repairing your TASCAM 122mkii speed issue

there is a common problem with the tascam 122mkii (and other mk's) , after a certain age the motors start running really fucking fast, to the point of being completely useless. anyone that has ever had this issue has more then likely contacted tascam and received a replay saying that a motor replacement will cost over $80. ridiculous, but some people have done it several times because this is a really nice deck. others have just pitched them out or sold them cheap as fuck to idiots like me ($10 off of craigslist a long time ago) that think they can figure out what’s wrong with them. i've searched and asked but never found a single person that could tell me what's actually wrong with these things. clearly the motor is not fucked or if would not work at all or it would work erratically or something. so a while later and several leaps forward in electronics knowledge i understood that the motor is actually controlled by pulse width modulation, ahhh...  there is an oscillator that tells it how fast to go, and nearly ever oscillator i know of is dependant on a capacitor to determine its range. well some old caps fail after about 20 years of constant use, give or take, and most fail closed, meaning their capacitance will diminish to the point of them becoming the equivalent of a jumper (often causing problems shorting the rails to ground in the power section of older gear too). when the caps capacitance begins to decrease in value it will force the pitch / rate to increase causing the motor to speed up. soooo.... if you replace the timing cap (or caps in this case) it will theoretically restore the motors speed control to the factory rate and kill the chipmunks living in your wonderful and at one point incredibly expensive tape deck.

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this is the cage for the motor assembly. you will need to remove it completely from the chassis to get at the PWM board. there are two screws along the top of the front panel and then two on each side at the base going down into the chassis. then you will have to pop off the front cassette cover. don't force it or it could break. then work the cage out and lean it forward so you have access to all 4 screws holding that vertical pcb along the back. then remove it and hold it to the side so you can gain access to the PWM boar

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this is the PWM board that you have been fighting to get to. its going to be kind of cramped to work in here so take your time and don't let your slaughtering iron damage the wires when you are focusing on the caps. if you are feeling adventurous then you could remove all the boards and motors so you can get to everything easily but that will probably be far more work then its worth. so i didn't bother.

so my first question was "which caps is the timing cap?" i'd guess the blue 5600pf mylar but after replacing it and 4 others and only getting small improvements i just said fuck it and replaced all 9. i'd guess that every case will be a little different, its not every cap in every deck will fail exactly the same way or at the same time. they will always be different. its possible that if you were to leave any in there that they could fail soon anyway so its silly to just replace one after going through all this work, so do them all. be careful when pulling the old electros out to not over heat and lift the traces which is very easy to do. if you do then just follow the trace back with a continuity tester to a point where you can attach a wire to restore the proper connection. also don't bother fucking with the SMD replacements. there is a lot of room in there so just use normal thru-holes components and save yourself some masochistic moments. the cans are electrolytic and the other 2 can be mylar or poly. when you are finished double and triple check every wire to make sure that nothing broke or was burned while you are holding things out the way. it happened to me and is very easy to do.

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here i listed the values just in case something happens and you need them. make sure all of the electro have their polarity correct or you could blow caps, which would suck.

there are a few other mods that you can do while you are in there. the vari-speed pot is 100k and can probably be increased in value to extend the pitch sweep. i know there are other ways to extend it that i've tested but that is the easiest. i'll test it later to be sure.

you could even add something like the parasites to the vari-speed section and make it voltage controlled, or maybe get some vactrols / opto-couplers and an LFO

also you could take a 100k (or larger maybe) dual pot and attach it between the input and output jacks and create a dedicated feedback control, then drop some switchable clipping diodes in there after the pot and connect them to ground to have a little bit of control over the feedback and add some distortion if you want. there are a few ways to do this

you can get more elaborate with the feedback loop of course. like bring it out to its own jacks on the back panel so you can insert things like EQ into the loop and really tailor the sound.

while you have the cage out you can look at the head assembly area and on the bottom left is the erase head. follow the leads back the pcb and then back up a couple inches and carefully slice into the insulation then snip just one of the two wires inside (i used the shield wire) and attach some long leads to each half the single wire and tape it up, and add a switch in there that you should pull out the front panel. this is a sound on sound control and it will turn on/off the erase head so you can just keep layering the sound on tape.