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Posted By

MMS
on 2020-05-26
17:09:20

ESD protection of TED?

There was a lot of debate and discussion of the potential failure mode of the TED IC.

Herewith I try to add one forum topic outside here, where they state, that "his PCB protects the IC chips (CIA, SID etc.) from ESD shocks originating from the joystick port. It's a common fault for C64."
Well, AFAIK C64 is more protected against such shocks, than TED, we are talking about even few thousand Volts/sparks (with very low energy).
https://www.lemon64.com/forum/viewtopic.php?t=73032

Also, there is an open project at PCBWay, where you can order a kind of TED protector / C64 joystick interface may do the same job for you. It is a project from SukkoPera.
I think MCeS called my attention to it.

I ordered few of them, and they look great. The PCB still not populetd with ICs.
https://www.pcbway.com/project/shareproject/OpenC16JoyAdapter_V2.html

It is clearly mentioned the PCB is based on Levente's work:
http://www.zimmers.net/anonftp/pub/cbm/documents/projects/interfaces/plus4joy/plus4joy.html
Worth to read.

Posted By

MCes
on 2020-05-27
06:23:43

Re: ESD protection of TED?

There is a simple way to protect the TED input pin... a zener diode soldered at each joy input on the relative FB wire.

Zener is a diode: if input become negative the zener will limit this -V to -0,7V, this voltage will pass inside the native diode (D1..10) becoming less or more 0V (inside the accepted voltage range of the TED chip).

If the input become more positive than Vcc the native diodes will be "open" protecting the TED input, but if the voltage will be over 50V the "native diode" can become a current passage to TED pin: the zener will limit the input voltage at level of its label voltage permitting to the "native diodes" to insulate perfectly (protecting) the input TED pins.
For example the zener voltage could be more than 6V and less than 24V, I suggest 6,2...12V

This solution is safe, cheap, and easy to assemble on motherboard without other cable/connector/ecc....

Posted By

unclouded
on 2020-05-27
05:58:54

Re: ESD protection of TED?

Is this similar to the recommended change for the serial port?

Posted By

MCes
on 2020-05-27
06:11:32

Re: ESD protection of TED?

@unclouded:
It's similar, it start from the same dangerous situation (extra voltage injection on sensible pins).

Another tip: people know that TED could be HW "stressed" by input pins connected with external world, also Commodore found that is necessary to protect this pins, but what about the CPU pins connected to cassette port? could it be the raisons of some CPU failures? "Cassette Read" line is not protected!

Posted By

MMS
on 2020-05-27
10:11:35

Re: ESD protection of TED?

Thank you for the details and the schematics. Yeah, it makes sense.

It is an interesting question, if those diodes (on the serial port) are in place on the early Mobos too?
(so it is JUST ht edocumentation, or there are different variations of the Mobo?)

AFAIK the similar joystick connectors are not protected in the same way, and as MCes told, the cassette read port behaves the same (on the other hand, everyone knew, that you should not plug in and plug out the datasette, but it was a common practice with the joysticks. Certainly it does not "mind" the ESD, if your computer is on or off, it just kills )

Posted By

Hifi
on 2020-05-27
13:58:32

Re: ESD protection of TED?

Helló,helló Újra Itt vagyok! Üdv Mindenki! Ez a joy (mérnökök által tervezett DIÓDÁS megoldás) kezelés egy egyszerű megoldás magában rejti a VESZÉLYÉT is.Például a már általam említett NE555-ös gyors tüzelésű joy-nál a négyszögből (5V) NEGATÍV feszültséget generálhatott,ami veszélyes a NEM védett CMOS eszközökre! A negatív feszültségre az akkori IC-k nagyon érzékenyek voltak (még ma is!)! A védelmet az IC-ből a gyorsabb működés elérése miatt kellett kihagyni!Persze a joy be- és kihúzásai is generálhatott veszélyes feszültségeket akkor is,HA a készülék kikapcsolt helyzetben volt! DE mint már említettem a TED tovább működött, a billentyűzet,a szín,a grafika,a RAM frissítés és a programok működtek,CSAK a joy rosszalkodott (SKORO of ASN gépénél is volt ilyen eset)! Persze hosszabb

használat után a TED is meghibásodhatott.....tehát ESD védelemről igazán NEM beszélhetünk ezeknél a gépeknél (esetleg valami minimumról!). Good-Bytes! HiFiofTLT.

Posted By

SVS
on 2020-05-27
14:26:21

Re: ESD protection of TED?

Back the years, Solder (Synergy) designed and made a protection circuit able to avoid the TED damages caused by joysticks.
I own one in my 256Kb Plus4 and it worked very well. See here.
I suppose there is the schematic somewhere.

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