Z80 Rev 4.0 board BOM

90 views
Skip to first unread message

Glenn Roberts

unread,
May 21, 2021, 4:24:23 PMMay 21
to se...@googlegroups.com

This may be a question for Terry Smedley … or Norberto (?):

 

I’m going through and ordering parts to assemble the 4.0 Z80 board.  from the comments in the BOM it appears that U113 (1.8432 Mhz full size oscillator) is not needed and can be omitted? The comment in the spreadsheet says “Replaced by 3.6864MHz Oscillator at U4”.  Is this a rework of some kind?  Odd that there’s a place on the final silkscreen for an oscillator that’s not needed?

 

Another question: I believe the 78L12 and 79L12 regulators provide the 12V signals for “true” RS-232 on the serial port.  Will these work with a PC style power supply (i.e. if they have 12 V on the input side)?

 

Also as an FYI to anyone else who’s buying these parts: there’s a comment in the spreadsheet to buy the 16.384 MHz oscillator on Amazon but I’ll point out that Tayda also stocks this item.

https://www.taydaelectronics.com/crystal-oscillator-16-384-mhz.html

 

I’ve gotta think that’s a typo on the quantity in stock!?

 

 

 

  • Glenn

 

image001.png

Terry Gulczynski

unread,
May 21, 2021, 4:58:09 PMMay 21
to se...@googlegroups.com
Glenn,

The CPU board allows you to install both oscillators, with a jumper to
select which one is actually providing the clock to the DUART board.

The 3.3864MHz oscillator allows the UART to run up to 230,400 baud; the
1.8432MHz oscillator maxes out at 115,200 baud.

(Side note: A 14.7456MHz oscillator allows up to 921K baud, which is
pretty close to instant screen displays when coupled with a fast CPU.)

The problem you will likely run into with the 3.6864MHz oscillator is
that all Heath software initializes the UART with time constants that
are based on the 1.8432MHz oscillator.

The end result is that it makes life a little more difficult, but also
allows faster terminal I/O.

Having said that, note that Heath software ALSO maxes out at 19,200 baud...


The advantage comes into play when you're using OTHER software/hardware.
For instance, Les' H19 emulator allows baud rates up to 230,400 - a
good fit for the 3.6864MHz clock.

You'll still have to (likely) do something about the Heath software that
insists upon initializing the UART at the pitifully slow baud rates
commonly in use 50 years ago.

That would go against the grain for those that insist upon the 'real'
Heath experience - 'Look and feel' is paramount.

On the other hand, a 12MHz Z80 looks to be a fast machine @ 230K baud,
but it still looks to be as slow as a turtle at 9600 baud.


Anyway, all that aside, the 1.8432MHz oscillator is probably the way to
go for most people - the 3.6864MHz requires modified software.

I have no idea how the currently available EEPROM code handles it or
what it expects.


Terry
> * 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
> <mailto:sebhc+un...@googlegroups.com>.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/sebhc/040e01d74e7f%24489f6de0%24d9de49a0%24%40gmail.com
> <https://groups.google.com/d/msgid/sebhc/040e01d74e7f%24489f6de0%24d9de49a0%24%40gmail.com?utm_medium=email&utm_source=footer>.

norberto.collado koyado.com

unread,
May 21, 2021, 8:17:53 PMMay 21
to se...@googlegroups.com
 Another question: I believe the 78L12 and 79L12 regulators provide the
> 12V signals for “true” RS-232 on the serial port.  Will these work with
> a PC style power supply (i.e. if they have 12 V on the input side)?

There are jumpers on the board to bypass such regulators; JP26 and JP27 when using PC style power supply.

Norberto

From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Terry Gulczynski <terr...@cfl.rr.com>
Sent: Friday, May 21, 2021 1:58 PM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] Z80 Rev 4.0 board BOM
 
To unsubscribe from this group and stop receiving emails from it, send an email to sebhc+un...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/sebhc/7244b6e2-25ea-e5ba-ad3f-aaf593cb6261%40cfl.rr.com.

norberto.collado koyado.com

unread,
May 21, 2021, 8:53:42 PMMay 21
to se...@googlegroups.com
 Also, as an FYI to anyone else who’s buying these parts: there’s a

> comment in the spreadsheet to buy the 16.384 MHz oscillator on Amazon
> but I’ll point out that Tayda also stocks this item.

The BOM has the Amazon and Tayda links for such oscillator. The user can select what is most convenient. 

The Z80 V4.0 provides the capability to integrate additional baud rate generators oscillators for high-speed connections over network for specific user needs. ROM/OS changes will be needed.
  • U113 - 1.8432MHz - for 115.2K baud. Jumper selectable (Heath default)
  • U4 - 3.68MHz - for 230.4K baud. Jumper selectable
  • X1 - On DUART module - 14.7456MHz - for 921K baud. Jumper selectable

Norberto

From: se...@googlegroups.com <se...@googlegroups.com> on behalf of norberto.collado koyado.com <norberto...@koyado.com>
Sent: Friday, May 21, 2021 5:17 PM

Glenn Roberts

unread,
May 21, 2021, 9:01:55 PMMay 21
to se...@googlegroups.com
Thanks Norberto!

Sent from my iPad

On May 21, 2021, at 8:53 PM, norberto.collado koyado.com <norberto...@koyado.com> wrote:



Gery Kissel

unread,
May 26, 2021, 10:04:35 AMMay 26
to SEBHC
I am also ordering parts so this is good info.
A question I have is on U107, the PAL.  The BOM lists a quantity of 2 needed.  Is there another location in addition to U107?
Gery

Glenn Roberts

unread,
May 26, 2021, 10:11:33 AMMay 26
to se...@googlegroups.com

I believe U5 (ROM decoder) as well..?

 

Terry S/Norberto: shouldn’t that line in the BOM read as follows?:

 

U107,U5               NC-61 (PAL)        2                              DIP20                  

 

Douglas Miller

unread,
May 26, 2021, 10:54:54 AMMay 26
to se...@googlegroups.com

There are two GALs/PALs, but they are not both "NC-61". U5 is a RAM/ROM decoder and is programmed with something different. I'm not sure if they both use the same part, either.

Terry Smedley

unread,
May 26, 2021, 11:30:35 AMMay 26
to SEBHC
Two GALs are needed, both can be same unprogrammed part number.  F16V8BQL is the current Atmel part.  Jameco still lists the equivalent, but discontinued, Lattice GAL16V8D.  The programmer needs to know which part you are programming, but once programmed the two parts are equivalent in function.

GALs are used in two places on the board:  one to decode the I/O addresses (U107), and the other to decode the memory addresses used by the ROM (U5).  Glenn, I will  update the BOM with the correct identifiers as you noted.

The .jeds to program the two GALs can be found here:


and here:


Norberto, if I have misspoken, please straighten us all out! 

Terry

Norby

unread,
May 26, 2021, 11:49:35 AMMay 26
to se...@googlegroups.com
Thanks Terry and send me the updated BOM with the fixes.

Sent from my iPhone

On May 26, 2021, at 8:30 AM, Terry Smedley <terry....@gmail.com> wrote:

Two GALs are needed, both can be same unprogrammed part number.  F16V8BQL is the current Atmel part.  Jameco still lists the equivalent, but discontinued, Lattice GAL16V8D.  The programmer needs to know which part you are programming, but once programmed the two parts are equivalent in function.

Gery Kissel

unread,
May 27, 2021, 5:07:20 PMMay 27
to SEBHC
I plan to go old school on this and use the 7805 regulators.  What is the recommended heat sink method?  Heat sinks are not accounted for on the BOM.
Thanks,
Gery

Norby

unread,
May 27, 2021, 5:20:27 PMMay 27
to se...@googlegroups.com
Do you need an H8 heat sink? Let me know.

Sent from my iPhone

On May 27, 2021, at 2:07 PM, Gery Kissel <gkisselsp...@gmail.com> wrote:

I plan to go old school on this and use the 7805 regulators.  What is the recommended heat sink method?  Heat sinks are not accounted for on the BOM.

Gery Kissel

unread,
May 27, 2021, 5:27:32 PMMay 27
to SEBHC
Are you referring to a mounting bracket?  I had planned to use one from my old cassette interface or 16k memory board.
Should I just mount the regulators to the bracket?
Gery

norberto.collado koyado.com

unread,
May 27, 2021, 8:13:56 PMMay 27
to SEBHC
Yes, the mounting bracket which is used as a heatsink as well for the LM7805. If you need another one, I can send you one. 

This is how it should be mounted (guideline): Or you can follow Heath latest info on how to mount them.

This board support the flat mounting bracket to avoid soldering cables to the LM7805 and just solder the 7805 directly to the board and use the mounting screws to hold the regulator in place. I prefer this method better.



Norberto

From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Gery Kissel <gkisselsp...@gmail.com>
Sent: Thursday, May 27, 2021 2:27 PM

Steven Feinsmith

unread,
May 27, 2021, 8:45:01 PMMay 27
to se...@googlegroups.com
I looked at the picture. The voltage regulators are mounted outside from the board via a bracket.
It will be better to mount the opposite side. The wires will not have to cross the metal edge. The short length of the wire is better than the long one.
The best way is to have the voltage regulators mount on the PCB and put the heatsink compound to mount on metal brackets to distribute the heat.

Steven

norberto.collado koyado.com

unread,
May 27, 2021, 8:49:01 PMMay 27
to se...@googlegroups.com
I will send you the correct picture once I get home.


From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Steven Feinsmith <steven.f...@gmail.com>
Sent: Thursday, May 27, 2021 5:44 PM

Glenn Roberts

unread,
May 27, 2021, 9:25:16 PMMay 27
to se...@googlegroups.com
The original Heath instructions used a 3-connector Molex housing to provide a detachable connection to the 7805. Not sure why they went this way. In reading through some of the old newsletters it appears this was problematic and a common fix was to simply solder the wires to the regulator.

Sent from my iPad

On May 27, 2021, at 8:49 PM, norberto.collado koyado.com <norberto...@koyado.com> wrote:


I will send you the correct picture once I get home.


From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Steven Feinsmith <steven.f...@gmail.com>
Sent: Thursday, May 27, 2021 5:44 PM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] Z80 Rev 4.0 board BOM
 
I looked at the picture. The voltage regulators are mounted outside from the board via a bracket.
It will be better to mount the opposite side. The wires will not have to cross the metal edge. The short length of the wire is better than the long one.
The best way is to have the voltage regulators mount on the PCB and put the heatsink compound to mount on metal brackets to distribute the heat.

Steven

On Thu, May 27, 2021 at 8:13 PM norberto.collado koyado.com <norberto...@koyado.com> wrote:
Yes, the mounting bracket which is used as a heatsink as well for the LM7805. If you need another one, I can send you one. 

This is how it should be mounted (guideline): Or you can follow Heath latest info on how to mount them.

This board support the flat mounting bracket to avoid soldering cables to the LM7805 and just solder the 7805 directly to the board and use the mounting screws to hold the regulator in place. I prefer this method better.

<image.png>

Steven Hirsch

unread,
May 27, 2021, 9:34:11 PMMay 27
to se...@googlegroups.com
On 5/27/21 9:25 PM, Glenn Roberts wrote:
> The original Heath instructions used a 3-connector Molex housing to provide
> a detachable connection to the 7805. Not sure why they went this way. In
> reading through some of the old newsletters it appears this was problematic
> and a common fix was to simply solder the wires to the regulator.
Yes, I'm sure the contacts in those connectors went the same way as the Molex
connector that ties the transformer to the PS board in an H89. Both of my
units had a burn spot about the size of a dime on the plug.

Terry Smedley

unread,
May 27, 2021, 9:34:58 PMMay 27
to SEBHC
This is the method that Norberto suggests.  It utilizes a flat mounting bracket.  The regulator can be mounted to the bracket/heat sink and the leads soldered directly to the board with no connectors or wires.  As Glenn noted, the 3-position connector that Heath used was prone to developing resistance over time.

Terry

H8HeatSink2.jpg
H8HeatSink1.jpg

Norby

unread,
May 27, 2021, 9:55:34 PMMay 27
to se...@googlegroups.com
Thank you Terry for the pictures. This is the alternative to avoid soldering wires directly to the regulators.

Sent from my iPhone

On May 27, 2021, at 6:35 PM, Terry Smedley <terry....@gmail.com> wrote:

This is the method that Norberto suggests.  It utilizes a flat mounting bracket.  The regulator can be mounted to the bracket/heat sink and the leads soldered directly to the board with no connectors or wires.  As Glenn noted, the 3-position connector that Heath used was prone to developing resistance over time.
To view this discussion on the web visit https://groups.google.com/d/msgid/sebhc/580fbd6c-111c-4989-9bdb-d37250105db7n%40googlegroups.com.
<H8HeatSink2.jpg>
<H8HeatSink1.jpg>

Peter Higgins

unread,
Jul 23, 2021, 12:47:02 PMJul 23
to SEBHC
Some updates to the BOM for this board:

1. The 72421 RTC (U103) is an obsolete part that Mouser (listed as the sole source in the BOM) no longer has in stock. It is also no longer available from DigiKey, and the usual sources of obscure and/or obsolete parts (like Unicorn and Anchor) do not have it. It seems the only remaining source is eBay.

2. The 5 position header for connection to the front panel (P201) is also an obsolete part no longer available from the listed sources (Jameco and Mouser). With an internet search one can find a few places still selling it, but you might end up paying $20 or more in shipping to acquire just this one $0.35 part.

George Farris

unread,
Jul 23, 2021, 2:36:48 PMJul 23
to se...@googlegroups.com
I just ordered 5 of the 72421A parts from Hong Kong, I will keep one as a space but the other 3 are up for grabs (assuming they are genuine:-))

Cheers
George
--
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.

George Farris

unread,
Jul 23, 2021, 2:41:05 PMJul 23
to se...@googlegroups.com
Just curious, are there any other "problem" parts that should be ordered right away?

George

Peter Higgins

unread,
Jul 23, 2021, 2:55:34 PMJul 23
to SEBHC
Other "problem parts" that will likely become hard to source:
- many of the 74HCT series devices
- the bus connectors P1 and P2. These have been previously discussed, and if you find a source with reasonable shipping costs you should buy them right away. The large suppliers currently do not have them in stock with possible return of stock later this year
- probably a good idea not to delay acquiring parts with a specific circuit board footprint (like the battery holder and the variable potentiometers) as listed in the current BOM

Steven Feinsmith

unread,
Jul 23, 2021, 4:13:27 PMJul 23
to se...@googlegroups.com
I started to notice many components were in shortage due to the pandemic situation. The price seems increased, and there is a lack of availability. I presume many leading vendors want to get rid of components from stock as possible and then put these popular components as obsolete products to reduce the inventory.

Steven

--
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.

norberto...@koyado.com

unread,
Jul 23, 2021, 4:15:01 PMJul 23
to se...@googlegroups.com

The substitute for the RTC-72421 is the surface mount RTC-72423. I will need to develop an 18 Pin to 24 pin breakout board. The pcb can install the surface mount part as my eyes are not that good anymore.

 

Something similar to this:

 

On the 74HCT parts, they can be substitute with 74ALS, 74F, or 74LS as needed. You can check this website as well: https://www.futurlec.com/IC74Series.shtml

 

For the 5-pin position you can order form amazon: https://www.amazon.com/dp/B01M69TKAM?psc=1&ref=ppx_yo2_dt_b_product_details as the other connectors are used across other boards and on the backplane.

 

 

 

Norby

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Peter Higgins
Sent: Friday, July 23, 2021 9:47 AM
To: SEBHC <se...@googlegroups.com>
Subject: Re: [sebhc] Z80 Rev 4.0 board BOM

 

Some updates to the BOM for this board:

 

1. The 72421 RTC (U103) is an obsolete part that Mouser (listed as the sole source in the BOM) no longer has in stock. It is also no longer available from DigiKey, and the usual sources of obscure and/or obsolete parts (like Unicorn and Anchor) do not have it. It seems the only remaining source is eBay.

 

2. The 5 position header for connection to the front panel (P201) is also an obsolete part no longer available from the listed sources (Jameco and Mouser). With an internet search one can find a few places still selling it, but you might end up paying $20 or more in shipping to acquire just this one $0.35 part.

 

--

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.

image001.png
image002.png

Steven Feinsmith

unread,
Jul 23, 2021, 11:47:58 PMJul 23
to se...@googlegroups.com
I have no problem getting an obsolete RTC chip. Here is:

5PCS RTC72421 EPSON DIP-18 4-bit REAL TIME CLOCK MODULE NEW 
5PCS RTC72421 EPSON DIP-18 4-bit REAL TIME CLOCK MODULE NEW
Total: $8.47
Order number: 25-07374-47107
Item ID: 144104528835
Seller: bestbuy_ca(10,968)
Money Back Guarantee


Peter Higgins

unread,
Jul 24, 2021, 12:53:29 AMJul 24
to SEBHC
Yes, I did mention that eBay now seems to be the only place one can buy an RTC72421, and there are at least 40 listings for this part :)

BTW, in case anyone is wondering about the difference between the RTC72421A and the RTC72421B since both versions are being sold by different eBay vendors:
- the  "A" version has a frequency tolerance of +/- .00001
- the "B" version has a frequency tolerance of +/- .00005
Reply all
Reply to author
Forward
0 new messages