a PWB for the IN-18 Blue Dream Clock  mine 
>>> is acting up and I am wondering how long it will last  so I am going to 
>>> try and purchase a new PWB kit to fix it
>>>
>>> thanks
>>> Dixter
>>>
>>

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[neonixie-l] Re: IN-18 Blue Dream PWB

[dixter]

PWB = Printed wire board or PCB= Printed circuit board   

On Tuesday, December 26, 2017 at 11:37:50 AM UTC-6, Greg P wrote:
>
> What is a PWB kit? 
>
>
>
> On Tuesday, December 26, 2017 at 10:35:46 AM UTC-5, dixter wrote:
>>
>> Any one have a source for a PWB for the IN-18 Blue Dream Clock  mine 
>> is acting up and I am wondering how long it will last  so I am going to 
>> try and purchase a new PWB kit to fix it
>>
>> thanks
>> Dixter
>>
>

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[neonixie-l] Re: IN-18 Blue Dream PWB

[Greg P]

What is a PWB kit? 



On Tuesday, December 26, 2017 at 10:35:46 AM UTC-5, dixter wrote:
>
> Any one have a source for a PWB for the IN-18 Blue Dream Clock  mine 
> is acting up and I am wondering how long it will last  so I am going to 
> try and purchase a new PWB kit to fix it
>
> thanks
> Dixter
>

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