Tascam 488mkii audio dropout problem

[GōST]

I’m having problems with audio dropping out on a few of the channels on my 488mkii. It’s the worst on channels 7 & 8, with 3 also being quiet and dipping in volume occasionally.

It seems to be during recording; upon playback the dropouts happen in the same spots every time. Also, flipping the tape over shows them happening on the corresponding/opposite channels. It isn’t an input issue, the meters all read perfectly and monitoring all sounds fine during recording, but when playing the tape back the dropouts happen.

I’ve tested this with 400hz tones from my phone on all the channels to get a constant level. I’ve switched between inputs, I’ve used all the buses, I’ve cleaned the entire tape path with 91% alcohol, it still happens.

I was never convinced that degaussing/demagnetizing wasn’t kind of a myth, but could that really be the issue? My understanding was that it’s supposed to cause bad high frequency response (which is why I used a lower frequency tone to test), and even then not total dropouts... I don’t know how to go about troubleshooting this any further, so any help would be greatly appreciated!

 

[SkywaveTDR]

The problem sounds like tape related as the heads would do the same thing again at different places but when it happen in the same place then it points to the tape. The age of the tape might have something to do with the recording. I have not seen this in my shop. I use a 1KHz tone sine wave but I do not use Iso alcohol but denatured which is the better stuff. Demagnetizing I found to be a lot of hype. I did tests at Teac on the bench to a deck that has never been degaussed and the loss of 10KHz was less than 1/2dB after 50 passes and this was done before degaussing the heads- With the Handy Mag kit I bought the measurement before and after was he same. So I think with my college training in Electromagnetics, I have a lot more knowledge than some of these characters not to mention I have been a Technician for 47 years now. The only time you need to degauss a head is when you apply DC to it as in testing a head for open coil. That is it. All these companies that say you must degauss a head also sold those devices- strange isn't it.

 

[GōST]

Turns out that’s exactly what it was. I had tried two Maxell XLIIs, bought at different times, and the results were similar so I thought I had ruled out the tapes. But I just tried a RadioShack HD60 I just got and the performance is normal. I will probably still do a more thorough cleaning with denatured alcohol when I can get some.

I had a feeling the degaussing thing was just snake oil. I’ve yet to find anyone actually posting before-and-after results, and opinions have always been split, with the only ones recommending it being companies selling the kits, like you said, and “audiophiles.” And I don’t trust audiophiles about anything. But after looking through this forum you seem to be the guy to trust on these issues, so I’m glad it was you responding. Good to have a trustworthy source on degaussing, and thanks for the reply about the dropout issue. Good to know that it’s not a problem you come across; I was sure it was the heads slowly dying, but turns out it was the simplest solution as usual. Thanks again.

 

[SkywaveTDR]

Well I have not come across any bad heads in any 488 yet. The 244 and 246 can have irregular surface due to wear and the magnified view will show a rippled or wavy surface that make head to tape contact hard and not real good. Those heads have to be changed and I did do a number of them but over at Teac and even 10 years after that in the shop that was run by the Teac manager, I changed out at least 1000 heads. I do it now even and just secured some more 122 Mk II heads which are not cheap. Most all other heads are a thing of the past.