Recent content by Vermithrax

Motorola Application Note AN-771 discusses expansion techniques for the MEK6800D2. https://archive.org/details/Motorola_AN-771

One caution: The MEK6800D2 requires a single +5 volt power source; however, the added SWTPc MP-M memory board requires 8 volts DC for the on-card regulators to work properly. This may explain that perforated board shown above.

The Southwest Technical Products Corp 6800 system featured a serial control board (MP-C) that was able to talk both to RS-232 and a 20 ma current loop. The assembly instructions included connection diagram for an ASR-33 Teletype, but the schematic is of more interest here as it shows the...

Monty: I need to dig through some files to see if I had run a disassembly against DDT 51.8 from the ROM image, but it has some similarity to the Board Bucket ROM version of DDT that I spent some time on. In your disassembly, starting at address $096F, is the native disassembler...

Monty: This is encouraging that the DDT51.8 works on the 4052 as well. As you noted, the base address of the DDT program when run is unknown at the time DDT was assembled, so relative addresses in the assembly are calculated as though the program runs from memory location 0000h. The engineers...

A couple of observations. A phone is connected to the Dial Central Office (DCO) through a two conductor telephone line that normally supplies 48 volts DC until the receiver is picked up by the user. At that point the voltage as measured across the line drops to a lower, holding value in the 5...

Found something interesting over the weekend - There is a wealth of HP documentation over at https://literature.hpcalc.org, if you select HP-35 as your model, look for "HP 82002A Cord Replacement" in the filtered results and download the document on the right side of the page. The document is...

My apologies, I just re-read your last post - Keep an eye on the 470 uF 16V elko capacitor. Electrolytics shouldn't run warm, if it continues to do so or you see the ripple come back, it may have been damaged by overvoltage.

I remember that switch, it was a bit tricky to get into position to reassemble the power supply. There are two primary windings on the transformer. That switch puts the primary windings in parallel (110 VAC) or series (220 VAC) to match the mains supply voltage. If the switch was in an...

I thought so, it looked familiar. For some reason, posting to the forum reduced the resolution on the GIF and made it more difficult to read. .5 volt is ballpark for a silicon diode while it is conducting. Electrolytic capacitors don't like being reverse biased. Low capacitance may be an...

Having another power supply helps, it rules out the calculator as the most likely issue. By the way, there is a switching power supply that develops the various voltages required by the P-MOS chips in the calculator that might account for the 505 Hz noise. For the HP-45, this is...

DrAlis: Looking at the circuit, it appears to be a full wave rectifier (the four diodes after the transformer plus the 400 uF filtering capacitor), and then Q1 transistor/D5 zener forms a voltage regulator feeding the calculator when plugged in; and a constant current source formed by Q2...

Hi Monty: Well, there is that. Both versions appear to be 51.8. I may have to take another look at the mag tape calls in the loader strings to see if they are throwing the errors. I have gone through the version of DDT included in the 4051 ROM pack included in the emulator, it uses an...

Dave, Monty: Lately, I have been processing some of the 4051 program files found on Monty's GitHub site to translate them from EXEC loader files to something that the f9 disassembler can take as input. That much is working fairly well. I have been intrigued by the inner workings of...

Monty: Got the message, and the note. Thanks! Nelson