Category Archives: Electronics

Pontiac renovations, part 17.

Having fitted the air cleaner assembly to the engine to test, I decided that there was no time like the present to finish cleaning it. I had done the main body but had the air cleaner element and the oil bowl were still dirty and as-found.

Oil bowl

The caked-on dirt- very fine prairie dust mixed with decades-old oil had done a moderately good job of protecting the metal from corrosion but it was time to clean it up and use paint for that purpose instead.

Bare metal.

All the dirt came off with some elbow-grease. The metal is in good shape for its’ age.


The outside was given a coat of etch primer, after having been wiped over with rust converter.

Gloss black enamel.

Final coat in black enamel. It hardly looks black, it reflects so much light. This enamel gives an incredible gloss straight from the spray-can.

Dirty filter element.

Next up, the filter element assembly. Again, more of the same scrub, scrub, scrub.

Filter element coming up clean.

Again, it came up remarkably well to bare metal with just a wire brush.

New filter mesh added to element.

All of the original filter mesh was gone. I’m not sure if it was cotton wadding type or steel, but some mice had been in there and had left none at all.

Filter element painted.

The inner element assembly is visible from the outside, so again, primed and painted in gloss black to match the rest of the assembly.

Entire air cleaner assembly fitted to engine.

All together and looking rather good, for the first time in many years.

Checking alignment and clearances of air cleaner.

I adjusted the mounting bracket that I had made, having seen a photo of a factory install. the filter sits almost directly over the mounting stud, with just enough clearance for the water pipe to the top of the radiator.

Washer bottle frame.

Next up, I did a little research and found that only the later Trico model screen wash brackets were blue. The early ones were plain mid-silver.

Pale blue-gray final color.

I chose a very pale blue instead, keeping the the car’s “blues” theme.

Paint color testing.

I experimented with some new paint colors. Off-the-shelf is a poor match for any bodywork colors on the car. On the left of the arch, by the washer frame is French Blue. On the right is navy. I think the navy will possibly tie in better because it’s close to the color of the roof.

Trico screen-wash reservoir and pump.

I bought a used washer pump/bottle off eBay for a good price. It was complete and looked to be in good shape. I took it apart, found the seals to have dried up over the years. Pressed them flat again and cleaned it all up.

Dissolving old under-seal.

The outside of the jar was covered in under-seal over-spray. It was left to sit in gasoline for a couple of hours and it all wiped off.

Jar fitted and filled.

Keeping with blues on blues, it was filled with fresh screen-wash and tested. It works in a strange fashion- there’s a spring-loaded double-ended plunger into two separate cylinders. Vacuum is applied to the top cylinder and the piston moves up, bringing the lower piston up and drawing fluid in from the jar. Release vacuum and the spring pushes it back down, expelling fluid from the top pipe in a stream until the piston bottoms out.

Delco radio set.

Next “new” item was a radio set. the car did come fitted with a radio but it was a “modern vintage” style tape deck. First, it didn’t fit, second it was missing a dial knob, third it was ugly. I decided I was going to retrofit the original AM Sylvania/Delco radio. They pop up on eBay from time to time in varying states of disrepair. This one looked moderately good and had the correct dials to match the rest of the dials in the car. There are four variants of knobs that I’ve seen, depending on what model variant you bought. Plain black plastic for the basic model, black plastic with a silver insert for the standard, silver outer with a black insert for the Deluxe (what mine has) and all silver (I think for the Catalina Coupe).

Undoing the front panel.

Disassembly of the unit was straightforward, just a number of 1/4″ bolts and a few nuts holding things in place. My idea was to gut it and fit something modern if it was in bad shape internally, or refurbish and restore if it was in good shape.

Radio circuitry and tuner.

Inside, it’s in really quite good condition. It’s pre-PCB so all the components interconnect each other and solder directly to the chassis in places. The tuner was jammed up solid.

Lubricating moving parts.

All the moving parts were lubricated. The tuning mechanism was then free to move, including the preset buttons. Unfortunately the metal case that holds the tuning coils has what is known as “zinc pest”, where lead impurities in the alloy react and cause crystalline fractures to grow. The metal then becomes weak and breaks like shortcrust pastry. It has expanded a little and bent out of true but for now isn’t too bad.

Front panel, ready to be cleaned.

The rear of the case is painted silver and is in very good condition. the front had been painted black and was covered in surface rust. I sanded it down with fine grit paper on my DA.

Front panel, stripped.

Back to solid, clean metal. Most of this will not be visible as it is mounted behind the dash, with just the chrome dials and scale showing at the bottom. The sound passes out through the large circular grille in the middle of the dash.

Front panel, still wet in satin black.

It was given a coat of primer and then a coat of satin black paint, to match the original finish.

Copper coat.

The speaker mounting screws would have been untreated steel originally, and as such had also gone rusty. I scrubbed them down with a wire brush, cleaned them further with ionic removal in a salt/vinegar bath and then plated them with copper.

Nickel coat.

The copper coating was then given a nickel coating to protect the screws and give a modestly shiny surface.

Dial knob comparison- dirty vs. clean.

The dial knobs were very grimy.When the set first arrived, a cursory glance looked to be missing chrome in places. It turned out to be thick dirt, all of which cleaned off with a wire brush.

Radio reassembled, clean.

I test-refitted the front panel, bezel and knobs. Looks much better than it did.

RF, IF and audio pre-amp section.

I turned my attention back to the circuitry. It’s a bit of a mess of seemingly randomly-placed components but there is a degree of logic to the assembly. I had started to measure some of the values (the Rider manual uses M notation for resistance in the k scale, and Meg for M) and quickly discovered that my tube meter was not functioning.

Heathkit VTVM in pieces.

I took it apart and had a poke about. The tubes both lit so the heaters were all good, there was voltage at the plates and no signs of any stressed components on the board. I twiddled the calibration pots but that was not the problem. It ended up being a poor contact on the connection to the meter. There’s a battery in the circuit that gives a permanent positive bias and that had made the brass peg of the meter’s terminal corrode slightly.

Working meters.

I cleaned the terminal up, re-calibrated the meter as per the factory manual and checked the voltage of a 9v battery I had on the desk. Both meters agree, which is good. I ran out of time to carry on, but all the test equipment is in place. What I need now is a 12V power transformer, the 12V variants of the tubes, possibly replace the rectifier with a couple of diodes and add a modern solid-state vibrator to generate the high voltage.

Luggable overhaul: Part 2

I placed an order for some more tantalum bead capacitors a while back and they finally arrived in from China. 10uF, 25V so rated at a higher breakdown voltage than the originals (16V). I’m not a huge fan of tant beads but they are compact and this is preserving a moderate amount of originality.

Tant beads

I started removing the old capacitors and soldering in new. Three layer boards are awkward enough to work with through-hole, but this went smoothly enough.

back of video board

Worked my way through, this is the multifunction card (RAM, serial, clock, parallel ports etc).

multifunction card

You can see where the tantalum beads are failing- they crack open in some cases and vent. The mark on the top of this one is just visible.

broken tant

I also wanted to change the LED on the board. Not because it didn’t work, but because Compaq used a very pale red epoxy cased LED that looked cheap. It spoiled the look of the board.

LED comparison

Side by side the old one and its replacement. The replacement one is older by a few years, but it from the era where the packages were nearly clear but much darker red plastic.

on the board

It’s a better contrast to the color of the board. Lights up a very deep red compared to the newer LED.


A pointless aesthetic? Yes. But it makes me happier to look at the board.

Luggable overhaul: Part 1

I had set my Compaq portable up on the table in preference to the Macintosh, with an idea to use it more regularly. It started up okay but made a rather unpleasant burned smell after about twenty minutes so apart it came.

expansion slots

Nothing particular showing up, so lifted all the expansion cards out and then removed the motherboard.


There’s a couple tantalum capacitors with cracks in, so they’ve gassed up and are not long for this world. The video output has been a little wobbly since I got the machine, particularly in low resolution mode. It’s all packed in fairly tightly.

vdu and psu

So, out came the VDU. Picture tubes always look so forlorn when they don’t have any cases or bezels fitted.

picture tube

There’s always one part that makes a bid for freedom. Tonight’s candidate was this washer:


The power supply is all plugs, making a note of what goes where as there are quite a lot of them..

power supply plugs

Everything all lifted out quite easily.

all boards

These are the two boards that need the most attention. The power supply (the highest power most compact board designed to date at that time) and the video board, powered by the power supply on the 12V rail.

vdu and psu

The connector was showing signs of high current draw so it’s definitely time for a rebuild. The power supply is marked “upgrade” on the back, so that’s positive.

Cycle rectification

I had pulled all my test equipment out to align my radio again;

test bench

So, I started my bike up and checked the output of the generator with my oscilloscope.

scope on bike

The output was rather spikier than hoped for into the negative, so redoing the rectifier was in order. Possibly the vibration was too much.


I finished up the latest revision of the regulator board, with a new Zener to bleed off any excess input voltage, a resistance across the input capacitor to bleed off any stored charge, a mechanically better connection to the board and some adjustment pots.

More generator issues

Checked the output of the generator with nothing connected.


With no load it was causing the capacitor to saturate at about 46 Volts. Not so good!


Also, the main voltage regulator chip had vibrated loose and fractured off. I made a bracket to secure it to the board better.


Bolted down securely, and relocated the capacitor; however with only the rectifier in place I’m reading a fairly significant AC component on my multimeter. I’m going to hook my oscilloscope up to it and see what the output looks like. I have a feeling possibly one (or more) of the diodes have failed.

Processor and a monitoring panel (plus holiday oddments)

After the previous discovery that the -12V rail was collapsing under load, I read up on the datasheet for the 8080A processor. It states that the voltage rails must be brought up in a particular order (-5, +5, +12) and if the -5 is missing then there’s a very high chance of damaging the processor. The 8085 negated this and required a single, positive power source- the 8080 has strict requirements.
The 4116 RAM states that it should be brought up with the -5 first then the +5 and then the +12 but any of the rails missing should not cause damage to the chips. Bonus there.
So, I decided just to fling a processor at it. For $4 a pop, I decided that it was worth a shot, having fixed the power supply.


Same behavior upon power-up. At least I have a couple spares now.

repeating trash

Pulling the video RAM does show a different pattern on the screen so that at least is moderately positive- it initializes the memory in the same fashion each time it it switched on. Pulling the CPU and I/O cards and powering up the video card only liberates a solid beep, no crackling warbles.


Bought some little voltmeters from China- self-powered with internal self-regulated reference. They work from about 2.5 Volts all the way up to 30 which is impressive.


Also, bought some red transparent acrylic to serve as a mounting plate and to act as a contrast-improving device for the displays.

cut out

Marked up, cut with a hacksaw to size and sanded down smooth. Gently heated it up with my butane torch and bent it into a shape that stands up by itself.


Measured up for the meter locations, drawing the positions on the front in Sharpie.


Spread a thin layer of PVA glue on to each meter. It’s nice because it dries clear and doesn’t attack the plastics.

row of meters

Five meters stuck on and waiting for the glue to dry.

heat shrink

Trimmed the wires down to length and soldered on a length of multi-core wire, and using a spoon as a heat shield, added some heat shrink tubing to each join.


Soldered some test leads onto the other end of the cable and marked them up as to which is which.

plugged in

Got everything hooked up onto the appropriate locations on the PSU.

meter on

With a few labels to show what’s what (and a couple others because I got carried away) the output of the PSU is monitored fully. Everything is in spec, all loaded down with all boards fitted. Now that I have this set up, I’m happier in the knowledge that everything is doing what it’s meant to in terms of power.

Next up, pulling it all out of the chassis to get the analyzer clipped on properly.

new light

Back to the house, I bought a new 4′ Lithonia light fixture to replace the junky Lights of America one that refused to light one tube and barely lit the other. Wired it up, fitted the old 25W tubes and flicked the switch. Nice bright light with instant start, too.

recapped tv

Recapped a TV for someone at work. The ventilation grilles at the back had become lodged with dust due to the location it was kept in (TV stand with no access to the sides) and as such, had cooked itself. Uprated the heat ratings of the replacements (all the originals were 85C, the new ones went in all 105C with a few in really warm locations at 135C) and ran it for an evening. Worked well.


Traded the Challenger in against a new vehicle- Jeep Grand Cherokee. A bit more practical than ferrying the family around in a 2-door muscle car.

drip drip

Changed the ignition amplifier in the Renault and also a new distributor cap and arm, along with the crank position sensor. The CPS was at fault causing the non-running but the ignition amp appears to have been a bit marginal because it has a lot more torque now. Also, the power steering has stopped leaking and is holding fluid. The gearbox is leaking though, along with a weep of coolant onto the exhaust manifold that I need to find the source of because it smells when I start the car up. Other than that it is actually working moderately well.


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.


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.


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.


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.


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.


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.


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.


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.


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.