H19 Keyboard Compatibility (1878 vs 1981)

[Scott Miskiv]

Hello there.  You helped me previously identify the tube color/type and I thank you all again for that help.

I am hoping to tap into you experience here again if I can. 

I have two H19 terminals, one from 1978 (non-working) and the other from 1981 (working).  The 1981 unit has a bad key which I may have to delve into further to see if it can repaired.  One of the switch poles is broken unfortunately.  In the mean time I was wondering if I could use the 1978 keyboard in the 1981 unit, or is it incompatible possibly due to the Keyboard encoder, or something else?

BTW, searching through all the conversations here, I saw the new project in which the keyboard is replaced with a modern equivalent and I would love to go that route if that is a possibility at some point in the future. Great engineering!!!

Thanks, 

Scott

[glenn.f...@gmail.com]

I believe all the H19/89 keyboards are interchangeable.

 

It’s true that a few of us have implemented Terry’s re-engineered H19 keyboard. We don’t yet have this in “production” but I’m happy to help pave the way for that if I can help. Perhaps we can get Todd to stock some blank PCBs…

 

• Glenn

--
You received this message because you are subscribed to the Google Groups "SEBHC" group.
To unsubscribe from this group and stop receiving emails from it, send an email to sebhc+un...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/sebhc/17e993a4-4c13-4fde-a51f-1fbed39326d0n%40googlegroups.com.

[Todd Goodman]

I'm happy to stock boards and perhaps take a look at qty discounts on keyswitches and caps?

Todd

To view this discussion visit https://groups.google.com/d/msgid/sebhc/008501db6133%242e8f2100%248bad6300%24%40gmail.com.

[Scott Miskiv]

Thanks Glenn!  Appreciate the quick response. Definitely interested in Terry's re-engineered H19 keyboard project as well.

[Scott Miskiv]

I'd be interested Todd! 

[Lee Adamson]

I have used the 89 and 89A keyboards interchangably.  As far as I can tell, the only difference is that the -A keyboard is a little better shielded.  Maybe to cut down on RFI on broadcast TV?  If that is the case, it probably doesn't make any difference anymore.

[Scott Miskiv]

Hi Lee,

That's good to know that the 89 and 89A keyboards are interchangeable as well (if I ever get one of those)! Interesting observation on the shielding.  Thanks for the info.

[glenn.f...@gmail.com]

One of the primary goals of the H89A (and the H19A) was to add appropriate RF shielding.  This does make it a little more challenging to work on the “A” versions…

 

 

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Scott Miskiv

Sent: Wednesday, January 8, 2025 11:01 AM
To: SEBHC <se...@googlegroups.com>

--

You received this message because you are subscribed to the Google Groups "SEBHC" group.
To unsubscribe from this group and stop receiving emails from it, send an email to sebhc+un...@googlegroups.com.

To view this discussion visit https://groups.google.com/d/msgid/sebhc/e6b6fc3e-5435-4b5a-a8d7-e5de50f7a415n%40googlegroups.com.

[norberto.collado koyado.com]

The keyboard was shielded to dissipate ESD as the Keyboard IC was being damaged when people discharged such voltage when touching the keyboard. 

Get Outlook for iOS

---

From: se...@googlegroups.com <se...@googlegroups.com> on behalf of glenn.f...@gmail.com <glenn.f...@gmail.com>
Sent: Wednesday, January 8, 2025 8:05:32 AM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: RE: [sebhc] Re: H19 Keyboard Compatibility (1878 vs 1981)

 

To view this discussion visit https://groups.google.com/d/msgid/sebhc/077d01db61e7%24257f21f0%24707d65d0%24%40gmail.com.

[Scott Miskiv]

Thanks all for updating me on H19 vs H19A keyboard shielding.  I was wondering about that when I switched the keyboards and noticed the cable connections on both sides of the metal bracket of the keyboard. Makes sense they had to fix the static discharge problem.

[Terry Smedley]

I have a Z19-CN, the commercial version of the H19, which I believe was introduced after or about the same time as the H19A (1981)?

I found it interesting that the commercial version did not include the braided ground connections or shielded ribbon cable for the keyboard that were introduced with the H19A. 

tas

[Glenn Roberts]

Wondering if the RF shielding rules were the same for home-use vs. commercial equipment?

Sent from my iPad

On Jan 9, 2025, at 12:35 PM, Terry Smedley <terry....@gmail.com> wrote:

I have a Z19-CN, the commercial version of the H19, which I believe was introduced after or about the same time as the H19A (1981)?

To view this discussion visit https://groups.google.com/d/msgid/sebhc/747df7fa-36af-48e4-b61a-dea39d0b8496n%40googlegroups.com.

[Terry Smedley]

I assume that Zenith registered the Z19-CN as a Class A device which would permit more emission than a residential Class B device.  I can't find an FCC label on mine.  But I was surprised that the static discharge issue wasn't considered a problem with the Z19-CN design.  I assume that the purpose of the braided ground connections to the steel mounting brackets as found in the H19A was to bleed a discharge away from the keyboard in a less harmful fashion than through the innards of the MM5740.  I would have thought that would be at least as important in an office environment.

Venturing off topic here, but overall, the Z19-CN feels like it has undergone a round or two of manufacturing cost reductions compared to the Heathkit versions.  For starters, we can measure the temperature of that tiny power transformer.....

tas

[Joseph Travis]

The additional shielding, ground straps, etc. were only required on computers intended for home / personal use.  The Zenith versions were considered to be commercial use and did not have to meet the same FCC RFI requirements as the home computers.

BTW - There isn't any static discharge problem - I don't know where that idea came from.

Yes, the Z19-CN is a reduced cost (higher profit margin) version of the H19A.  I think they came out in '83 or '84.

Joe

To view this discussion visit https://groups.google.com/d/msgid/sebhc/db9b035c-36f8-426d-945b-35b50906c397n%40googlegroups.com.

[glenn.f...@gmail.com]

There was a discussion back in 2012 on the static issue and the MM5740.  Here’s a piece of that from Lee Hart:

 

Lee

<leea...@earthlink.net>

Sep 3, 2012, 12:12:00 PM







to se...@googlegroups.com

On 9/3/2012 9:44 AM, Jack Rubin wrote:
> Apparently, they are extremely ESD sensitive. I'm hoping Lee Hart will add
> some info. I've had prior communication with him about the encoder (several
> years ago) and he may be able to provide more details and field experience.

The MM5740 is a very old PMOS chip, which predates NMOS and CMOS
technologies); thus the need for a -12v supply. I have a printed data
sheet on it if anyone is interested.

It is normally a very reliable IC. In my experience, the two most common
ways to kill it are loss of the -12v supply while the +5v supply is
still present, and to zap it with static electricity.

The -12v supply can be lost if the -12v regulator on the TLB fails, or
something on the TLB board shorts it (like failure of the RS-232 driver
or receiver chip). Static can zap it if you handle the TLB board outside
the case, and touch the keyboard input connector before something that's
grounded (the heatsink along the top is good).

Warning: There is a ROM inside the chip that determines the output
codes! The 3 letters marked xxx (MM5740xxxN) define the codes; the final
"N" says it's a 40-pin DIP package. Heath used the MM5740AACN. If you
get a chip with a different suffix, it will produce the *wrong codes*
for the H19 keyboard!
--
Results! Why man, I have gotten a lot of results. I know several
thousand things that won't work. -- Thomas A. Edison
--
Lee A. Hart http://www.sunrise-ev.com/LeesEVs leea...@earthlink.net

 

 

And more of the thread:

H19 input problem

 

I know I’ve lost at least one of these chips over the years and there were other similar stories shared at the time. Mark found a source and we did a group buy. Lee’s comment about vulnerability to damage if -12V is lost is interesting given how often people have issues with tantalums (especially on the +/- 12V sides).  Perhaps that explains the failures as much as any static issue ???

 

• Glenn

To view this discussion visit https://groups.google.com/d/msgid/sebhc/CAGQDgBApvphd0dZX0tYxAbuiSz1wt9u5k8HCbTN4N7grBUEGow%40mail.gmail.com.

[Joseph Travis]

Thanks for the additional info Glenn.  However, ESD is more of a handling issue, not an operational issue.  If there was a static discharge issue that shielding and ground strapping solved, certainly you would see it in all versions of the terminal / computer.

Joe

To view this discussion visit https://groups.google.com/d/msgid/sebhc/0a5701db62e0%24681cb5f0%24385621d0%24%40gmail.com.

[Joseph Travis]

I apologize for the tone of my previous response.   It wasn't my intention to come off that way.

Joe