Announcement

Collapse

Forum etiquette

Our mission ...

This forum is part of our mission to promote the preservation of vintage computers through education and outreach. (In real life we also run events and have a museum.) We encourage you to join us, participate, share your knowledge, and enjoy.

This forum has been around in this format for over 15 years. These rules and guidelines help us maintain a healthy and active community, and we moderate the forum to keep things on track. Please familiarize yourself with these rules and guidelines.


Remain civil and respectful

There are several hundred people who actively participate here. People come from all different backgrounds and will have different ways of seeing things. You will not agree with everything you read here. Back-and-forth discussions are fine but do not cross the line into rude or disrespectful behavior.

Conduct yourself as you would at any other place where people come together in person to discuss their hobby. If you wouldn't say something to somebody in person, then you probably should not be writing it here.

This should be obvious but, just in case: profanity, threats, slurs against any group (sexual, racial, gender, etc.) will not be tolerated.


Stay close to the original topic being discussed
  • If you are starting a new thread choose a reasonable sub-forum to start your thread. (If you choose incorrectly don't worry, we can fix that.)
  • If you are responding to a thread, stay on topic - the original poster was trying to achieve something. You can always start a new thread instead of potentially "hijacking" an existing thread.



Contribute something meaningful

To put things in engineering terms, we value a high signal to noise ratio. Coming here should not be a waste of time.
  • This is not a chat room. If you are taking less than 30 seconds to make a post then you are probably doing something wrong. A post should be on topic, clear, and contribute something meaningful to the discussion. If people read your posts and feel that their time as been wasted, they will stop reading your posts. Worse yet, they will stop visiting and we'll lose their experience and contributions.
  • Do not bump threads.
  • Do not "necro-post" unless you are following up to a specific person on a specific thread. And even then, that person may have moved on. Just start a new thread for your related topic.
  • Use the Private Message system for posts that are targeted at a specific person.


"PM Sent!" messages (or, how to use the Private Message system)

This forum has a private message feature that we want people to use for messages that are not of general interest to other members.

In short, if you are going to reply to a thread and that reply is targeted to a specific individual and not of interest to anybody else (either now or in the future) then send a private message instead.

Here are some obvious examples of when you should not reply to a thread and use the PM system instead:
  • "PM Sent!": Do not tell the rest of us that you sent a PM ... the forum software will tell the other person that they have a PM waiting.
  • "How much is shipping to ....": This is a very specific and directed question that is not of interest to anybody else.


Why do we have this policy? Sending a "PM Sent!" type message basically wastes everybody else's time by making them having to scroll past a post in a thread that looks to be updated, when the update is not meaningful. And the person you are sending the PM to will be notified by the forum software that they have a message waiting for them. Look up at the top near the right edge where it says 'Notifications' ... if you have a PM waiting, it will tell you there.

Copyright and other legal issues

We are here to discuss vintage computing, so discussing software, books, and other intellectual property that is on-topic is fine. We don't want people using these forums to discuss or enable copyright violations or other things that are against the law; whether you agree with the law or not is irrelevant. Do not use our resources for something that is legally or morally questionable.

Our discussions here generally fall under "fair use." Telling people how to pirate a software title is an example of something that is not allowable here.


Reporting problematic posts

If you see spam, a wildly off-topic post, or something abusive or illegal please report the thread by clicking on the "Report Post" icon. (It looks like an exclamation point in a triangle and it is available under every post.) This send a notification to all of the moderators, so somebody will see it and deal with it.

If you are unsure you may consider sending a private message to a moderator instead.


New user moderation

New users are directly moderated so that we can weed spammers out early. This means that for your first 10 posts you will have some delay before they are seen. We understand this can be disruptive to the flow of conversation and we try to keep up with our new user moderation duties to avoid undue inconvenience. Please do not make duplicate posts, extra posts to bump your post count, or ask the moderators to expedite this process; 10 moderated posts will go by quickly.

New users also have a smaller personal message inbox limit and are rate limited when sending PMs to other users.


Other suggestions
  • Use Google, books, or other definitive sources. There is a lot of information out there.
  • Don't make people guess at what you are trying to say; we are not mind readers. Be clear and concise.
  • Spelling and grammar are not rated, but they do make a post easier to read.
See more
See less

Powertran Cortex

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Originally posted by tms9995 View Post
    Had a quick look at the circuit diagram and IC47 is the first, IC46 is the second and IC45 is the third. Good luck and let us know you have a working Cortex Basic!
    Thanks for the info. I put the new eproms in and no luck! - All I got was a constant tone and the "MEM" LED lit.
    I then decided to fit my Forth eproms and got similar results. After a few resets I got the LEDs to stabilize and ended up with the "RUN" LED lit but then couldn't get any text prompt on the flickering video output. The whole set-up seems to be a bit unstable and the LEDs keep changing state if I move the chassis. I'll have to check the supply voltages and hunt around for loose connections etc. I seem to remember that the video output was always a bit unreliable.
    I like a challenge !!!

    Comment


      I've just had another look at my dead Cortex and have got a few questions:

      What is the normal sequence for the front panel LEDs after a reset - I can't remember and can't find my original guide, but I'm assuming that a healthy Cortex just has the "BASIC" LED lit if all is OK. Mine seems to mostly display a dim / flickering "RUN" led and constant "MEM" led, if this means anything.
      I've checked my PSU output and measured: + 4.3v, +11.73v, -12.1v using the 0 volt line on the PSU output connector. - ( For some strange reason if I measure the voltages using the chassis earth, I get + 4.94v, +11.92v, -12.02v ).
      Does anyone know what the tolerances are on these voltages? -- I suppose I could get a PSU from an old PC just to be sure.
      Last question - When I put it together in the 1980's, I decided to use dual-contact sockets in every IC position, in case I had problems and needed to replace any ICs.
      Do you think that the contacts on these socket could have oxidised over 27 years and maybe I should remove and re-seat each IC in-turn, or would I be wasting my time.

      Any advice would be appreciated.
      Last edited by andyp; January 26, 2010, 12:49 PM. Reason: Spelling

      Comment


        Originally posted by andyp View Post
        I've just had another look at my dead Cortex and have got a few questions:

        What is the normal sequence for the front panel LEDs after a reset - I can't remember and can't find my original guide, but I'm assuming that a healthy Cortex just has the "BASIC" LED lit if all is OK. Mine seems to mostly display a dim / flickering "RUN" led and constant "MEM" led, if this means anything.
        I've checked my PSU output and measured: + 4.3v, +11.73v, -12.1v using the 0 volt line on the PSU output connector. - ( For some strange reason if I measure the voltages using the chassis earth, I get + 4.94v, +11.92v, -12.02v ).
        Does anyone know what the tolerances are on these voltages? -- I suppose I could get a PSU from an old PC just to be sure.
        Last question - When I put it together in the 1980's, I decided to use dual-contact sockets in every IC position, in case I had problems and needed to replace any ICs.
        Do you think that the contacts on these socket could have oxidised over 27 years and maybe I should remove and re-seat each IC in-turn, or would I be wasting my time.

        Any advice would be appreciated.
        The power-on sequence takes about a second and involves mainly the RUN LED being lit until the initialisation is complete whereby it will sit at IDLE with the BASIC LED flashing about once per second. The MEM LED indicates the Memory Mapper has been turned on with a CKON instruction and doesn't sound normal for powering on.

        There should be a good solid 5V measured on the board (eg across the power pins of any IC). Maybe you've got a bunch of ripple due to bad PSU capacitors? As far as the ICs go, I would definitely recommend reseating them as they do tend to oxidise up.

        Comment


          Ditto, I would also add check the rectifier is happy, it sounds to me like terrible ripple is the first problem to look at.
          "Don't it always seem to go
          That you don't know what you’ve got ‘til it’s gone" (BANG )

          Comment


            Thanks guys,

            I'll have another look at the 5 volts as suggested and keep you posted.

            Comment


              Guys,

              I checked the 5 volt supply across the pins on an IC and got 4.4v and the voltage at the fuse before the 7805 is 10.2v.
              I can probably get hold of an oscilloscope to see if there is any ripple and I think I've got a spare 7805 but what's got me a little confused is I appear to have a different set of component lists / schematic diagrams to those listed on WHTech. I can only assume that they were issued to me in the kit from Powertran. My sheets have additional hand written notes on them and there is a note printed on the power supply overlay saying :
              * = vertically mounted 4R7 resistor (Drawn on overlay adjacent to BASE lead of Q1) and + = vertically mounted 100R resistor (Drawn on overlay between the COLLECTOR lead of Q1 and the output lead of the 7805 IC1) plus the comment "Fit only if the voltage is low (less than 4.8v on the TMS9928 )".
              Looking at my power supply I must have experienced low voltage issues when I first built it because I have the 4R7 resistor in place but I then appear to have by-passed it at a later date probably because it didn't work and I couldn't be bothered to take the PSU out again to remove it.
              It's all very confusing because they have not modified the circuit diagram so there is no way of telling exactly where these two resistors were intended to be connected. (I seem to have tried to fit the 4R7 in series with the 0 volt line of the 7805)
              I realise that this description is probably very confusing, but using your expertise, where do you think a 4R7 resistor and a 100R resistor should be fitted to increase the ouput voltage - I am assuming that as they state the resistors are vertically mounted they are intended to be in series with two of the Q1 / IC1 leads but I don't know which ones.
              The PSU component overlay also states that it is "ISSUE B" PCB.
              Last edited by andyp; January 27, 2010, 12:10 PM. Reason: spelling

              Comment


                On your schematic differences, there were apparently at least three different revisions of the board, but I have never seen a set of schematics reflecting all of the differences between versions Andy. If yours are different than the ones we have, it might be a good idea to scan them in too as a help to any others who may have that board revision. I'll have a look at mine to see if the resistors are in place as you describe.
                Enter My Mind At Your Own Risk!

                Comment


                  Interesting & confusing. I understand the circuit in the schematic. So I hope you won't mind me talking through it in order to get a better idea of what's going on.
                  the 7805 is using it's output to monitor the 5v rail, if it's a bit low, it supplies a little current. it gets this current from the base of Q1, thereby turning it on a bit, increasing the current flowing through Q1 to the collector, and out onto the 5V rail.

                  I'd be separating the psu by now! It's all too easy to put a high voltage onto the main board. Load is crucial to the operation of the circuit so use a dummy load like a car headlight/brake light bulb.

                  I'd go back to the original circuit, Isolate the 7805 reg from the transistor output & test the regulator gives 5V. It's possible that the input voltage is not high enough to operate it properly. If it doesn't give 5V perhaps you should replace it with a "low dropout voltage" version.

                  (More thoughts in a minute when I've threaded this earth wire & picked my daughter up!)
                  "Don't it always seem to go
                  That you don't know what you’ve got ‘til it’s gone" (BANG )

                  Comment


                    AAAhhh if you've bypassed the 4.7ohm resistor between +ve & the base of q1, you've turned Q1 off! Which may mean that the computer is running off just (a very stressed) 7805.

                    (now covered in mouse poop, & going to pick other daughter up)
                    "Don't it always seem to go
                    That you don't know what you’ve got ‘til it’s gone" (BANG )

                    Comment


                      Ksarul,

                      I've since noticed that the pages I have state that they are:
                      "Reprint of article published in Electronics Today International ( With corrections and amendments necessary to be consistent with kit )
                      When I get to grips with my 5 volt issue, I'll scan and send them to you.

                      Nige,

                      Followed your advice and isolated the PSU from the main board and used a car light bulb as a load ( Draws about 1.3 amps at 5 volts )
                      I've now removed the whole back panel / PSU / transformer, to make it easier to work on.
                      Had some more strange voltage measurements - When I first checked the 5 volt on the output connector I had 4.7v but if I checked it at the floppy disk supply connector I had 5.02v ?? - Even though the 2 supplys come from the same point on the circuit ?? And with power off, when I check for continuity between the floppy 5v and the main board 5v plus 0v to 0v on the different connectors all is OK !
                      I then removed the PSU board and decided to tidy it up and remove the by-passed resistor and investigate where these add on resistors were designed to go.
                      Judging by the pre-drilled holes in the PCB, the resistors referred to in my amended notes are designed to go as follows:
                      100R between the +5 volt output of the 7805 and the CMN terminal of the 7805.
                      4R7 between the CMN terminal of the 7805 and the 0 volt rail. ( This was the one I listed as by-passed in my earlier post and it looks like I had also cut the 2nd 100R resistor off the PCB)
                      I assume that these 2 additional resistors are intended to bias the 7805 CMN terminal to approx + 0.3 volts to increase the output slightly if required.
                      With the 4R7 resistor removed, the CMN lead on the original 7805 was now too short to re-solder to the board, so I have replaced it with one from Maplin (QL31J) - Not sure if this is a "low dropout voltage" version. Everything is now as per the original circuit diagram ( i.e. All additional resistors removed) and the fault is still there.
                      What I find most puzzling is the voltage reduces bit by bit as I get closer to the main board ICs.
                      These voltages are approximate (from memory) but there is 5.02v at the PSU floppy connector (not used), there is a bit less at the PSU main board connector 4.8v, a bit less where the supply cable is connected to the main board 4.6v and even less across the main board ICs 4.4v.
                      I can't see any evidence of dry joints and as the PSU floppy connector seems to have a rock solid output of 5.02v, I was thinking of trying to feed the main board from that point.
                      PS. I hope you don't mind me posting all this on the forum.

                      Comment


                        Posting the data here is a very good thing, Andy--especially if it helps someone else avoid a similar problem once the final details of the isolation process are completely documented here. I'll have to go into mine soon to add the floppy controller and the memory mapper sections of my board, so all the data you've posted here may come in very useful, as it will tell me both normal and abnormal behavior for the motherboard. If your schematics say they are the corrected ones, it would be very good to put them up on WHTech.
                        Enter My Mind At Your Own Risk!

                        Comment


                          A quick update on my dead / dying Cortex and a plea for advice on what to check next.
                          As per my earlier post, after tidying up the PSU board I could only achieve 4.4 volts on the main board.
                          With the bias resistors re-fitted, as per the construction guide and a new 7805, I achieved 5.25v at the PSU output and 4.9 Volts on the main board.
                          All the ICs were then removed, cleaned with a fibreglass brush and re-seated
                          I then fitted my new BASIC eproms and applied power. The Cortex gave a continual alarm tone, the "RUN" light flickered and the "MEM" light was lit.
                          I then fitted my known good FORTH eproms and the fault was still there.
                          Assuming the PSU could still be suspect, I took a known good PSU from a working desktop PC, checked the output and cabled it to the Cortex.
                          From memory I was then seeing +12v, -11.65v and +5.25v at the PSU output and +4.9v across the ICs on the main board.
                          With power supplied from the new PSU the "RUN" and "MEM" lights were lit as before but there wasn't the same continuous tone from the speaker. However I did hear a faint "crackling" sound from the speaker after pressing the reset button, this sound would disappear when the LEDs had settled down.
                          Being a total novice when it comes to this sort of thing, can anyone suggest what I should be checking next.
                          I am working on the following assumptions
                          1) If I continue using the desktop PSU we can eliminate any power issues.
                          2) At this stage I don't need the video output.
                          3) At this stage I don't need the cassette interface.
                          4) At this stage I don't need the E-bus.
                          5) At this stage I don't need the keyboard.

                          Could any of the above interfaces be dragging the system down? I can unplug the keyboard but should I be removing any ICs to the isolate the others or is this a waste of time.
                          I have access to a DVM, a logic probe and possibly a scope - Can anyone suggest a way foward?
                          Last edited by andyp; February 2, 2010, 12:37 PM. Reason: spelling

                          Comment


                            Dead Cortex

                            Andy,

                            Could someone perhaps supply you with a single EPROM containing a small program that does nothing other than cycle one of the LEDs on and off? This would confirm that a bare minimum of circuitry was working. Whether this works or not, it would give you a known base to start testing from.

                            I'd also be inclined to replace IC44 and IC97 - a pair of 74LS245s that you can get off Ebay for a few quid. The '245s are quite prone to blowing, as far as I understand.

                            Stuart.

                            Comment


                              Stuart, - Thanks for the info, I'll follow your advice and get some spare 74LS245s.

                              I notice from the ETI description that one of the 74LS245s is a data buffer connected to the DRAM chips and the other is used by the EBUS - Could I not just swap these around or try them one at a time in position #44 to see if it makes a difference. Or do they both have to be fitted at the same time?

                              Does anyone know if ALL the DRAM chips have to be fitted for correct operation and if one of these memory chips was to be faulty could this be preventing my initial start-up sequence
                              It occurred to me that if the contents of the eproms are transferred into the DRAM at start up, then in theory could I get away with fitting 3 x TMS4164 at a time.
                              I could then try different combinations of my 8 DRAM chips in batches of 3 to eliminate them as faulty. Would this be a usefull exercise?

                              Comment


                                The 74LS245 at position IC44 is the critical one as it buffers the DRAMs. You could try swapping them over. If IC97 is not fitted, that shouldn't be a problem as far as I can see.

                                Each DRAM is only 1 bit wide - so you always need 8 of them to form an 8-bit byte. If any one of them is bad, it is possible that could be causing the problem (or of course it could be any of the other chips on the board).

                                The processor itself has 256 bytes of RAM, so it should be possible to develop a routine to test the DRAM, with the routine in EPROM and using the processor RAM for workspace, and giving feedback through one of the LEDs. If no one else chips in with an offer of help then I'll see if I can get a TMS2564 and cobble it to work on my programming board, which supports only up to a 2532. What would be useful is if a UK owner was able to test any such routine on a known-working Cortex just to make sure it works first.

                                I'm up in Southampton. You got a new Maplins in Barnstable last year was it?

                                Stuart.

                                Comment

                                Working...
                                X