Studer Recap: Part III, some guitar work

Finished recapping the power supply today. Here’s what it looks like:


As you can see, I took out those tantalums and instead installed Panasonic FC series caps. These are low ESR can can tolerate high temperatures (the tants could too), and most importantly, they don’t short when they fail.

The big filtering caps are snap-ins and I’m not crazy about that. They didn’t really snap into the PCB and I had to bend their legs a tiny bit to fit the holes. Also, the legs are really short so I’m not feeling 100% about them being physically stable. The reason I got those is because the “long leads” caps that I could find that were rated at 105C were rated for 1000 hours at 105C. I don’t think these caps ever make it to 105C, and 1000 hours is equal to 41 days of the machine being on non-stop, so those probably would have been ok, but still. The snap-in caps I installed are rated for 3000 hours (4.7mF) at 105C and 5000 hours (10mF) at 105C. They should last for a while.

I also wrote down the values for the motor phase capacitors since the power supply is out (makes it easier to access them).

I’ve also made some progress with the cauls for the F30. Basically everything is glue and I need to make sure the top caul matches the fretboard perfectly. Maybe it’ll be done at the end of this week?

Studer B67 recap: Part II, other studer work, some guitar work

I edited this post on September 22nd, 2015. If you’ve referenced it before that day, you might want to re-read it.

The next step after replacing the caps on the motor control boards was to check the voltages in the power supply. There are test points on the stabilizer’s PCB, so that’s easy enough to do. I did that and the -12V rail was reading 0. So I decided to take out the power supply and recap it. Removing it is a bit of a pain. There are two screws on the top, one horizontal screw that you need a 6″ T-Handle wrench to undo, a bunch of connectors that need to be removed, and the 50/60hz switch on the power supply.

The PCB is different than what the manual shows: The -12V regulator is a Motorola MC7912CK while the manual shows National LM320K-12. The manual shows some SAL caps next to the regulators while my PCB has all tantalums there. Turns out, my PCB is the same as what they used on the Mk I of the B67 (figured that one out after downloading the Mk I manual). The Motorola regulator is a variant of the LM320K-12, so no problems there, and the tantalums can be replaced with high grade electrolytics (which I’m going to do). They layout of my PCB seems to otherwise be identical to the Mk II manual, and the Mk I manual also shows a very similar layout. The only differences I could see are that D4 and D5 are interchanged (shouldn’t matter since they’re oriented the same way), and that the Mk I uses a 4.7mF cap for C3 where Mk II uses 10mF.

While waiting for high grade electrolytics to use instead of the tantalums, I replaced the axial lytics and a couple tantalum caps. I ordered a 1000uF filtering cap instead of 10000uF, so I’m waiting on the big caps until it’s all here.


See those blue tantalums? Those are the ones that should have been SALs.

I also recapped the little monitor board under the front panel. The one that drives the built in speaker. No pictures of that because it was late and I forgot.

I also cleaned the front panel of the machine real nice. Someone said that toothpaste is good for that, and holy cow – it is! It’s much better at removing years old grime than isopropyl alcohol. I also poked around the card cage and noticed that the stabilizer card has a blown capacitor. I’ve never seen anything like it! The is torched and got black sooth all around it. According to my french friend who’s a Studer expert, this is the result of it being really close to the heat sink. I’m going to replace those tantalums with electrolytics also.

As far as guitar work, I think I mentioned making cauls to fix my F30. Trying to shape a single piece of wood to have 12″ radius did not work. I did something similar when I built my neck rocker, and it came out somewhat ok, but required a lot of rasping, chiseling, and filing. I thought I’d have better luck here, but no dice. It was too hard to maintain the radius along that block of wood.

I was at the hacker space trying to figure out how to do this, and a guy suggested cutting the radius on a bunch of small pieces of wood and gluing them together. Then another dude suggested doing that with the laser printer/cutter. I complied, and the thing does cut a very accurate radius, but it can only cut slightly thicker than 1/8″ pieces of wood, and since I need a 5″ long caul, that meant having to cut (and glue) lots of pieces. I tried gluing all the pieces at once and it was a disaster. They kept slipping, then the glue was drying real fast on me (what the hell, it’s Titebond Extend which is supposed to have longer open time).

So I googled and found this page. I followed his advice and cut 7 pieces from pine on the bandsaw. Here’s what one piece looks like:


I’m gluing them up in pairs (to avoid what happened last time), and it’s working out well. Only one piece left to glue.

I hope this guitar will be fixed by the end of this week. I still get filled with sadness every time I think about it.

Studer B67 recap: Part I

Started the B67 recap today. A bit of background first:

I think I mentioned it before, but this machine’s biggest problem is that as soon as it’s turned on, all three motors spin and nothing can stop them other than turning the machine off. Each motor (supply, capstan, takeup) on this machine has a little control board that “mixes” the AC current from the motor and DC current from the Transport to create a constant torque. Honestly, I’m just parroting what I was told here. Anyway, these motors control boards have suppression capacitors, made by Rifa, and being old and also kind of crappy, they fail and short, and when that happens the motors spin like I described above. So first order of business was to replace those.

Supply motor control PCB

Before: supply motor control PCB.

Rifa caps. See those cracks? Those mean the capacitors are on their way to Valhalla/already there

Rifa caps. See those cracks? Those mean the capacitors are on their way to Valhalla/already there.

New, modern capacitors.

New, modern capacitors.

Turned the machine on, and the motors still spin. Bummer, but I didn’t expect this to be an easy fix. Not knowing if I somehow botched the things in the recap or not, I remembered reading that it’s possible to disconnect the motor control PCBs from the transport and thus isolate the problem to either the transport or motor controls. Here’s where I read that. So I did that and the motors stopped spinning.

So the problem is at the transport. This is a good thing, because it means I didn’t mess anything on the control boards, but on the other hand, the problem could be a dead IC in the transport, and those are said to be rare and expensive. There’s one on eBay UK right now for ~$69.

I’m thinking what I should recap next. At first I thought it should be the transport, because the problem is most likely there, but then I thought about it a little more, and if something is messed up at the PSU, then the whole machine will be out of whack. I don’t know if PSU failure would manifest itself by freaking out the motors, though.

FWIW, I don’t think the Rifa caps on my machine were bad. Usually when they die they let out a lot of smoke, and I saw no signs of that. However, it’s good that I got rid of them because they’re a ticking time bomb.

Differences between Studer B67 Mk I and Mk II

There’s not a lot of information on the web about the differences between the two versions of the B67. A list of functional differences is available here, but the visual, just-glancing-at-this-machine, differences aren’t mentioned anywhere (not that I could find). The machines just say “Studer B67” without marking which version it is, so if you’re not familiar with these machines you’ll have no idea which one it is. According to my friend from the Studer list, there are a couple of visual differences that set them apart:

1. The Mk II machines have vertical grey plastic bars between each pair of big and small rollers, and the Mk I machines don’t. 

2. The Mk II machines have a screw on the top of the timer roller (big one on the right), while the Mk I machines don’t.

These two photos illustrate these differences:

Studer B67 Mk II

Studer B67 Mk II

Studer B67 Mk I

Studer B67 Mk I

The B67 Mk II photo was obtained from here, and the B67 Mk I picture was obtained form here. All rights belong to the respective owners of these images.

Studer B67 meters faceplates

I couldn’t stand the meters on my Studer B67 being so scratched up and hazy. It’s wasn’t just a matter of looks but functionality also – it’s not easy to read the meters. Definitely not from a couple feet away.


I know from working on guitars that I can wet sand and polish out the scratches and haziness, but it wasn’t clear how to remove the panels from the meters, and if it necessitates removing the whole meter. I talked to a friend I made on the Yahoo Studer mailing list, and he said that the panels come off by pulling them. I tried that, and there was some movement, but it felt like I might be tearing out the whole meter. I asked around online and got nothing. I checked the manual again, and while I didn’t find anything that explicitly says how to remove the panels, I did find the section about changing out the bulbs. To do that, the manual says to “open the VU meter panel”, and I took that to mean that there really isn’t anything very sophisticated about this. So I tried again with a bit more wiggling and the panels came off.

If you got here because you were searching how to remove the VU meters’ front panels – they come off by pulling. Wiggle them gently as you pull and they will come off. Be careful because the needle assembly is right under them.

The A80s have the same meters, so I believe their panels are removed the same way.

Here are pictures of each panel before I started working on them:



Here’s the first one when I was done with it:


Here’s a comparison between them on the machine:


Then the left one after it was done:


And the two back on the machine!


I followed the same sanding process I always do – start with 400 grit and go up to 2000 without skipping any grits in between (so 400, 600, 800, 1000, 1200, 1500, and 2000). Then buff using McGuire’s Ultimate Compound and Ultimate Polish. With the left meter (see that crack?), I first got superglue into the crack, let it dry, then scraped the glue off and did the sanding and polishing. The crack is visible, but I didn’t try to remove it – the purpose was to stabilize it.

Sorry for putting so many pictures up. For once I remembered to document the process, but I’m also very proud of the job I did and wanted to show off a bit.

Guild S300-D finally done! Studer caps ordered!

This process took a while, partially because I’m lazy, but also because of other projects. Here’s a recap of what was done:

-The nut slot was cut too low. So I cut a piece of Mahogany with the grain oriented the same as the neck. Thickness-ed it and glued it to the nut slot with hot hide glue.

-Frets were removed, which was a little painful because I was getting a lot of chips. I glued the chips back in, and used some ebony dust where needed.

-Fretboad sanded and leveled. I could have really just waited to do that and then put superglue wherever the fingerboard was chipped.

-Frets installed, and I dripped superglue into all the slots to keep those little bastards in place. This was my first refret and not all the frets were seated wonderfully. The old frets’ crown was .106″, and I always felt like I my fingers couldn’t fit on the neck once I passed the 12th fret, so I went with smaller frets. I got StewMac’s Medium/Highest. The crown is 0.80″ and that makes a lot of a difference.

-Fret ends cut, filed, etc. Basically whatever is needed to be done so that they don’t poke you when you play.

-Leveled the frets. That came out really well. Maybe my best fret leveling job to date? Also dressed the corners of the frets, of course.

-New bone nut. I wrote all about it already.

-Pickups were potted by Fralin. Also talked about that already.

-Little bridge pickup mishap. These pickups are held in the rings with three screws – two on the bass side, one on the treble side. This way the angle of the pickup can also be adjusted. To do that, Guild (or Dimarzio) soldered a two-hole tab to the pickup’s single hole tab. Anyway, that two-hole tab broke and the pickup was jiggling around. Soldered the tab back on.

-Replaced the neck pickup with the a Guild S100 humbucker I bought for very little money from a friend.

Done. I’ll edit this later to add pictures.

I also ordered the caps I need to (partially) recap the B67. Going to do the suppression caps first, and see if it’s working alright. Then do all the electrolytics and tantalums in the PSU, Transport, and whatever else that has tantalum and isn’t in the audio path. Once the machine is working I’ll do the motor phase capacitors (big ones that are hanging from the chassis), and start working on the audio cards one by one. I’ll pose a list of the capacitors here for my own and others’ sake.

I have a few more things to post about the B67, but I’ll get to it later.