Hi again, I checked your video when you test the recorder around the 20 minutes mark and I can hear the same noise as in mine, a sort of grinding noise coming from the toothed gears. Have you tried silencing it ? I tried adding tiny drop of grease onto the gears, but it has no effects. This is similar to the noise some panasonic walkman have nowadays due to ageing - gears shrink and no longer match perfectly. That noise is tolerable in playback, but it makes bad recording with the built-in mic; not that I plan on using this recorder for anything other than playing with it, but I would like to make it as close to "new" as possible. Thanks !
Hi, yes I noticed that but I didn't go through it yet, and the built-in mic could also be very sensitive and catch also this kind of sounds coming from the unit itself. If the noise is not fixable, there should be at least a way how to regulate the Mic sensitivity according to my service manual, but I really can't understand how I'm supposed to do that. However, for my project, I don't use that much the built-in Mic, but an external Mic instead (for field recordings) and the external Mic port as Line-In if I want to record some lofi compositions I make, on a microcassette. There are still several small details I want to fix in my M100B I have, and I will find some time for it soon. I will let you know if I'll find out something. I guess it could also be some gears which are loose and they tend to move a little bit while turning and make some noise.
Do you have the service manual for the M-100B ? It is only available on paper on ebay, but it would cost more than the unit itself! I could not find a pdf version and i do not think there are other similar units sharing transport and electronic.
Hi, you can find the servicemanual here: http://freeservicemanuals.info/en/servicemanuals/?search=m100b&brand=Sony&sorttype=asc&sort=typea
Thanks for the serivce manual, no idea why it was not showing in google searches. The mic sensitivity adjustment has just two different positions (two solder bridges) for two different mic types, it is not to improve record sensitivity. In my unit mic sensitivity is fine, it records clearly people speaking within a couple of meters. The transport noise is indeed clearly audible so it is captured by the built in mic too; those recorders are supposed to be dead silent, but this is not the first that it is a bit noisy. It is nice to know it has only tantalum caps, no electrolytics. I was told tantalum is not the best for audio application, but I do not think it is making any difference here. On the plus side they do not dry, but when they fail they are a dead short (in PC motherboards they literally explodes) Checking the accessories list I also see I have the bundled 30 minutes tapes too. I thought it came from an answering machine, I see very little use for 15 minutes of tapes on a dictaphone.
Today I disassembled again the recorder to find the origin of the transport noise, but while I did not find anything conclusive, I have a suspect. First I removed the take-up hub (don't do it, there are those tiny spring contact that detect the motion, the reason why your first recorder stopped after 7 seconds of play) to verify if it was the take-up gear causing the noise, but it does not make a change. Thus the noise origin is down to the flywheel and/or the intermediate gear (the one with brass core and white plastic teeth). I looked carefully at the underside of the flywheel and there are tiny brass wires where the plastic toothed gear is attached to the brass flywheel core. The flywheel is held in place by the white plastic piece housing the capstan; I suspect that overtime, due to the tension of the belt, the capstan housing has slightly bent and the tiny wires under the flywheel scratch against something. One way to prove that theory would be to add an extra washer under the flywheel so that it sits slightly higher. I do not have such washer, but if you have two M-100B just take the metal washer from one flywheel and add it to the other. If the noise disappears, that is is the reason, otherwise it is really the gears and there is nothing to do about it.
