View Full Version : Netronics Explorer/85

September 8th, 2016, 04:08 PM
My Explorer/85 board arrived today.



Looks to be in decentish shape. I was hoping for the variant or 'level' that had the case, PSU and keyboard, but, these are exceedingly rare (this is the first one that has come up I think in 2 years plus), so I'll take what I can get. Netronics stuff seems to be hotly contested these days on ebay so it was nice to get it for just over a couple hundred dollars.

I suspect this was together with that keypad we saw. The same seller also sold an expansion board that increases the number of S100 slots to 6. But for some reason some knuckleheads fought over it and it was at almost $130USD which I thought a bit much for what it is. Do kind of wish I'd grabbed the keypad, but I'm hoping the serial terminal function exists and works on this.

I *think* that 25 hole area shaped like a DB25 is probably the serial connection. I'm really not sure how this thing was interfaced before, probably just by hex keypad. Key will be figuring out what level it is and then working backwards from there. The board is a Rev C. I notice they didn't solder in a reset button, so I'm assuming that must have been done via keypad.

I don't unfortunately have any power supplies that crank out 8V.. so probably time to invest in a good bench supply so I can roll with these things.

I've put higher res pics here for those curious:


September 8th, 2016, 04:23 PM
Darn. I just looked on ebay and noticed I missed the power supply for this thing from the same seller. Someone grabbed it the second they put it up (it was BiN).

I also noticed this card: http://www.ebay.ca/itm/VINTAGE-VECTOR-BOARD-with-SN74154N-DM74154N-DECODERS-X0-X1-IN-X0-X1-OUT/351831471348?_trksid=p5411.c100170.m2943&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1% 26asc%3D20140616153347%26meid%3Dcf1036fef8244306ab 759b4cfb764aab%26pid%3D100170%26rk%3D1%26rkt%3D15% 26sd%3D351831471348

Kind of looks S100? Wonder if it was what they were using for input/output.

September 8th, 2016, 04:42 PM
Yeah, that's a Vector S-100 protoboard. Probably some parallel I/O interface to an experiment or project.

September 10th, 2016, 05:39 PM
Hi Falter,
Did you get some manuals or documentaion for it? I have bought one from a guy here in Surrey, BC (looks like it was made from scratch--Netronics kit?). It is comprised of a big board like yours, an ASCII keyboard and some manuals or documentaion. Was lucky to get it for $40Cdn but that is about 3 yrs ago. Unfortunately, I have not touched it since I got it.
I may have to dig it from storage and see what else came with it. I believe this was lower level as per Wiki.


BTW...THE MANUALS can be downloaded from here (maybe you already know����)

October 26th, 2016, 04:26 AM
I'm trying to get a couple of dead S-100 systems up in running after having them in storage for years (decades?) and recently dug out my Netronics Jaws 64K Ram board I bought for use with my Quest Super Elf single board computer (also dug out) back in the early days. I also have a Netronics video terminal board that needs some TLC to get up and running again. A couple more projects to try to make work.

October 26th, 2016, 05:35 PM
I've figured via the manual out that mine was in fact configured for hex keypad use.. so that is at least known and that is what that keypad was for. Still kicking myself for missing the psu but whatever.

The manual is a bit circumspect on how to wire up for serial terminal. There are holes on the board arranged in a pattern that look suspiciously like a DB25 but for some reason I can't find a pinout for it.

I wish I'd grabbed the expander. And although it is unlikely I hope a case appears some day.

December 2nd, 2016, 06:32 AM
Took me years to get a case - wound up buying a whole "new" EX-85. Did you fined a Power supply yet? I may have an extra one if I can locate it.
Do you have a way to read the monitor chip love to get a copy of the keypad monitor. I have the files for the Keyboard monitor and the MS basic as well. My programmer can program 8755s if you need on made.

FYI my first EX-85 was a kit purchased new in 1979 (also my first computer) The monitor is heavily based on the SDK-85 so you might want to look at documentation as well.

December 2nd, 2016, 06:42 AM
Forgot to mention looking at the pics of the board, if you haven't figured it out yet the 24 pin socket net to the monitor is the keypad interface, I believe that version did not support a serial console.

December 3rd, 2016, 10:13 PM
I was reading through the manual a while back.. IIRC my board is version C. In the manual they describe jumpers you can set to use a serial interface. But yeah.. I don't recall where one hooked it up.

December 4th, 2016, 08:15 AM
Physically it will support serial interface but I think the hex monitor does not have a serial console routine. You would have to load a program for that. Can you burn 8755s? If so you can replace the hex monitor. I would like a copy of the hex monitor if possible. If you can't I think I have an extra 8755 I could burn the serial console monitor in to.

The board uses the SID and SOD pins for serial in and out and for the cassette tape in and out. J1-3 is the output and J1-2 is input J1-1, 7, and 19 are all grounds.

February 12th, 2017, 12:18 PM
I still have my old Explorer/85 and documentation if anyone needs more information. You are correct the the DB25 is for the serial port, but there were two different versions of the ROM monitor that supported either keypad or terminal. IIRC, there were also some jumpers that had to be installed differently.

I'm currently building a functional clone of my old Explorer/85 using more modern components, like a single 32K EEPROM and 32K RAM. It's actually running Microsoft Basic/80 on a horrible rat's nest of wires on a solderless breadboard.

February 13th, 2017, 03:56 PM
Thanks nib!

I seem to recall reading in one of the online copies of the docs that the 'ikbd' chip was the ROM monitor? Is that correct? For some reason I can't find it now.

February 13th, 2017, 06:21 PM
I agree there were two versions - one for the terminal using the serial port and one for a hex keypad that if I understand the documentation did not support the serial terminal. Interested in hearing more about your project - are you going to incorporate the s-100 as well? Is it a serial terminal version or the keypad version? Been looking for the contents of the keypad version - would like to convert one of mine.

I have 3 EX-85s the one I am looking at has an 8355 with EXPL85 on it. My original has an 8755 that was a replacement from Netronics - a log time ago when it was my primary(Only) computer probably 1979 or 80.


February 17th, 2017, 07:44 PM
The 'ikbd' doesn't sound familiar. The ROM monitor is contained in the 8355 chip. My monitor listing document is titled "Terminal Version" and there is no code in it to support the keyboard.

February 18th, 2017, 01:33 PM
Jim - Definitely no S-100 or anything that ambitious. I was a poor high school kid when I build mine originally, so I'm just trying for something that will run Basic and the Monitor like the original. My new board is a simple 8085 with a single 32K RAM and a 32K EEPROM. The trickiest part was the power-on jump circuit that allows the RAM to be in the lower half of the address space. I'm trying to pull all of the project notes together to put the pieces on github. Along with the hardware, there's an Arduino-based programmer for the flash and a cross-assembler that is compatible with the format of the original Monitor source code.

I've never run across the Monitor ROM for the keypad version. They were marketing this as a larger system and I suspect that they didn't sell a lot of the keypad variant.

February 20th, 2017, 07:25 AM
That sounds like a pretty nice project is it working yet or do you still need files?


February 21st, 2017, 02:33 PM
I got everything I needed by booting the old board and capturing monitor dumps to a terminal. The computer portion itself isn't very novel, but a few interesting tools came out of the project. I'll start a new thread when I get all the documentation together so I don't hijack this one any further!

February 23rd, 2017, 06:07 AM

I just took another look at your photos and realize what you meant by ikbd. You are correct - that is the ROM monitor burned into an 8755. Mine is in the factory-programmed 8355 instead. I'll post a pic so we can compare boards. Yours has the connector for the keypad next to the 8755, so it looks like you do have the elusive keypad ROM. I'd be interested in seeing the differences between that one and the terminal version. I have the printed ROM source listing and have disassembled and reassembled mine to relocate a few things, so I'm familiar with the code.

In this pic, one side of the serial port is going to and actual PC serial port. The other side had a blown transistor, so an FTTI chip (and an inverter) are connected directly to the TTL output. It put one side of the conversation in one terminal window and one half in another. Awkward, but it worked well enough to dump the contents of the ROMs.

February 23rd, 2017, 11:12 AM
Do you have the actual manual for the monitor. I too spent time dissembling the ROM but I now have the manual. I too am interested in the keypad ROM. I did discover a lot came straight from the SDK-85 monitor so I suspect the Keypad ROM does too. Are those the Basic ROMs in your board curious as to what is on the labels?

Link to Monitor listing and Basic user manual.


February 23rd, 2017, 01:15 PM
Those are the Basic ROMs. Two new photos are attached that show things a little clearer.

Thanks for the link. I have those same manuals, same versions, although not scanned in. I should probably have the Basic manual under glass. It was probably stapled by Bill Gates himself.

I originally tried to scan the Monitor source to OCR it, but the columns and the line wrapping were a mess. In the end, I scanned the last few pages of symbol table and OCRed them without too much trouble. Then used that and the binary as input the the most excellent dasmx and got a more-or-less exact copy of the source minus the comments. I've gone through and commented at least the breaks between the routines, so now I have a pretty good version of the Monitor source to work with.

I've looked around for the SDK-85 monitor, but haven't found anything other than user manuals. At this point I suppose it doesn't matter much because I have good source to work with.

February 24th, 2017, 07:11 PM
I also used DASMX - great tool when I started I didn't have the monitor manual so most of my notes came from the SDK-85 monitor where they matched The listing is in the back of the SDK-85 manual (and about half of the early 80s microcomputer text books it seems) - also been using DASMX on the Basic off and on for years, one day maybe I finish it. Looks like you have the replacement ROMS for D000 and D800 - there were problems with the originals. Wouldn't mind a dump to compare to mine.


February 24th, 2017, 07:39 PM
Were you looking for this?

Intel SDK-85 monitor ROM version 2.1

February 25th, 2017, 04:15 AM
Thanks but I was looking for the Netronics Explorer-85 hex-key pad monitor version. There were two versions of the EX-85 one with a serial terminal monitor and the hex-key pad monitor - I don't believe very many of hose were ever sold. I have had my first EX-85 since 1979 (My first Computer but now have 3 of them) and was also a subscriber to Explorations a news letter for the EX-85 - I believe at most there were only about a 100 of us getting the newsletter and almost everyone had trouble with the kits but there were quite a few that were eventually satisfactory systems there was even a bio-medical group (In Wisconsin I think) that had 5 or 6 of them running with hard drives even. The Jade DD S100 disk controller with 8' Siemens drives was a popular set-up.


February 27th, 2017, 06:28 AM
gslick - Thanks! I've been curious to compare the SDK-85 to the Explorer. I'll track down the manual for the listing as well.

Jim - I'll find my Basic dumps for you. I can't remember if I used mine or one of the images I found for my board, so I need to sort out my files to figure out which is which. I also started running Basic through DASMX. It's a way-back burner project for me as well. There are some disassembled versions of the Altair that provided interesting clues.

My single-board design is posted. I'll start a new thread for that.

March 4th, 2017, 03:56 PM
I finally found my Explorer-85 box that was sitting in my shed for 2-3 years and found it not even close to what Falter have in terms of the board contents. Based on the documentation (assembly instructions), I have a level A (probably the minimum level kit from Netronics) and is EX-85 (configured for RS232) based on the chip (I think!).
https://s6.postimg.org/9wy49rgl9/Riz_Thomas_Ex85_001.jpg (https://postimg.org/image/9wy49rgl9/)

Here is the close-up of the chip that seems to indicate so.... also note the ribbon cable wires (only four) that goes to the other (vid-1) board.
https://s6.postimg.org/3xeyjul6l/Riz_Thomas_Ex85_002.jpg (https://postimg.org/image/3xeyjul6l/)

However, along with the box, it came with this Netronics ASCII Keyboard and VID-1 board (there is a missing key--got to find one).
https://s6.postimg.org/5dqh1zo3h/Riz_Thomas_Ex85_003.jpg (https://postimg.org/image/5dqh1zo3h/)
Notice the RF - Video interface (not a Netronics kit).

It did not come with a power supply but instead - 3 RadioShack Intel 8085 reference manuals. But there is a instructions assembly manual for it, plus other related Manuals...
https://s6.postimg.org/4k99vmsot/Riz_Thomas_Ex85_004.jpg (https://postimg.org/image/4k99vmsot/)

I don't know much about this system so I am going to start slowly on it by first trying to build the PSupply of -/+8Vdc.

BTW: Thanks to Nib for sharing his Simple8085

March 4th, 2017, 07:59 PM
Your 8355 has "EXPL85" which is the terminal version especially since you have a terminal same set up my first one from 1979 was.

Could you scan a copy of the AP-1 power supply instructions - I don't have that document and would like to add it to my collection.

Not sure where to get new key-switch and the proper key cap but one a key cap from a different keyboard might work. I think the reset and interrupt keys on the EX-85 board may be the same and maybe try a different key for one of them.


March 4th, 2017, 08:39 PM
That terminal brings back memories. I had the same one for my system, but can't find it now. It may have gotten trashed at some point. My system had problems with the RS-232 blowing out the driver transistors. One of them is bad on the board currently, so I just bypassed the whole thing and hooked an FTDI adapter (and an inverter) directly to SID and SOD on the CPU to get it talking. Good luck getting it running. It's a pretty neat little design.

March 4th, 2017, 08:41 PM
Here are photos of the AP-1 Power Supply. I'll get the manual scanned and will post that as well.

March 4th, 2017, 09:04 PM
Scanned in a copy of the AP-1 instructions and schematic:

March 4th, 2017, 09:29 PM
Thanks Nib...for sharing the pics. ...I guess I don't have to scan mine.

I wonder what is the spec of the power transformer... 20v ct or 16v ct? I could use some help...thanks

March 4th, 2017, 10:40 PM
I'm still kicking myself for missing not one but two auctions for an AP-1. The first was the one the originally belonged with my system... don't know why but the seller parted the system out, sold the board, keypad, psu and s100 card cage separately. A second one popped up after but was sold before my search alert caught it. Man Netronics is really hot.

March 5th, 2017, 05:38 AM
Thanks for the PS document. I acquired a AP-1 from a surplus store in Orlando for about $5 - just sitting in a bin with a bunch of miscellaneous power supplies but I knew what it was right away.

March 25th, 2017, 10:09 AM
from my last message..

I wonder what is the spec of the power transformer... 20v ct or 16v ct? I could use some help...thanks

May I ask the experts what specs they think should the Transformer be for this power supply (to obtain the +8V/-8v and a 20ppv output based from the schematic). My first thought is a 16V CT Hammond transformer or 18V CT.

Can I have some comments please... Thanks

March 26th, 2017, 05:57 AM
I would think either of these should work - If I remember correctly my first power supply use 12.6 volt center tap but cannot check because it is long gone.

April 10th, 2017, 11:04 PM
Aaaaaagh! I missed this.


I hate ebay. This is the third time something Netronics has come up at a really good price and my @+!?! alerts didn't go off. I'm following, it's set to email me right away.. ugh. People snap up Netronics soooo fast.

I'm actively working on getting mine up and running btw.. just trying to find a burner that can read my keypad rom (so those interested can have it) and then burn the serial terminal rom.

April 11th, 2017, 06:14 AM
That looked like a nice one. Too bad you missed it.

If you want to read your ROM and don't mind doing a small breadboard project, I could probably modify my Arduino-based EEPROM programmer to read 8755 chips. It should be an easy mod, because it wouldn't even require the shift registers that are in the current design. Let me know if you are interested.

April 11th, 2017, 08:48 AM
Oh wow - my alerts also did not notify me. I can read and write the 8755s if you don't find a solution.


April 25th, 2018, 11:34 AM
Hello. I'm in the UK and have just joined the forum. I have a number of Netronics bits and bobs, including my original 1979 fully expanded EX85 in its proper blue box. I'm sure I have manuals for the JAWS RAM card (I have 2 64K cards) and the floppy controller Netronics did...I actually thought I had a floppy board but can't find it.

I remember building an SDK85 based 8755 programmer, I still have the documentation I did at the time.

In the meantime does anyone have or know of a little Arduino or PIC project that can read and program 8755 monitor chips?

Oh, I also have an S100 'Wildern Electronics' CPU board...which is basically a fully expanded EX85 motherboard on an S100 card.

Cheers for now.


April 25th, 2018, 06:25 PM
Welcome to the group - Do you have any pictures and documentation on the "Wildern Electronics' CPU board"?
Also I would like to see the SDK85 based 8755 programmer.
I don't know of any Arduino or PIC project that can read and program 8755 chips - do you need one programmed?


April 26th, 2018, 01:42 AM
Hi Jim

I've only just brought everything out of dry storage to play with. I'll sort out some information shortly and share it on the forum. Last night I came across someone who had made a device to read 8755's using an Arduino...I'm sure I'll be able to modify the sketch to write back to another one. I have four boards that need EXPL85 monitor ROMs and I'd like to look at SDK85 too. I just have to find my nest of 8755s first...they are the original purple ceramic and gold ones from memory. I seem to remember one or more of them are still programmed.

Cheers for now.


April 27th, 2018, 10:54 AM
You may also want to look at the Arduino-based programmer I built for my Netronics 8085 project. It is designed for 32K EEPROMs, but the design is modular and could be easily adapted to 8755s. It wouldn't be much more than ripping out the address shift registers and wiring pins to the 3 address lines and the ALE. The SetAddress routine in the software would then need to be modified for this simpler wiring. I'll see if I can hack one together this weekend that will at least read 8755/8355 chips.

The problematic part for me would be the switching of Vdd between 5V and 25V. That's a little beyond my hardware knowledge. Does anyone have any thoughts on that?

Here's the project: https://github.com/TomNisbet/TommyPROM

April 27th, 2018, 02:52 PM
Wow 4 ex - 85s? cool I have 3 ex-85s and 3 Intel sdk-85s also a clone sdk-85 but uses a 2716 instead of an 8755 and has a breadboard with a separate keypad and display board, and I also have a home built sdk-85 built on 22/44 connector boards.

The monitor for the EX-85 is based on the SDK-85 monitor.

May 2nd, 2018, 08:00 PM
I've had partial success modifying my arduino design for 8755s. The software and hardware modifications are done for reading and it is able to read and checksum the 8355 from the Explorer/85. Working now on a circuit to switch between 25V and 5V for the write code.

May 4th, 2018, 08:50 AM
Hi nib. Here is the article from 1979 which my programmer was based on. Maybe it will help? Simon4532945330

May 4th, 2018, 11:36 AM

That looks to be just what I need. I drew up something similar, but my 5V side was much more complicated than it needs to be. Just shows what happens when software guys try to do analog hardware.

Can you take a closer photo of the schematic? I'm having difficultly making out some of the values.

May 10th, 2018, 07:31 PM
My updates to the Arduino EPROM programmer for the 8755 worked. I'll create a post with the schematic and new code. The hardware design is simple. It has just needs two transistors and a few more components to switch the VPP voltage between 5V and 25V. It can program the whole chip in about 90 seconds. Picture attached.

Dwight Elvey
May 11th, 2018, 05:51 AM
Do note, programming the 8755 and 8755A are different! I don't recall what was different but when I worked for Intel, the UPP required a different programming card. So, are you sure you are doing 8755 or 8755A.

Dwight Elvey
May 11th, 2018, 05:55 AM
Ignore this second post, the MB is really flaky this morning.

May 11th, 2018, 07:47 PM
Dwight - I didn’t realize there was a difference. I lucked out and my parts and data sheet were both 8755A, so I didn’t need to debug a mismatch problem. I’ll update the project to note that it is for 8755A and will hunt for the 8755 datasheet to see if I can find the differences.

May 14th, 2018, 09:55 AM
Hi nib...sorry, I've been away for a few days...here's the image you asked for, just in case you still need it. I'd love to be able to recreate this so let me know when you post the info. Thanks.

May 17th, 2018, 08:47 PM
I finally got the EPROM programmer design updated to support 8755A chips. There is a new thread on it in the Tech Support goup here: http://www.vcfed.org/forum/showthread.php?63732-Simple-Arduino-based-EPROM-programmer

Dwight Elvey
May 17th, 2018, 09:31 PM
It would seem that the programming is the same except the adapter card is different.
See: http://www.bitsavers.org/pdf/intel/upp/9800133F_Universal_PROM_Programmer_Reference_Manua l_1977.pdf
in section 9.
The only difference I see is that there is a Schottky diode, 1N5821, between Vcc and Vdd for the 8755A part.
It would seem that a simple switch on the diode would handle the difference. It would seem that Vdd is to go to 0 volts between programming pulses for the 8755 while it is to go to 5V for the 8755A.

March 18th, 2020, 09:35 AM
Did you get your Explorer 85 running? I just found an Explorer 85, and 2 CDC floppy drives at a yard sale. It was missing the 8085/8155/8755's, and there is no ram installed. I've been going thru the manuals and double checking the components to make sure it was assembled correctly. There is some terrible soldering in there, and I know for a fact this came from an electronics technical school in the late 70s.

I ordered the missing cpu and supporting chips, and I have an eprom burner to write the monitor rom.

I have two floppy drives and a floppy which has basic, and some other programs on it, but did not find the floppy controller card : (

Is it difficult to use tape storage? I haven't looked to see which routines are included in the monitor for tape io.

Are any of you actually using the 8" floppy drives or tape drive with your Explorer?


March 19th, 2020, 01:27 PM
Support for the tape interface is built in to the monitor. I had to replace a bad transistor on the driver, but otherwise mine was still working after all these years. I can get you an image for the 8755 if you don't have it. I also have a good scan of the schematics.

No experience with the floppies to offer - I could never afford them!