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Old 22 February 2019, 23:31   #1
simulant
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Problems with Serial port on Amiga 4000D

Hi I wondered if anyone can help.


I use Term 4.8 with my Amiga 600 and 1200 to telnet BBSes with a wifi modem and it always works great.


I recently managed to get an upgrade and bought an Amiga 4000 - it is pretty yellow and battered but boots up and seems to all work ok.


I obviously want to try to sell the 1200 and/or 600 and use the 4000 with my wifi modem instead. I also use it with some other old DOS/IBM XT and a few other machines too and they all also work fine.


BUT I'm having a weird problem on this 4000. In Term the modem outputs fine but I can't type commands. It just won't let me type at all as if the Amiga TX line just isn't working... I tried a few other serial terminal programs too in case Term wasn't working properly but they all do the same thing. They print out what is received from the serial port but won't let me type anything back out to the modem.


It seems odd to me and I wondered if I was just missing something obvious with the 4000 - is there a jumper pin on the motherboard or something else I need to do hardware-wise, OR something that would conflict with the serial port in some way? I have a FastATA MKIII Zorro card with a CD drive connected but that's about all really.


Can anyone help or does anyone know of any issues with Amiga 4000 serial ports? The motherboard doesn't show any visual signs of anything bad etc.


Thanks for any help.
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Old 23 February 2019, 01:06   #2
grelbfarlk
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Usually no. But having a messed up -12V or 12V can interfere with the serial port.
The serial port is on a little removable connector on many A4000s, you could try cleaning or reseating that.
I guess you've probably ruled out an alternate serial.device being a problem, don't know if this is a fresh install or not.

Other than all that if I remember correctly the TxD comes out of Paula so if there is electrolytic cap damage in that area, that could also be a concern.

A null modem cable might be helpful to test the serial port if you have one or can make one up.

So if all or none of that applies, get to testing the TxD output from Paula then to U304. You should be able with even a simple multimeter some output from TxD on Paula and then to/from U304.
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Old 24 February 2019, 00:34   #3
simulant
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Hi thanks for the reply.

Before I start pulling everything out again to inspect and reseat the port etc - I just wondered about the alternate serial.device...

It isn't a fresh install in as much as I didn't do the install - so it seems fresh but I don't know for sure. I don't think it can be the serial.device driver though as I've booted ColorTerm from a floppy disk and that wouldn't work either? Is it worth trying an alternative serial.device or is that a waste of time do you think if a floppy-based term wouldn't work?

Thanks again
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Old 24 February 2019, 01:39   #4
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Quote:
Originally Posted by simulant View Post
Hi thanks for the reply.

Before I start pulling everything out again to inspect and reseat the port etc - I just wondered about the alternate serial.device...

It isn't a fresh install in as much as I didn't do the install - so it seems fresh but I don't know for sure. I don't think it can be the serial.device driver though as I've booted ColorTerm from a floppy disk and that wouldn't work either? Is it worth trying an alternative serial.device or is that a waste of time do you think if a floppy-based term wouldn't work?

Thanks again

An alternate serial.device was a pretty unlikely possibility, but I mentioned it just in case. I mean you can just do a 1> list devs:serial.device and see if the size is correct for whatever version of Workbench you have installed.



Or if perhaps there was another program in your startup-sequence that was patching it for some reason, perhaps by the previous owner. Again this is not all that likely but some hardware that might have been previously installed might have monkeyed with this.



Booting from a floppy is a pretty safe way to verify, or booting a Workbench floppy and running term that way.


Or if you happen to have an old modem around try sending some AT commands to it.



Just trying to rule out some unknown incompatibility with your wifi modem. Or is it powered by the serial port? Maybe it's drawing too much power if that's the case, which leads back to checking your power supply.
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Old 24 February 2019, 19:50   #5
lesta_smsc
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What about serial test using Kier systest?
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Old 25 February 2019, 00:29   #6
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Thanks grelbfarlk,


Ok I've not had much time to spend on testing so far but I took the motherboard out and examined it. I don't seem to have a removable serial socket that I can reseat... But I used a multimeter to check each pin is connected with continuity test to where the pins are soldered on the board and they all seem fine.


I know the wifi modem is also fine as I've instead tried plugging a USB to serial ttl adapter in - I can use SCREEN command on linux to send and type stuff from my linux box and it shows up great on the Amiga - but again I can't type anything on the Amiga and nothing shows from it on the PC.


The USB to serial was also quite handy as it has LEDs on - the RX led is constantly lit!! Right from boot it is lit like it is receiving from the Amiga port. It doesn't flash though and is just on all the time. When I type on the linux box the TX light flashes as it should, so I would expect the RX should not be lit and flash as I type on the Amiga...


Not sure what is going on there.. I haven't checked the power coming in to the motherboard yet - any tips which wires are which and what to check there? Also I can't see any problems around Paula. Do you know pins to test with the multimeter on Paula to U304, I don't want to damage anything else on the motherboard jumpering the wrong contacts with my Multimeter!!!



Quote:
Originally Posted by lesta_smsc View Post
What about serial test using Kier systest?

Hi thanks for the suggestion - I've downloaded this but on booting it I read that I need to make a dongle. I'll look into the dongle and see if I can put one together and try that test too


It just seems very odd that the Amiga works great in every way except the TX pin on the serial port!! How bonkers is that? I assume that because my USB to Serial adapter shows a led on all the time for rx that it can't be drivers or startup sequence? It is happening as soon as I switch the power button on...


Thanks again for any help I'd really like to get this fixed somehow
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Old 25 February 2019, 00:39   #7
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Quote:
Originally Posted by grelbfarlk View Post
An alternate serial.device was a pretty unlikely possibility, but I mentioned it just in case. I mean you can just do a 1> list devs:serial.device and see if the size is correct for whatever version of Workbench you have installed.

Thanks also I forget to say I did list devs:serial.device and it shows 5412 1 file - 12 blocks used. I'm on 3.1 Rom with Workbench version 40.42
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Old 25 February 2019, 01:02   #8
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Perhaps your TxD pin is just stuck high.
I assume you're using a null modem cable to connect the Amiga to your USB to serial adapter-I hope?

With a serial to USB adapter and a null modem cable as I recall I see a brief flash when the Amiga turns on.

U304 pin 8 should be the TxD OUT.
And pins 9&10 should be the _TxD IN on U304.
And on Paula _TxD is pin 43.

You also have the 22uF electrolytic caps which leak around the serial port, the electrolyte could be bridging connections in that area-replace them if you have not already. Test the caps and resistors in that area to see if you have short to ground or 5V, some are located on the backside of the motherboard.

Super good schematics are here:
https://www.amigawiki.org/dnl/schematics/A4000_Rb.pdf

Also amigapcb.org.
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Old 25 February 2019, 01:15   #9
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This might help you visualize it a bit:


The caps circled in red are the leaky ones in the area.
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Old 02 March 2019, 13:08   #10
simulant
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Thanks That is really very useful and highly appreciated!! I'll let you know how it goes when I get a bit more time to take a look. Thanks again



Quote:
Originally Posted by grelbfarlk View Post
This might help you visualize it a bit:


The caps circled in red are the leaky ones in the area.
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Old 02 March 2019, 17:05   #11
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If I plug a wimodem232 into my A4000’s serial port it stops my Ratte Switch working in standard rgb modes I guess the switch uses the serial somehow to detect mode switches from rgb to rtg and back again.
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Old 02 March 2019, 22:17   #12
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ah that's interesting!! thanks for the reply. hmm, well I just use a VGA adapter from Amiga Kit:

http://amigakit.amiga.store/product_...roducts_id=183

Mine is the buffered version for A4000 - could this somehow cause the same problem you have with your Ratte Switch??

What a weird issue if that is the cause...
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Old 02 March 2019, 23:44   #13
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Quote:
Originally Posted by simulant View Post
ah that's interesting!! thanks for the reply. hmm, well I just use a VGA adapter from Amiga Kit:

http://amigakit.amiga.store/product_...roducts_id=183

Mine is the buffered version for A4000 - could this somehow cause the same problem you have with your Ratte Switch??

What a weird issue if that is the cause...

No that's not the issue. Ratte's monitor switch uses the CIA CTS serial to send a signal to the switch to tell it to switch inputs. Your VGA adapter has none of that.

Last edited by grelbfarlk; 02 March 2019 at 23:53.
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Old 26 March 2019, 17:36   #14
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Thanks for all the help - rather than taking the motherboard out again I actually ended up buying a second-hand Hypercom 3/4 Plus zorro board which adds extra serial ports to the back of my A4000 - these extra serial ports work great so I've now got it working that way. Hopefully those dodgy caps or whatever is wrong with the built-in serial port won't show their ugly head in the future in some other way.
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Old 26 March 2019, 20:08   #15
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I used a Hypercom 3/4+ in my A4000 for many years. Faster too
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Old 27 March 2019, 21:58   #16
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Quote:
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Thanks for all the help - rather than taking the motherboard out again I actually ended up buying a second-hand Hypercom 3/4 Plus zorro board which adds extra serial ports to the back of my A4000 - these extra serial ports work great so I've now got it working that way. Hopefully those dodgy caps or whatever is wrong with the built-in serial port won't show their ugly head in the future in some other way.

I call shenanigans on this whole thread. I was waiting for a resolution and you just cheated by replacing with a whole different serial port. Mods!?!?
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Old 27 March 2019, 23:33   #17
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Just noticed another Amiga owner in York! Cool!
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Old 28 March 2019, 11:26   #18
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I call shenanigans on this whole thread. I was waiting for a resolution and you just cheated by replacing with a whole different serial port. Mods!?!?

Haha yeah a total cheat solution, however I'd already had the motherboard out a few times and it is a real pain to keep taking it back out and put it all back again when you want a working system and don't have much time. I may revisit it hopefully one day!



Quote:
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Just noticed another Amiga owner in York! Cool!

Yeah I always used to go to Rufforth Car Boot sale circa 1992/3 with my Dad. I wasn't aware of the problems that bootlegging and piracy had when I was 12 haha. I don't know if you ever used to go but as a kid it was just completely mindblowing and so exciting. They'd have all the genuine boxed up stuff out front - as a kid you'd be looking and you'd get a nod or invite from a stall holder/trader. Then all the kids would go through the little back doors behind the stalls and there would be several vans lined up outside (ready to make a swift exit if the police turned up) and boxes of thousands of floppy disks. £1 a disk it used to be, with every release you could imagine.


I couldn't wait to go each week, not knowing what games my pocket money could get me next or what new releases would be there or other software. Obviously this was in part what killed the Amiga, but when your family doesn't have much money and like I say; to a 12-year-old you just want the new games and software that all your friends are also buying.


Big games like Kings Quest series and other Sierra stuff etc used to be a hard choice, do I spend all my money on a lot of disks for one game (haha Beneath A Steel Sky...??) or do I get a few games with less disks instead?


I really miss those dodgy van setups. York was rife with it, Wigginton Car Boot sales had those types of stalls too but Rufforth was the best and most well organised for bootleggers... I may of thought twice if I'd known I was contributing to the downfall of the Amiga but I guess all systems have always suffered this problem to an extent.
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Old 28 March 2019, 13:05   #19
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I only moved to york in 1997 as a student, and at that point i was only interested in booze, climbing and girls. I came back to york permanently in 2010 but have not tried any of the boot sales locally for retro stuff. I wonder if there's still bargains to be had? Doubt it as 'retro' and 'ebay' and 'RARE' and 'price-gouging' are all now synonymous!
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Old 07 April 2019, 15:42   #20
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I only moved to york in 1997 as a student, and at that point i was only interested in booze, climbing and girls. I came back to york permanently in 2010 but have not tried any of the boot sales locally for retro stuff. I wonder if there's still bargains to be had? Doubt it as 'retro' and 'ebay' and 'RARE' and 'price-gouging' are all now synonymous!

Well to relive those childhood memories I went back to the same local York car boots last year that I used to go to as a kid. The only computer and gaming gear there was all from "pro" resellers and there wasn't a bargain or even home seller in sight. When i asked someone; apparently the resellers get there as early as they can and buy any tech bargains for their stalls before most of the "general public" arrive.
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