Alas, not forever. This original battery was now reading 0V.

Battery replacement is widely understood — desolder the original from the board, solder in some other 3V non-rechargeable battery (perhaps in holder), and away you go.

Here’s my choice of replacement aesthetic. I definitely wanted to use a holder so I wasn’t desoldering and resoldering every 10-20 years; but many of the holder approaches are on fly wires and then either bang around inside the synth or have to get stickied to a nearby surface, neither of which appeals to me.

This CR2032 holder had both solder tabs protruding outside of the footprint for easy hand-soldering, fit the footprint of the generous solder pads, and came in black (brown? brack?) that I felt didn’t draw attention to itself inside the synth.

I may go back and add yet more solder to the pads to replicate the vintage giant blobs; but it’s already working and saving sounds with the synth off.

While performing a pre-sale test, the seller and I determined that something about oscillator 1 (of two) wasn’t working right on one the six voices. What follows is the process to determine which voice, determine which chip in that voice, and then replace the chip with a modern equivalent.

The Symptoms

The effect of the failed IC was that some notes didn’t sound the same as the other notes … but not always the same note. Since the JP-6 has only six “voices,” as you play keys, it dynamically maps a new voice to each new key that you play. As long as I didn’t play more than six keys, it was always the same note failing; and when I played more than six keys, it’d be a new note that didn’t sound right.

The ones that didn’t sound right had a simpler timbre than the ones that were working. Once I noticed the problem, I used the Mixer knob to listen to just the sound of Oscillator 1 on different notes, then just the sound of Oscillator 2. The problem was clearly in Oscillator 1, on just one voice. On that voice, Oscillator 1 played an octave higher than it should, and (apparently) more quietly than Osc 1 on the other voices.

Determining Which Voice

As the Jupiter 6 has six voices, a function called the Assigner maps keys (or received MIDI notes) to voices. It’s essentially NATting keys to voices. And as with actual NAT in a network device, you may or may not know the order that the mapping will be performed. I did not, nor did I find it documented.

Fortunately, on p 4b, the service manual gives a sleeper of a description of an incredibly useful diagnostic feature: the JP-6 constantly samples its different internal control voltages and constructs a cityscape waverform of those sampled voltages, available on a test point on each of the two voice module boards.

The right pin (from the perspective of the front of the synth — the boards are in the synth “upside down”) is ground; the left pin has the diagnostic waveform; and the center pin has a trigger sync that turns out to be 5V falling-edge to tell your scope when the diagnostic waveform is restarting.

Clearly I need to build myself a hook probe with a big ring on the back to connect probe ground clips, for when I’m connecting multiple probes.

Conveniently, the CPU PCB sends its 12-MHz CPU clock to the two voice module PCBs to use on their CPUs, so the diagnostic waveform turns out to be perfectly in sync across the two voice modules and I was able to display both waveforms on my scope at the same time. I looked at the service manual’s key for the diagnostic waveform to find what signals immediately preceded the oscillator 1 control voltages and dialed those features to max to create a visual landmark.

Then I played keys and watched which oscillator’s control voltage increased. Here it was four-voice board voice A (yellow) …

Four-voice board voice B (yellow) …

Two-voice board voice A (violet) …

These did not actually happen in a predictable order; I’ve reassembled here for easier discussion. When I played enough keys that two-voice board voice B lit up on the scope, I could hear the problem in the audio and I knew that the problem was on that voice. Further, I’d already determined it was with oscillator 1.

Determining Which Chip

Next, I traced and checked the control voltages being fed to the oscillator IC, to make sure they were correct. The voice boards’ CPUs actually each have a single D/A converter that’s fed through a 4051 analog mux to a bank of capacitors, which hold the control voltages for different features long enough to be refreshed by the CPU coming back around to generate a new D/A for that feature; and the CVs are TL084 op-amp buffered to the different chips that use them;

so I checked the B1 CV (main pitch control — sum of pitch from octave range selector, keyboard, LFO pitch modulation, and detuning setting) and FREQ (pitch adjustment — sum of internal tuning and envelope pitch modulation) signals to make sure they were similar between the buffers feeding a working oscillator and the nonworking B1. Which they were. Similar. The problem didn’t appear to be in the control voltages.

Testing the CEM 3340 Voltage-Controlled Oscillator

So with the problem downstream of the oscillator control voltages, I reviewed the datasheet for the Curtis CEM 3340 VCO IC used in the Jupiter 6. Interestingly, it generates three waveforms all the time; and interestingly, it generates them at different voltages. First it synthesizes a 5V triangle wave at the right pitch, then by an undisclosed method converts it to a 10V rising sawtooth, then by a comparator converts it to a 12V PWM waveform.

I played a six-note chromatic scale to prime all of the voice chips with as close to identical pitches as possible and put my scope on the A1 (yellow) and B1 (cyan) voices’ 3340 triangle outputs. Oh my, those pitches are not that similar.

Then scoped the allegedly-sawtooth outputs. A1 has definitely converted that 5V triangle to a 10V sawtooth, but B1 sure hasn’t. The B1 3340 was definitely faulty.

Confirmation and Replacement

I stickered the A1 and B1 3340 chips so I wouldn’t lose track of which was which. Then I carefully desoldered them, which was a delight with the solder side of the board so clearly labeled for anticipated field service, then soldered in sockets.

I swapped the 3340s, reconnected the scope to the test points, and verified that the problem followed the original B1 chip to its temporary A1 position. Yup, that chip is bad.

It turns out the CEM 3340 was such a popular VCO that not only has Curtis reissued the chip, but other vendors have made pin-compatible replacements with even better thermal stability. I ordered the ALFA RPAR AS3340 from synthCube, popped it in (upper right of the four 3340 chips surrounded by SIP resistor arrays) today when it arrived, and everything is now working as designed.

The Internet told me that the buttons are tactile switches and I figured I could easily replace them. YouTuber “Unrelated Activities” measured the switch dimensions and found a specific replacement that’s not available to me, but the dimensions were very handy. Searching Amazon for 12mm tactile switch got me what looked like a close-enough replacement, with the 7.3-mm height from base of switch to tip of stem, allowing me to order the switches in advance and open the sequencer once instead of opening it and waiting for delivery.

With the plausible replacement switches in hand, today I did the replacement. After removing the bottom panel and the screws from the bottom PCB, “fold” it up and unplug the white wiring harness from the bottom PCB. It helped to flex the connector away from myself, toward the back of the sequencer, slightly to break 40 years of stiction. Then fold it further up and it makes room to unscrew the control panel. (I didn’t bother figuring out how to detach the power wires in the back corner and remove that bottom PCB entirely.)

The replacement buttons (at top) continued to look plausible. I found it easiest to remove the keycaps by putting my pocketknife’s can-opener attachment under one end at a time and gently camming it to lift them off the stems. I desoldered and replaced all of them.

The switch mechanisms under the large Record, Stop, and Play buttons were different:

Without my contact burnisher handy, I folded fine sandpaper and lightly sanded the contacts.

Reassembly is easiest with the sequencer right-side-up, placing the control-panel PCB back in from underneath. Focus on folding the white wiring harness under the sharp burred edge of the metal rail and lining up the LEDs into their holes and everything else falls into place.

On the first reassembly, several buttons were pinned in place, pressed/engaged by the control panel. I thought I must have got them out of alignment, but I hadn’t. I noted that a slight relief on the PCB screws disengaged them and I thought some must have dangled loose while I was soldering and were installed with a gap between them the board, but they weren’t. I thought that the tolerances were different and I’d need to shim up the PCB with washers under it, but I didn’t. I realized that the stems of the replacement buttons were just different enough from the originals that instead of the keycaps snapping into place, they have a tight friction fit and I simply needed to press them all further on. Success!

I mean, mostly success. The original buttons were well-manufactured and have very little yaw. The replacements have considerable yaw internal to the mechanisms, so the buttons are all snaggletoothed unless I carefully turn them all into perfect alignment and then don’t touch them. I don’t care for this and I may have to print little shimming jackets to put around all of them … but it will require busting out the Ender 3 that I keep fitted with a 0.2-mm nozzle, because in spite of appearances, there’s only about 0.5 mm total clearance in the X and Y directions.

Nevertheless, every button now works on the first try and it’s a dream to navigate the menus. Looking forward to the next sequencer project.

Solder Rework Station

I’ve had the privilege of watching a couple of my buddies use their solder vacuum pumps to desolder PCBs for me, and those machines are a real treat. For a long time, they cost more than I could justify with my infrequent use; but a few months ago I check again and the Yihua 948D III, well-regarded by online communities, is only $140. I bought one and it’s not quite as fast and probably not quite as fancy as what I’ve seen used, but I’m thrilled to have it.

I have no affiliation other than being a happy customer. If you’re in the market and that’s in your price range, I think it’s worth a try.

Incidentally, if you want to be able to take it on the go, it packs into a Harbor Freight Apache 4800 case with a little bit of layout and planning.

This is the power supply from the Dell Poweredge 750 (yes, that’s 750, not R750) server from which, if it is still near the year 2021, you are being served this web page. A couple of weeks ago, it developed the new behavior of powering up perfectly well to start booting the server and start running the BIOS tests and then shutting off again.

Being in a bit of a hurry at the time, I grabbed my spare ATX power supply and hooked it up to get the server running again with the lid open and deal with the original power supply later. But with the new power supply connected, the server wouldn’t boot at all, because

what is this??? Oh, for a larff, let’s move the purple 5V standby wire from the ATX mother board connector to the PCI power connector, har har! So with the spare power supply connected, the server wasn’t receiving 5V standby [where it wanted it] to run the On button to turn on the power supply and the server.

I got it running temporarily by jumpering the /PS-ON pin to ground. As one does. And thus sits the server.

I shopped for a replacement power supply but found only one direct replacement, which appeared to be old stock, and by old stock, I mean this server is circa 2003 and so I believe was the power supply for sale; so I didn’t have a lot of faith in its longevity. I found no alternate power supplies with ATX connectors that would fit in the 3.5″ x 11.5″ x 1U space this power supply has inside the server case.

I had a look at the original power supply last week; checked the electrolytics with the Capacitor Wizard (they are, surprisingly, fine); and then noticed that one of the two fans was completely seized. And they’re three-wire fans. Oh, says I, perhaps the power supply is giving both fans a while to spin up and when it detects that one hasn’t, it shuts down to save itself. Very reasonable.

I removed the fan and did my trick of peeling back the foil sticker and putting one drop of oil at a time onto the shaft while spinning the blades to work in the oil, with which method I’ve got years of additional use out of seized fans. It worked superbly and soon the blades were spinning freely and striking the fan housing. Yes. The only thing previously keeping the broken fan’s blades from hitting the housing was that the fan was seized.

I ordered a replacement 40x40x28-mm fan, which arrived today; as well as a JST-PH connector set, since that’s what’s in the power supply and the fan came wired with what I know as a TE CST-100 II connector on it.

I had poor luck crimping the JST-PH pins (2.0-mm spacing) with this crimper that works well on JST-XH pins (2.5-mm spacing) — it squashed the barb meant to keep the pins in the housing — so I surrendered and spliced the old connector tail onto the new fan. Alas, the power supply still has the same behavior as before, albeit louder now that it has two fans running enthusiastically.

So. Unless another idea arrives via personal brilliance, comments, or email, I’ll be ordering a “fully modular” ATX power supply (with all of the cables detachable from the power supply), modifying the new power supply’s cables either to reroute the “green” 5V standby wire over the motherboard’s PCI power connector or to jumper the “purple” /PS-ON wire to ground, preconnecting the cables inside the 1U server case and running them out the hole in the back where the original power supply mounted, closing the case, and connecting and sitting the ATX power supply on top of the server in the rack.

Shamefully long ago (cue Wham’s delightful “Last Christmas” and sing along to ignore the guilt), one of the two redundant Pollcat telephony call-detail-monitoring gateways at work didn’t recover after datacenter electrical maintenance. Last weekend I finally looked at it, confirmed that the power supply was dead, and confirmed that the rest of the unit operated fine when run from bench power.

I couldn’t find a reasonable source for the original model of power supply (the right of the two, toward the center of the photo); so after a bit of searching came up with different a 5-VDC 2-A open-frame power supply (the left, on some bubble wrap) that can physically fit into the available space in the enclosure and that can also operate from 100-240 VAC (important for datacenter 208 VAC) for a very affordable $10. We ordered a couple of them and I got it replaced this afternoon. I expected from the beginning to have to make a mounting adapter, but I also had to mind the polarity of both the AC and DC power connectors.

The new power supply came without connectors installed for the AC input and DC output. Fortunately each connector has the same pin spacing on the old and new power supplies (even though parallax in my pictures suggests otherwise), making my job easier. But the DC pins are in the reverse order, so I checked the connector orientation twice before soldering and once after.

The AC side of the replacement power supply has only a two-pin connector — which is all that’s connected from the power line anyway, but required chopping the original plug to get it to fit. Here again, the two pins (load and neutral) are in reversed positions from the original. I was able to remove the hot pin from the plug and move it from the right end to the left, so it all fits together.

I drafted the mounting adapter with the corner flanges the same thickness as the original PCB so the standoffs are at the same height as before. I was prepared to recess the new power supply below the upper surface of the adapter; but the new power supply is shorter than the original, so I was able to leave it like this.

Of course, on the first draft of the mounting adapter, I angled in the stems from the outer corners and had the inner frame inset below the power supply instead of surrounding it … which interfered with the solder-side of the through-hole components.

After final assembly, I did a bench test to make sure it all works. Now it can go back to the office with me on Monday.

All of which is to say: Replacing failed power supplies with different models is commonplace when there’s a lot of room in the case; but even when space is tight, the resources we have available today make it pretty doable.

… And this post is documentation for whoever does the next one, when the power supply in the other Pollcat fails a few years from now.

The left two are open — you can see the broken wire at the bottom of the left coil and the top of the middle coil. (As always, click for full-sized image.) The right one is shorted and I haven’t found where.

I find it interesting that these are wound with round wire and the replacements are wound with flat-cross-sectioned copper “ribbon,” to get more current capacity in the same vertical space.

I tend to assume that batteries I happen upon will not be charged. Also that lead-acid batteries I happen upon will be low on water, even so-called sealed lead-acid batteries.

I wanted to start charging the batteries from my “new” scooter while working on other aspects of the project and the scooter didn’t come with a charger — I’ll deal with that later. Not knowing much about the wiring circuit yet, I didn’t want to connect an external charger to the batteries while they were still in-circuit and chance damaging the speed controller, so I needed to disconnect and remove them.

Wiggle wiggle wiggle <grunt> wiggle pull <grunt> WIGGLE WIGGLE BEND <grunt>

Wha?

Who does this??? When they said solder the quick-disconnect terminals, they meant the wire side.

Fine. My uncle’s iron and a pair of pliers solved that problem.

Two batteries, extricated and not yet cleaned.

In spite of being “sealed,” you can pry off the cover (preferably after cleaning, which I did first with Goo-Gone and then with dish soap and water)

and get to the cell caps, each with a little absorbent pad in case the cell venting carries too much moisture.

I could see no water in any cell of either battery. I borrowed a jug of distilled water from my folks (I don’t know why Mom always has some, but she does) and started filling them up … after taking measurements.

I filled each cell, waited for air bubbles to trickle to the top, refilled, waited, refilled, waited … I’m guessing between the initial fill and while charging, I ended up putting at least 10 ml of water into each cell.

Then put battery 1 on my variable power supply with the voltage set to 13.8 V and the current limited initially to 0.1 A, raising the current limit to 0.3 A as it was clear that nothing horrible was happening. I checked on it every half-hour to hour, frequently refilling at least one cell in which I could no longer see any water.

After about four hours, it was up to 13.5 V. The water level in the cells had risen to overflow the opening and fill each reservoir. If I watched long enough, I could see the water in a couple of cells <pop>, indicating they were just starting to gas and it was time for me to stop this method of charging for the day. (More on that on a subsequent day, hopefully tomorrow.)

While battery 1 was charging, I was also checking water levels in battery 2 and refilling low cells, just sitting on the counter.

Recalling that it had an initial 10 V charge to battery 1′s 11.7 V, noting that they had been connected in series, and knowing that the worst cell in a battery generally has a cascading failure, I expected a different charging experience from battery 2, and I was quite right.

I connected it to the power supply and it immediately showed 13.8 V at a 0.1-A current draw. Now, about an hour later, it’s at 13.5 V and 0.3 A and most of the cells have overflowed. It’s nearly done charging but I haven’t put nearly as much energy into it as I was able to put into battery 1 — that is to say, it’s not “taking” as much of a charge.

Tomorrow, schedule willing, a load test and an attempt at desulfation.

All of the wires are cut, the deck is missing, the rear wheel was unattached, naturally the drive belt was missing, and no charger.

$10. I bought it. Sounds like a fun project, eh?

The battery and speed-control bucket could use some repair but seems at least functional. I started working on the batteries but as soon as my brother was available redirected my attention to reattaching the rear wheel.

The rear wheel is belt-driven and needs to be positioned to align with the motor pulley but the spacers were absent and it slid freely from side to side.

A trip to the hardware store resulted in a roll pin with ID slightly larger than the 1/4″ axle diameter and length slightly greater than the two spacers needed, for $1.89. Then my brother’s giant chop saw made short work of creating two pieces from one.

Touched up a bit on the bench grinder, ends rounded over with a file, and interiors cleaned out with a round file, spacers fit perfectly and the rear wheel bolts on securely. We “kicked” our way up and down the driveway and are eager to get the scooter powered up.

Next: Battery investigation.

I’ve made time to do a little server work; I’m trying to build a more consistent set and get my servers all up to current OS versions. I have three nice rackmount server cases, and while scrounging ATX motherboards to put into them, I ran across this.

The electrolytic capacitor just to the right of the center of the image is seriously bulging, as is the out-of-focus capacitor behind it. They both test good with the Capacitor Wizard, but I wouldn’t trust either of them with power applied, at least not inside anything I care about. Always at least visually check electrolytics before you power up something that’s been off for a while.

Desoldering was easy — heat both leads and gently rock them out.

Cleaning the solder out of the through-holes was trickier. At least one of the holes was attached to one or more large copper planes and kept sucking away the heat — I had to add solder, keep it preheated with the iron so it stayed liquid through the hole’s whole depth, and quickly slip the solder braid into place. Heating solder braid on top of a topped-off through-hole wicked away the top solder before heating it all the way through.

And then I ran out of solder braid. Ended up drilling out the holes, which I’d wanted to avoid in order to avoid any risk of damaging the plating. But I picked a small enough bit that I didn’t even remove all the solder, and it worked out okay.

The replacement capacitors I had on hand were a little wider and crowd adjacent components, but at least are rated for 105°C like the originals. And they seem to work; the board is now cheerfully running my new backup server.

I was given this high-quality, hefty, well-balanced, well-performing LED flashlight several years ago with batteries already in it. I keep it in the glovebox; and recently when I needed it, it didn’t power on.

In my decades of using consumer electronics, there’s only one brand of alkaline cells that has never leaked in my equipment — even things I’ve forgotten about and found again years later — and I drive miles out of my way to buy them.

Doubtless someone will pop up with their own horror story, but I’ll still make the claim: You will never, ever, need this.

Cleaning the Flashlight

In order to get out the crud, I disassembled the flashlight completely and cleaned it with a wire brush, a wire wheel on the Dremel, a wire brush on the Dremel, and a toothbrush and dishwashing detergent. I went a little overboard to make sure I had got it all, but at every stage I was getting out more crud.

I’ve long been impressed with the heft and solidity of the flashlight; now that I’ve seen the inside, I’m equally impressed with its design and with the ease of (dis)assembly.

Loosely clockwise from the left, the reflector isn’t adjustable for beam focus but screws off anyway. The heatsinked LED has a separate plastic housing with beveled forward edge that centers the LED against the back side of its reflector cone. The LED housing’s retaining ring doubles as one of the LED terminals.

The aluminum head holds the LED housing and the separate LED driver housing, dropped in from the tail end, and screws tightly to the reflector. The plastic housing for the tiny power switch and LED driver board is made of two identical, completely reversible parts, holding in the inner power switch pushbutton on the one side and leaving a window to check board orientation for assembly on the other.

The rubber outer power switch pushbutton installs after the LED driver is dropped into the head and does not seal against the housing, suggesting that the o-rings on the aluminum housing are for a great feel during assembly and battery replacement rather than for water resistance.

The battery cage holds three AAA cells and assembles easily. The stiles are marked with the cell orientation; the filled cage looks a bit like a C cell and drops into the flashlight handle, with the spring-loaded button and the metal ring contacting corresponding surfaces on the bottom of the LED board.

The tail cap doesn’t make electrical contact with the battery’s negative terminal and the flashlight body doesn’t conduct current, as it does on many less expensive flashlights (not that I think I care).

Cleaned, reassembled, and with AAA cells reinstalled, it once again works perfectly. I look forward to many more years of service … and to not having to clean it out again.