Tascam 388 insanely hot resistor help

  • Thread starter Thread starter jon83
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The stock lamps are likely 55mA. You said the ones you bought were 100mA right? Just add up the total mA of all the lamps stock and aftermarket.

Regarding the transistors, the 7805 is easy...that's a +5V linear power regulator. Just do a search for 7805 regulator at your fav electronics supply house. Very common part...readily available. The one you said is labeled "7820" are you sure that's not 7824? Either way, same deal as with the 7805. Readily available, but would be a +20V regulator for the 7820, and +24V for the 7824.

The 2SD313 and 2SB507 parts are complimentary NPN and PNP 60V 3A power transistors:

http://pdf1.alldatasheet.com/datasheet-pdf/view/107687/SANYO/2SD313/+007799VPvMZPcBVpvNC+/datasheet.pdf

I'll have to search for equivalents.
 
This might be of interest to you....Might not. :)
I replaced all the bulbs in an old Kawai organ with LEDs not long ago but had to drop the voltage just as described.
 
I put LEDs on the Otari - got them off ebay pre-supplied with resistors - 470 ohm, I think. The biggest issue is that they're running on a 6VAC bus. LEDs these days seem to be reasonably happy to accept AC without damage, but it does mean they flicker at 25Hz. This is only really noticeable if you're standing right in front of the machine, or filming it with a video camera.
 
Okay.

If the M5230 IC that you are talking about is on the power supply card, then I wouldn't be surprised if the 2SD313 and 2SB507 transistors you are talking about that are heat damaged are Q2 and Q1 respectively on the heatsink...the ones that plug in to the Mother (2) PCB on the red 6-pin connector J8. Those three components are all involved in regulating the +/-15V power supply rails for the audio electronics throughout the 388. I have no idea why those are damaged, but if I'm right about which ones are damaged on the heatsink (you didn't say), they are all related, and that's a concern. You can get the SIP-8 packaged Motorola M5230 NOS on eBay. You can also use an NTE 7090. The 2SD313 and 2SB507 parts can be found NOS...do a google search. You could also try the ON Semiconductor TIP31AG and TIP32AG complimentary power transistors:

http://www.mouser.com/ds/2/308/TIP31A-D-116282.pdf

They have the same pinout as the 2SD313 and 2SB507 parts...60V 3A. You want to make sure whatever you get you get it in a TO-220 package.

The +24V regulator U2 on the heatsink is indeed supposed to be +24V. Somebody put the wrong part in there at some point...the 7820 part. It is supposed to be a 7824. Your entire transport is running on 20V instead of 24V. Why somebody did that I don't know. You might put the right regulator back in there and you might learn some other problem that explains why the 7820 was kludged in there. But it is possible the input voltage to that wrong 7820 part (the input voltage designed for a 7824) is on the high side and has stressed the part and it's failing. Again, that doesn't explain why somebody put the wrong part in there. If you get a new 7824 part, be mindful of the pin assignment. NOT ALL TRANSISTORS ARE CREATED EQUAL. There is an input, an output, and a ground. Look at the schematic to verify the pinout so when you put the new part in it is right. Do it wrong and you will fry the part and possibly other stuff too.

Please proceed carefully, methodically and slowly, step by step. Electricity kills. I'm not responsible for whatever may happen to you or your 388. I hope you are successful, but it is becoming increasingly clear your 388 has got some jank in it. I'm sorry that's the case, man. Ask questions. Keep us posted.

[EDIT]

I would for sure also replace caps C1, C2, C3, and C4 on the little transistor board on the heatsink.
 
Did you end up getting NOS parts or the NTE 7090 and ON Semiconductor power transistors?
 
Can you clarify what you mean by "transport board"?
 
388

jon83 said:
hi all,

sweetbeatz has been helping me the last few weeks with getting my 388 back in order, but he's advised me to start a new thread with a new problem that it's developed.

I've had problems with the motor engaging. Reflowed all the joints around power, servo and mother boards, which sorted the motor no starting problem, but i've now noticed a resistor on the motherboard that is getting insanely hot. I smelt burning before i reflowed the solder but figured it was to do with the motor issue, but it's this resistor. I've put a picture of the one in question below, it's on the right side of the mother board, right next to the transformer.

It's also developed a problem of rewind and fast forward being real slow. The motor problem i had was intermittent, so when it was working the ff and rr worked fine, it's only since i've put it back down flat that theres been an issue. I've tried adjusting the servos but no joy. It's like they start normally when i press rewind, but the rollers lift up like they do when you use return to zero, to slow the tape before it stops. It still plays, records etc fine.

Any help would be massively appreciated! Sure it's something stupid i've done when i was fixing it, but your own stupid's hard to spot.


View attachment 98868
Click to expand...

not a resistor.. Capcitor
 
You need to make up some extender cables so you can isolate the power supply and test all the output voltages, both for proper amplitude, but also to ensure there is no AC in the DC rails or DC in the AC rails. This is always step 1 with a problem is to check the power supply, and it needs to be isolated from the system to test it alone because obviously something is drawing too much current. Either the supply is bad or something downstream but you don't know anything until you check the headwaters and test that supply. You have a complicated set of issues with your 388...multiple things going and, at this point, throwing parts at it is not going to resolve things IMO. If you don't know how or don't have the resources to make up a set of cables, it may be time to take it to a repair shop. I used to have a set of cables I made, but I loaned them out and never got them back.
 
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