Saturday, October 3, 2020

Side project while waiting for outdoor air to become fit for human life - restore a Power Designs 2005P Power Supply - Part III


I went through the power supply, tracing out, beeping and and measuring components to determine what was different between this 2005P supply and its cousin the 2005 for which I had schematics. In fact it was a very minor set of changes. 

I took the schematic for the 2005 and erased the extraneous gear and made the corrections. Now I have a schematic of my unit. I posted this as the prior blog post for anyone who has this unit and is looking for the drawing.

Portion of 2005P schematic covering adjustment

As is shown above, the Programming Constant trim pot is R21 and it is wired to deliver 0 to 200 ohms of resistance from one end of the range to the other. Above it, there is a parallel set of resistors, one fixed at 5200 ohms and the other (R CAL) chosen to make the effective resistance correct for operation.

In my unit, the value of R CAL is 100K such that the equivalent value of the parallel resistors is 4,925K. Since the circuit when adjusted all the way to one end of the Programming Constant trimmer pot, where the resistance is 200 ohms, is insufficient to make the output low enough, the equivalent resistance of this pair is too low. 


I will snip out R CAL and test the resulting output voltage. Based on where the output voltage is with the trimmer pot halfway, I will determine an appropriate parallel or series resistor to make the output of the supply match the external resistor in K ohms by adjusting the Programming Constant pot. 


I set up my resistance board for as close to exactly 20,000 ohms as I could get and wired it into the supply rear terminals as the programming resistance. After cutting out the R CAL resistor, I was able to adjust to 20.000 volts with the Programming Constant trim pot somewhere in the middle of its range.

I did have to recheck and readjust the Zero Trim pot, then finesse the Programming Constant but once that was done, I could set up my resistance board to any value I wanted between 0 and 20K and I would see a voltage equal to 1/1000 of the resistance. This project is complete. 


My 2005P power supply is only adjusted as accurately as the resistance I hooked up and as accurately as my VOM could measure. When I am next in a lab with multiple higher quality instruments, I will recheck the resistance and output voltage but that will be a matter of a minor adjustment of the trim pot.

Power supply with 'programming' resistance board on top

Power Designs 2005P power supply schematic

 This is a schematic I created by correcting the model 2005 version for the differences found in the 2005P, since there seem to be no extant schematics for the latter model.

Friday, October 2, 2020

Side project while waiting for outdoor air to become fit for human life - restore a Power Designs 2005P Power Supply - Part II

The wine country fires have dumped large amounts of ash and smoke into the air, with that particle laden air wafting down to my area. Air quality is Unhealthy and will likely remain until those fires die down or the wind patterns change. I continued working on the side project for now.

First step was to drill the holes in the top cap, just to the side of the slot where the inner circuit board juts out. Then the wire will bend 90 degrees to exit sideways from the top of the red outer can. As you can see from the pictures below, it has extra room above the top cap to permit the wires to fit.

Top cap on left, outer can on right

I used a small drill bit and a handheld drill on the outer can because of its cylindrical shape, but was able to use the same drill bit in a drill press for the top cap as its bottom would sit flat. With holes drilled and a test made for the wire clearance, I began to think about assembly.

The thermostat wires are too short for the run from inside the oven, out the top cap, along the entire length of the outer can before it is slid down over the oven and still have the wire come out the side holes. Therefore I need to extend the wires by soldering new lengths to the ends and insulating. These new segments should be rated at least the same 105 C as the thermostat existing wires. 

Holes drilled and wire fit tested

The last safety check was to ensure that the shrink wrap tubing that would insulate the solder joints was also capable of safe operation up to 105 C, the same limit as my wiring. I found that the materials used were intended for operation at levels from 125 C up to more than 220 C depending on the particular type, thus making these suitable for my project. 

With the new thermostat installed, I stuffed the insides of the oven with the glass wool and replaced the can covers. I then routed the external wires down the side of the oven can and to the terminals underneath where the thermostat circuit is connected.

Oven back in place ready for rewiring

The next task was to solder all the connections back on the oven terminals. Several of them had 3 or more leads, but most were single wire per terminal. I found for the multi-lead ones I had to completely clean the terminal, clean up the wires and wrap each around the terminal lug ends before I could reliably solder them.

One final check shows connectivity of the thermostat contacts and of the heater, but no shorts, so I tidied up and applied line voltage to verify that this heats up then cycles to maintain target temperature. According to the manual it should take about 10 minutes to reach working temperature after which the thermostat will open and then cycle to maintain the target 70 C.  

I found it was only about 4 1/2 minutes until the oven light extinguished. Since the ambient temperature was about 38 C and the can had been in full sunlight before I put on the cover and started, that is a reasonable warm-up interval. I suspect the manual assumes an air conditioned lab and has some padding in the estimate to ensure the 

Now that the oven is working properly, I have to turn my attention to the process of calibrating the unit. There are meter adjustments, zero voltage adjustments and a 'programming' linearity that ensures that with a perfect 20K ohm resistor attached, the unit will deliver 20V with a variation of no more than 7 millivolts. 

The procedure to adjust the output accurately covers the situation I faced, where the trim pot doesn't get all the way to the desired value when turned to its extreme. There are a set of resistors in a division network on the board, on which you solder jumpers until you get the zero voltage point with the trimmer pot set about midway through its rotation. In other words this is a normal part of adjusting the unit. 

My zero point delivered about 4 mv at its lowest on my VOM, not zero, with the zero trimmer set to its extreme end of the range. To eliminate errors from the alligator clip jumper resistance and the VOM accuracy, I put in a good solid conductor jumper for the resistance and made use of my oscilloscope for the voltage measurement. The results were consistent - I need to change the resistance to achieve a real zero setting with the trimmer pot.

Jumpers on resistors thus only 16.2K (R9) is in circuit now

The four resistors from left to right are R40 (4.32K), R13 (8.25K), R9 (16.2K) and R41 (32.4K) thus they can be set for resistances for 4.32K up to 61.17K in approximately 4.32K increments. These resistors feed one side of the comparator in the oven to match against the target resistance connected to the programming terminal. 

I will cut the existing jumpers and use alligator clip jumpers to experiment, then solder in new jumpers to the desired resistor value I select based on the outcome. The correct combination in circuit were R40 and R13 for a combined resistance of 12.58K ohms. I was able to set the zero point with the trim pot and the unit was very stable within the precision limits of my VOM. 

Setting the zero point with short on programming input terminals

With the zero point properly set, I attached my resistor board and set it up for 10K ohms. My VOM shows the resistance at 9.9K within the precision of my unit. Then I attempted to set the linearity to achieve 9.9 volts where it is between 9.893 and 9.907 on the voltage measurement, again subject to the precision and accuracy of my VOM, in order to meet the specifications for this unit of +/- a millivolt. I could not. At one extreme of the programming constant trim pot, it was still over 10.3V output. 

Unfortunately, the schematics I own are all for the regular 2005 unit, not the 2005P that is programmed by external resistance. In the regular units, high precision resistors are wired onto the setting switches and necessary adjustments are made internally, but on my unit there is a trimmer pot to make sure that 1000 ohms produces exactly 1V +/- 7 mv. 

To finalize the restoration of this unit, I will need to reverse engineer the circuit portion that includes the trim pot to see where I might be able to adjust other values so that the trim pot can set the target somewhere near the middle of its adjustment range. Stay tuned for part III of this project.

Wednesday, September 30, 2020

Quick verification of communication between CISCO 2911 router and my laptop


The ethernet connection between my laptop and the fast ethernet port of the Cisco 2911 will be used by the DLSW encapsulation function of the router to contact the 'other router' to carry the SDLC traffic between the serial port on the router, hooked to my IBM 3174 terminal controller, and a mainframe system. 

The other router is really code built into the 3705 emulation function of Hercules which strips the SDLC from the link and processes it as if a serial line were configured between a real 3705 communications controller and the remote 3174. Thus the mainframe emulated by Hercules thinks it has a 3705 using a leased line to talk to the 3174. 

IBM and Cisco developed the DLSW encapsulation as a way of transporting the serial traffic over a TCP/IP network instead of Telco leased lines. The 3174 on one side and the 3705 on the mainframe data center side both have serial port connectors, but instead of those being cabled to modems, they hook to serial interfaces on Cisco routers. The routers carry the serial traffic inside TCP/IP. 


I hooked up an ethernet cable between the laptop and the router. I set up the fast ethernet port of the 2911 as and configured my laptop's ethernet port as I then booted up the router making use of a USB serial link for the console port of the router and the command processor of Windows on the laptop side.


I did some pings to see that the packets were sent both ways over the ethernet cable, then started a telnet client on windows and pointed it at the router address. This opened and I had the logon prompt that I could use to connect to the router's IOS environment. This ensure that I have a good link on this end. 


Once the outdoor environment is healthy I will hook the serial port of the router to my 3174 and cable the ethernet to the laptop. After I boot the router and start Hercules, I am IML the 3174 controller. If all goes well, the serial link will be established between 3174 and 2911, then I can start DLSW and IPL the MVS 3.8J image under Hercules.

Tuesday, September 29, 2020

Side project while waiting for outdoor air to become fit for human life - restore a Power Designs 2005P Power Supply - Part I


The many wildfires, most started by lightning during one day of thunderstorms, have been joined by fires up north of California and a few new blazes started later, to produce staggering amounts of smoke and ash. While I am safely away from any fire danger, the air quality has had very large quantities of 2.5 micron or finer particles that are quite unhealthy. 


I have set up tables with the various 317x terminals, the 3174 controller and the other components for my main project driving the green and color screens from MVS running on PC based Hercules and a P390 mainframe. The bad air has been an impediment to further testing, thus I have been spending my time in alternate projects and reading.


I had bought a 2005P power supply from eBay because it is a highly accurate supply with an internal oven to ensure excellent regulation and accuracy of the voltage produced. The model I bought is remotely programmed, which simply means that an external resistance is used to set the voltage. It produces 1V for every 1000 ohms of resistance across its 'programming' terminals.

I have a resistance substitution board that produces essentially any resistance I want from 1 ohm to 11.1 MOhm by setting switches, which when connected to the power supply programming terminals will let me produce voltages from .001 to the full 20V capability of the supply. It also supports current regulation, thus will be a good lab tool when used for experiments where controlled targeted voltages are important. 

There are some adjustments that I can't make with the extreme range of the calibrating pots, but that I something I can deal with by adjusting some internal resistances and pots. The more serious issue I detected is that the oven is not heating up. Any time the supply is plugged in, even if the switch is off, it should warm the oven and maintain its  temperature. 

The amplification and regulation components are set inside an oven can where a heater is thermostatically operated to establish a narrow range of fixed temperatures for the remaining parts. Operation of the heater is shown with a neon indicator bulb on the supply faceplate, but it remained dark.

Further, I checked the terminals on the oven that feed the heater inside and found zero voltage on the pins. Checking the pins for the thermostat, I found it stuck open when it should be closed at room temperature. I therefore have to disassemble the oven, find the thermostat and attempt to fix it. If I can't fix it I will need to replace it with a comparable unit. 

Oven with components inside

Oven desoldered and removed from the main turret board

Following the instructions got me to the point where I can see the board with all the amplifier components mounted on it but when I grab it and try to pull it out it isn't moving. Moreover, the diagrams of the board don't have the thermostat (or heater) on them so they may be embedded inside the base of this can. I did have to pick out quite a bit of glass wool that is the insulation inside. 

Amplifier components on small turret board inside overn

I suspect the thermostat is inaccessibly embedded in this nylon base

While there is no definitive spec for the temperature inside the can, several others who have restored these units report that it activates at 70C. Some have chosen a lower set point of 50C, claiming the regulation is just as good and they believe the lifetime of the components would be enhanced. 

I shopped for a 70C thermostat. There must be room inside to mount it and a way to connect the wires to the pin on the base, or a way to route the wires out without compromising the heat seal of the oven. Putting it inside the can won't be a problem, I believe, but the wiring is challenging. 

70C Thermostat

My plan was to drill two small holes in the base for a snug fit and epoxy the thermostat wires in place. The body of my new thermostat is metal thus I had to ensure that it was fully insulated from the components on the small turret board. Fortunately it comes with a plastic cover.

Drilling from the bottom was too risky, since I can't see inside the nylon base. My plan B is to drill holes in the top metal cap to allow the thermostat wires to protrude, then bend them 90 degrees and route them out a hole in the top of the outer metal can. This won't be ideal cosmetically but should minimize additional heat loss and most importantly, work properly. 

Tuesday, September 1, 2020

Setting up laptop for private ethernet link to Cisco router


The SDLC (VTAM) version of the project is to connect my IBM 3174 and its attached 3178 and 3179 terminals to MVS running under Hercules on my laptop. This uses an IP encapsulation protocol DLSw implemented by Cisco that will wrap SDLC packets inside an IP protocol. This was used to route links to remote 3270 terminals using IP networks, with both endpoints stripping the DLSw and implementing SDLC links to mainframe and 3174 ends. 

The Hercules project implemented a DLSw socket on its 3705 communications controller emulation function, which strips the outer protocol and pretends that there was a native SDLC link hooked to the 3705. The other end of the DLSw link is the CISCO 2811 router, which believes it is talking to another Cisco router rather than Hercules. 

The serial connection on the Cisco router is hooked to my 3174 cable and speaks SDLC. My IBM 3174 thinks it is talking pure SDLC over telecom lines to a physical 3705 controller on a mainframe. 


I configured my laptop's ethernet port with a static address. It is and it uses as the default gateway for routing. Of course, the Cisco router is configured so its ethernet is and its default gateway is my laptop's address. 


To bring this up, I have to boot up the Cisco router and attach an ethernet cable from it to my laptop. Pings from both the router console and from my laptop will show whether the IP connection exists. The DLSw link itself uses TCP port 2065 on both end, but that will be tested once I bring up the entire test setup. 

Monday, August 31, 2020

RPF working well now


There were quite a few differences but I first zeroed in on the variations that I suspected might have caused the observed symptoms. Some I ignored because they didn't seem likely to account for the misbehavior - for example, the good system has RPF V1R5M3 while the bad system was running a newer V1R8M0.

I began to narrow down my investigation to the parameters and procedures that start up TSO under TCAM. In the parameter library SYS1.PARMLIB, the primary member that controls TSO is IJKPRM00 but there is also a member TSOKEY00 to consider. Nothing in the SYS1.PROCLIB procedure that starts timesharing looked meaningful, nor did the CLISTs executed at login. 


I carried the entries from the TK4- system back to the Moseley MVS 3.8J and updated IKJPRM00 and TSOKEY00 there. When I then logged into TCAM TSO and ran RPF, it worked perfectly! The likely causes are the buffer size and quantities specified in IKJPRM00. While I could do a binary search changing individual lines in the file, that isn't important to me. What matters is having full RPF use.