488 mk 2, loud static noise in line/ mic configuration

Dominic34j

New Member
Joined
Feb 16, 2019
Messages
2
Karma
0
Gear owned
Tascam 414mk2, 488mk1&2
Hi Folks, I need some help diagnosing a problem I’ve encountered with a 488 mk 2. I bought a 488 on eBay after looking for a long time. The one I got is in A1 condition everything works on it, faders feel like new, no wow or flutter that I can hear, pots smooth no crackle, recorder section works just as it should, play/ record/ erase heads look brand new no signs of wear. I really think this thing has been in a closet for 20myears and before that only had cursory use. The problem with it is with channel 03, with nothing plugged into the line/ mic input and the trim level turned right down there’s quite a noticeable hiss when I monitor it through either 1/2 or 3/4min the monitor section. The hiss becomes a really loud static hiss/crackle as the trim is turned up. I can still record onto the track from another input and when I switch it to tape it plays back perfectly with no noticable increase in background hiss, likewise I can monitor it through tape cue. I got a copy of the service manual for this model and when I look at the block diagram there’s a preamp first in the signal chain in either the line/ mic or multi mix input. Is it likely that the preamp,is the issue, what would cause it to fail, could it be its solder joints or us there another more likely suspect. I’m aware that there are some issues with this model re one of the tape mechanism gears binding due to the lubricant solidifying and the belts tend to degrade, would you recommend changing these pre emptively . I’m based across the pond in Northern Ireland half way between Belfast and Dublin on the east coast.
 
Hi Dominic,
The gear is going to break at some time so the Gear C is best changed to prevent a failure when you least want it. The grease in the mechanism is also cleaned out and Lubriplate 105 used to replace it and this grease as far as my working with decks for 45 years has never failed.
As to the Channel input problem it could be a bad cap, bad IC but solder joints don't usually cause this. The way they blow out as in some of my clients admission is that they plug power amps into the inputs. These power amps made for speaker loads put out plus or minus 50 Vac in some cases and the op amps maximum is 15V approximately so they damage this section. It is not really a failure of the deck but a matter of abuse. You will need to get a scope and trace out where the noise is coming from then replace that part- that is what I do all the time in Chicago.
If you with the service manual can not do this then you will need to search out a person in Electronics that can. These are kind of specialized devices and so it may scare most Technical people away but a real Technician would not be afraid of such a thing as I have worked on them from when they came out back in the early 80's. The 144 was the first unit. Typically I would get the scope and go probing from a output section of the mixer going back to find out the cause. It is not that hard once you get into it and you can compare signal types with the good working channels. I put in 1KHz sine wave at -10dBV to see what it is doing to the signal- that is probably distorted too.
 
Thanks for the advice, I understand from a brief reading of the forum that you do, or used to, supply a version of the gear cast in a better material. Is that still the case? If I removed the mixer board from my 488 and shipped it to you would you be able to look at it or would it require shipping the whole unit? I’m cleaning up a 488 mk1 at the moments as well, initially there was a problem with no play function I thought correctly that the belt might have broken so I got a replacement belt but still no luck I saw that the gears where quite stiff to turn by finger but assumed that it was the capstan motor, I managed to get one that looks NOS from a guy in Mexico and I’m waiting for it to arrive, it’s probably worth changing out the gear at the same time. Strangely with that one the mixer side sounds great with no issues. Best Regards
 
Unfortunately I would have to have a unit here to put the mixer into to work on it. To do something like that would end up with astronomical labor cost. It would not be a savings and I don't do things like that. It is best to just fix the item while it is in the unit. That way you know it works with all the other associated parts. If you have many of these you will need to know how to service them.
Yes I still sell the Gear C that is Resin cast. They are selling world wide. They are $30 but the shipping to the UK even by first class is like $15.00. Still I have sent them over there, Singapore, Brazil, Australia, New Zealand, Portugal and so on. I do transactions by Paypal for this but also can take credit cards.
The old grease which is like a dried out damping solution needs to be cleaned out of the deck so that the gears move well. The problem is in some old gears I have tried to take off the shafts to clean have broken apart- they are very dried out and brittle. I would put a new one on as the teeth will break and then you end up with the blinking LED's which tells you it is an error mode.
I can be contacted more directly at skywavebe@sbcglobal.net
 

New posts

New threads

Members online