Tascam 38 No sound in Sync Mode!

E

edthebear

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Tascam 38
Hi everybody,
I wonder if I can ask for some advice. I bought my 38 a couple of years back (for spares or repair.) However I have been rather obsessed with getting it to work fully. I have cleaned the machine thoroughly throughout, changed the heads, replaced the Record Produce Amp PCB and now I am left with one enoying problem to solve in order to get this show on the road. I have no sound from the microphone on track 6 while in Sync Mode. the VU meter shows a signal. Does anybody have any idea what I should look at next. As my previous posts indicate I am no electronics expert by any stretch of the imagination! I have just received a 38 Reel To Reel Selector PCB (PCB-104) which is said to work fine. Do you think that this maybe the problem as it only relates to 1 track?
Thanks for reading.
Ed
 
Sounds like a relay issue on a sound card.

Each card has three relays. They are known to go bad.

You might be dealing with this isue or bad solder joints on the main board.

What do you mean by "replaced the Record Produce Amp PCB"?
 
Hi Gcalo,
Firstly thanks for replying to my post.
Because I had problems with several tracks not amplfying I purchased 8 cards from the USA which were said to be checked and passed as working. They did the trick for me except for track 6. I interchanged the track 6 card with others from other track which were working OK on the other tracks but the problem was still there on track 6!
This leads me to believe that the card isn't the problem.
I have replaced the motherboard due to an accident I had with the machine. i.e. I didn't have the machine held secure enough when I was working on it and it fell back and badly cracked the MB. (idiot!) This machine has cost me far more than an up and running one would have cost me in the first place, but there is just something about it that I have just got to get it running. Don't ask me why?
I am now in the middle of changing the mode selector PCB to see if that does the trick.
 
Then I do suspect it is bad solder joints on the M-B. The mode selector if bad might affect more than just one card. So I doubt it is that.

Get a 25-30 watt solder iron and with card # 6 installed in place slowly and carefully re-heat each pin on the top of the M-B from left to right so the solder flows briefly.

Take your time and be patient

The 30 series units are notorious for bad solder joints.

I am familiar with your plight as I have a 38 now I on which I have been working that is a bear with problems.

I have no idea why I keep fighting with it either!

Try that.

Why did you replace all the sound cards?
 
I had amp problems with 4 tracks. I thought "in for a penny in for a pound" as they say here in the UK. I didn't know how difficult it might be to get parts in the future so I bought the lot. The postage to the UK cost more than the parts and took a month to get here. I think it might be quicker if I lived on the moon? I don't think they are all as good as the guy said though 2 had the same problem on other tracks. I will try your suggestion though. Many thanks. I will let you know how I get on.
 
don't throw out the original cards! Hold onto them.

I have revived a few as usually the problem is with the relays on them.

Try the solder trick. Be patient;take your time, and try a round tip on the solder iron.

The 30 series are wonderful machines but can be a pain to get going 100%.

The mode selector swith has about 6-8 electrolytic caps, and two are non-polar. They are reliable, but I always replace them all.

I also fully rebuild the power supplies. It makes a huge difference.
 
Thanks Gcalo,
I will be retiring soon. A year early! This will keep me busy. This is a strange diversion. I have perfect pitch with my voice but didn't care much for the digital results so someone suggested going back to analogue. I played back some material that I recorded on a Fostex A80 (couldn't afford the Tascam!) back in the 80's. it sounded pretty damn good so I thought I may now be able to afford a Tascam 38. I lived near a music shop in Bristol, England back then and I remember standing outside looking in at all of the Tascam gear he sold and wished that one day I might be able to buy a 38 and here we are.
Many thanks again for your advice. I will keep you posted as to my progress.
Ed
 
Hi again Gcalo,
I have replaced the Select Mode PCB and it's as you predicted things are the same. Therefore the next step is the re-soldering on the MB as you suggested. I'll keep you posted and thanks once again!
Ed
 
Hi Gcalo,

I'm also modding the tascam 38 and I'm interested in what you've done with the power supply. Which new values did you use and which one did you bypass with WIMA's?

Did you also change any values on the capacitors in the sound cards? Or just used the stock ones...

Thanks man, you would be a great help!

I'm really looking forward to get some new life into this machine!

Bram
 
I replace every cap in the power supply. I use Nichicon PW series caps with higher voltage ratings than the OEM.

Many of the larger values I will double in mfd size and to do that have to us the VR series by Nichicon. The VR series has slightly smaller physical can sizes for the large values. Sometimes needed to get the larger values to fit the board where 3-4 caps are near eachoter.

All caps 1,000 mfd and larger I bypass with a .01 WIMA 63 V cap.

For a 38 there is a ton of caps on 8 sound cards to replace but you can. It will take some time. I use the Nichicon FG series as those are high grade audio caps.

Other mods can include replacing the 4558 IC's with better units.

There are even other mods available. It can get crazy.

In many cases I remove all three (3) relays, solder in new sockets, and then replace all the relays.

It is a huge job but if done slowly it can produce fantastic results.
 
Thanks man, really appreciated!

Normally I'm getting a batch of Panasonic FC in the near future, so I'm probably gonna use these. I hope they will fit.

So you kept on using the same values for capacitors in the audio path?
Which are larger values for you, 1.000 mfd or already .470 mfd's? And then you doubled these values?

Thanks again!
 
You must measure the height of the OEM caps and stay w/in that parameter as there is limited height when the power supply goes back in. If too tall the board will not fit!

I will double the larger values; usually the 2,200 to 4,400 or 4,800 mfd. I leave the 1,000's alone although those probably could be increased. I leave the values the same of anything below 1,000 mfd.

If you change caps on the audio cards the use high grade audio series caps such as Nichicon FG series.
 
Thanks for your detailed help!
I still assume you've used the same values as the OEM caps on the rec/play pcb's?

Panasonic FC's are high grade caps, I think.
 
Yes to same value caps on rec/play boards.

I have not yet spent time to find where I can substitute a high grade film cap on the input side of the board but may in the future.

I have not used Panasonic caps, but I understand those are OK. I stay with Nichicon because they offer everything I need and are easier for me to acquire.

If Panasonic is more abundant use those but be consistent. Use the same series on each card.

BTW, I go to much higher voltage ratings especially on the P/S caps. At times the cans are larger in diameter, and this is where you have to be careful for sizing.
 
Hi Gcalo,
I just wanted to say thank you for all of your help with my problem
I have just finished re-soldering the pins on the motherboard and the 38 is now working perfectly, absolutely great! Many thanks once again!
Kind regards,Ed
 
Gcalo said:
Yes to same value caps on rec/play boards.

I have not yet spent time to find where I can substitute a high grade film cap on the input side of the board but may in the future.

I have not used Panasonic caps, but I understand those are OK. I stay with Nichicon because they offer everything I need and are easier for me to acquire.

If Panasonic is more abundant use those but be consistent. Use the same series on each card.

BTW, I go to much higher voltage ratings especially on the P/S caps. At times the cans are larger in diameter, and this is where you have to be careful for sizing.
Click to expand...

I've just done the whole mod and I came across a problem. When turning on the machine only the VU bulbs and output select leds turned on. When trying to press play, nothing happened. The leds on the function select also doesn't work.

So I began to check the back of the tascam again and I saw fuse F507 has broken down. That's the fuse that comes before the rectifier diode in front of the bigger capacitors on the PSU PCB. Connection number 24 on the PSU PCB.
On the schematic it is stated as 7A? But the fuse itself is 5A.

Do you think the PSU now is delivering to much power that drains to the fuse and blows it up? Should I try a bigger amperage fuse?

I also used 0.01 uF (100V instead of 63V) for bypassing the big capacitors and 1 Nichicon PM (instead of PW) 470uF (100V instead of 25V) on C829, but that shouldn't make any difference.

Thanks for your help!
 
If the circuit calls for a 7 A fuse use that and see what happens.

If the 7A blows then there is a problem somewhere else.

Check over the P/S to make certain all the caps are placed in the correct direction. Polarity is important.
 
I have changed the fuse, but that didn't do anything, so I checked all the connection to de PSU. Then I saw 23 and 24 was switched. 24 (brown cable) should be going to the fuse that burned down and not 23. So I switched them around, but the power back on and 3 logic boards (U501-U504-U513) burned down and the fuses all stayed intact. What the hell? So I desoldered all the connections and checked the PSU. Everything is in order there. What to do now? I already ordered new NAND IC's...

You're really sure there isn't a design flaw? Because I'm pretty sure everything seemed fine on the PCB/connections.

Thanks again.
 
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