Dick Smith / EA function generator

[BCNZ]

I was given this recently and while it's not a piece of test gear I would really use (I have commercial gear to do this stuff) I thought it was
an interesting piece and worthy of at least making it work.
The Dick Smith code is K-3520 and it featured in the April 1982 edition of EA.
It produces all the waveforms that it's supposed to, but the frequency display doesn't work as it should.
I've been looking at some of the timing signals throughout the various ICs and what I am seeing doesn't look right, but I can't see why.
I've swapped out the ICs for new ones and that hasn't remedied it, so now I am to the stage of looking for one of these machines
that is in working condition so I can compare signals.
Anyone have one on their shelf?

[wotnot]

I guess you already found this? -->

It produces all the waveforms that it's supposed to, but the frequency display doesn't work as it should.

Can you elucidate a bit about the actual nature of the display failure?

[BCNZ]

Hey Wotnot, it doesn't display the frequency - usually just random numbers or stuck on one number (as shown in the photo).
I've been looking at the logic levels and waveforms of the counting section and something isn't right but as yet I can't see what that is or what's causing it.
Yes - I have the construction manual for it, with the schematic etc - thanks

[wotnot]

Hey Wotnot, it doesn't display the frequency - usually just random numbers or stuck on one number (as shown in the photo).
I've been looking at the logic levels and waveforms of the counting section and something isn't right but as yet I can't see what that is or what's causing it.
Yes - I have the construction manual for it, with the schematic etc - thanks

Have you addressed the addendum/errata at the bottom of page 7 (under circuit diagram)?

At which point in the circuit do the logic levels get screwy?...(and define screwy =)

[BCNZ]

Yes, the modifications in the two subsequent errata were done, but I tidied them up as the previous owner or whoever did them wasn't the neatest with their soldering - and therein lay a clue to the problem.
I was puzzled by the waveform at IC7b.
A reasonable square wave was going in on pin 3, but coming out as a bouncing square wave on pin 4. It just wasn't right.
Something told me to take a closer look at the tracks on the underside, specifically the track from pin 4 across to IC6.
Close inspection using more magnification than what my eyes could provide showed a small solder splash between the track and the one next to it which goes to pin 12 of IC6 - so effectively pins 12 and 13 were shorted together.
It's working as it should now.

Thanks for stopping by and offering your input!

[wotnot]

Yes, the modifications in the two subsequent errata were done, but I tidied them up as the previous owner or whoever did them wasn't the neatest with their soldering - and therein lay a clue to the problem.
I was puzzled by the waveform at IC7b.
A reasonable square wave was going in on pin 3, but coming out as a bouncing square wave on pin 4. It just wasn't right.
Something told me to take a closer look at the tracks on the underside, specifically the track from pin 4 across to IC6.
Close inspection using more magnification than what my eyes could provide showed a small solder splash between the track and the one next to it which goes to pin 12 of IC6 - so effectively pins 12 and 13 were shorted together.
It's working as it should now.

Thanks for stopping by and offering your input!

Totally makes sense, and good find! Typically I check mods very carefully, as they've often been the root cause =)