Kenwood TS-530S Alignment

December 27th, 2014

Vintage radios work exclusively in the analog domain, with alignment done by adjusting numberous discrete coils, capacitors and resistive elements in the system. This is vastly different from my experience with digital computers, where, for the most part, the equipment works or it doesn’t and seldom is tuning required.

Though my Kenwood transciever has been working pretty decently, it did have one apparent issue that made me think that it needed an alignment. When switching from USB (upper side band) to LSB (lower side band), the “tone” of the audio output changed a little bit. I didn’t think that this was correct behavior and have been intending to do an “alignment”, which involves following a rather involved 25 step tune up proceedure. This is one reason that I have been acquiring test equipment, like the Marconi signal generator and Fluke counter.

Yesterday, I spent a couple of hours in which I started the alignment process. I made it through steps 1 through 7 of the 25 step process. Oh, and I also had to skip ahead and do steps 11 and 17 when I adjusted components on the IF board instead of the PLL section ruining previous settings. As I move through the rest of the steps, I’ll have to redo those steps as the intention of the process is to do things in a certain order. This is so that later steps don’t ruin the settings of earlier steps.

I found that the job takes a lot of time, but I didn’t have any particular difficulty with any one step, other than adjusting the wrong components. This makes me think that the sections of the radio that I have adjusted don’t have any major problems.

The good news is with the completion of these steps, the difference in audio from the LSB and USB has disappeared and no other ugly phenomena has surfaced. I must be doing something right, or else I’m pretty lucky.

The reason I stopped at step 7, is that steps 8, 9 and 10 requires either going through a range of frequencies manually with a signal generator or the use of a sweep generator. I started working on building a sweep generator a month or two ago, so I’ll wait until either the sweep generator is working or is given up as a failure before continuing with the alignment. I’ll talk more about my sweep generator project in a future post.

Video Posted Showing RTTY RX with Vintage Gear

December 25th, 2014

Check out my latest podcast.

feed://www.willegal.net/feed.xml

The Radio Teletype receive function seems to be working real well. The work I did in the “lab” preparing for this, resulted in almost immediate success upon hooking up my rig to a real HAM receiver.

Before I can start transmitting over the airwaves, I still have to do some work with antenna tuning, write an Apple IIe RTTY transmit driver and generally check things out in the lab. I also have some kludged cabling going on that needs to be fixed.

That said, I think that KC1CKV will soon be on the air…

73

HAL ST-6 RTTY TU Restored to Operating Order

December 22nd, 2014

In a previous post, I showed a picture of my HAL ST-6 RTTY Terminal Unit.

Now that I had the SCELBI 8B working, in my spare time, I have devoted a few hours to getting the ST-6 up and operating. For those of you who aren’t aware, an ST-6, demodulates a Radio Teletype (RTTY) signal and presents a current loop data stream to an external device. It was intended for connection to a Teletype, but I’m connecting it to my vintage computers.

The HAL ST-6 is quite a different beast, as compared to the computers I’ve been working with over the years. There is a lot of hand wiring in it, and each module is filled with discrete components along with a few op-amps.

inside the HAL ST-6

inside the HAL ST-6

The RTTY signal comes in several forms. My mid 70’s era HAL ST-6 was designed to support demodulating a signal with frequency shift keying offset of 170, 425 or 850 Hertz. Instead of a teletype, my plans are to have a vintage computer decode the serial stream and display the incoming data. I’m starting with an Apple IIe and have written a driver for the old serial printer board that supports current loop. The driver reads 45.45 baud 5 bit BAUDET format, converts it to ASCII, and displays it on the screen. Eventually I hope to be able to port this code over to a SCELBI.

For testing purposes, I’m using an internet RTTY audio stream. This audio is routed from a computer speaker output to the HAL ST-6 audio input. This audio stream replaces the radio’s audio output of a real RTTY stream, which would normally come from the speaker output of the radio. At this point, except for a few quirks with my Apple II software, it seems to be working quite nicely. Once I get the kinks worked out of the software, I’ll hook it up to my radio, and see if I can tune in some real RTTY broadcasts.

RTTY tuning in the old days was enhanced by hooking an oscilloscope in XY mode to the oscilloscope output of the ST-6. I have done the same with this test stream and think I have a pretty good pattern.

RTTY eye pattern

RTTY eye pattern

Getting the HAL ST-6 up and running wasn’t trouble free. At first, the output of the 170 Hertz filter/limiter wasn’t working at all. It took quite a bit of debugging before I discovered that a potentiometer case was shorted against the windings of a coil. While debugging this issue, I found and repaired a broken wire on another coil. I also tweaked the “alignment” and spent considerable time just checking out the circuit to make sure everything was working correctly. I also spent a lot of time chasing “issues” that turned out to be operator error, but I learned a lot in the process.

Once I get reception working well, and get a handle on how real operations work on HAM RTTY, I’ll start working on the transmit side of things. This HAL ST-6 has an audio FSK modulator incorporated in it. I’ll have to be cautious about how I bring it up, since AFSK operations are well known to have a lot a issues with harmonics and spurious noise.

VCF presentations added to Apple II repair pages

December 20th, 2014

I’m not sure it will be of much help, but I just added links to a couple of presentations that I made at VCF over the last couple of years to my Apple II repair pages.

http://www.willegal.net/appleii/appleii-repair.htm

SCELBI PCB update

December 19th, 2014

Here’s a brief SCELBI project update. There were 16 different PCBs made by SCELBI for the 8H and 8B computers. The current status of my reproduction efforts of each of those cards follows.

Main System Cards – working reproductions of all 10 cards types have been completed
Reproduced
1100 CPU – 8H/8B
1101 Data bus buffer – 8H/8B
1102 Input – 8H/8B
1103 Backplane – 8H
1104 Front Panel – 8H/8B
1105 1K SRAM – 8H
1106 Memory Expansion – 8B
1107 4K SRAM – 8B
1108 Backplane – 8B
1109 PROM – 8B

Peripheral Cards – 1 reproduced, 1 in progress, 4 haven’t been started
Reproduced
2104 Teletype interface*

In progress
2103 Audio Tape read

Not started
2105 Keyboard
2100 Oscilloscope digital**
2101 Oscilloscope analog
2102 Audio Tape output

* not as high as normal vector boards
** double width vector board

A pretty conservative estimate is that I’ll have cassette interface read and write cards completed and working in the first half of 2015. I’m kind of hoping I’ll have them going by VCF east, but I’m not committing myself to it. I’d like to complete the Oscilloscope and Keyboard interfaces by the end of 2015. It’s really hard to say if I’ll actually finish them by the time the year 2016, comes around.

Apple PROM board, MEA/Apple TTY emulation update

December 13th, 2014

The SCELBI PROM board is working fine and I was able to create a small program in the editor and execute pass one of the assembler with MEA. I can’t completely assemble a program and run it until I get the cassette interface built and operating. Pass two of the assembler writes the output to cassette tape. I’ll have to hold up doing a video until I can get the complete package going. My impressions of the MEA package are quite positive. It’s not as elegant as later software you might be more used to. However, considering the time frame it was made and the platform is the 8008, it’s a pretty nice package.

SCELBI PROM and extra SRAM boards cost $50 each and are available now. This recent work also confirms that the TTY board is working fine and those are available for $30.

I’ve been using an Apple IIe in 80 column mode with a bit-banged serial serial card to act as TTY emulator. However there are a couple of fairly significant issues that need to be solved before publishing this teletype replacement solution. It’s usable for me, but there are some problems. The two issues with my current Apple II TTY emulation solution are:

  • 1)The Apple II isn’t fast enough to scroll it’s screen at the same time it’s receiving data in a bit banged mode. It drops a few bits from the next character while scrolling the screen. This means that I’ll need to come up with a special designed card to support 110baud current loop with a UART. Since I’m doing a new card, I’ll consider figuring out how to add paper tape support and possibly printer support, as well.
  • 2) In 80 column mode, the screen driver doesn’t support carriage return, without also doing a line feed. In other words, you can’t move the cursor backwards to position 0 on the same line, like a real TTY would when it receives a CR. I’ll have to look into a software fix for this, but it might take sending the cursor to home and then moving it back down to the correct position on the page or something like that.
  • SCELBI running MEA

    SCELBI running MEA

    This image shows the Apple IIe acting as a TTY for the SCLEBI 8B on the left. The screen contains a small program entered with the MEA editor. The listing of the program at the top of the screen has two extra lines at the end. The “D 000 006,000 007″ is an editor command that deletes lines 6 and 7. The “L” command lists the text buffer. The last two commands “P1″ and “P2″ are pass 1 and pass 2 of the assembler. Pass 1 shows no errors. Pass 2 writes results to cassette tape. Since the cassette isn’t installed in my system it actually does nothing. If I had a tape, pass 3 would read the object back into the system so it could be executed.

    The “E”s on the left side of the screen should be the first character of the next line, but the Apple IIe can’t scroll fast enough to be ready to receive the first character of the new line, so it receives a partial character.

    yeah – MEA running on reproduction SCELBI 8B

    December 10th, 2014
    MEA dump memory command - Apple IIe used as TTY emulator connected to reproduction SCELBI 8B

    MEA dump memory command – Apple IIe used as TTY emulator connected to reproduction SCELBI 8B

    Here is the dump of memory from the SCELBI PROM card from addresses 060-000 to 0600-037 as displayed on a 40 column Apple IIe, running some very simple TTY emulation software.

    To interface to the SCELBI, I’m using an Apple IIe with an old serial interface card. The Apple Serial Card is the first serial card released by Apple, and was intended to connect to serial printers. It included support for current loop and 110 baud rate. It’s the only thing I own, that supports that combination of baud rates and interface protocols. Be aware that this card is not the same as the very common Apple Super Serial card, which does not support current loop.

    For TTY terminal emulation purposes, I’m doing a major rewrite to the driver, as the default printer driver is not suitable for TTY emulation. I’ll post the emulation software and directions on connecting this serial card to the SCELBI TTY card as soon as I clean up a number of small issues.

    More updates on this exciting development to come soon.

    SCELBI PROM Board Progress

    December 6th, 2014
    SCELBI PROM Board

    SCELBI PROM Board

    The PROM Board is built, installed and appears to be running. However, it’s not completely checked out. I need to hack together a simple Apple IIe TTY emulation program that will work with Apple’s old serial card. That card is the only card that I have (outside of my SCELBI stuff) that will run at 110 baud, but it was designed for printing, so I couldn’t find any ready made terminal program for it. The standard PROMs on the SCELBI 8B assume either a keyboard/oscilloscope interface or a TTY interface at 110 baud. Since we don’t have the keyboard/oscilloscope software, I burnt the TTY software into PROMs.

    It should take me a day to two to complete the TTY/terminal program hack for the Apple II, at which point, I will probably make short video showing the capabilities of the SCELBI 8B minus the cassette interface.

    I used black tape to cover the windows on the EPROMs because I’m told that sunlight will erase them after a while.

    Meanwhile, you can run the software in my OS/X emulator by downloading the MEA hex file from scelbi.com and jumping to 060-000. In a quick trial, it appeared to work ok for me. Be aware that I don’t currently have the cassette interface emulated, so cassette operations will not work. Cassette emulation is one the things on my to do list.

    High Value/Low Voltage Capacitor Capacity Test Circuit

    December 5th, 2014
    High Value Capacitor Value Test Circuit

    High Value Capacitor Value Test Circuit

    This simple circuit can be used to test the capacity of low voltage, high value capacitors.

    Use the well known RC formula: Time = Resistance * Capacitance

    Connect a DC voltmeter between TP1 and TP2. Start with the 10 volt power supply switched off and the capacitor discharged. The voltmeter should read close to zero. You can short positive and negative sides of the capacitor with a resistor to discharge it.

    You start the timer and switch on the power supply. Stop the timer when the voltage reaches 6.3 volts.

    Since time and resistance is known you can now solve for capacitance.

    Capacitance = Time/Resistance.

    So if you have a 470 uF capacitor, with a 10K series resistor in the circuit, it is supposed to take .000470 * 10000 = 4.7 seconds to charge to 6.3 volts. If, in your test, it actually takes 10 seconds to reach 6.3 volts, you can calculate the actual capacitor value. In this example, 10 seconds /10000 ohms = 1000 uF.

    You can increase the value of the resistor to check lower valued capacitors, but it will hard to check real small capacitors with this circuit. You can use a 555 timer circuit to check real small capacitors, but thats a subject for another blog posting.

    Brain Board Inventory Down to Two Kits

    December 4th, 2014

    I have two Brain Board Kits left and don’t think I’ll do a rerun anytime in the near future.

    I had a total of 59 made in early 2011 and it’s taken a while to sell the last few kits after a fair level of initial interest. Given the numbers made, these are likely to be hard to come by in the future. If you don’t already have one, this may be your last opportunity to get one for some time.