Tascam 38 Odd inputs work, even inputs don't

[Calzone]

I recently picked up a 38 which appears to be in good condition. I had to replace a melted capstan belt which wasn't too bad of a job, but now have been checking various functions.

The motors operate, play, forward, reverse, stop, braking, etc. All the meters light up, record lights and output select lights.

I switched to monitor inputs and started testing the inputs. The odd channels; 1,3,5,7 all get signal and display levels on the meters appropriately. But none of the even channels; 2,4,6,8 will move the meters with the same input signal.

Would anyone know if there is a separate power for odd channels and another power for even channels? Any ideas where I should start looking?

Thanks in advance,

 

[SkywaveTDR]

No There is not a different supply or anything like that- all channels are given the same signals.
It might be that some yahoo took out the cards and put all the bad ones in even channels to finish a project. This is very unusual for even channels to go bad and if the deck was in my shop I am sure it could be fixed. What happens if the odd card is put into a even slot? Be careful as there are conditions where the wrong person will go down the channels starting at 1 and doing the same thing to all of then causing the failure to all. Common problems seen are bad solder joints and bent pins on the motherboard by not putting the cards in like I do them. There is a special feel you get when a card is position correctly before you put it in. Those that jam them in any old way usually bend pins over and sometimes worse.

To examine this deck like a professional you will need to have a good look at the motherboard with a good light, look for bent over pins, look for damaged edge connectors and also damaged pots at the top end. You would think that bad technical people would only damage a certain part but NO they usually go through the whole unit see what else they can screw up. They don't belong working on this stuff.

 

[Calzone]

Thanks for the information. I removed the boards for channel 7 & 8. The pins look fine. I worked in the computer industry a long time and know what you mean about people and bent motherboard or backplane pins.

I swapped the 7 & 8 cards and tried it again. Still, channel 7 works, 8 does not. Same for channels 5 & 6, so I assume the problem will remain for channels 2 & 4.

I totally agree, that even and odd doesn't make sense, but since the audio cards seem fine, there must be a common aggregation routing point for the even input signals?

Unfortunately, I don't have a take up reel today to test playback to see if that path exhibits the same behavior or if this issue is isolated to the input path.

Thanks again,
c

 

[SkywaveTDR]

Hi Calzone, An interesting name indeed. Where are you located? ATR has new reels I am not sure with three benches I need to supply if I have extras laying around. You are going to need some SM911 tape to use the machine anyway. If you are entering the service business then you will probably want to talk to me anyway. But if not, by the time you buy all the test tapes and meters and other equipment it is often times cheaper to have a pro do it for you- it will take less time. Either way I help a lot of people all the time.
https://www.atrtape.com/products/master-tape-12-empty

 

[Calzone]

Hi, I live in central Mass, not close to anything but trees. I do appreciate the assistance. I'll let you know what I discover, I may have to give you a call.

Yes, I had all the equipment and MRL tape previously when I had an Otari mx5050-8 and did all my own maintenance. Fun stuff, most of the time!

 

[SkywaveTDR]

I think if you have this experience the service manual- a good one will make the most sense and you will be able to resolve these problems. I have seen Marcon caps on some decks and they have already shorted on me so I replace those things on sight- the 220uFd and 100uFd 16 and 25V types. I also keep an eye out for those 10V caps- they have given me failures a lot of times over many different brands- anything from a NAD 6300 to a Teac Z7000.

 

[Calzone]

Hi Skywave,

Great input on the caps. I wonder if they are some of the problems I am having.

I received my take up reel and new pinch roller which enabled me to playback one of my tapes to test the playback signal path.

The meters only worked on channels 3 and 7 meters. However, I tested all outputs and signals were fine. So connections to the meters is suspect.

The tape had recordings on all tracks.
With the SYNC head selected, it played channels 1-7, but nothing on 8.
With the REPRO head selected, I had channel 8, but a number of other channels did not play.

I suspect the issue I was having with the input signal metering might be associated with the meter issue as well. More investigation is needed.

Thanks again

 

[SkywaveTDR]

Yes, You need to get in there and take one channel and one problem at a time. People that ask for help often times go at these trying to fix everything at once and they get confused and don't know what they are doing. Work like this- If channel one has a problem then determine if it is on the card or on the motherboard. You do this by taking a card that is known good and plugging it in to that channel. If the problem persist then it is likely a motherboard issue, if it is then fine, the card has an issue on it. Also inspect that all pin are straight where the cards plug in. I put cards into the slots and I feel for the pins to be in the right pace when inserting a card then alternatively push it in with pressure from each side. This has worked thousand of times for me and I never have connector pin problems. If the card does not feel right I do NOT push it in.

In several of those units the feed through joints have had to be resoldered with Kester 44 solder. Some at the bottom of the board and some at the top. If the deck is on it's top with a bright light showing in and all the cards out the motherboard can be soldered from the bottom. Do not join any pins as some pins have 15 and -15Vdc on them. To do the top of the board some connector have to be taken off and the rear RCA panel removed. It can be done but is not the easiest way to do this. I had one unit here that had cracks on the motherboard and for the first time I took the transport off the audio section so that the Motherboard was exposed completely. This took a lot of screws to come out. There were still wires attached. Connector are color coded with the resistor code. So brown is 1, Red is 2 and so on. You also have to realize that you might be getting into this to the level that I work on them. You have to have good solder equipment and solder and denatured alcohol for cleaning the cards off- I use an old tooth brush for this. I have a couple of those here to work on myself.
You are going to have to use analytical skills. Work on one problem at a time and then move on to the next when that is fixed. That is what I do.

 

[Calzone]

Awesome guidance and information!

Thanks for your experience with caps. I am aware of the short life expectancy of electrolytic caps. Your information is excellent. I've also read about problems with the relays that are used on the cards. Can you advise on a recommended relay replacement if I need them?

I set up a 1KHz test tone into all channels and created a matrix of the results from input, sync and repro. Once I had levels on the inputs, I recorded about 30 seconds on all the tracks and then identified channels which work properly so they are my reference to swap with other channels.

It seems that these cards and connectors have a lot of cold solder joints, based on what I read. Fortunately I have a temperature controlled soldering station and a lot of the proper solder. Better find my solder sucker for replacing components!

One interesting note: when testing the INPUT, I set the level so I had 0db on the working meters. A number of the 'none working' meters started working once I increased the levels quite a bit, essentially kick starting them. Have you seen this before?

 

[SkywaveTDR]

There are a number of different relays on the cards so you need to tell me which one you are looking to replace- do not replace parts by what some bonehead tells you but after you have determined it is bad. The relays I see on a card I have at the bench are PG1A-24 (K102) this is a mute relay that I put Coto relays in to replace- it is for power mute and it coil on pins 2 and 6 have opened up but that may not be the only failure of them and some people hook Phantom devices to the deck through adapters and put 48Vdc to the relays and can blow them out contact wise. K103 is the record relay and the K101 is the repro/ Sync head relay. It is a GE2-187P M 24V relay. Most all Japanese equipment is made by wave solder manufacturing and this put very little solder on joints and they are not shiny like a real technician will do with Kester 44. Unless a joint has a break in them as in a round circle around the component lead then they may not be bad just not good. Many product that come in get resoldering by me for no other reason to cover my 6 month warranty and it is what I call reliability soldering as these joints will never break. As I look at this board I see a 100uFd 16V Marcon cap in the center and a 100uFd 10V cap called C102 on the side near the transformer- I would replace those two as a minimum from that companies history plus I never like 10V caps- I think they are drop outs of the 16V manufacturer.
The Coto relays I put in AMP IC sockets so that should another failure ever happen pulling the card and putting a new relay in would be faster. Helps save the board as well. To date I have never had a Coto relay fail yet- I do use the 2 pole ones in 1 pole positions as you can do that but you can not use a 1 pole relay in a 2 pole circuit of course.
The forum will not let me upload a file so contact me at skywavebe@sbcglobal.net and I can assist you further with parts I use. Most of them are at Mouser and also DigiKey.

 

[Calzone]

Awesome info! Many thanks. My initial instinct are the sync/repro relays. But I'll be doing detailed troubleshooting soon

 

[SkywaveTDR]

I had a TSR8 that has the Repro Sync head problem and I did not know where it was coming from until I flexed the card at the relay location. After finding out that the flex which probably moved the contacts on the common pole of the relay moved a bit then started to work I then set out to find the small little relay that was the replacement for the original one. You can not open or clean this relay like larger ones.
G6E-134P is one I would check out for the data and fit you need.
https://www.mouser.com/ProductDetai...134P-ST-US-DC24?qs=Pjd0UV7BHP%2BaRK4ck7OtCg==

 

[SkywaveTDR]

An additional note- I know these cards are not easy to work on without an extender card which are hard to come by- I have one because I worked at Teac and I got it when they closed. BUT you can still work on cards if you take the other 7 cards out and put the defective card in slot 8 at the bottom then at least in only that slot you would have pretty good access to the top of card for probing and scope readings. This is not all that fancy of a trick if you just think about it. Tapping on a relay sometimes will tell you if it is defective in that you cause the relay fingers to move on the common pole that is atationary, Most Technician know this trick even from other equipment- this does not work on reel relays like those the Coto relays are replacing.

 

[Calzone]

Hey Skywave, thanks for all your guidance and experience! I wanted to give you an update.

I started by providing 1KHz tone from my DAW to all inputs of the 38 in INPUT mode, but as I described, not all the meters were working, however, all the outputs were. I was able to create a matrix of the various modes INPUT/SYNC/REPRO and which meters and which channels worked. Only two channels demonstrated complete meter and outputs across the various modes.

After swapping a couple of other cards with my "Gold" reference cards, it provided me a game plan and I was able to determine that the problems resided with cold solder joints on the motherboard.

As you suggested, I started by pulling the 8 cards and worked from within the chassis. I would take high res pictures of the sections and enlarge them to evaluate the joints. I was able to find quite a few poor connections and repaired them. It is amazing just how many poor joints there were.

I then went top side, removing the I/O panel and worked the same there, using an LED light and my phone camera to position and get shots, to find opens. though difficult to get up to slot 1, it all worked out well.

All the problems were resolved and I am happy to say all functions appear to work great. I don't have my MRL tape any longer, but had an 8 track tape I recorded a 1KHz reference on with my Otari previously which I used as my reference to tweak meter and playback levels. The output levels I checked with my DAW for consistency.

It's a very nice machine.

Thanks again for all your insights.

Regards,
Cal

 

[-mjk-]

"Cold" solder joints most likely were well formed at the time of manufacture. However, since the intermetallic bond continues to grow over time, with vintage equipment eventually all of those joints will have to be resoldered as the intermetallic bond will take over the entire joint and make it unreliable. If you go to the trouble of taking a card out of a vintage unit, you should consider touching up all of the solder joints as a SOP (that is, if you are experienced at soldering).

 

[SkywaveTDR]

Further than this the soldering done by wave solder machines was pretty terrible. I have to deal with it almost every day. A person with excellent soldering skills can do aerospace grade solder joints using Kester 44. My joints do not break. They are shiny and have more solder on them. Most repair people do not know good soldering- that is the hacks that work on them before I get them. You must use a small tip iron like a weller WES51. Radio Shack soledr irons do not work well at all. Everywhere there have been double sided cards and many years of age there are broken feed thru solder connections. These can be seen on Pioneer RT-1050, Teac A3440 and anywhere else like the 38. The better Tascam products like 40 series and above do not normally have this kind of problem.
Good that you were able to fix the problem. Sometimes FETs like 2SK68A are a problem but these days I put there 2N7000 transistors and they work fine. Same specs. They have them at Mouser.

 

[Calzone]

have a roll of Kester 44 I use and a Weller soldering station with small tip, I know what you are saying.

I calibrated everything including BIAS for the tape. So everything was perfect, but now channel 1 doesn't record. All the others are great. All the playback levels, meters, etc are fine. It seemed to stop right after I set the bias. Any suggestions? Do those adjustable for the bias go bad? they look pretty simple.

thanks

 

[SkywaveTDR]

I do not suspect part unless they have a history of going bad. I have never had a bias cap go bad on a 38 but there are other things that could happen- channel one is at the edge and dirt can stick there and also the edge of the tape can be damaged. Again you switch cards to see if the card is causing this or something else. Feed through solder can always get you a second time as you may have missed one. They are hard to get all the way up at the front I can tell you. Might be a relay on the card- I think the record relay is the one with the metal can on it.

 

[Calzone]

Yes, I switched cards and it followed my channel 1 card. I looked over the card and resoldered edge connectors and K103. I pulled 1 & 2 and touched up a few inside as well, but now I'll go back topside of the MB and hit all the channel 1. I ordered a couple of the k103 relays in the event I need to try swapping.

 

[SkywaveTDR]

Usually if a relay is bad you can test that theory with tapping on the relay while in record of that card to see if it kicks in at some point. If it does cut in then the relay has bad contacts. The relays under the metal cans could be taken apart and burnished and treated with Deoxit but it is usually not a long term solution. Might bet you past 90 days though- I have seen it done. I think the warranty at the shop in Chicago was 90 days. Mine is 180 so I can not do low grade work or I work on it again.