Posts Tagged ‘dat’

broken DAT / degraded mouldy tape

Saturday, August 18th, 2012

Early tape based digital formats such as DAT, Tascam DTRS and ADAT, etc are often problematic now, partly with tape issues and also reliability and spares availability. In 20 or even 10 years time these machines will be much less serviceable than the analogue tape machines of the previous generation and as a result more obsolete and a higher priority to migrate to a file based digital format.

We’ve also started to see a particularly nasty problem with some, and usually the 120 minute length, DAT’s. The first symptoms are a broken DAT tape usually on wind.  The tape pack seems to become slightly sticky, with intermittent tension between the layers of tape and with the thinner tape in 120 lengths this can sometimes break the tape on wind.

2012 08 17 19.01.15 broken DAT / degraded mouldy tape

You can see in the above image how the tape sticks slightly to the pack and then releases when hand wound. With the greater tension of a machine wind and the tape also wound around the head drum this becomes risky.

With large transfer jobs checking each DAT by disassembly is not feasible but the permanent damage and / or part loss of a section of audio caused by a break is not feasible either!

repair snapped DAT

Wednesday, October 19th, 2011

dat snapped repair snapped DAT

We often get sent Digital Audio Tapes or DAT’s for transfer to .WAV computer files. As these recordings are already digital or ‘born digital’ the process should be straightforward. Our audio interface cards accept the SPDIF or AES digital audio stream from the DAT machine and record this as a WAV or BWAV file. This file can then be burnt as a CD or delivered digitally on a hard drive or removable media.

The big problems though come with the tape that these digital recordings are made on. The tape is only 3.81 mm wide and moves at a very slow 8.15 mm/sec. The tape is also very thin at 13 microns. The recording system and transport used is helical scan just like in video recording but with the very slow tape speed and small tape dimensions any defects or problems with the tape can result in many errors which may not be correctable by the error correcting system of the DAT machine.

One problem we’re starting to see more and more are tapes that snap. The tape pictured above was a D120 which was never recommended by the DAT machine manufacturers but was still often used for it’s extended recording time. This tape snapped without warning a quarter of the way through the recording. There were no outward signs or potential problems just a sudden clean break on a diagonal.

dat tape broken 300x151 repair snapped DAT

To recover this tape it could have been spliced with splicing tape of the correct width like in analogue recording but there is a high risk if not done perfectly of unrepairable damage to heads on the drum. Even with this type of repair some of the material would have been lost. A safer solution is to rehouse each spool in another shell this lets you recover as much as possible from the tape without the risk of head damage.

Whichever solution you decide the DAT shell must be disassembled. A small crosshead screwdriver needs to be used to remove all the case screws. There are two hidden ones, accessed by sliding part of the cassette shell down:

dat case screws 300x204 repair snapped DAT

You can now carefully lift both halves of the DAT shell apart, making a note of the tape path inside the shell. Be careful not to touch the tape with your bare skin as fingermarks and grease can cause head to tape contact problems and audio errors and dropouts.

 

 

 

Sony PCM 7030 DAT repair

Friday, October 14th, 2011

sony pcm 7030 Sony PCM 7030 DAT repair

We have several of these large, wonderful machines. It’s not often we need or want to get involved in DAT repair as generally they are not easy to service machines and many key transport parts are becoming unavailable. The Sony 7030 DAT though has been designed with easy servicing in mind. There’s alot of room in these things and each section is clearly marked and separated into distinct boards much like Sony Broadcast video machines.

These are timecode DAT machines and were once common in video post production houses and the more well funded recording studios. The problem with some of this well built kit though is exactly that it works too well and gets left on for long periods through it’s life and this can take a toll on certain components, especially electrolytic capacitors. Heat builds up in electronic circuits, especially in switch mode power supplies that larger broadcast items often use. Capacitors have a rated life at 85°C or 105°C at several thousand hours. With hotter environments, substandard parts and long operating hours these capacitors can soon outlive their original design life.

Our 7030 DAT had started behaving oddly and at first the display would flash on and off after a short while powered on. Another machine would power up for 30 secs then just die. Before delving into the enormous service volumes it’s always worth replacing the Switch Mode Power Supplies (SMPS). These like many broadcast machines use supplies that are sometimes generic made by other companies and which can be bought at Farnell or RS. We did it the harder was and desoldered all the old capacitors in the power supply and replaced these with high quality low ESR Panasonic ones which should give us another 6000 hours of running time. So far this machine has worked perfectly although you do need good soldering and desoldering technique on these boards. A powered air desoldering station is a good idea, much, much better than a hand solder pump.


designed and developed by
greatbear analogue and digital media ltd, 0117 985 0500
Unit 26, The Coach House, 2 Upper York Street, Bristol, BS2 8QN, UK


XHTML | CSS
greatbear analogue and digital media is proudly powered by WordPress
hosted using Debian and Apache