Tascam 246 - for COVID-19 relief

I have had his Tascam 246 for a long time- almost a decade - and only used it very occasionally. Being shut in for the foreseeable future, I thought I would take a look at this and see if I could use it to get some creative juices flowing while I am unable to do my usual band practices.

Last time I got it out, before we moved to our current house about 2 years ago, it would not play or fast forward properly. Specifically, when you pressed play, it would fast forward with the heads engaged (bad for speakers!) and when you pressed FF nothing would happen. Getting it back out yesterday, I confirmed that the same issue was present.

I did a little internet research and learned that if the heads and pinch roller do not fully engage, that the tape will fast wind. So at least I knew where to start looking. I pulled the back cover off, to inspect the transport mechanism. The smaller (control) belt looked a little suspicious, and I confirmed that if I helped the cam along as it engaged the heads and pinch roller, that it would play properly. So clearly a control belt issue.

I saw a youtube video where someone used regular rubber bands to test the mechanism of a 244 (which has the same transport as the 246) so I thought, why not? In our kitchen junk drawer I found a rubber band of approximate shape and size and slapped it in (the red one in the photo below). That did the trick! Play and FF now work as expected. I hope this rubber band fix will keep me going until I can order an official belt set and install it.

Yamaha SK-15 Cleanup

For EXEDO, Christine and I bought a Yamaha SK-15 string organ synth from 1981. It is a sturdy, well made instrument which worked pretty well out of the box for a well used (even dare we say vintage) instrument. Nonetheless, the knobs and sliders were very dirty and had a lot of dropouts. The master volume knob sent waves of deafening crackle through the amp when you turned it. One of the keys was intermittent. so I opened it up and gave everything a good cleaning. The top metal cover has a few screws holding it closed which, once removed along with the fader caps, allows the panel to hinge up and out of the way. The faders and knobs all got cleaned with isopropyl alcohol, the corner of a folded paper towel, and a little bit of deoxit fader lube. the faders were pretty easy to get into the fronts, once the felt dust cover (shown below) was removed.

 To clean the keybed, you have to remove a couple screws from the underside of the front edge, and the entire keys assembly tips upward. then you have to remove the white plastic things in this picture below to expose a conductive plastic strip with a rubber contact strip that lies under the keys themselves. The header connectors shown below need to be disconnected, as well as some grounding wires that connect the key assembly to the bottom of the case. In between the rubber strip and the conductive plastic (Sorry I didn't take any better pictures) I found a lot of dust and debris. After cleaning with IPA and re-assembling, no more key dropouts!

To hear this string/organ synth in action, you can listen to the EXEDO demo or else check out this youtube vid:

Ibanez Echo Shifter Review/repair

While on tour in 2018, I thought my delay pedal (DOD Rubberneck) was broken so I went to a local music store to see if there was an inexpensive replacement. They had one of these Ibanez Echo Shifters available, and it wasn't too pricey so I picked it up. It lacks a lot of the features of the Rubberneck, but I considered them nice to have and not necessary (tone on repeats, modulation speed, the pitch shift/rubberneck function). I really like the temporary feedback feature on the Rubberneck, and while there's not a stomp switch dedicated to it on the Echo Shifter, it does have a toggle switch to activate additional gain in the delay feedback to create self-oscillation.

I swapped the Echo Shifter in to my pedal board, and we had a little rehearsal the day before our first show. Everything went nicely, the sound of the Echo Shifter was right in line for what I want in an analog delay. However, at the show that night, the slider for echo time snapped off, like three songs into the set. I am not a wild man onstage, and I would expect a little more from the slider given that the rest of the construction on this pedal is nice and solid. I finished out the tour with the pedal - I pretty much left the delay time setting in the same place anyway - and came to appreciate its sound.

Some other review notes: For my taste the modulation depth control has too much range. I really don't know who uses delays with pitch sweeps of almost an octave on the repeats, but someone must because you can go there with this pedal. Another thing, it would be lovely to have a tails option when going into bypass - I really like that about the Rubberneck as well. Last, I am a fan of stomp switches that have a positive click when you engage them. This wouldn't be practical on the tap tempo switch, but I would prefer it on the bypass switch. It's a small thing though.

After coming home from tour, I discovered that the Rubberneck was just fine after all, luckily. The issue was actually with how I had set up my power supply. Lesson learned - when going overseas invest in a pedalboard supply that accepts dual voltage input so that you don't have to use a stepup converter. The one I was using introduced a lot of noise into the line voltage and I think that was messing with the digital circuitry of the Rubberneck somehow. Interestingly, other digital or hybrid pedals on my board, like my Strymon Blue Sky and DLS Rotosim, were not similarly affected.

On to repairing the Echo Shifter. There are a number of people who have posted repairs to these, including this nice post with info on the replacement of the slider control. I didn't want to just do that- after all it broke almost immediately and I knew it would happen again. Also, I don't generally need or want to change the delay time on the fly, so the ability to push the slider with my foot wasn't a concern. I decided to try to shoehorn in a standard rotary potentiometer as a fix.

First step- disassemble the pedal and remove the broken component. This is a little time consuming due to how the pedal is designed. It's not as easy as pulling apart an MXR or even a Boss style pedal. Lots of loose parts to keep track of.

Here's the circuit board with the slider removed and three flying leads attached to the now vacant pin locations. The pot is a 16mm Alpha, 10K linear. This one came from Tayda Electronics (I like this place for DIY project parts, a lot easier to browse than Mouser or DigiKey) and it has a plastic cover on the body. The part is a very tight fit and there are only a couple of places along the footprint of the old slider that will work, since the 16mm pot is wider than the slider and all those DIP chips come right up to it. I wound up having to cut off the plastic cover from the pot, and since it looked like it would potentially contact traces or solder pads on the board I put a single layer of electrical tape on the bottom. Alternatively, I could have sourced a square format pot like the factory-installed ones elsewhere on the board which should fit pretty much anywhere along the slider's footprint, but I already had the 16mm pot in hand and it wasn't too difficult.

I drilled the top panel for the pot shaft. As I said above, this hole has to line up with pretty much the only place on the circuit board where there's enough space to squeeze in the pot body. A 9/32 or 5/16 hole should do it. Since you're drilling on top of an existing slot, a drill press is a nice to have. If I didn't have a drill press, I would probably have done this with a rat tail file, or a grinding stone in a Dremel tool. In a handheld drill, the bit would just "walk" along the slot and not make a nice clean hole.

Here it is all put together. I had an old skirted knob in my spare parts stash that looked appropriate on the pedal even though it isn't an exact match (and MXR/Rickenbacker style knobs like these are easy to come by if you really need it to look the same). Someday, I will make a modification that will allow the oscillation to be engaged by either the toggle switch, or an external momentary stomp switch, to make it function more like my Rubberneck.

SPX90 Repair

This repair would probably have taken someone who knows what they're doing about 5 minutes... it took me significantly longer than that. 

Many years ago, I got this Yamaha SPX90 as a throw-in when I bought my Tascam 246 Tape machine. It hasn't gotten that much use over the years - occasionally I would use it on the effects send of my headphone mixer to give singers a little reverb in their headphones, but that was about it. It always worked when I needed it to, until recently when I plugged it in and got nothing, no lights on the front panel at all.

I opened it up, put a voltmeter on the power supply rails and could see that it was not outputting any of the required voltages. The internal fuse was fine, though. This has a switch-mode power supply which is not a design I've ever worked on or troubleshot before. So, I did a little research first (this article by Scott Dorsey, in particular, was helpful) and then started hunting down sources of the issue.

The first thing I looked at was Q1, which is the main high current switching transistor that feeds the main transformer. I pulled it out and sure enough, it was shorted. This is a 2SC2555, which are no longer made but I found some NOS ones on ebay. Once those showed up, I put one in, and still nothing. At this point, I knew I should really get systematic and check everything in the circuit. I started with the other transistors, and discovered that Q2 was also kaput. This is a 2SD1207, also obsolete. I checked all the diodes, there are quite a few, and all those checked OK. Then I started looking at passive components. I discovered that R2, which directly follows the bridge rectifier and feeds the entire circuit, was failed open. So that would explain a significant reason that the supply wasn't working.

I decided that if I was going to be replacing a bunch of parts I should do the large filter capacitor, so I put together a Mouser order with the power resistor and the capacitor, and a substitute for Q2 that I thought was reasonable - not a pinout match but similar specs, or so I thought.

When all that stuff arrived, I loaded them into the board and applied power. The switching circuit fired up, but before I could even verify voltages, most of the electrolytic caps on the low voltage side of the supply let out their magic smoke. I guess my slick substitute transistor was not a great idea. I was really careful to modify it for the correct B-C-E arrangement, but I think there was some other specification that I overlooked that was causing trouble. Not something I am experienced enough to diagnose.

Once all the low voltage caps were removed, I made yet another order to get the replacements (even ones that hadn't popped). I sprang for low ESR Panasonics, since I read this is a good idea.

Here is the PS board waiting for its new capacitors and the replacement Q2 that I got off ebay - correct part this time.

Here is the board with all the components installed and back in the chassis. That long metal bar that connects the power switch to the front panel is a real pain, since it requires the removal of the front panel to get the PS board in and out. I assume it's set up this way to keep the mains voltage wiring segregated to the back corner of the chassis and away from the audio signals. I tested the supply voltages with the headers disconnected, and all the rails looked good!

It's alive! Now I can make all my cool lo-fi 80s gated reverb drum sounds that this thing has in its presets. Next time I have to mess with a switching power supply, I will hopefully not make so many mistakes. Overall, this probably cost me $25 or so in parts and shipping. Part of that is the sellers of these obsolete transistors make you buy more than 1.

When I got the SPX90, I also got  a lot of documentation. In addition to the manual, I also got these:

The one on the left has some pretty funny stuff in it. Here are my two faves: