AY-5-1202A clock IC
 

1970s digital clock kit I made as a boy was working until recently. The colon no longer flashes and the buttons don't set the time. All the discrete components check out, so I think the AY-5-1202A integrated circuit may have failed.

Does anyone know where I can get a replacement AY-5-1202A?

I would really like to get this clock working again for sentimental reasons - thanks.

Re: AY-5-1202A clock IC
 

Here's one:

https://www.donberg.co.uk/catalogue/ay-5-1202a.html

Re: AY-5-1202A clock IC
 

Donberg in the Republic Of Ireland have them, but at a high price:

https://www.donberg.ie/catalogue/sem...y-5-1202a.html

Edit: Cross posted with Dickie

Your symptoms suggest that there is no clock input to the IC - I would expect the clock input pulses for this type of IC were derived from the mains input frequency, so make sure there is no fault in that signal path before replacing the IC.

Re: AY-5-1202A clock IC
 

In case you haven't already got one, the data sheet for the IC is here. https://islandlabs.eu/_media/ay-5-1202.pdf The display has all digits lit, so the multiplex clock and multiplexing must be working. Check the clock input on pin 24 and that there is no leakage in the switches, especially the reset switch as the pull ups in the ic are weak and it doesn't take much leakage to cause the pin to be stuck low, also the ic socket contacts must be clean

Re: AY-5-1202A clock IC
 

Thanks for the ideas and the links.

Referring to the IC's block diagram, I suspect the fault lies in the "divider logic" section, as none of the switches work, and the mains 50Hz pulses are not getting through.

@Rubberfingers, I added the IC socket after the fault occurred so I don't suspect the socket. I also checked for high resistance leakage in the switches (especially reset), but they all are fine. Good idea though.

The General Instruments AY-5-1202A chip seems to be pretty rare. Does anyone know of any other product that ever used it?

Re: AY-5-1202A clock IC
 

Fingers, well done finding that link, I hunted for that datasheet absolutely everywhere and could not find it.

The IC obviously does have the multiplex clock on pin 23 because the multiplexed display is being maintained. loss of 50Hz / 60Hz input to pin 24 could still be the cause, both of the clock not running and the adjustment buttons having no effect, if you have not specifically checked for that yet.

Do you have a scope which you can use to take a look on pin 24? If you have a look at the two application circuits at the end of the datasheet these give some idea of how the 50Hz / 60Hz is sampled from the AC side of the mains transformer - the circuit for your clock is likely to be very similar.

Another thing you could try is to (temporarily) disconnect whatever is connected to pin 24 and supply your own alternative low frequency clock to that pin to see if that makes the clock run.

With the chip apparently being so rare and expensive, I would explore every possible avenue before going to the expense of replacing the chip.

Re: AY-5-1202A clock IC
 

Clarification, that should have read

Re: AY-5-1202A clock IC
 

It looks like there's no mains transformer in this clock, just a 1uf capacitive dropper, in fact it's likely to be based on the second circuit diagram on the datasheet that I posted previously, so do not connect earthed test equipment to it without powering it from an isolation transformer.

Re: AY-5-1202A clock IC
 

Thanks @SirusHardware

According to the datasheet "Multiplex Oscillator - An external capacitor is used to select the multiplex frequency". So the display multiplexing is asynchronous and independent to the mains clock frequency. As no 50Hz is actually steered into pin-23.

I'll put a scope on pin-24 (clock input) with respect to pin-1 (ground) and see what's there. And obviously power the clock through an isolating transformer.

BTW - there is a typo on the schematic Fig.2 on the datasheet. The pin-2 voltage should read -17V not 1.7V.

Re: AY-5-1202A clock IC
 

Oops, crikey, I didn't see that coming. I thought the mains TX must just be out of shot somewhere - but I see i4cy has his eye on the ball anyway.

Capacitive droppers have one Achilles heel - they rely on the mains frequency being low so that the (low value) capacitor presents a relatively high 'resistance' at that frequency. The problem is that the capacitor will be much better at passing on any sharp (ie, high frequency) spikes which may occur on the mains - I'm not really a fan of capacitive mains droppers for that reason.

Re: AY-5-1202A clock IC
 

There was a General Instruments application note that referred to the AY-5-1200 - I recall this having
built the digital frequency meter circuit based upon its stablemate, the AY-5-8100. I used it in conjunction with my homebrew FM-DX tuner (P.W. 'Sandown') and thereafter, the early range of tunerheads/tunersets marketed by Ambit International. Keeping the 'shash' out of the low-level RF stages was almost impossible (even when using the likes of a diecast box, feed-through capacitors for the Futaba 5-LT-03 vacuum fluorescent display driver lines etc.etc.). It was a self-started developmental experience which subsequently prompted William Poel to look at the the likes of the Xylex DTI-100 and upcoming Large-Scale-Integration chips such as rhe MSM5526/5527 from Oki Semiconductor (Ambit catalogues refer).
Guy

Re: AY-5-1202A clock IC
 

Oh yes, this design uses the capacitive dropper technique to keep cost to a minimum. Indeed this method is not immune to spikes, I'm not a fan either, but that is how this 1970s kit came, and it had been working for decades. When it is working again I will include an MOV surge suppressor.

If I cannot source a replacement AY-5-1202A easily, I may be tempted to emulate this IC using a VFD driver and microcontroller.

Re: AY-5-1202A clock IC
 

Here's the link for the GI General Product Catalog 1977:

http://www.wass.net/othermanuals/GI ...977 - Full.pdf

It's 22.7MB.

Page 24 covers the AY-5-1200A/1202A clock IC; the data on AY-5-8100 on page 43 shows the basis of an MF/HF/VHF radio frequency read-out system (and also refers to AY-5-1200A/1202A).

Hope this helps! :)

Guy

Re: AY-5-1202A clock IC
 

That AY-5-1202A looks like it is sitting in an IC socket. There may be tarnish on that IC's pins and also the individual sockets of the IC socket. Before buying a replacement AY-5-1202A, check the state of the IC pins (cleaning them if required) and possibly replacing the IC socket.

Al.

Re: AY-5-1202A clock IC
 

The socket (only recently fitted) was mentioned in #4 and #5. The IC was presumably still soldered in directly when the fault originally manifested itself.

Re: AY-5-1202A clock IC
 

Correct.

Re: AY-5-1202A clock IC
 

I've done some checks with a scope and meter using an isolation transformer.

• IC supply voltage is -16.03v (should be -17v)
• 50Hz clock input goes to -16v with respect to Vss. See scope picture.
• All three switches are internally pulled to Vdd when not pressed, pressing each shorts to 0v.
• -35v supply reads -33.8v.
• Checked ESR of 50uF - checks out GOOD.

As suspected, all points to the IC having gone to silicon heaven.

Re: AY-5-1202A clock IC
 

To be honest I initially thought that the fact that the clock was nowhere above zero volts must be a fault but I see from the data sheet that the chip does expect a negative going -(8V) clock. I live and learn.

Sadly, must agree that it is seeming increasingly likely to be failure of the first stages within the chip, maybe the clock input itself got zapped.

Re: AY-5-1202A clock IC
 

Indeed, and from a time when it was fashionable to use a positive ground.