last time i bought used a Tascam 238 nice tape, but with a speed issue.
It's runs fast and make a jumbo jet noise.
Reading around internet sites, the problem is on the capstan motor or...the control board.
I've changed all the caps...but still the same..fast..
Searched around internet...goggle...but didn't found a replace board...
Any body knows where i can buy one?
Please need help.
The direct drive motor need recapping as I typically do in 122 Mk III decks. It will not work correctly until you get rid of the leaking SMD caps that were used.
The pitch control board can have defective pots or parts on it. These can also affect the speed of the motor. The C2 of the servo board is changed to Polystyrene in my case. What did you use or did you forget that part?
SkywaveTDR can you plz help. I have a Tascam 238, Tascam Germany replaced the capstan motor around 2013 and the 238 worked well all the time except one point. I discovered this little issue last week, because after I transmitted all my analog tapes into Protools, I like to give away my 238 and did a full check. If I set the speed from fix to vary and the pitch knob in the middle ( 12 o clock neutral position) it runs way to fast. I have to set the knob around 10 o clock to make the speed the same like in the fixed position. I set the position of resistor R14 on the Pitch PCB fully counterclockwise and hope to fix the issue, it gets slower now, but again I have to set the knob to 11 o clock to get same speed like in the fixed position. I asked Tascam for a replacement part of the Pitch PCB, but its not available anymore. Did you know this issue and how to resolve this? Maybe replace the capacitors or the resitor? I disasembled the Pitch PCB and the capacitors looks OK so far (not bulged on top) But I found hard and translucent brown looking moisture at the bottom of the circiut board but dont if this is normal or not. I cleaned the circiut board with acrylic thinner and it was possible to wipe away the hard moisture without any damage.
Hope you are able to help, I like to sell my 238 in perfect condition (cosmetical it looks like brand new and it sounds perfect) and make the new owner happy.
Hi Jurgen,
I fix these motors all the time and have two unit here. The motors are sensitive to leaking electrolyte from bad surface type capacitors. There is a 100% failure rate with all these motors of this design. What I do is get the transport out and then unsolder the FG wires so that the board can be lifted out of the machine with the removal of the three screws. Being I work on the part just outside of the transport as it sits on a old side board from an open reel placed on the deck over where the transport is suppose to go.
The surface mount caps as well as C2 have got to get off. I use solder wick type braid desoldering aid and an iron (Weller in my case) to heat and slide the old caps off the pads. This is done to not damage or lift the pads. The once heated will twist so that they come off in up to two heatings per side. After a cap is off then the board is cleaned with denatured alcohol which is methanol that you can not drink. There are 7-8 capacitors that must come off. 3 10uFd/16V and 1 1ufd/50V then two 3.3uFd Bipolar 25V and then the C-2 which is the small disc ceramic that is adjacent to the Zener diode on the board. The C-2 is replaced by a Polystyrene .001uFd 50V cap that has very stable characteristics. There is a 4.7uFd at 35V that is near the lower edge. After the board is clean and the pads have some solder applied to them, through hole capacitors are set up for install to be standing up as space is not a restriction here. The leads are cut and then pliers used to make a gull wing shape. The caps leads are soldered to so that they accept the pad solder- I place them in position and heat each joint. The wide part of the notation of the board silkscreen is the negative terminal. On the two Bipolar caps it does not matter. Once these better grade caps are put on this board then it is assembled and tested. The flywheel in my case is pulled out and the capstan shaft cleaned then I use AMS Signature Synthetic oil for the capstan bearing. Work the shaft in and out a few times to distribute and then put the motor together. BEFORE running the motor with tape make sure to clean the oil off the capstan shaft in the front so that oil is not placed on tape or pinch roller. This is another good time to service the mechanism as well taking the old grease out of head base slide plate and off rear gears. I use Lubriplate 105 on those places. The old grease is cleaned off with cotton swabs and denatured and the gears might be cleaned with a old tooth brush with denatured as well. The Lubriplate grease is not known to deteriorate with time and will be the final solution. Do not get alcohol into the front of the capstan bearing but just enough to saturate the swab. I recondition the pinch rollers too at this point. I know that this system works as I have done about 45 units so far and get about 98% repair rate. Some motors worked on before I get them might need more parts. On motors that do not start can be due to the coils breaking open on that board. They measure around 16 ohms and if one measures open I have to go looking for the reason and generally it is due to too much tension put on the coil when it is mounted. I scrap the enamel wire with a razor blade and attach a piece of wire wrap wire so the lead wire may be lengthen to the solder terminal and it has always worked. The flux they used may be the reason for this too. This gets pretty small so most of the work I do this with magnifiers on.
When the motor is running again there is a adjustment on that board so place all other pots at center and then get the 3000Hz as on test tape to be around 3004Hz. Then do the other calibrations. the Pitch control on the board can be damaged due to impact. If this is suspect then it can be taken out of the machine and measured. If the pot measures open end terminal to end terminal then it needs to be replaced. The part is difficult to get due to the length of the shaft. I have 15mm length shaft pots here but not the 30mm ones that some decks use. If the pot is OK then maybe the calibration pot has been damaged. You never know what some people do to them. The boards look like this when they are done.
Thx Skywave for your extensive reply! It seems the capstan motor isnt the problem. All runs smooth and perfect until I set the pitch control to the "Vari" position. So I think the problem is something at the Pitch PCB. If I turn pitch on and the pitch knob is set to center I asume it should have the same speed like in the "fixed" position. But it runs faster, maybe around 4-5%. I have to set the pitch knob the 10 o clock position to get the "neutral" speed. Opened the 238 and turned the resistor "R14" (marked in red) fully counterclockwise and was hoping to fix it. But the adjusting range of R 14 is to small to set the neutral speed in vari pitch mode. It slows down but even it runs to fast. around 2-3%, now the pitch knob at 11 o clock for neutral speed.
So maybe some of the parts marked in red blue and white are damaged?
The green marked area the brown and hard translucent moisture was found. The picture was taken after the clean up. If you look close little of that moisture remains around the 4 pin connector lefthand.
The moisture thing may just be solder flux when they made this board. If the motor has not gotten new caps on it then all bets are off as these motors really are failing a lot due to the caps and the damage they do to the foils. The Mylar or other caps are probably not involved. I think if a resistor is plugged into the connector at about 54K that will allow the motor to fun so you could have a dirty switch contact. On the 238 there is an external signal type adjustment too that the R14 might be for. Suffice it to say that on some decks there were mods released to change some resistor values and there is the possibility that the pitch center pot has something wrong with it too. I change them for Cermet type trimmers that have a higher reliability and sometimes the value is extended to cover additional range- such as a 30K to a 50K pot.
Looking at the Pitch pot in your picture reminds me of the pot I took apart and tried to repair and what happens is that the wiper section attached only by one stud of plastic grows weak and the wiper can break off and be non conductive- this is why I have had to sub on different pots for that part. I presently have the pot in 15mm length bit am working on a viable extension system. Why can't they just make 30mm D type linear pots again? I guess if you had the money to order 100,000 they would make you a run of them. I don't have that kind of money to sink into one part.
