Questions on 7400 +7410 ics

Thread Starter

Earl Wright

Joined Jul 18, 2021
16
The issue i'm having is LD56 10 point and LD54 (mislabeled as 66) 1000 point are both flashing together and sending a signal to the displays which are advancing both the 10 and 1000 point digits. This is after the ball in play switch has been cycled and the logic (playfield logic reset) is released. I've followed it back to the 555, LD53 is flashing at the same rate. It also looks like it might go to another area. This is where I am, trying to locate what might be happening. There does not appear to be a stuck on switch on the playfield.
 

Thread Starter

Earl Wright

Joined Jul 18, 2021
16
No unfortunately not, however, good news, I was double checking my 10 point circuit and discovered a previously overlooked contact that was stuck closed. After I isolated it the 10 point problem has gone away. It was the contact, so I’m guessing the 1000 point is the same but no direct 1000 point contacts on playfield, going to look further.
 

MrChips

Joined Oct 2, 2009
23,891
How would an oscilloscope help? I’ve used one in the past
With an oscilloscope you can probe exactly what is going on at any node in your circuit.
Here are some examples of things that can be observed:

1) when there is excessive noise on the power supply lines, e.g. defecting filter capacitors
2) a drooping power supply voltage or transient, for example, when a solenoid is activated
3) noise or artifacts on signal lines and power supply lines
4) invalid voltages on a signal line, for example, missing or faulty pull-up resistors, bad switch contacts
5) weak output signals from a gate output pin
6) too slow or too fast rise-times caused by defective capacitors on signal lines
7) actual frequency or pulse widths on clock signals, e.g. 555-timer circuits
8) malfunctioning switches, gates, components etc.

In other words, the oscilloscope is your best and essential diagnostic instrument in this line of work, much more useful than a DMM (but also complements it) .
 

Thread Starter

Earl Wright

Joined Jul 18, 2021
16
Thank you, I shall consider it. Post 23 above, the 78H05 regulator , its a 5A, is smoking hot and as it warms up the voltage will slowly sink to 4.8. There is a modification memo to this that it is an issue, not big enough. I'd like to increase the capacity of this i.e. get a bigger one, what would you folks suggest as an upgrade to power capacity here? The caps are new and 10,000 mfd. AC ripple as measured by VM is very low.
 

Thread Starter

Earl Wright

Joined Jul 18, 2021
16
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.
 
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