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Vercus
November 27th, 2009, 09:29 AM
Hello,
I messed around with the DECPrinter again today, attempting to figure out why it won't print. It passes the self-test, but won't respond to incoming signals, despite matching baud rate.

I'm thinking it must be something in the serial interface card- possibly a bad 1488 or 1489? However, I totally don't have the soldering skill to take one of those out. I've always been very sloppy with a soldering iron. About all I can do is swap out capacitors on old tube radios, and even that's a challenge sometimes.

Does anyone happen to have one of these boards that would be interested in swapping? Or perhaps someone has a suggestion on how to work on it?

I'm afraid to take to it myself for fear or ruining a trace, as the pins and traces on the underside are pretty small.
-Jon

tradde
November 27th, 2009, 02:10 PM
Hello,
I messed around with the DECPrinter again today, attempting to figure out why it won't print. It passes the self-test, but won't respond to incoming signals, despite matching baud rate.

I'm thinking it must be something in the serial interface card- possibly a bad 1488 or 1489? However, I totally don't have the soldering skill to take one of those out. I've always been very sloppy with a soldering iron. About all I can do is swap out capacitors on old tube radios, and even that's a challenge sometimes.

Does anyone happen to have one of these boards that would be interested in swapping? Or perhaps someone has a suggestion on how to work on it?

I'm afraid to take to it myself for fear or ruining a trace, as the pins and traces on the underside are pretty small.
-Jon

If you have a scope or access to one. Or a logic probe along with the schematics of
both of those you might be able to deduce if it's indeed bad. It could be something
as simple as a bad solder joint somewhere else. The other thing you can do is to cut
each leg of the IC and then suck the solder from each hole and put in a socket for
the replacement IC. You need to figure out what's wrong before just removing stuff
and replacing. A scope or logic probe comes in mighty handy.

How do you know it passes the self test? Wouldn't part of that be printing stuff?

Lou - N2MIY
November 27th, 2009, 02:20 PM
Jon,

Before you go changing the 1488 and 1489, verify that indeed one of them is the problem. A scope would be helpful for this. It's a matter of making sure that the inputs look like the outputs on these buffers (but the voltage level will be shifted.) Trivially simple with a scope.

As for through-hole component removal, I have been a big fan of the radioshack 64-2060 solder sucker. It's a great tool for $11. I use it regularly to desolder stuff as big as 40 pin dips without causing destruction to the board or chip. I should note though that I replace the tip after every few jobs because it erodes over time.

Jon, I suggest you get some junk boards, one of these RS desoldering irons, a good iron, some good solder, and start working on your soldering skills. Desolder and resolder junk parts on the junk boards. This is a skill that will last a lifetime.

Lou

Vercus
November 27th, 2009, 04:37 PM
In reference to the self test:
I turned on the self test switch under the cover and closed it, and it printed the standard test pattern, so that's why I said it passed the self test. To me, this indicates that the print head and motors work. However, it doesn't print when a computer prints to it, which was what made me think of the serial interface card.
-Jon

tradde
November 28th, 2009, 09:03 AM
In reference to the self test:
I turned on the self test switch under the cover and closed it, and it printed the standard test pattern, so that's why I said it passed the self test. To me, this indicates that the print head and motors work. However, it doesn't print when a computer prints to it, which was what made me think of the serial interface card.
-Jon

Ok, that makes sense. What do you have it connected to? A PC? Serial port I seem to
remember? A breakout box from Radio Shack might help too. You'd then see which signals
are being set. Are you sure this does not need a gender bender? I'd think a printer would
not, but you never know.

Vercus
November 28th, 2009, 09:39 AM
Hello,
I've tried it with a PC serial port set to every baud and bit combination possible, as well as a DEC VT-102 terminal, and no dice. I've tried 7 bits and 300 baud on both machines, as well as tried different baud rates by changing the dip switches on the printer.
I agree, I need to do some further diagnostic / troubleshooting / signal tracing, I'm just not sure how to do it yet. Plus, I'm limited on funds right now, so I'm having to focus my spending more towards Christmas shopping.
Perhaps after Christmas I'll have the time and money to do more with it.
-Jon

tradde
November 28th, 2009, 09:48 AM
Hello,
I've tried it with a PC serial port set to every baud and bit combination possible, as well as a DEC VT-102 terminal, and no dice. I've tried 7 bits and 300 baud on both machines, as well as tried different baud rates by changing the dip switches on the printer.
I agree, I need to do some further diagnostic / troubleshooting / signal tracing, I'm just not sure how to do it yet. Plus, I'm limited on funds right now, so I'm having to focus my spending more towards Christmas shopping.
Perhaps after Christmas I'll have the time and money to do more with it.
-Jon

You've tried the serial port with the printer and a VT-102? And neither worked? Maybe
your serial port isn't working. I am pretty sure you do need the gender changer for
using a terminal. If I hook one up and it doesn't work that's the first thing I try. If
that doesn't work then I start checking other things.

Vercus
November 28th, 2009, 10:41 AM
Tim,
What I meant was, I hooked the printer up to the serial port of my computer, and I hooked the printer up to the VT-102. Sorry for the confusion.
As far as gender changer, I'm just using a straight through DB25F to DB25F gender changer for connecting it to the terminal. Or, for hooking it up to the computer, I used a DB9 to DB25 null modem cable.
-Jon

tradde
November 28th, 2009, 01:54 PM
Tim,
What I meant was, I hooked the printer up to the serial port of my computer, and I hooked the printer up to the VT-102. Sorry for the confusion.
As far as gender changer, I'm just using a straight through DB25F to DB25F gender changer for connecting it to the terminal. Or, for hooking it up to the computer, I used a DB9 to DB25 null modem cable.
-Jon

Do you have a straight through DB9 to DB25? I'd try both with and without a null modem.
I mentioned gender bender earlier but meant null modem. Sorry.

MikeS
November 28th, 2009, 08:20 PM
Tim,
What I meant was, I hooked the printer up to the serial port of my computer, and I hooked the printer up to the VT-102. Sorry for the confusion.
As far as gender changer, I'm just using a straight through DB25F to DB25F gender changer for connecting it to the terminal. Or, for hooking it up to the computer, I used a DB9 to DB25 null modem cable.
-JonThose are all DTE devices, i.e. equivalent to a terminal, so you'd need a null modem no matter what you're connecting to what; you may also need to assert some status signals.

I recall having lots of fun trying to connect DEC LA100 printers to PCs way back when; they needed to have a jumper added to enable proper handshaking for the PC but it was not documented in any of the service manuals or schematic print set.

I spent an hour on the phone with several DEC service organizations as well as the local DEC office but no one had an answer, so I finally called DEC HO in the US. I asked to speak to a technical guru, but instead of just transferring me, the receptionist asked me for the details of my problem; annoyed at having to explain it once again to someone who obviously wasn't going to be able to help I grudgingly explained it, and nearly fell out of my chair when she explained to me in detail exactly which pin on which IC I needed to connect to where!

After amusing herself a little with my astonishment and bumbling apologies for having assumed I was wasting my time she finally revealed that an engineer familiar with the issue was standing beside her and had overheard my question...

You really need something like a breakout box, or at least to be able to monitor some signals and perhaps make some extra connections; there are several different ways to connect a null modem...

Vercus
November 29th, 2009, 05:26 AM
Hey Mike,
Thanks for the information. It soudns like a breakout box is in my future...
-Jon