Tascam 388 problems Part 2

ok

OK well i got the cables, hooked them up correctly, and now im going to look over the tests and see if i can figure anything out.

Do i disconnect P4 from the card or the board way inside the 388?
 
Ok ok

I unplugged the P4 from both, and its been on for awhile now, and the heat sink is still cold. By now it would have been ragingly hot.
 
Hey Cobb.

Okay. Glad they got there. Doesn't matter about unplugging P4 from the motherboard, the PSU PCB or both. If you do it from the PSU PCB and the extender cable is still plugged into the motherboard just be SURE the other end is secure so it doesn't come in contact with anything and short...probably safer to pull it from both which is probably what you were thinking huh?

I imagine that Ethan is going to want to know the results of the tests so do those. Ask what you need to ask in order to do them. Tests 1 and 2 are done with all the extender cables plugged in. Tests 3 and 4 are done with P4 disconnected.

I will start looking at the schematics and wiring diagrams in anticipation of what will be the logical way to start isolating system components so we can hunt this gremlin down a mercilessly squash it...
 
test 1

So in test 1, i am securing the black probe to the chassis, and am i touching the red probe to the metal pieces the arrows are pointing at in this pic (not simultaneously of course)? Basically im just trying to figure out where to touch the red one to.
 

Attachments

  • 388stuff3.jpg
    388stuff3.jpg
    60.9 KB · Views: 49
Yes. That is correct. Set your voltmeter to DC, measure P4 pin 2 to ground, and then measure pin 5 to ground and tell us what Mr. Voltmeter said...
 
Your test results look A-OK to me though I would like confirmation that the unregulated voltages (i.e. +27.1VDC and -27.2VDC) at P4 pins 2 and 5 are okay. I will wait and see if Ethan or anybody else chimes in on that and if we don't get any input I'll see if Ethan can take a peek when he has a chance just to confirm.

Does the heatsink get hot if you have everything on the power supply board connected except P5?

If it stays cool with P5 disonnected, here is what I would do next: Assuming the heatsink stays cool with P5 disconnected it can be said (as far as we know at this point) that the power supply is working right (i.e. voltages look good, heatsink is cool when the pertinent power rails, the +/-15V, are isolated from the system, etc.), so I would disconnect system components and then strategically reconnect them one at a time until one of them makes the heatsink heat up. This is not fool-proof, as it is possible that having a combination of things connected is what's causing the issue, but IMO this narrows us down to the culprit most of the time. The 388 is nice because so many of the system components are on plugin cards.

I'm going to have you do this in a couple phases since all the plugin cards are easy to pull, and once you pull those there are four plugs on one of the motherboards that become accessible and once you pull those the only components still connected to those +/-15V power rails are the mixer channel 1~8 boards and the two buss master boards. If the heatsink still heats up then we can assume the problem is with one of those or a combination of those. Since it is a little more involved to pull power from those we'll start by pulling the plugin cards, and those four connectors and then hopefully the heatsink stays cool and we can assume that the channel cards and buss master cards are A-OK and I'll walk you through a somewhat systematic approach to plugging the connectors and cards back in.

I really hope this is not too confusing at this point.

If you are having a hard time getting the cards pulled (i.e. they are stubborn), especially the amp cards and the dbx cards, you can cut a piece of coat hanger and use pliers to make a puller that helps. The cards have holes on each top corner to receive the puller. Shape the coat hanger wire like a squarish letter 'U' and make hooks at the top of each side of the 'U'...turn it upside down and hook it on to the card...viola! A handle. I can put up a pic of what I'm talking about if the description doesn't make sense but the "handle" helps to be able to gently rock the card from side to side which really helps to get it pulled.

Here's a step-by-step procedure:

  1. Make sure the 388 is off and disconnected from the mains power. Doh. I have to say it because I can remember the times I have reached into something and was lucky I didn't get zapped or cook the gear because I thought I had pulled the power plug. Badbadbad sweetbeats.
  2. Remove all the plugin cards (i.e. the 4 record/repro amp cards, the two dbx cards, the balance amp card, the 2 bias amp cards and the reel servo card)...look on pages 1-26 and 1-27 for the layout of these cards in the cardbay...***label the 4 amp cards, the 2 dbx cards and the 2 bias cards as you pull them so they go back in where they came out*** You won't kill anything if you don't, but you'll likely save yourself time later because each card was calibrated at some point for the channel(s) it is plugged into so no sense swapping that all about...
  3. Remove four connectors from the Mother (2) PCB: P15, P17, P32 and P34. The Mother (2) PCB is the same one that the Power Supply PCB plugs into. Look at page 3-11 for a diagram of the PCB to help you locate those connectors if needed. The connectors are also labeled on the PCB.
  4. Now the +/-15V power rails should only be going to mixer channels 1~8 and the Buss L and Buss R boards.
  5. Plug the Power Supply PCB into the cardbay (no extender cables...phew! :D) and fire it up.
  6. Does the heatsink heat up?
  7. If yes, stop and post back and we'll (figuratively speaking) drill down into the mixer section.
  8. If no, proceed to the next step powering down in between each step, connecting the plug or card indicated and then powering back up to see if the heatsink gets hot and if it does, post back indicating at which step the heatsink became hot.
  9. Reconnect P32 to the Mother (2) PCB
  10. Reconnect P15 to the Mother (2) PCB
  11. Reconnect P17 to the Mother (2) PCB
  12. Reconnect P34 to the Mother (2) PCB
  13. Plug in the Reel Servo PCB
  14. Plug in the Balance Amp PCB
  15. Plug in the Bias PCB (1)
  16. Plug in the Bias PCB (2)
  17. Plug in the dbx PCB CH 1~4
  18. Plug in the dbx PCB CH 5~8
  19. Plug in the Rec Play PCB CH 1&3
  20. Plug in the Rec Play PCB CH 2&4
  21. Plug in the Rec Play PCB CH 5&7
  22. Plug in the Rec Play PCB CH 6&8

Everything should be plugged in now and something should have caused the heatsink to heat up.

Good luck, proceed at a comfortable pace and make sure you understand what you are doing before you do it. No question is too dumb or small.
 
Ok

Ok well i disconnected everything. First thing i plugged back in was P32. The heatsink got warm starting on the left as usual, but it didnt get hot, just warm, even though its been on for a long time now. Normally, it would be raging heat if i left it on this long. Im going to continue with the tests until it gets hot like it was (untouchably hot).

BTW, it stayed cool with just p5 unplugged, before anything was pulled out card-wise etc.

Plugged in p15, still just warm.
Plugged in p17, still just warm.
Plugged p34, Reel Servo PCB, Balance Amp PCB, Bias PCB (1), and Bias PCB (2) all one by one, still just warm.

OK, once i put in the DBX 1-4 there was a noticeable increase in heat. Not enough to make it untouchable, but it got hot a lot faster. I unplugged it and turned it on again without it, and the heat sink went back to being just warm as before. I tried plugging DBX 5-8 into its slot, and it was similar to when i put in DBX 1-4 (noticeable increase in heat). I want to try to put in the other cards without the DBX ones in to see if it gets hot, but i got to get some sleep because i have to work in a couple hours. So ill try that along with anything else you can think of tomorrow. Thanks for your help, as always.
 
Last edited:
Did the heatsink get warm with just the power supply card plugged in but all the other cards and P15, 17, 32 and 34 unplugged, or did it stay cool?
 
nope

With just the power supply card plugged in, and p15, 17, 32, and 34 unplugged it doesnt heat up at all. Dead cold.

I wish i knew how much "warm" was normal. I mean, i know that when its getting really hot (untouchable) thats not normal, but i wish i knew if it shouldnt even be getting warm nearly as fast as it is even when it just stays mildly warm. You know what i mean?
 
Hey Cobb...

I turned on my 388 to compare heatsink temp. This is very subjective so I don't know how well you'll be able to compare, but here were the conditions:

* I left it on for 20 minutes
* The room is probably about 55 degrees
* I just came in from working in the unheated shop and its in the low 40's so my fingers were cold
* My amp cards, dbx cards and bias cards are out of the unit, but all those plugs on the Mother (2) PCB are plugged in so the full mixer and all the transport logic are powered.

And the result is (drum roll).....tepid.

With my cold fingers nested into the fins of the heatsink (if that makes sense) it felt warm...not warm-warm but nice to my cold fingers.

I hope that helps. Let me know how you think that compares.
 
"warm"

I think it would be near what you are saying you are feeling from your description and the amount of time you left it on.

So far it "seems" that it stays just mildy warm until either one of the DBX cards was in either slot, thats when it started to seem to get very warm. Not as hot as when the whole thing is all plugged in, but warm enough that it seems notable.

The balance card being inserted didnt seem to effect the temperature at all.

Im going to redo all the tests, and pay even closer attention to what im feeling, but im fairly certain it will be the same results exactly that i gave the first time. I was very careful to do everything perfectly and really observe the result i was getting.

Do you think there is anything to the fact that Ethan said i should be getting + and - 20 volts on the first test and i was getting + and - 27.1?

BTW, i just replicated your heat test (other than the room temp), and yes, under those conditions (card configuration/time) the sink only gets mildly warm.
 
Last edited:
Do you think there is anything to the fact that Ethan said i should be getting + and - 20 volts on the first test and i was getting + and - 27.1?
Click to expand...

Cobb...yeah that's why I was flagging that in red at the top of my post of instructions. I'm going to see if I can hail Ethan.

See, the thing is that the dbx cards run on +/-12V. The regulated +/-15V power coming off the power supply on P5 get regulated down to 12V by some components on the Mother (1) PCB...that's the one that the amp cards, dbx cards, Balance Amp PCB and Meter Amp PCB plug into.

Questions/instructions:

  1. When things heated up with a dbx card installed, did you have the dbx switched ON on the control panel or OFF?
  2. What happens to the heatsink temp if you have everything plugged into the 388 except the two dbx cards?
  3. How do the dbx cards look? Do you see anything that looks like its been hot or otherwise jes' don' look right?
  4. Pull the Balance Amp PCB out and shine your flashlight down into the cardbay at the front right of the Mother (1) PCB (i.e. the corner closest to the faders and the power supply. There are two electrolytic caps C101 and C102, two regulators U101 and U102, and a diode D101 down there. Those are the components that regulate the 15V power down to 12V...How do they look? Does it look like they've been heated up? Suggestion: now might not be a bad time to tip the 388 up on its side and remove the bottom panel and have a look at the Mother (1) PCB from the bottom to see if anything looks funky down there.
  5. Lastly, let's see if our 12V rails are indeed 12V. Take your "P6" extender cable (the 4-pin one) and plug it into P112 on the Mother (1) PCB...that's a 4-pin array right toward the back of the 388 from D101...its where the dbx card gets its 12V power. Now go ahead and turn on the 388 and measure pin 2 to ground, and pin 4 to ground. What do you get?

My advance apologies if, in my amatuerishness I'm sending you on a wild goose-chase and wasting your time...at least you are getting familiar with the guts of your 388... :o:D
 
ok

pin 2 is +12.4 and pin 4 is -12.2

No, the DBX wasnt engaged during the times when it was plugged in.

No signs of heat or burning/leaking anywhere.

Ive been experimenting with plugging and unplugging different cards in different configurations, to see how hot it gets. I allow sufficient cool down time in between so that the heat coming off the sink isnt just accumulative.

I dont know what it means, or if this is of any use, but it seems like it only really starts to warm up when any of the rec play PCBs or either of the DBX PCBs are plugged in. This is with or without any of the bias or reel servo PCBs hooked up.

For example:

No cards of any kind plugged in -> heat sink stays relatively normal feeling (minor warmth)

All bias and reel servo PCBs plugged in -> heat sink stays relatively normal.

Now, with or without the bias and reel servo PCBs plugged in, even 1 of the rec play PCBs will start it to get warmer than youd think it should be. It doesnt matter which one, or whether its a DBX or rec play PCB that you plug in, same result, the heat sink starts to get warmer than it seems it should.

ALSO, im beginning to think that the amount of heat is equal to the amount of rec play PCBs that are plugged in simultaneously. Ive been messing with it in this way since i got home, and for what its worth i believe the more rec play PCBs or DBX PCBs that are plugged at once, the hotter it will get until its untouchable.

Does this seem like useful information? I hope im not the one leading you on an impossible goose chase!!
 
At some point in the coming days I will plug all the cards in my 388, turn it on and see what the heatsink feels like.

Those voltages look fine.

I sent Ethan a PM so he may chime in here at some point.
 
Power dissapation

The heatsink gets hot because the PS is working . It gets too hot because it is working too hard. The record/play PCB and DBX PCB are the ones that are causing the PS to work too hard. More bad cards = more overload = hotter, sooner.

This is good news in a way. You have isolated it down to 2 card types.

Pick one card (the record/play PCB for example) and work on one of them till you figure out what is its problem. I suggest that you put in a card that allows you access to the components. Power it up with that one "bad" card in and turn it on. Let the heatsink get hot. Then power it off (and pull the plug) and feel around on the record/play PCB looking for a hot component or fed. This localizes the fault even more.

I'm just wondering it these cards have onboard regulation of if they have lossy local filter caps.

The power has to go somewhere. You might want to take one of the boards and cut the + and - 12 volt traces to "depower" the board and then test it again to see if the PS overheats.

Regards, Ethan
 
Cobb,

I just had my 388 powered up with everything plugged in except the dbx cards...left it on for about 20 minutes and at that point the heatsink was warm...warmer than before but definitely not hot...like cozy for my fingers...warmest at the bottom of the heatsink toward the left. Totally unalarming in temperature. So how does yours compare?

Ethan, the 12V power only goes to the dbx boards.

I have no idea what a lossy local filter cap is :o, but the amp cards do not appear to have local regulation. The 15V rails power the audio IC's and the +15V rail goes into the...some other area of the board and of course the 24V rail powers the switching relays.

Cobb, tell us what happens when you have everything in except the dbx cards to compare to my account above. Then try Ethan's suggestion if things heated up...put an amp card in, maybe for tracks 1&3 since you'll be able to get to the component side with it still in the machine and feel around for heat (after powering down and unplugging of course).

Ethan...any concern over the unregulated source of the +/-15V rails running around 27V?
 
ok

Alright i powered it with just 1 rec play card in, and felt around for a hot component, they all felt cool.

Right now i put all the rec play cards in and im letting it stay on for a bit to see how much hotter the sink gets. I should reiterate, it doesnt get HOT unless many cards are in.

Also, I replaced the fuses awhile ago. So far fuse F3 (the one that blew before) is getting yellowed and looking slightly distressed. Fuse 2 and 4 look brand new, and fuse 5 looks new except the glass is getting milky colored. I dont know if any of that is worth mentioning but its there.

Ill keep testing the boards etc and post back when i find anything.

OK... with all the rec play boards in and none of the dbx ones its getting super hot again, even within just 5-10 minutes.
 
You must log in or register to reply here.
Back
Top