Tascam 388 problems Part 2

I've been pondering

I took some time to look over the schematic (A fuzzy schematic really hampers me plus I'm missing some pages) And think about what you have got.

I'm thinking that the +-15 volt supply is being overloaded. I'm thinking that the +15 rail is the one being overloaded (based of fuse discoloration).

I'm thinking that the supply is not overloaded with the channel and DBX cards out but as you add them in the overload increases until thermal runaway happens.

I don't think that the channel cards or DBX cards are the cause (presumes good) but rather the cumulative load is it.

Other cards use +15. I suggest that you pull other cards in the mixer section (or connectors) to get the load down and then try the heatsink heat test with no mixer but with all channel/DBX cards. The idea here is to start at near zero load and add just the channel/DBX cards so as to show the PS can handle their current needs without overloading the PS.

It would be instructive to find out each cards current usage. You could do this a number of ways. One would be to put your meter on amps and insert it in series with the +15 (or +12) rail. THis would require breaking a trace or using some extension cables like Sweets made. Another was would be to remove the (F3) +15 fuse, hook come clips up to the fuse contacts on the fuse board, then connect one clip to the fuse, a new clip to the other end of the fuse which coes to the amp meter (set on AC Amps) and the other probe of the meter goes back to the fuse holder.

PCB----fuse----PCB <----------Before meter

PCB----AmpMeter----fuse----PCB <----------After adding meter in circuit

In short just put an AC ampmeter in series with fuse F3

The idea here is to find out the total current drawn and to then attempt to locate the source of the excessive current draw.

Regards, Ethan
 
alright

evm1024 said:
Other cards use +15. I suggest that you pull other cards in the mixer section (or connectors) to get the load down and then try the heatsink heat test with no mixer but with all channel/DBX cards. The idea here is to start at near zero load and add just the channel/DBX cards so as to show the PS can handle their current needs without overloading the PS.
Click to expand...

Alright, first things first, let me say thanks for taking the time to address this problem of mine. Im beginning to feel like its a lost cause, so any help really puts me in a better mood.

Second, much of what you just said i dont quite understand, but let me start at what i presume is the beginning (in your quote above). So you are telling me to disconnect parts of the mixer guts (like the EQ sections etc), and leave the rec/play, and dbx PCBs and see if it gets hot? Do i need to find a specific connector to do this, or should i just be taking off the faceplate and pulling entire channel cards in the mixer section out?
 
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I think this is the time for sweetbeats to chime in as that he can "translate" for us. I'm going by the diagrams in the fuzzy manual and he has a unit to look at.

What we are doing is dividing the parts into sections with one section powered and the other not powered. At some point we will realize that it only gets hot with section X powered up. Then we will know that the problem is there and can work on looking for the faulty part.

So by pulling the connector that supplies the mixer we depower it and then if the heatsink stays cool with the channel/DBX cards in we could say the the channel and DBX cards are not the problem.

Audio wise, what works with all cards in? At lease till it gets too hot?

--Ethan
 
everything

With all cards in everything works. The recorder has zero performance problems as far as recording, inputs, EQ, switches, and all transport functions are tight and responsive. Even with the recorder on for a long time, everything sounds and performs fine. If it werent for the fuse blowing i probably wouldnt even know there was anything wrong.

EDIT: Ok there is 1 flaw, the meter for track 7 is burnt out, but the needle still works. But other than that, perfect.
 
The Great Cobb said:
With all cards in everything works. The recorder has zero performance problems as far as recording, inputs, EQ, switches, and all transport functions are tight and responsive. Even with the recorder on for a long time, everything sounds and performs fine. If it werent for the fuse blowing i probably wouldnt even know there was anything wrong.
Click to expand...

That's good to know. But it makes figuring this out harder. Put that amp meter in series with F3. Let's see what current we are talking about. AC amps start on the 10 amp range. We can get Cory to do the same and see what is normal and abnormal.

--Ethan
 
Things can be connected in series or in parallel. With a meter you measure voltages by placing the meter in parallel with the thing you are measuring. ie you measure across the thing.

To measure current the meter has to be in series with the current flow. The current has to flow through the meter. So to measure the current through the fuse you wold set your meter for AC amps (the current at the fuse is AC) and lift one end of the fuse out of its socket. then one lead of the meter goes to the free end of the fuse and the other goes to the connector.

The current flows from the socket into one end of the fuse, through the fuse, into the meter and then back to the other part of the fuse socket.

Start with a high setting (typically 10 amps) and use jumper clips if you have them. If not you may want to attach the meter leads to the fuse and socket with tape in a way that the leads do not come off.

--Ethan
 
Give me a day or so, fellas...I'll measure the current draw at idle of my 388 and post that up.

Cobb, if you haven't done so already get prepared to pull the bottom cover off of the 388. That's where you'll get to the connections of the channel cards. No need to take the cards out...we'll work from underneath. I'll have a look and put up a picture or two of which connectors to undo to disconnect the mixer from power.

Ethan, you keep talking about a fuzzy manual copy...are you using the copy downloaded from the internet or the high quality scan I took of a Tascam copy?
 
meantime

In the meantime im going to clean some of the dust and hair and stuff out from the insides. Its not horrible, but i might as well do it now. Thanks for the help guys.
 
sweetbeats said:
Give me a day or so, fellas...I'll measure the current draw at idle of my 388 and post that up.

Cobb, if you haven't done so already get prepared to pull the bottom cover off of the 388. That's where you'll get to the connections of the channel cards. No need to take the cards out...we'll work from underneath. I'll have a look and put up a picture or two of which connectors to undo to disconnect the mixer from power.

Ethan, you keep talking about a fuzzy manual copy...are you using the copy downloaded from the internet or the high quality scan I took of a Tascam copy?
Click to expand...


Cory,

It's got to be from the internet. Your copies are great.

-_Ethan
 
sweetbeats said:
Give me a day or so, fellas...I'll measure the current draw at idle of my 388 and post that up.

Cobb, if you haven't done so already get prepared to pull the bottom cover off of the 388. That's where you'll get to the connections of the channel cards. No need to take the cards out...we'll work from underneath. I'll have a look and put up a picture or two of which connectors to undo to disconnect the mixer from power.
Click to expand...

OK well i got the back off and i can get to it from underneath whenever you are ready.
 
evm1024 said:
To measure current the meter has to be in series with the current flow. The current has to flow through the meter. So to measure the current through the fuse you wold set your meter for AC amps (the current at the fuse is AC) and lift one end of the fuse out of its socket. then one lead of the meter goes to the free end of the fuse and the other goes to the connector.

The current flows from the socket into one end of the fuse, through the fuse, into the meter and then back to the other part of the fuse socket.

Start with a high setting (typically 10 amps) and use jumper clips if you have them. If not you may want to attach the meter leads to the fuse and socket with tape in a way that the leads do not come off.

--Ethan
Click to expand...

So i set the multimeter dial to the settings that are marked with an "A"? Do i plug the meter leads into certain jacks on the meter itself? Meaning, does the black lead stay in the COM jack and the red one goes into the "A" instead of the "V"?
 
Huh!

Hey, Cobb...

Y'know what? When you unplug P32 on the Mother (2) PCB that pulls all the power from the the mixer and the meters...all 8 channel cards, the Buss A and B PCB's and the Monitor PCB. So after you measure the current draw of the unit with all the cards plugged in, then pull P32 and measure what the draw is. Then we want to know if the heatsink gets hot.

So i set the multimeter dial to the settings that are marked with an "A"? Do i plug the meter leads into certain jacks on the meter itself? Meaning, does the black lead stay in the COM jack and the red one goes into the "A" instead of the "V"?
Click to expand...

What make/model is your meter? I am fairly certain the answer to your question is "yes"...that you plug one into the COM jack and the other into the A jack, but I'd hate to misadvise you. If you can put up a pic of the face of your meter that'd be best.

Do you understand what Ethan is talking about as far as putting the meter in series with fuse F3?
 
Okay...good. That'll work.

Yes, one lead on the COM jack and the other in the A jack, turn the dial to the A section...I can't quite read what the options are in the A section...I'm on a mobile device.

Use electrical tape to support the fuse and the probes to accomplish the meter-in-series connection. If you are not sure how, post back. I can take a pic of a suggested method within a day or so.
 
No need to proceed....

That meter does not measure AC current. It has DC current only.... That's OK.

For fun we could measure the AC voltage across F3. Set meter to 200 mV AC, place the probes on the metal part of F3, one at each end. I wold expect a low value.

Beats, good find RE P32. I was thinking that there shold be a single connector to depower the mixer section.

Lets see what the heatsink does with P32 pulled.

--Ethan
 
Tascam Portastudio 414

I have purchased a Tascam Portastudio 414 model. When I play any older tapes that I recorded or a tape of any other kind, I find when playing these tapes that they are playing at a faster speed. The pitch control is set at it's slowest speed. What can be wrong will this recorder, is there another adjustment on this unit that I can not find.
 
herbpd, next time start a new post...your past has nothing to do with this thread. :)

What were the older tapes recorded on? The 414 is a high-speed deck. It records and plays back at twice the speed of consumer tape decks so if you record on it and then try to playback on a regular tape deck it will sound really slow...conversely if you record on a regular deck and play back on the 414 it will sound really fast.

Ethan, duh, I'll have to check the meter I just used...betcha it also is DC current only. I got 0.03A at F3 with everything hooked up and dbx off, 0.028A with P32 disconnected and dbx off, and 0.048A with P32 disconnected and dbx on. Seems quite low.

WITH P32 DISCONNECTED THE BIAS AMPS U101~401 ON THE BIAS PCB's GOT HOT...ENOUGH THAT I COULD SMELL JUST A HINT OF THAT LOVELY HOT ELECTRICAL SMELL...ETHAN, NO TIME TO CHECK NOW BUT IF YOU CAN COULD YOU SUGGEST WHY THAT MIGHT HAPPEN? MIGHT IT BE BETTER FOR COBB TO PULL THOSE BIAS CARDS IN CONJUNCTION WITH P32? :eek: I wasn't expecting that...glad I have spares. Not sure if anything got cooked but I donzt want Cobb damaging things further. :o
 
I'm nervous that if the bias cards were getting overloaded there may be other things as well, so I'm going to look at what else is getting carried over P32 and advise that Cobb hold off...what do you think?

Hm...I wonder...I did press the track arming switches while P32 was disconnected and they didn't all flash...they did until I pressed #8 with 1~7...then they all stopped flashing...then they (1~7) started again when I unlatched #8. urg...I REALLY hope I didn't cook my 388...:(
 
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