Category Archives: Electronics

Eighty-Eighty

I decided that I had wanted to give myself a little bit of mental exercise so I started work on the Lanier again.

Lanier on table

This began by dumping the thing on the table, pulling the CPU card out and trying to begin modeling its schematics in KiCAD. This is slow, problem-riddled (the board traces go back-front-back-front and are difficult to follow).

Made a decision to power it up after far too long sat up doing nothing. Pulled the PSU out and brought it up slowly on the Variac.

slowly, slowly

Same old nonsense, the thing didn’t do a whole lot of anything to begin with, a bit of a beep, floppy drive lights on. Hooked it up to my new logic analyzer on what looks to most likely be the bus on the backplane.

logic analyzer

There’s a bit of life, and the behavior begins to change. The floppy drives begin to clatter and rattle. I solder a bypass onto the video card to make the screen always show what’s on-screen (blanking bypass) and it’s got some nonsense changing here and there, occasionally filling the screen with alternating patterns.

logic traces

The logic traces look “dirty”, there’s a lot of glitches and the machine in general seems rather unhappy.

omooikkiakka

Some of the random content on the screen can be moderately amusing though.

Right around this point I was contacted by a guy in Ireland who used to service these things, still has one, schematics, discs and spares- everything I thought I’d never got for it. He says it’s a real early model with the screws holding the case on at the sides (probably circa 1975).
His suggestion was check the power supply, because random freaking-out type behavior is normally bad power.

power

I pulled the PSU and checked the voltages present. Everything was where it was supposed to be. Plugged the boards back in and same problem. Started to probe voltages on-load and found that the -12V rail had dropped down to +0.4V which is rather odd. Put a light bulb across the rail- it flashed then went out. Pulled the video card out and the rail stayed stable.

Zener

The RAM in the machine was all 4116, which requires +12, +5 and -5V supplies to work. I had replaced the CPU board with 4164, which needs only +5 so that cuts down on heat and current requirements significantly. The video board still uses 4116 so would definitely not be working without -5, which is derived from the -12 rail. The circuit is rather simple, a diode to the -12V rail, through a 330 Ohm resistor and the other side of that held to a stable voltage by a 5.1V Zener diode. I pulled one leg of the Zener off, removed all the RAM chips and put the video card back in and powered the machine up. The screen filled with [] symbols, which was expected as the RAM is not present and all lines would remain at zero. The -12V rail stayed stable also so the Zener was suspect. I’ve had them fail in the past and turn into almost a dead short. Found a temporary replacement in my box of stuff (half the Wattage rating but OK for a temp try).
Back into the chassis and still the -12V rail collapses. Start tweaking the crowbar adjustment and manage to get it to an unhappy -11.5V before it would just trip out over and over. Turn the PSU over.. and the -15 rail, which the -12 comes from.. is the only line I’d not replaced the main filter capacitor on.

capacitor

It’s all leaky up top, the vent is showing signs of having vented out. Not good. That’s most likely going short, drawing too much current and when the boards are added to that draw, the over-current crowbar is kicking in and shutting the rail down.
I had a dig and find a 15000uF, 50V capacitor with clip lugs. Soldered that in on short flying leads and powered the PSU up. -12 rail is at 12.04V, -15 at 13.3 unloaded so I adjusted them and then hooked up the computer boards. Made a slight tweak to all the voltages and got them within 0.01V stable.

There’s still something that’s not happy because switched on cold it beeps (with a somewhat crackling warble modulating the beep) and the drives click. Once it’s been on for a while it begins to not beep any more and it still goes a bit haywire but at least now I know that the main supply is good. I need to order the correct screw-in capacitor and a higher Wattage Zener for the -5 rail supply on the video card, but this is positive progress.

Mac back on track

Despite the little set of ceramic capacitors I put in having a combined value in an acceptable range for C1, it would appear they were either breaking down or otherwise incapable of sustaining the horizontal frequency of the screen scan.

caps being meaured

So, a different set of capacitors was used and that brought the screen back to life.

working again

That appears to overall conclude the work on this machine.

Broken Macintosh

Very short-lived, this one. I took everything apart and adjusted up the screen so it was central.

Nice and even

Set it on the side to do a bit of a burn-in test, and the decoupling capacitor for the horizontal yoke let out all its magic smoke, the screen went a bit funny and I switched it all off quickly.

c1

Decided to build the little capacitor network suggested in the manual, of several ceramic capacitors in parallel to build up the capacitance but reduce the ESR.

c1c1c1c1

Put it back together and again we have screen but.. the horizontal isn’t aligned any more. The two interlaced pieces of the screen, all stretched out – do not line up.

interlaced

I’m going through the schematic, I’ll check all values and make sure that the capacitor failing did not draw too much current through the flyback and fry one of the windings.

Rejuvenated Macintosh

I decided that the wobbly-screen Macintosh needed to have a bit of work done to make it a bit more trustworthy and reliable. The electrolytic capacitors had been installed in it since 1985 (8113th device produced in the 24th week of 1985 in Fremont, per the serial, so a real early 512k).

mac on table

Took it to pieces after ordering a bunch of spares (total about $15, so not bad), with the replacement caps rated at least one voltage rating over what was fitted and 105C rather than 85C as fitted originally to try and keep them a little more stable.

logic board

Not many capacitors on the logic board, though it is a 4-layer PCB so extra care had to be taken. I’ll give them this, it’s a well made PCB.

logic board closeup

Tried to keep the solder-work neat. Don’t think I did too bad a job, to be honest.

work in progress

Got stuck in doing the power and sweep board, which has the majority of the capacitors.

powered up

First test, and things were promising until the brightness control decided to stop working.

broken brightness pot

Turns out the center carbon track had completely fallen apart. Checked the schematic, fairly standard 16mm 1MOhm linear pot, so went on the hunt for something similar in the electronics catalogs online.

new pot

Closest modern variant I could find. The board is the right size and the connecting pins the correct length, important in this application because of the way the computer is assembled.

take apart

Carefully undid the new piece, as the thing was essentially backwards from how it needed to be.

sweep

This side is where the old one had the handle coming out. I removed the crimped section and split it all down, had to file the ears of the board a little to make it fit but managed to put it back together again, and have it test good and smooth operation across its range of travel.

reassembled pot

Put that back in the circuit and the brightness is now adjustable again. Checked the voltages and the 5V rail (the master) was a bit low at 4.72V so that was tweaked up to 5.00V. The 12V rail, slaved from it sat happily at 12.2V so that’s all well within limits.

5 volts

The screen became a bit intermittent- traced that eventually down to a couple broken solder joints on the connector to the end cap of the tube.

broken joints

Removed the old solder and re-added new.

working now

All up and working again. Need to adjust the centering of the screen a little, I think I must have knocked the centering rings when I put the wiring back in. Overall, a lot better than it was.

New Arduino Project – matrix LED display

I salvaged a couple of displays from some old equipment that was being thrown away. Pulled up the datasheet and started trying to make my Arduino Uno display things.

gibberish

After bit-bashing in some dots, I managed to get it to correctly display a letter, this case a lowercase “a”.

a

Now it actually works- I’ve made it scroll text input from the Serial port, full ASCII table. 3.8kb of code, not bad compiled from C.

nmmm

The above was from a leafed/paged test of the full ASCII table I made it loop.

Wipe and wait

My car has a 4-position windshield wiper stalk; off, intermittent, slow, fast.

While the motor needs to be pulled and serviced because there’s little difference between slow and fast, the intermittent wipe had always been somewhat pathetic.

Selecting intermittent would make the relay click, and as soon as the wipers returned to the parked position, click again and they would almost immediately wipe again.

Pulled the dash shroud down and located the clicking box at the top left. (Top right is the key-in/seatbelt buzzer, bottom left the cruise control stalk, above that with the finned heat sink the dashboard dimmer control).

relay delay box

Took the circuit board out and drew up the circuit diagram by following the traces, to get a better understanding of the circuit and its method of operation.

board

Culprits were most likely the electrolytic capacitors. One had a high ESD and the other was meant to be 22uF, it measured in at about 100nF. Replaced them both. Now the wipers wipe and wait about 5 seconds before wiping again on intermittent, and added bonus, they now wipe 3 times after spraying screenwash onto the screen. Not bad for 45 minutes’ work and spares I had in stock.

Co-processing.

I decided to buy a little something for myself, so eBay was opened up and I hit “Buy It Now” on an item.

Package

3 weeks later, it arrived from Kowloon, Hong Kong. The reason for the package? This empty socket.

socket

As if by magic, it was filled with a suitable device:

387

Upon fitting a 387 co-processor, a jumper needed to be shorted to inform the board to use it.

jumper

CheckIt determined that the thing was working (which is good, as there are surprisingly quite a lot of fake/broken chips circulating the market).

checkit

It was then tidied up into the desk. Makes a significant improvement where a math co-processor is utilized.

lotus 3

A bit of fun, reminder of days gone by.

Film photography and a 386

I went to an estate sale at the end of last week and picked up a few things, the computer below and a camera, of the notably interesting items.

386

A 1993 Magnavox (Philips) 386 SX/20, with optional CD-ROM sitting on top. It was grimy on the outside, filthy inside as to be expected from an older system.

A1

After a thorough cleaning, the Canon A-1 camera. 35mm film camera with fully automatic exposure (AE). View through the viewfinder (this shot before I had cleaned the lens and filter, so it’s a bit hazy) shows the aperture and exposure time in f/stops and 100ths of a second respectively.

viewfinder

It’ll calculate that and set itself if you leave it in fully programmed mode.. fancy stuff. Bought a new battery for it and a foll of Fuji 400.. have been shooting some pictures so once that’s finished I’ll see if they came out OK.

wolfenstein

Got the computer running after giving it a thorough clean and fixing a couple contacts. Found a cable to replace the one in the back to link to the CD. Added a network card so it has CD interface, network and sound. Multimedia on a 386, before “multimedia” was a coined phrase!

cd working

Added a larger hard drive in (540Mb, or rather, 30Gb but partitioned down to the max the BIOS can handle without an overlay) and got the CD to read. 1x so it’s not fast but it does work!

AM Radio

This is a fun one for me- I’ve had this radio since I was about 12- I had gone to my school for the tombola/fair/jumble sale. I bought one of two radios, initially the one I god was a white plastic deal, brand I forget, and one of my friends- Alex Biffin- bought this one, for 50p (about, what, $0.75 these days). I bartered this one for his radio as this one worked better. It’s a Roberts RIC-1, the first radio to be produced in the UK to incorporate an integrated circuit (IC) into the design, making the design a lot smaller.

radio

It worked for a while until I dropped it and it stopped playing. I took it apart and determined the cause was the IF oscillator coil because it would sometimes crackle into life if I twisted the can. I tried to search around, went to the radio shop in Wells (long since gone) but nobody had the part available, so I shelved the radio.

Fast forward two decades and I decide to pull it off the shelf and try fix it, with greater knowledge, experience and Internet behind me these days. I found a service manual for it, something that was totally unavailable back in the day.

apart

Took it to bits, gave it a bit of a clean up as it was rather dusty. The loudspeaker wire had also broken off so that got re-soldered on. Still, nothing from the speaker as before.

LP1175

The offending article, a twin transformer coil in a can marked LP1175, apparently a fairly common part made by Philips back in the day.

angle

Same device, from a different angle, also the TAD100 IC that gives the radio its’ name.

can removed

De-soldered the IF can and set it aside, looking at the connections.

coils

Further dismantled the can, removing the outer shelding, and also the inner ferrite shield that surrounded the primary winding. Pointed at there with the tool is a glob of glue where the primary coil windings pass through- which was fractured and had broken the fine wire.

new wire

I managed to unravel one length of wire from one end of the coil and re-soldered it to its leg, the other one was underneath the rest of the windings and wouldn’t come undone far enough to be long enough to reach. I took a piece of regular multi-strand cable, took one strand of copper out of it and fixed it to the short leg- the rest of the windings are covered in varnish so wrapping it around wasn’t a problem.

extension

Attached the extension piece to the leg it needed to be fixed to. Put it all back into the circuit, twisted the power dial and POPCRACKLEHISS. Wonderful! Tuned in a local station, a joy to hear audio from this radio after so long.

The loudspeaker had seen better days so I carefully made some repairs with coffee filter paper and Elmer’s glue (PVA) after doing a bit of research on the Internet about basic cone repair.

coffee paper and speaker

Cutting out more pieces and carefully reshaping the edges lef to an acceptable repair that no longer vibrates with bass notes.

fixed speaker

With that done, I set up my test rig and began aligning the radio- it wasn’t bad but it is now easily capable of picking up WSM that broadcasts from Nashville, TN.

aligning

It’s nice to have this radio working again. It got the kids interested in the theory, so with the new Snap-Circuits set (circuit building set we got from Elenco) built a small, basic AM radio. Fun times!

Finding a leak that doesn’t exist, and a broken timepiece.

I’ve been having a hard time finding a few problematic issues with the Renault lately. Particularly it had started to leak power steering fluid quite badly, which would mark the floor where parked up and also get onto the auxiliary belt and make that slip.
Looking down from above, past the alternator and air conditioning compressor the pump looked rather wet, so I splashed out $14 and bought a full seal set for the pump. I decided to clean everything up with degreaser and refill the system, to hopefully see where the oil was leaking from.

dismantle

Begin by taking everything out, including battery, battery tray, moving the air conditioner comressor, remove the alternator and the brackets holding it all in.

empty

That leaves good access to the power steering pump. The corrugated plastic tube is the wiring for the front of the car, the braided hose is the gravity feed to the pump from the reservoir.

scrubbed up

Cleaned up the pump with an old toothbrush and engine degreaser. Rinsed it all down with warm water from the potato pump.

clean

Got a bit carried away as I had water left, so I cleaned down the inside of the hood where the oil had flicked off the belt, and the surrounding areas also. Topped up the oil and left it to dry overnight an in the sunshine.

full

Left it for two days, then checked on the level. Unfortunately the oil was all there still.

still oil

Another two days. Nope, there’s still all the oil left in there. The leak has miraculously fixed itself. Normally, hot, cold.. didn’t matter. It would leak regardless of it it was run or not. Now it’s not leaking!

clean pump

The pump is clean and dry, no signs of leakage.

oily frame

The only other place I can see is the return line, from the rack back up to the reservoir. If that has a crack or a pinhole it could be leaking. The engine cradle frame is a bit oily down under the back but I cannot see anything else that would be causing a leak. Further investigation to follow.

The second thing that irked me was the previously well-working clock had quit.

broken display

The display had taken to showing mostly nonsense, or nothing at all.

clock out

Took the dash to bits (again) and liberated the clock from the little cubbyhole it’s attached to.

polished

Cleaned up the smoked plastic section of the clock as it was all scratched and hazy.

components

Figured there were a couple pieces that might have failed and caused it to not work. Replaced the electrolytic capacitor and transistor. No joy.

circuit diagram

Followed the traces and built a diagram of what went where, to get a bit of an idea of how it all worked.

dead

Tested it but the chip was dead. No oscillator, just noise. The clock circuit boards are available, but they are a Jeep Wagoneer part, and as such suffer heavily from Jeep Tax and are therefore expensive.

zeroes

Upside-down image but poking power to the grid brought some nonsense up on the display so the VFD was all still good.

9

Poking about a bit more showed that some of the logic was alive, as various numbers could be liberated. Nothing sensible though.

led

Purchased a little LED clock with voltage and temperature capability for ten bucks, with the intention of fitting it into the clock as shown- looks OK but a little out of place and the very-bright display has no dimming capability.

dismantle

Decided to strip the board down and re-use the VFD, with the new clock module providing the logic. I’ve ordered a little 50V boost converter to drive the VFD, that will be proven to work first then I shall go ahead and get some high voltage transistors, pull the LED’s off the clock and use the output (multiplexed in the same way thankfully) to drive the VFD. Original clock, original display, just now with time, temperature and voltage display. Watch this space for updates.