• Please review our updated Terms and Rules here

Netronics Explorer/85

So I finally received the 8212 which was the last chip I was waiting on. When I power up I see activity on the address bus but no red led even after a reset. If I cycle the power a few times, I can eventually get the led to flash randomly a few times after power up which tells me the cpu is executing uninitialized memory which is a good sign that it is alive.

So, the cpu is alive. I know my eprom is good so I am not sure why I am not getting the red led after a reset. I guess I'll need to verify each address/data line is connnected between cpu and eprom.

Only other thing I can think of is that I have a jumper set wrong and it's not booting from the monitor rom?

Also should serial port be 8n1 or 7e1?

thanks
 
According to the notes in Mame, the terminal should be set up for 9600 baud, 7e1.

Once the system is powered, you must press Space, then you'll see the start-up text.

EXPLORER-85 VER 1.4
COPYRIGHT 1979
NETRONICS R&D
NEW MILFORD, CT.

All input to be in Uppercase.

If anyone has other versions of the bios, I would be most interested in having a copy. Also, I'd be interested in the Hex Keyboard bios.
 
As Robbert notes, you need to press the spacebar to auto-detect the serial. Speed can be anywhere from 110 to 9600.

Here is a photo of my board if you want to compare jumpers. Just don't mock my soldering skills - I built it with a $10 Radio Shack soldering iron when I was 16 years old. I'm amazed it works at all! https://github.com/TomNisbet/Simple8085/blob/master/docs/explorer85.jpg

I did have trouble with the transistors that drive the RS232 blowing out. You may want to scope the lines on the other side of those. In fact, the last time I used it, I just connected one of those FTDI USB adapters right on the TTL side (possibly with some inverters) and used that to talk to it.

Robbert - I also have the 1.4 ROM but have done some mods to it. I'll PM you details.
 
nib said:
As Robbert notes, you need to press the spacebar to auto-detect the serial. Speed can be anywhere from 110 to 9600.

Here is a photo of my board if you want to compare jumpers. Just don't mock my soldering skills - I built it with a $10 Radio Shack soldering iron when I was 16 years old. I'm amazed it works at all! https://github.com/TomNisbet/Simple8085/blob/master/docs/explorer85.jpg

I did have trouble with the transistors that drive the RS232 blowing out. You may want to scope the lines on the other side of those. In fact, the last time I used it, I just connected one of those FTDI USB adapters right on the TTL side (possibly with some inverters) and used that to talk to it.

Robbert - I also have the 1.4 ROM but have done some mods to it. I'll PM you details.
Click to expand...

Thanks, thats funny I was literally just studying that image today looking for anything I'd missed. My board does not have any dip switches installed, the 4k of ram, or the MSBASIC eproms (yet). When the ram, eprom sockets, and 8pos dip switches arrive I'll install all that.

What has me wondering is that I am not getting a lit red led after reset. I know the led works, because if I cycle power a few times eventually it will execute some "garbage" in memory and the led will turn on and off a few times. When I his reset, it goes off and stays off.

I checked all of the address lines and I can see the CPU cycling thru memory addresses on both the CPU and the eprom.

Going to try to get a connection again now. Thanks guys.

BTW your soldering looks great compared to my board. It was obviously built by a tech school student and they managed to burn off most of the pads. There are a lot of point to point wiring repairs.
 
Last edited:
The most common problem on any of these boards is the RAM. I made some kit to make 6530 replacements and a board that had simple diagnostics on a EPROM, for the KIM-1. After getting feed back from those that bought them. Not one needed ether of the dreaded 6530s. All but one was the RAM. The one was from the decoder chip used to select the RAM.
I not one for doing easter egg hunts but if you have little programming ability, I'd recommend socketing the RAM and swapping them out, one at a time.
If you can program in assembly and use it to program EPROMs, I recommend writing some diagnostic code.
Dwight
 
If you are just debugging the base board (and I hope you are), then the only RAM present is the 255 bytes in the 8155. It might be useful to burn a new ROM just for debugging that does something really simple, like toggle the SOD line. That would verify that the 8085 and the 8755 are working.

That would also help verify that your EPROM programmer is really working. I didn't test the 8755 burner design beyond just burning a chip and running a checksum on it. Maybe pull the 8755, read it back, and compare the binaries just to be sure.

It's good that you don't have the other EPROM and RAM installed yet. Less to debug!
 
You inspired my to drag my Explorer out of the box to power it up. Attached is a photo with the franken-RS-232 connection. It's just a FTDI connector with an inverter on the two data lines and then connected to the TTL side of the I/O. That gets all of the analog RS-232 stuff out of the way.

It booted to the monitor and connected at 2400 N81 after hitting the spacebar. Mine seems to be a bit flakey too. Sometimes, after reset, the LED comes on but it doesn't respond to the terminal. Once you have it hooked up, try reset then spacebar several times. Maybe it is behaving similarly. Once I do get a good boot, it seems solid. I have it running now, so if you want me to scope something out for comparison just let me know.
net85-1.jpgnet85-2.jpg
 
nib said:
If you are just debugging the base board (and I hope you are), then the only RAM present is the 255 bytes in the 8155. It might be useful to burn a new ROM just for debugging that does something really simple, like toggle the SOD line. That would verify that the 8085 and the 8755 are working.

That would also help verify that your EPROM programmer is really working. I didn't test the 8755 burner design beyond just burning a chip and running a checksum on it. Maybe pull the 8755, read it back, and compare the binaries just to be sure.

It's good that you don't have the other EPROM and RAM installed yet. Less to debug!
Click to expand...

I examined the eprom again and the binary appears to match. I didn't compare byte for byte, but in the dump I can see the netronics 1979 text ending in IF NEG in the dump which matches the binary I have for the rom. I wasn't able to download the dump and do a diff though... I must have dislodged a wire somewhere in my breadboard because it hands when I try to download via xmodem.

I'll try to find that tomorrow.
 
nib said:
If you are just debugging the base board (and I hope you are), then the only RAM present is the 255 bytes in the 8155. It might be useful to burn a new ROM just for debugging that does something really simple, like toggle the SOD line. That would verify that the 8085 and the 8755 are working.

That would also help verify that your EPROM programmer is really working. I didn't test the 8755 burner design beyond just burning a chip and running a checksum on it. Maybe pull the 8755, read it back, and compare the binaries just to be sure.

It's good that you don't have the other EPROM and RAM installed yet. Less to debug!
Click to expand...

Yes just the base board. No eproms other than the monitor, no additional ram other than the 256 bytes in the 8155.

Not a bad idea to write a quick test program and burn it. I was just going to pull the 8755, power up and verify the address bus isn't doing anything. Then hard wire NOP at the 8755 socket, and verify the CPU is running.

But, I can already see the CPU is running because address lines on the 8755 are counting away as the CPU is accessing them. Seems like the CPU is running a loop so I think it might be waiting for space bar. I may have dead transistors on the serial port, sounds like thats common.

I wonder though why SOD line is always low? I pulled the CPU and the LED comes on. I tested it by grounding the SOD line and the LED went off, so that circuit seems to be working.
 
nib said:
You inspired my to drag my Explorer out of the box to power it up. Attached is a photo with the franken-RS-232 connection. It's just a FTDI connector with an inverter on the two data lines and then connected to the TTL side of the I/O. That gets all of the analog RS-232 stuff out of the way.

It booted to the monitor and connected at 2400 N81 after hitting the spacebar. Mine seems to be a bit flakey too. Sometimes, after reset, the LED comes on but it doesn't respond to the terminal. Once you have it hooked up, try reset then spacebar several times. Maybe it is behaving similarly. Once I do get a good boot, it seems solid. I have it running now, so if you want me to scope something out for comparison just let me know.
View attachment 60381View attachment 60382
Click to expand...

Thanks I have an FTDI board here, I'll try that next with an inverter.
 
I think you are on the right track. A simple program in the ROM sound like a good next step. That way you can do something that doesn't depend on the 8155 RAM and really minimize the amount of circuity under test.

This was the approach I did when I brought up my breadboard 8085. Started with just the processor and ROM and wrote a test to toggle the SOD line and then another test that just hard-coded a bit-banged single character out the SOD as serial data.

I took another look at the monitor ROM and it doesn't appear that there are any places for it to get tripped up before it does the baud rate detection code. It isn't reading anything before that or waiting on any other hardware. That makes be suspect either something fundamental like a shorted address/data line or the RS-232 hardware. Or possible the reset circuits.

I'll send you a PM with some resources that might help.
 
The reset circuits are notoriously know to fail. They use high value resistors and subject to even slight contamination there.
Dwight
 
mykrowyre said:
Ok thanks for the help guys.. I'll be back after some digging around.
Click to expand...

Ok I burned an eprom with just the led flash routine on the SOD line. Didn't work. Same problem, cpu starts, all address lines are counting away.

VCC is clean and stable, clock signal looks good.

I pulled the eprom, and it did the same thing. I pulled the 8155 and same. I pulled the 8212 and still, the CPU is counting away. I pulled the cpu and checked all the address at the socket to makes sure they are not all grounded (as NOP) and they are all in NC state. Weird! So I hard wired a HLT instruction at the 8212 socket, and still the CPU is counting away unfazed by my blatant attempt to stop it. It does eventually stop, but when it stops even the RESET OUT pin stops responding so I think the CPU is dead at that point.


I'm wondering if both of my 8085s are bad (ebay) so I'll need to test those individually on a breadboard.

It's entirely possible some enterprising young man pulled these from a salvaged submarine then dunked the entire board in a bowl of molten solder to knock out the cpus.
 
Last edited:
I breadboarded the two cpus I have and hard wired HLT on the AD bus, and the CPU continues counting on all the address lines.

Is it possible the AD bus pins are all shorted to ground internally?

Both came from the same seller as "Found in a repair shop".. maybe the junk bin haha.
 
Ok well I forgot that these are multiplexed bus... so I am think I was confusing what I was seeing.

I think my CPUs are working correctly, but still no output on the SOD line. I found I had a bad CPU and 8212 socket, and repaired those.

I noticed all four 8216 buffer chips getting quite warm. Is that normal? I put a scope on them an see logic activity on all of the data pins.
 
Do all the 0 volts look good? The high levels can have a lot of variation, depending on which chips are driving but the 0 level should always be solid. A lifting of the 0 could be an indication of contention.
I don't have a working machine with 8216s to compare with the temperature but I wouldn't be surprised if the did run warm, being early ttl buffer chips.
Dwight
 
26C6E5CE-1784-492C-9A0E-5D760CBBD78E.jpeg
Dwight Elvey said:
Do all the 0 volts look good? The high levels can have a lot of variation, depending on which chips are driving but the 0 level should always be solid. A lifting of the 0 could be an indication of contention.
I don't have a working machine with 8216s to compare with the temperature but I wouldn't be surprised if the did run warm, being early ttl buffer chips.
Dwight
Click to expand...

Hi Dwight, good call! Thanks!
 
Last edited:
That looks to be contention but it could be a floating bus. It is low enough to look like contention though. The highs can often vary by 1 Volt but not the lows.
You can check to see of it is a float by attaching a ~5K pullup resistor. If it is floating it will go higher a lot higher.
Do you have a schematic? The one on, found on the the web looks to be a newer version.
Dwight
 
You must log in or register to reply here.
Back
Top