newbie tascam 388 questions

I can't tell which one is D141 in your picture. Is the label covered up by the component? It's like a search and find lol.

Here's the diagram.

You'll have to remove the diode from the board or at least one of the tails.

image.jpeg
 
oh sorry of course. its the component in the middle of the picture that is more spherical than the surrounding components.
 
ive tested it on the V- setting as this is what the manual suggested to test voltage. I wasn't sure what value to set it to but i ended up going with 2? So when i touched the battery terminals it gave a reading of 1. or -1. depending on which probe went to which terminal. Is this correct?

So put the diode in the path, if I was measuring the diode with the black band touch the negative terminal of the battery then I could get a reading of 1. if i flipped the probes I would get -1.

Not sure if this is right but seemed consistent to me at least.

When I measured the diode with the non-black band side touching (google leads me to believe this is the positive side of diode?) the battery then it reads .018

I hope this helps, i know my explanation is a bit convoluted but just wanted to make sure I'm getting numbers that actually mean something.
 
Oh geez that's a zener diode...

Try this:

Set your meter to ohms, connect the probes to the tails of the diode, mark down the reading on the meter, flip the component and document the reading. Report back.
 
at the 20M setting i get: normally connected: 13.80 (it took a long time to get there and then it dropped all the way to zero. Did this twice. Flipped: 10.20 (much more stable)

at the 200M setting I get: normally connected: 162.7 (also took a long time to reach this figure and the dropped) Flipped: 01.1 (stable)

why are zener diodes such trouble?
 
There not any more trouble. I just didn't realize it was that type of diode and that because of that I wanted you to do a different test.

Does your meter have a "20" setting for continuity as opposed to "20M"?
 
it has a 20k setting also for continuity, but it seems to read nothing bar the number 1 when i use it. it has a 200 (with no letter) setting for continuity however it also give no reading other than 1.
 
It should be set to the 200 setting. What does the meter say when set to "200" with the probes touching nothing?

And just to confirm, you're doing this test with the diode removed from the board right?

1. Set the meter to the "200" setting (that sets the range of the multimeter to read up to 200ohms...ohms is a measure of electrical resistance...the higher the number displayed means the more resistance there is in the electrical path being measured)
2. Touch your probe tips together. What does the meter say? It should be a very low number, like 0.3 or something. That means very low resistance which you would expect if you are not measuring a part or a pathway, but just probe to probe.
3. Now let's measure the diode again. See how the diode has a black or silver band that is closer to one end of the part than the other? Put the + probe at that end and the - at the other. What does the meter say?
4. Now swap the probes (the - probe now at the end of the diode with the band, the + at the other end)...what does the meter say?

Diodes are like a one-way gate...they let current flow in one direction but not the other. So when you measure for resistance it should be very low in one direction, but very high in the other. With the meter set to "200", anything over 200ohms should display as open-circuit, no continuity, no connection...infinite resistance. The diode should read something less than 1ohm in one direction, but should appear as no continuity in the other direction with meter set to the "200" range.
 
yes it is out of the board and I've done as you outlined. When the probe tips are together is it does read .3 but when I'm testing the diode, it reads |1 . | on the screen with the decimal quite far to the right . . . if that makes sense lol when the probe tips aren't touching anything it also reads 1. like when I'm testing the diode
 
So you didn't answer all the questions...there are two ways you are measuring the diode. What does it read in each way? You just said "it reads |1 . |"

Do you mean the meter displays "1" regardless of which of the two ways your probes are connected to the diode?
 
yes sorry it reads the same each way on the diode, and it also reads the same 1. when the probe tips aren't touching anything at all
 
So, based on what you are telling me, the diode is bad.

There may be, and likely are, other bad components on the REEL SERVO PCB and other boards...and there may be damage to one or more of the power supply rails.

If this was going to be done right, you would isolate and test the power supply and once that's all healthy bring in other systems one at a time, tracing out faults systematically.

The quick and dirty is to replace the diode D141 and try it out.

My opinion is you should replace the diode and at *least* check the power supply out.
 
I'm getting some conflicting results in my parts search...the part identifier for the original diode is 1R5DZ61. That is an obsolete part. Some results say its a rectifier, others say a zener. The schematic shows a rectifier. The picture of the actual part you posted I'm not sure what it is.
 
Diodes are not rated in ohms...they are rated in watts. Resistors are rates in ohms. Contact your supplier and tell them you need to replace a 1R5DZ61 diode and see if they have an equivalent. I think it is a 1W 5% tolerance rectifier diode, but I'm not certain.
 
My research leads me to this, some datasheets recommend the uf4007 as a replacement but the BYV96E seem to me to be exactly what im after? The 1n5408 seem to actually be a better replacement than the uf4007 really. . . I'm going to go contact the shop but past experience has told me that they often don't really know what to recommend.

BYV96E | Vishay BYV96E, Switching Diode, 1000V 1.5A, 300ns, 2-Pin DO-204AP | Vishay

1N5408 3A 1000V Diode | Jaycar Electronics

UF4007 1A 1000V Diode | Jaycar Electronics
 
the guy at the electronics shop said to go higher so I went with 3A, unfortunately the part doesn't actually fit through the holes of the pcb. So get the same reading of 1. when measuring the new diode with the multimeter still. How would I measure the original part if it is basically a standard rectifier diode? I shouldn't be using the ohms setting then right?

https://webshop.cashconverters.com....-digitech-qm-1320-fequency-digital-multimeter

Sorry, but the is the best picture of the settings my multimeter that i can find online. if you click the pics they get just large enough to get an idea. Maybe this will help?
 
3A is complete overkill. Even 1A is overkill. The original part is rated at 1watt. It's a 24V circuit. 1watt at 24V equals about 0.04A nominal load. So the sold you a part capable of handling about 75x the current of the circuit in question. More is not always better.

Are you concerned the new part is faulty? Is that why you're testing it?
 
yeah see I never have that much confidence when asking for advice at jaycar and this is why.

and no sorry it's just that i'm not sure i'm measuring the original diode accurately if it's not actually a zener diode as suspected, maybe it's still okay?
 
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