The former is not to be underestimated. In 1980 we were nominally at 220V AC, whereas today this has risen to 230V. The 550 was built for 220V. Oh, its transformer has a 240V tap, and its output cabling seems to be present at the bottom of the deck, but as the power supply board has soldered connections, tens of them!, removing it to fish up that cable and substitute it for the 220V connection to the front panel power switch seemed a risky business. So I left it, deciding to upgrade all elcaps close to the incoming AC. The diagram for the 550 power supply is not available. I studied the schematics of the 500/510/601, but all of these seemed to be significantly simpler than the really large PSU board of my deck. And with the board oriented as it is, reading off all caps' values and voltage ratings was not easy. I ended up measuring the voltages present over all (the highest I found was 39V). The replacements were Panasonic FCs, some of them a great deal smaller in dimensions than the originals, even when of equal or greater voltage rating. Access to the solder side was easy, and the board quality good enough to allow quick desoldering with a simple manual suction tool. Many caps were glued together in clusters of three or four, hindering their removal a bit.
The blue caps are the new Panasonics, the black ones are originals too deep in the spaghetti bowl for easy replacement. After removing and replacing a group of capacitors I halted and checked the deck for proper operation, before proceeding to the next group. Here is what I pulled out of the deck:
1 x 3300uF 25V
3 x 1000uF 50V
1 x 1000uF 35V
1 x 1000uF 25V
1 x 470uF 16V
4 x 330uF 35V
I left the control board alone. Once again, a circuit diagram seems not available on the net, it is not very accessible, and slightly off-spec electrolytics are not likely to harm its functionality.
The audio board then. A bad copy of its diagram could be found at hifiengine (not anymore, but check again). Further, the main board of the CX-650R is very similar to the 550RX, including the PCB layout. You can find it here https://www.hifiengine.com/hfe_downloads/index.php?teac/teac_cx-650r_service.pdf (registration required). Use it with care, because there are tiny differences in part numbering and location!
The deck's bottom half beneath the audio board can be opened. This requires the removal of a number of screws around the perimeter of the panel, but also of two screws in the middle of that panel. Access from the top side is had by removing two screws from the dbx board and swinging it out of way on its hinges. Even so, with the deck repeatedly turned upside down and back again, this dbx board was a serious pain. I worked in groups of 6 or 7 components, first fixing them in place with small balls of blutack, then desoldering (the blutack keeps them from falling down and disappearing into the transport, you really don't want that!), flipping the deck around, removing the old components, inserting the new ones, blutack again, and then once more a flip to get access to the solder side.
Referring to the actual A-550RX diagram I replaced C102, C106, C120, C122, C131 with equal-value Elna Silmic. C110 and C111 were replaced with NOS Rubycon ZA ultra-low impedance types. C508 and C509 were also changed, although 509 seems part of the control scheme and is not critical. C150 got an additional 220uF Rubycon ZL in parallel to it, aiding in driving low-impedance headphones. The emphasis of my replacements is on the replay side, because I do not think this deck will ever be used for much recording again.
The amplifier board contains tens more of elcaps, but mostly in supportive locations. I thought replacing these far too time consuming. The dbx board I ignored as well. (Why the Rubycon ZA/ZLs? I purchased hundreds of them very cheaply in 1999 for my DIY projects, and many are still left. They are old now, so I test them before use, sometimes even burn them in when I find the time and energy to build a jig. But I no longer use them in high-ripple applications such as right after rectifiers.)
The heads looked in reasonable shape. I did not feel a ridge in the RP head's surface, so any wear must be fairly low. However, it was tarnished or corroded outside of the active area (the picture below makes it look worse than it really is, though).
Polishing the head with Brasso (blue bottle, red label) helped. I did so in three sessions, after which the head became shiny again. Looking at it closely then revealed some surface pitting. This head might be a candidate for relapping, but that is beyond my abilities.
Part 1: http://audiochrome.blogspot.be/2017/12/restoring-teac-550rx-cassette-tape-deck.html
Part 2: http://audiochrome.blogspot.be/2017/12/restoring-teac-550rx-cassette-tape-deck_30.html
Part 3: http://audiochrome.blogspot.be/2018/01/restoring-teac-550rx-cassette-tape-deck.html
