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Trying to get a Cromemco 2-ZD / 4FDC talking

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    A bit more clarification.

    I have three boards, all identified as Cromemco DPS-1 Rev B.

    I have two cards with THREE 7812 Voltage regulators and ONE 7805 voltage regulator. The THREE 7812 Voltage regulators appear to be configured in parallel. These cards don't have the two diodes fitted to them - and there is a wire link on the underside of the PCB.

    The third board is different. It seems to contain TWO off +15V regulators in parallel (each via the two diodes) feeding ONE off +12V regulator and a separate +5V regulator. This card has the two diodes fitted with no wire link on he underside.

    All three cards only feed one disk drive.

    Can you just double check whether you actually have two +5V regulators (7805) or not on your board?

    I suspect someone is over-stressing the regulators on your card by feeding two separate disk drives from one regulator card.

    Dave

    Comment


      If you are concerned with excessive heat on the DPS unit, you might want to take a look at the offerings of Pololu (the D24V22F12 for example)? They have replacement switching voltage regulators (both 12v and 5v) that are far more efficient than linear regulators. More efficiency == less heat. I believe they are available in a configuration that is a direct replacement for TO-220 regulators? There is another company with similar products (ezSBC), but I would avoid them, if possible. I got a very expensive, high current 5v regulator from them (in the TO-3 footprint) that failed within seconds of first power up. I tried to get product support from them, and encountered "crickets"!

      Roger

      Comment


        Thanks for these ideas. Yes I verified the board really does have 2 7805's and 2 7812's.

        I seen this just went up on ebay. https://www.ebay.com/itm/294562403776 maybe I should grab it and power each drive separately? I notice this one has the diodes installed and appears to be set up to power a single board.

        Comment


          I would recommend a second board. The original design called for a regulator board per drive. The 2 x 7815, 1 x 7812 and 1 x 7805 was the original per the schematic below.

          DPS-1 Schematic.png

          James

          Comment


            Originally posted by jima View Post
            I would recommend a second board. The original design called for a regulator board per drive. The 2 x 7815, 1 x 7812 and 1 x 7805 was the original per the schematic below.
            Thank you. I snagged the board from eBay. Hopefully that'll help smooth things out!

            Comment


              Yes James, that's exactly what I worked out for my 'original' disk PSU board.

              I have a couple of others that have been modified by someone (no diodes D1 and D2), different regulators (7412 instead of 7815) and some hand wiring...

              I will cross-check the hand-wiring now you have given us the schematic.

              Dave

              Comment


                So this board I just purchased is Rev A. My original board is Rev B. It has the missing diodes, and hand wiring as well. Do you think I should modify it back based on these schematics?

                Comment


                  I am still intrigued as to how yours is wired though with two (2) 7805 voltage regulators. Any chance of posting a front and back picture of the board - making sure I can see the regulator numbers that are fitted?

                  Dave

                  Comment


                    Here you go...

                    A 7805 and 7812 on each side. You can see there were a few modifications made to the board too (top & bottom), including some cut traces and wire work.

                    20211120_183053.jpg
                    20211120_183032.jpg
                    20211120_183041.jpg
                    20211120_183106.jpg
                    20211120_183118.jpg

                    Comment


                      It certainly looks like a non-factory mod to power two drives from one board with what seems to be a 7812/7805 pair for each drive. With two heat sinks doing the job of what should be four it's no wonder they get warm. Were it mine I would be reverting to one of the classic designs for peace of mind if nothing else. The 7805 part on it's own would be fine on your board but the 7812 would have to drop up to 8 volts (the nominal +18v rail can float high as it has to potentially power 21 cards) hence the 7815's and IN4001 diodes which means the 7812 drops just 2.3 volts nominally.

                      Comment


                        Thank you, yeah I've already gone ahead & ordered the diodes and 7815's - will be restoring this one back to stock.

                        Comment


                          Yep, someone's done a bodge job !

                          By the way, are you two guys members of the Cromemco Google Group? I have just joined. Well worth joining if you are not !

                          Dave

                          Comment


                            Is there any discussion of cromemco unix-xl V.2 over there? someone just sent me a set of version 3.0 double-sided 8" disks and the format seems really weird, as in not recognizable by Imagedisk
                            unix-xl.JPG .
                            I don't even know what model systems were capable of supporting those diskettes.

                            Comment


                              Originally posted by daver2 View Post
                              Yep, someone's done a bodge job !

                              By the way, are you two guys members of the Cromemco Google Group? I have just joined. Well worth joining if you are not !

                              Dave
                              I am although I had forgotten as I try hard to avoid all things Google - I'll take a look in a bit and see what's cooking over there.

                              Comment


                                Originally posted by Al Kossow View Post
                                Is there any discussion of cromemco unix-xl V.2 over there? someone just sent me a set of version 3.0 double-sided 8" disks and the format seems really weird, as in not recognizable by Imagedisk I don't even know what model systems were capable of supporting those diskettes.
                                I don't know about any discussions as I only visit here very occasionally but if it helps, as these are 8-inch and ftar archives they are likely in Cromemco's Cromix/Unix file system. ftar was a Cromix+/Unix utility which implies something like a System 300 or something with an XXU/XMU combination to run Unix System V. Note that anything which can run Cromix+ and has ftar would be able to read the archive for imaging even if it couldn't boot from the extracted files.

                                You may already have seen these but if not they may help point the way.

                                https://groups.google.com/g/cromemco...m/j-bxWfHcBQAJ

                                https://github.com/dwildie/cromix-fs/releases/tag/R2.2

                                James

                                Comment

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