Technical Notes

These detailed items are for those who are technically capable of understanding them and implementing them. The reason is that it is a way to share what is determined, designed or found to need correction on the various models noted. It will allow a technician who works on tape decks to benefit from my observations and design mods to make their repairs better or more accurate.

Do not hesitate to contribute if you have a proven and tested design mod.

15 thoughts on “Technical Notes”

  1. The Teac X1000R Open Reel deck speed difference from different directions. Often times I have been having to deal with a deck that has correct tensions on it but the speed is just too far off from correct in a direction different from the forward. I knew this was going to have to happen sooner of later but here goes.
    This allows an added pot to be added to the capstan servo control board for the purpose of getting more exact speed calibration for each direction. How it works is that I take a ground signal from off the direction change solenoid and supply that through a 100K resistor to the base of a PNP transistor that then switches on in reverse and enables further adjustment to a 50K Cermet trimmer connected to pin 3 of the J1 connector. So as the speed test tape says 3005Hz in forward but Reverse mode shows 3033Hz this is unacceptable but using this modification the 3005Hz can also be adjusted for the reverse direction and so this is better accuracy. I grown tired of accepting sloppy designs and once in a while I make a change that will benefit anyone who tries this for this model. It will most likely work on X10R, X2000R and X20R decks as well. Schematics to follow.

    1. Well in applying this mod to another machine I became aggravated by the interaction of the two pots involved. This then required customization of each machine. Well I do not like to waste that time so a new design was come upon the does the job with much better accuracy. This makes use of a small dip relay that switches Pots depending on the direction of travel of the deck. This mod will allow using Cermet trimmers to have exact control of the speed for whatever direction you are going- I tested it last night as I adjusted the speed to 3004Hz and each direction stabilized at that speed. It has no adverse affect as the wow and flutter was around .03% on this test machine. I will come out with schematics and parts list shortly. It is another refinement of a machine that should have been designed into it in the first place and I do them out of necessity.

      1. Further- I figured why do half a job and I made a circuit diagram of a mod to change the speeds of both direction at both speeds- that Means 4 pots instead of the two and they are Cermet trimmers not that cheap carbon ones. The mod board although I have not had time to make one with the 4 pots on it will piggy back the original servo as no adjustments are needed there once the mod is applied. This then insures that all directions and all speeds can be adjusted exact offsetting any causes in the speed being different.

  2. The Tascam 38: I thought that these were built well for what they cost and they are to the most part but last night I had a unit that the counter was out and I found a 24Vdc supply that was only at 12V.
    So going further and spending many hours taking this apart, I find that here we are back again at the yellow glue syndrome where some idiot in Washington started to dictate through the FTC that all these large caps had to have glue on them. Well I bet he was in the glue selling business. The results is that the glue takes on moisture and becomes corrosive to the parts that it touches. Think Teac was the only place this happened? Akai is well known for the glue problem, NAD6300 has failed due to this glue in my shop as well as a few other brands. When I extracted Q911 and the Zener diode near it the transistor only had one lead on it and the Zener came off with one lead missing. Now that all the caps have been pulled and that glue extracted totally, do you think that any of the capacitors I put in are falling off due to no glue on them? No they are not. This is why it is good for some government rules to be ignored as they are just based on total rubbish thinking and other motives are behind this. Pioneer used good glue- why did Teac not consult a chemist about this? Well it just mean more work for me and most cost to the customer. I am not to wild about their head mount method on these decks either- most all heads are mounted wrong and are tilted.

  3. Well I just installed a joint part that was 3D printed in a Tascam 234. This part may also be applicable for many other decks that use the cam system transport such as the V-9 and V900X. This is the forked part that goes onto the pot that provides feedback to the deck controller about where the cam gear is at position wise. I know I have seen a lot of them broken in the years- mostly by amateurs working on decks and putting them together wrong. A part is soon to be available.

    1. Hi Sam — Very interesting as I was about to ask you if 3D printing had found its way into the tape repair field for ‘manufacturing’ HTF or unavailable small parts. Do you have such a source of custom parts or are you going to make them yourself now that the printers are more reasonable? Cheers……. Alex

  4. I don’t like 3D printers but when I have to get a part that is not all that complicated to make they will do. I am going to see how they try and make tape guides- those devices that screw into the frame and allow the cassette cover to snap on but I am not sure they will do but we will see.

    1. Sam, do the more complex 3D printed parts fail… or have poor tolerances or something? I realize the tape path in particular requires precision parts. Have you had negative experience with other printed parts?

      1. Until now this part that is colored in yellow orange is the only part that I have been able to have made as all other requests just fell on people that did not take action. There have been no failures at this point and I have only tried it in one or two units so I suspect that they will be fine. So now Gear C, The cam joint and maybe a cassette guide will be done but we will see on the last one. At least I have a guy willing to try and make parts now.

  5. Tascam 38- Bias amplifier block.
    When this stop working you are in trouble fast- no record and no erase because no bias. Well this was a thorn in my side for a while now as they are small and not so easy to get but recently I repaired one due to a shorted blue capacitor that is labeled 332J. It is 3300pF and most likely 100V but the new one I put in got the deck running again. Keep in mind when these are made they use part only as good as needed to make them work for a while- not for 40-50 years. The good news is that the block is not potted and can come apart pretty easy. The transistors inside in one case I upgraded to Ic=1 amp. The parts get hot inside so it is better to have some extra capability so that parts do not burn out so easy.
    This is like an RF device but only around 150KHz not higher. There could be other failures but so far transistors and this blue cap was the only thing I have discovered.

  6. New Developments- Tascam 48. While this is a terrific machine only time will tell what kind of parts they used in it will react like. Well recently and still on my bench are the capacitors that shorted on those cards not just one in the deck but a lot of them. Wonder why a deck loses channels and runs hot? The fuse resistor are heating up because these Marcon 220uFd 16V caps are either leaking and or shorting totally. If you have such a deck it might be smart to replace them with Nichicon or Panasonic higher grade caps. These are C006 and C007 right above IC U001 and would be below the two canned relays. K003 and K004 fail in the coils regularly and one is the mute relay for the balanced output and the other for the RCA output. I put 14 pin sockets in these places and then a Coto relay in the sockets.
    If you need the Mouser part number for the relay I can provide that too. The same one a double pole relay will work in both positions. I have had 0 failures of Coto relays.

  7. Very interesting RE the Tascam 38’s overheating & channel loss. Are Marcon caps possibly bad in other machines as well, in general I mean? Something to look out for?

    Have the replacements solved the issues now? Kudos on the good work, I bet it has been frustrating!

    BTW I notice you are seeking an associate to come work with you — if my situation were different, I’d be there yesterday. But I’d probably want to bunk in your spare room (?) since I know no one in Chicago!

      1. The 38 may have them too- the bad ones I found previously were in a Z7000 $1600 cassette deck that we are having nothing but troubles with these days.

    1. Marcon caps are all through some Teac newer models while the Nichicon and other lasted at least 50 years so far. It is interesting that these Marcon have also been found in other brands like NAD and they too were bad there too. They were 220uFd 10V. I have an allergy against 10V caps and I change them from sight. Hell there is a lot of work here piling up and some of them are 1/2 16 track and 1″ 24 track decks. I have no spare room until the shed gets insulated and heat and AC but I bet that will be like a little house when I finish with it maybe this Summer. I have a lot of help from one of my customers.
      I hate to bad mouth a certain brand but the marcon caps seem to be the ones I keep on coming up against in failures kind of like the purple Mashushita caps used in Technics and other decks- they were low grade garbage as we all find out today.

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