ADAT SVHS recording - anyone have any knowledge

[Mars Amp Repair]

hello folks,
I have an Alesis ADAT II model LX20 that I am attempting to repair. In the '80s & 90's I was at the journeyman level of VCR/camcorder repair, so this is not a complete mystery to me by any stretch.

We just didn't get involved with the DAT stuff.

I get an 'error 7'when trying to play the tape which indicates that the video heads need cleaning.

I know their clean as I have monitored the RF output from the heads & it's there as well as looking with a very strong magnifying device I used back in the day...but, there is missing data at the exit side of the drum assy just before head switching. The tape path alignment is correct as I cannot get that part of the envelope to expand by increasing the back-tension slightly (by hand) or by slightly moving the exit guide post.

What I've come up with is that the tape supplied was recorded this way. The tape is not physically damaged, either.

Next problem I have I have no source for either a good prerecorded SVHS ADAT tape.
what also is a bit confusing is that the unit has the ability to record the Time Code on the fly or by pre-formating the tape. Even when I try that, while recording I still get the same error indicating the video heads are dirty. I can still see the playback RF while the unit is attempting to record. I'm not familiar enough with how the unit records the TimeCode to know if it does it with the stationary head or with the video heads in what might be considered the Vertical interval, like VHS does.

Does anyone have any insight or know a source for this kind of just technical operation for the ADAT type II format?

Thanx, glen

[olddawg]

Try this.. Use a new clean good quality tape. With the tape loaded and running lightly press your finger on the back side of the tape against the spinning drum. You will feel the heads bumping against your finger. That will usually clear a stubborn head. If that doesn't work you may have to remove the upper drum and re-solder each individual head. It sounds to me that you are missing the output of one head. If you have a known good recording you can monitor the RF envelope. Make sure you sync the scope with the RF switching pulse. It's been a while since I worked with this technology myself.

[Mars Amp Repair]

Yeah,
heads weren't dirty...I could see that with my super powerful magnifier I used during the vcr haydays...saved me from replacing heads that were just stubborn as you mentioned. I mostly cleaned the actual head chip pieces with tightly wound que tips except when they moved to the dollar sized 8mm heads.

I was able, thanx to the wonderful internet, to find the head switching E-adjustment procedure. I could see in the RF waveform compared to the head switching signal that the head that was leaving the tape was not being turned off while the two heads were both on the tape...hence, the gap in rf signal at the exit side of the switching pulse.

Apparentyly on the ADAT's, there are factory specs for that particular ADAD machine that they make notes on about on a label under the cover...specs for the capstan as well as what they call 'PG delay' (or head switching).

On this one even setting the spec under the lid did not remedy the problem, so I just adjusted it for overlap in the RF waveform & all was well with the unit...

I left the video field in about 1998 when it was obvious to me that it was a dying proposition..No where I ever worked dealt with the ADAT or DAT units. Same basic servo principal, tho.

thanx for the suggestions....glen

[Jazz P Bass]

Cool post.
Thanks.

[olddawg]

The good ole' Pg shifter adjustment. I used to have the vertical deflection on my bench monitor collapsed a little so I could see them. Yeah, I was an authorized tech for everything from U- magic to mini DV and everything in between. Got old, blind, and obsolete. People still bring me stuff though. The younger techs are amazed that I troubleshoot to component level. Glad you figured it out.

[jrfrond]

We lived on ADAT's here for the longest time. Just dumped a ton of old parts. Like VCR's, sometimes you have to "massage" them a little to get the RF pattern just right. ADAT's were finicky at best.

[km6xz]

Are both of the head signals present, and are they both showing the same waveform collapse? Can you post a photo of the wave form?
We probably repair more ADATs than anyone, 5,000 in the first couple years and then took over all "factory" repair for Alesis before they went bankrupt so total, probably 20,000 repairs of ADAT format machines. We saw a lot of err 7. There was a period about the time the LX20 came out where the video amp inside the head has a defective mask and thousands failed and produced err 7. We rebuilt many head for other shops as well as for Alesis.

[Cosmos]

Hi Glen.. Alan here... I hope you can help me out with an Alesis LX20 I have. I bought it off of Craigs list cheap/dead. Fixed the power supply. tried formating tapes, but when trying to play.. says no format. After many attempts I decided to try slightly move the right side guide next to the Helical head. Time code showed up. So, as I tried mech adj's I got it worst. I have a 60 Mhz DSO. So... do you still happen to have the link to the e-adj. I will be getting a formated tape from someone today. Not sure it will help though.. Any help.. Appreciated..... Thanks....

[Mars Amp Repair]

Hello Allan,
Send me an e-mail & I'll send you all that I have found about this...I'm not certain where I found it all.

FYI. I would strongly advise against adjusting anything in the tape path until you check the RF waveform coming off of the helical heads to determine if the physical tape path even needs adjustment. Once you get the entrance/exit guides out of alignment, you'll need some kind of reference tape to get it back to where it should be to ensure interchangeability.

The PG shifter is the most likely culprit. You'll need to first set the pg shifter as described in the documents I'll send. Getting the entrance & exit guides set correctly does require some experience & sometimes finesse. I'll be glad to assist as you get into it...glen@MarsAmpRepair.com

[Daveplv]

Late reply

hello folks,
I have an Alesis ADAT II model LX20 that I am attempting to repair. In the '80s & 90's I was at the journeyman level of VCR/camcorder repair, so this is not a complete mystery to me by any stretch.

We just didn't get involved with the DAT stuff.

I get an 'error 7'when trying to play the tape which indicates that the video heads need cleaning.

I know their clean as I have monitored the RF output from the heads & it's there as well as looking with a very strong magnifying device I used back in the day...but, there is missing data at the exit side of the drum assy just before head switching. The tape path alignment is correct as I cannot get that part of the envelope to expand by increasing the back-tension slightly (by hand) or by slightly moving the exit guide post.

What I've come up with is that the tape supplied was recorded this way. The tape is not physically damaged, either.

Next problem I have I have no source for either a good prerecorded SVHS ADAT tape.
what also is a bit confusing is that the unit has the ability to record the Time Code on the fly or by pre-formating the tape. Even when I try that, while recording I still get the same error indicating the video heads are dirty. I can still see the playback RF while the unit is attempting to record. I'm not familiar enough with how the unit records the TimeCode to know if it does it with the stationary head or with the video heads in what might be considered the Vertical interval, like VHS does.

Does anyone have any insight or know a source for this kind of just technical operation for the ADAT type II format?

Thanx, glen

Adat formats 16 or 20 bit 44.1 or 48 k digital audio. 9 channels exist on the tape after format. 8 for each audio channel and one for smpte audio synchronization code. There is no video on svhs and svhs must be used. No other VHS tape will work. And it is due to the fact that side stream video format is used on VHS with linear two track Audio.linear eight track is used on svhs. In other words the chemical and magnetic formats between svhs and regular VHS are completely different.

[Daveplv]

Are both of the head signals present, and are they both showing the same waveform collapse? Can you post a photo of the wave form?
We probably repair more ADATs than anyone, 5,000 in the first couple years and then took over all "factory" repair for Alesis before they went bankrupt so total, probably 20,000 repairs of ADAT format machines. We saw a lot of err 7. There was a period about the time the LX20 came out where the video amp inside the head has a defective mask and thousands failed and produced err 7. We rebuilt many head for other shops as well as for Alesis.

Can I get the contact info for your shop, and do you know anyone looking to buy a gold face xt and elco cable for cheap. 200? Dvdpllm@ gmail.com
Thanks

[km6xz]

I doubt the tape was recorded with missing portion of the waveform, it would not record at all if that is the case. Find someone with a known good ADAT formatted tape and look at the waveform again. Is the waveform missing fully half of each rotation(trigger your scope on the test point for PG). If so, as is my guess, you have a problem with the head and it is not dirt. The most common problem causing those symptoms is a bad balanced line video amp ic inside the head, in the top of the lower (non-rotating) portion of the head stack.
Don't adjust the tape path unless you know you are seeing a waveform for both sides of the head stack rotation, it should look like a dense block of signal over the entire 360 degree rotation of the head.
If you have one full 180 degree rotation with a full block but the next 180 degree segment is less than full, or trails off in amplitude at the end of that 180 segment, adjustment is needed of the tape path but only do it with the help of either an alignment tape (if you ever want your tapes to be interchangeable with other machines) or at the least, a tape formatted in a known calibrated machine.
I am not sure of what the poster above it talking about, there are no linear tracks for audio or samples, but there a track that records and repros a sync pulse needed for course sync, a single pulse for each head switch transition, no data is recorded on that thin linear track. All addressing, tracks and fine sync signals are otherwise recorded on the diagonal tracks created when a tape is wrapped at an angle across a canted rotating head path.

Parts are not easy to find for some parts of the system but there are enough junkers out there to keep any machines alive for a long time.
I have all the service manuals back in the US but that does me no good here 10k km away so I can't tell you precisely where the test points are since I have not worked on an ADAT in 9 years.

[km6xz]

Can I get the contact info for your shop, and do you know anyone looking to buy a gold face xt and elco cable for cheap. 200? Dvdpllm@ gmail.com
Thanks

I am sure someone who needs to transfer a lot of old tapes to other media would buy a XT-20 in good condition. If I was there I would pick it up but I am now living far from "home".
My shop was given to my employees when I moved from the US. They ran it for a couple years and sold off all the test gear and shut it down about 7 years ago. I have recently opened a small shop here in Russia to fill a need of no commercial shops for pro audio in the region. You can contact me through the messaging system of this forum.

[HSLand]

This is an old thread but quite relevant to my issues.

I'm a musician, not a tech, so I don't have a scope, the other tools and the know-how to get my ADAT XT machines up and running. I can do the usual -- clean heads & tape path, replace pinch roller & idler wheel etc, but there's obviously something else going on with my machines.

Some of these XT machines have under 100 hours on them but I get a "no good tc" and constant Error 7 on them. Funnily, they still play, but not without errors. I could try adjusting tape tension and also do a PG Delay adjustment but I'm not sure what the process is. If that RP1 head preamp chip thing burned out (is it if I can still hear audio?), I'm not sure a repair would be worth the time.

Just wish I could get these things working

[Enzo]

There was a time I used to wade into ADATs, but long past. Perhaps Stan will come by this thread, he knows a lot about them, having serviced them by the truckloads. But there may be others here who can help. If the simple stuff you are used to doing doesn't help, then you are probably best sending to someone. This is not the thing to dive into as a novice.

Welcome to the forum.