Hamfest acquisition: Fluke 8600A DMM

The other $5 digital multimeter that I picked up at the Shelby Hamfest was a Fluke 8600A DMM. This one was quite a bit heavier than the 8000A.

Fluke 8600A digital multimeter
Fluke 8600A digital multimeter

Like the 8000A, there’s a label on the bottom that lists the specs and configuration. This unit came with the rechargeable battery option, which would explain the extra heft.

Fluke 8600A specification label
Fluke 8600A specification label

Unfortunately, this one didn’t do anything when the power button was pressed. Getting the cover off the DMM is a simple matter of removing one screw just above the power connector (normally covered by a “Calibration void if removed” type sticker).

The insides are a considerably more complex than the 8000A. A large chunk of the space toward the transformer and power plug end of the board are taken up by the rechargeable batteries. This DMM appears to have had some modifications or repairs made to it.

Inside the Fluke 8600A digital multimeter
Inside the Fluke 8600A digital multimeter

A cursory inspection shows one significant issue: leaked batteries.

Leaky NiCad batteries
Leaky NiCad batteries

At some point, one of the D-cell NiCad batteries was replaced with an AA sized NiCad battery.

The manual I found (dated 1981) says the batteries can be replaced, but the ones in this unit have been tack soldered to the terminals. Perhaps the battery options were changed in later models of the meter.

Another IC (possibly a ROM) was also added to the meter and connected to the board with some ribbon cable. The ribbon cable is soldered to a DM47S188AN (256 bit PROM) and the mystery IC is just attached to the RF shield of one of the daughter boards with some electrical tape. Maybe a repair job, or a modification?

There are four daughter boards in the case that attach to the main board via pin and socket connectors. One board is marked as a battery power supply, which I’d guess takes care of charging the NiCad batteries.

Battery power supply board
Battery power supply board

Board #2 is marked “OHMS CONV ASSY”

Board #3 was marked “INPUT DIV”

Input divider board

Board #4 was a fairly large one with a large shield on it. No clear silkscreen markings labeling the board like the others but according to the manual, it’s the AC converter board. it also had a holder for a spare fuse. Very thoughtful.

AC converter board

Other than the batteries, I don’t see any obvious problems with any of the other components in the meter. I’m thinking maybe if pull out the leaked batteries, that might get the meter running but I’ll need to study the schematics to see how the batteries are connected to everything to figure out if that will work. This thread on the EEVBlog forum has some potentially useful information.

I’ll put this with the rest of the project items in the stack.

Hamfest acquisition: Fluke 8000A DMM

Two of my Shelby Hamfest acquisitions were a couple of Fluke digital multimeters (DMMs) for $5 each. The seller had no idea if they were working or not, but for $10 I figured they would either be handy workbench instruments if they worked, or fun projects if they didn’t. A brief Google search brought me to a nice tear down/repair attempt blog post.

The Fluke 8000A is a pretty nice looking bench DMM with push buttons for function and range selection, and a handle that also doubles as a stand.

Fluke 8000A digital multimeter
Fluke 8000A digital multimeter

A printed label on the bottom provides specifications and indicates what optional features the meter has. Apparently a rechargeable battery was an available option which would have made it handy for field use. This one didn’t come with a battery.

Fluke 8000A specifications label
Fluke 8000A specifications label

A label on the top of the unit says this unit was last calibrated in September 1994, 27 years ago. Someone apparently decided at some point the meter wasn’t working properly anymore and wrote “BAD” on the sticker.

Calibration sticker dated September 1994 on the Fluke 8000A
Calibration sticker dated September 1994 on the Fluke 8000A

Much to my surprise, the meter turned on when I plugged it in. Testing with some precision resistors I have in my collection gave me some pretty good results.

Measuring the DC voltages of some batteries gave me results that compared pretty well with one of my handheld meters. I haven’t tried measuring anything else yet, but it seems like for $5, I’ve got a pretty decently functioning bench meter (at least for most of the things I’d need to do anyway).

First blog post + 18

First blog post was 18 years ago!

Old enough to vote now, if it could.

In Canada, it’s old enough to go hit the bars and have a drink.

3200 posts (including a few of draft posts that will probably never see the light of day).

Post volume has been pretty low over the past few years, but now that I have a tiny bit more free time and more projects to ramble on about, I’ll try to kick that up some.


Peeking inside the Altair 680

Let’s have a look inside the Altair 680 that I acquired at the hamfest a couple years ago.

Undoing four screws at the back of the unit releases the back (surprise!) and top cover to reveal the inside.

Inside the Altair 680 showing the power supply at the bottom, and circuit boards
Inside the Altair 680

The back plate has the power supply consisting of two chunky transformers, a fan, and DB25 connector. There’s also an empty spot for another DB25 connector. Thanks to the two transformers, the rear panel is fairly hefty. The DB25 connector looks like it only has 4 wires. Not sure what would be connected to it, but probably something serial terminal related. There’s not a lot of clearance between the transformers and the SRAM chips on the main board when the rear panel is in place.

Removing the expansion board (I’ll get to that in a bit) reveals the main board.

The Motorola MC6800 CPU that powers the 680 is up toward the expansion board connector. Toward the bottom rear of the main board are 8 1kbit Intel P2102 SRAM chips that provides the 680 with 1 kB of RAM. Above the RAM is an EPROM (looks like an AM 1702A EPROM). The empty sockets seem like they would provide space for 3 more EPROMs. The other notable chip on the main board is the MC6850 asynchronous communications interface adapter.

Over in the front corner of the board by the big 3.3 mF filtering capacitor, the silk screen says this 680 main board is Rev 1-6.

680 Main board Rev 1-6
680 Main board Rev 1-6

The only expansion board in this 680 appears to be a RAM expansion board. The riser card has room for 3 slots, but the two other spots are unpopulated.

Altair 680 expansion board with one connector and two unpopulated connector spaces.
Altair 680 expansion board connector

The RAM board contains an 8×4 bank of Semi 4200UCP chips. A Google search didn’t yield a whole lot of information about them, but they appear to be 4kbit SRAM chips, so this board provides the Altair with a whopping 64 kB of additional memory to play with.

Photo of the Altair 680 memory board.  A 8x4 bank of 4 kbit static RAM chips provides 64k of RAM.
RAM board

When I plugged it in and turned it on, the fan spun up and some lights came on!

Altair 680 front panel showing some data LEDs turned on.
Altair 680 front panel showing some data LEDs turned on.

No smoke released, but the data lights turning on even though most of the switches were in the down position indicates something’s not quite right. Changing the switch positions didn’t affect anything either. The Run light on even though the switch is in the HLT position also suggests something isn’t quite right. Toggling the HLT/RUN switch made the HLT LED blink on once. Toggling the RESET switch seem to affect anything. The address line switches all seem to work, but LEDs started blinking when A13 was switched on.

Looks like this unit might need some work to restore it to a functioning state. I’ll also need to do some more research to learn about how the 680 works.

Back into the closet it goes for now.

Motorola MC6809 trainer

One of the items donated to the radio club by an SK estate last year (now I’ve forgotten which one) was this microprocessor training laboratory (MTL-1) from Cleveland Institute of Electronics (CIE).

Presumably, if you had an interest in learning computer hardware and programming, you’d enroll in a class and get one of these along with class materials.  I’ve seen similar trainers in the past, but never had the opportunity to use them.  The breadboard area lets you wire up circuits that let you do things with the 6809.

This one is based on a Motorola MC6809, a contemporary of the 6502 and Z80 microprocessors.  After watching the one YouTube video I’ve found along with a bit of random button pressing, I’ve managed to figure out how to to go to different addresses and enter assembly code.  I haven’t entered anything that runs though.  I’ll have to find some time to learn 6809 assembly first.

Aside from the copyright date on the back, there’s no other indication of when this particular unit dates to.  Fun fact: 1984 was my first year of high school,

Surprisingly, I’ve found very little documentation about this particular trainer online.  I’ve found one video on YouTube where someone used it to demonstrate testing a RAM chip, and a few photos of similar units on auction sites, but nothing in the way of manuals or even course materials that might have used the trainer.

This seems like it would be a fun thing to play with, especially for anyone with a retro-computing fetish. The hunt for documentation continues. I’ve already found a few PDFs about programming the 6809, so maybe I’ll be able to figure out enough do fun things with this.