The 75492 driver chip has open collector output just like the MPS6531 transistor the way it is wired with no load. In order to see a valid logic level output you need to provide a load between the output and +V supply. Try a 100-1000 ohm resistor as a temporary load.

 

Okay, I see, thank you. However, since the light is dimly light when not on, the wiring from the output up to the 100 ohm "warm up resistor" to ground is good, so I have a light as a load. On other outputs that work, I have a similar test result as you said above. It seems when the light is on, I have neither a H or L at the output, but I do have -6V, which lights the light. does that come thru the 75492, or somehow thru the 100 ohm resistor? I have ordered some 75492s and I will probably replace this chip after some more testing.

 

No, you cannot use -6V on the load because the open collector output driver is an NPN transistor which sinks current from a positive supply voltage.

 

I understand now, I see what they are doing. I'll look over the board again with fresh eyes. Thanks to all of you for helping. The weather is slowly clearing after 20 years of non use...

 

I am not familiar with a USB power cube. I started to trace back the circuit for the thousand point and I found a bad solder connection on an ic pin, it fixed the problem. Moving forward. Re solder tomorrow.

do you have any phone chargers? Then you have a USB power cube. It is a cheap and ready source for 5 volts.

 

Hello folks,
Well here we go again. This 555 sits in a scoring circuit and is suppose to expand the pulses of the incoming pulse from the previous 555, or so it seems. The incoming (into pin 2) starts H and pulses L for about 1/10 of a second. I had issues with the C25 the .1 cap. The signal is fine up until the cap then on the other side, pin 2, it stays H. So the cap is blocking it somehow ? I couldn't find a .1 to replace, found a .01, but no change. I then bypassed the cap and the L is now getting to the 555, pin 2, but its still not working. The output (pin 3) remains H. I do plan on replacing the .1 cap. Voltage is good. How can I check this?

 

hi Earl,
How are you measuring the low going pulse on pin #2 of the 555.?
Scope, meter.???

E

Update:
On that 555 where is pin#4 , Reset connected.?

 

I then bypassed the cap and the L is now getting to the 555, pin 2, but its still not working.How can I check this?

Post the whole schematic, then we can recommend how to test.

 

I'm using a logic probe. Its a solid pulse, from H to L, it also goes to a decade counter to count down the bonus lights, works fine. I checked the board, pin 4 has no connection.

 

Post the whole schematic, then we can recommend how to test.

He already did on post #22.

 

I'm using a logic probe. Its a solid pulse, from H to L, it also goes to a decade counter to count down the bonus lights, works fine. I checked the board, pin 4 has no connection.

Make a connection from pin-4 to Vcc (pin-8).

 

okay, i'll try it

 

I made the connection today, pin 4 to pin 8 making pin 4 (reset) high. pin 2 (input) is getting the pulses but nothing is still happening. All pins except 1 (gnd) are now high. This 555 may be sour. Could I check the V on pin 7 (I think) to check for discharge on the timing circuit? 6 + 7 are tied together...

 

Could I check the V on pin 7 (I think) to check for discharge on the timing circuit? 6 + 7 are tied together...

hi Earl,
You should be able to see charge/discharge on those pins, using a Scope.

E

 

This https://forum.allaboutcircuits.com/threads/questions-on-7400-7410-ics.180630/post-1650573 guy is difficult.

To make it easier. put little balls on the wires except, when a ball enters a gate, it takes 5 delays to get out. Each ball is a piece of time.

Those devices have a propagation delay. so use closed circles and open circles within the gate mess.

It will make sense.

 

Finally some good news. I replaced IC#2 in post #34 (75492) lamp driver. The light now works. It was a bad inverter/driver in that chip for that point. Also in my latest posts, #46, I replaced the 555 IC10. It had to be bad, all pins were H. The timing circuit now works as its supposed to. I'm getting there slowly.