• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Help With Nakamichi Sr-2A

C

casiokorg

New Member
Hi all!

I was given a very good condition SR-2A, which when I hook up (properly) there is no sound! have tried all the usual tests to only receive silence. I checked the fuses, they look okay, yet are soldered into place so it was hard to see them 100%, but i didn't notice anything out of the ordinary. anything else you can think of trying? I really love the unit and would love to have sound! Thank you in advance!
 
Register to hide this ad
My first guess is bad solders on the to220 transistors in the +/-18V regulation.

Easy to find, one green and one black with small heat spreaders attached, located just a little bit south of the phonostage.
 
Mannegizen said:
My first guess is bad solders on the to220 transistors in the +/-18V regulation.

Easy to find, one green and one black with small heat spreaders attached, located just a little bit south of the phonostage.
Click to expand...
i think your exactly right, or its at least some of the problem! where the solder should be it appears to be all burnt with both of them. is this an easy fix?
 
casiokorg said:
i think your exactly right, or its at least some of the problem! where the solder should be it appears to be all burnt with both of them. is this an easy fix?
Click to expand...

Could be done within 30 minutes.

Don't just reflow the joints, the result might look good but there can be a layer of oxide that stops it from working. (been there, done that ;-))

Use a solder sucker and solder wick to remove the old solder.
 
Stop! I have worked on both the SR and TA series of these units. People replace all kinds of parts that aren't necessary. First you have to see if the unit is staying in protection mode . The led over power switch flashes red and then turns to a solid green. This flashing tells you something is wrong and will not allow the protection relay to close. Yes the TA series is known to have solder problems, but if you do not know what you are doing you will probably damage the circuit boards. If it is not coming out of protection there are two 22k 1/2 watt resistors that cook themselves if driven hard. They should be replaced by 1 watt 22k. If you need more info, just let me know. That is a nice little amp 40 wpc but sounds better than most 60 wpc. If you do get it going be sure to turn the loudness control full clockwise. If you turn it full CCW it sounds like a $50 table radio. What part of the world are you in? What speakers do you have?
 
Last edited:
Freddymac2 said:
Stop! I have worked on both the SR and TA series of these units. People replace all kinds of parts that aren't necessary. First you have to see if the unit is staying in protection mode . The led over power switch flashes red and then turns to a solid green. This flashing tells you something is wrong and will not allow the protection relay to close. Yes the TA series is known to have solder problems, but if you do not know what you are doing you will probably damage the circuit boards. If it is not coming out of protection there are two 22k 1/2 watt resistors that cook themselves if driven hard. They should be replaced by 1 watt 22k. If you need more info, just let me know. That is a nice little amp 40 wpc but sounds better than most 60 wpc. If you do get it going be sure to turn the loudness control full clockwise. If you turn it full CCW it sounds like a $50 table radio. What part of the world are you in? What speakers do you have?
Click to expand...

thanks for the tips! Def. not in protection mode - no red flashing, just green. I did notice it was very "burnt" looking around the to220 transistors. they also seem a little loose. Other than that it's very clean inside (although a little dusty). Can that make no sound come out all by itself? I have done solder work on synthesizers before, and i'd say I'm more than capable to replace the transistors if that is needed. I am located in Portland, OR. My speakers are a pair of bookshelf Sonys, that sounds VERY good with my current setup (Carver gear). Let me know if there is anything I should do to try to get this nice unit up and running again!
 
Loose transistors do not sound good. I have picked up 5 of these Naks and have been able to get them going. I do not know what Carver you have, but The $75 Nak SR 4a replaced a modified PAS 3 Dynaco, and a 200 wpc Ampzilla. The difference was so great I spent the next year rebuilding the rest of my system. Get the manual off of Hifiengine. You need to check the bias and offset voltage and get back to me. Be very careful you can blow things!!!!
 
Freddymac2 said:
Loose transistors do not sound good. I have picked up 5 of these Naks and have been able to get them going. I do not know what Carver you have, but The $75 Nak SR 4a replaced a modified PAS 3 Dynaco, and a 200 wpc Ampzilla. The difference was so great I spent the next year rebuilding the rest of my system. Get the manual off of Hifiengine. You need to check the bias and offset voltage and get back to me. Be very careful you can blow things!!!!
Click to expand...

Very good info! I guess I will start with replacing those transistors then? My sound system currently is:
Carver m-4.0t amp
Carver c-6 preamp
Sony ss-mj1 bookshelf speakers

Any tips on how to check bias and offset voltage would be great!
 
I'm going to guess the aforementioned manual may have that info.

Offset voltage is simply the DC voltage between + and - speaker terminals. See the sticky thread "DC Offset and You"
 
I just remembered the wire output clips can fail on the 2 and 3. If you have binding posts ignore what I just said. If you have head phones you can jack in, if you have right and left sound the amp is working. Either the clips or relay solder points at the board. What are you using for an input signal, CD is what I use for testing the tuner may not work without an antenna. The output relay is on the main mother board. If you gently tap lightly on the top of it a bad solder joint will make noise or fix itself temporarily. When they wave soldered these the thicker pins did not get enough heat, so you can have bad connections. Any work you do on the boards be carefull, you need a temp controlled iron. It is recomended that the old solder should be removed, with a solder wick and cleaned, re-fluxed and use GOOD 60/40 LEAD solder, I know how all you greenies are out in Washington State, but the lead free stuff doesn't work well! I do not like loose transistors because they cook with poor heat sink heat transfer. By the book they should be cleaned and new thermal compound, but be sure the insulator is not damaged, check for shorts to the transistor case or tab to heat sink. You may be very surprised how good this unit is.
 
It is in the manual but the connections are very close together in a white plug, if you short them POOF! . Yes between + and - speaker output connection but it will not work if the relay isn't working. The fact that you are not in protechtion, you are OK but try to check it. the bias should be about 20mv each modle is differnt. Is the heat sink hand warm in the front and the back, that says it is biased ok. Hot is not good POOF!! Clod means things aren't working at all. sorry about typing but just trying to get this to you
 
Freddymac2 said:
I just remembered the wire output clips can fail on the 2 and 3. If you have binding posts ignore what I just said. If you have head phones you can jack in, if you have right and left sound the amp is working. Either the clips or relay solder points at the board. What are you using for an input signal, CD is what I use for testing the tuner may not work without an antenna. The output relay is on the main mother board. If you gently tap lightly on the top of it a bad solder joint will make noise or fix itself temporarily. When they wave soldered these the thicker pins did not get enough heat, so you can have bad connections. Any work you do on the boards be carefull, you need a temp controlled iron. It is recomended that the old solder should be removed, with a solder wick and cleaned, re-fluxed and use GOOD 60/40 LEAD solder, I know how all you greenies are out in Washington State, but the lead free stuff doesn't work well! I do not like loose transistors because they cook with poor heat sink heat transfer. By the book they should be cleaned and new thermal compound, but be sure the insulator is not damaged, check for shorts to the transistor case or tab to heat sink. You may be very surprised how good this unit is.
Click to expand...
Thanks for this!

I have attempted all the input sources, but mainly focused on AUX in with an iPod. I tried with headphones and with speakers, no sound. I also just tried to tap what I thought was the output relay, but didn't get anything.

UPDATE. I just checked the fuses again in the daylight, and have noticed one that seems to be blown. its the one furthest south on the power side of the internals, and under it is marked "F401". maybe this has something to do with it???
 
I just looked up the Carver... Those poor speakers 375 watts ouch! I pulled one audiocom review, and the guy said that it was the most gutless 375 watts he has ever heard. I am not picking on you, just a review, many don't know what they hear anyway. On the other side I had never heard more guts from a small amp than the SR 4a in my whole life. I am 72 years old and have used the better amps of the day. My Dahlquist DQ10's are from the 1970's (you may have to google them, because you have never heard of them)
 
DO not put a new fuse!!!! make a dim bulb tester and put a 60 watt bulb in it, so you will not blow your outputs. do you have a meter. I am afraid about the loose transistors!! I did not look which fuse that is but I doubt it is blown!! F404 is a 4.5 volt supply for something not important. You do not have to replace any transistors, don't just swap parts test everything systematically shotguns don't work here, not all transistors are the same or available. If you do remove the trans don't put too much heat on them. Do the trans you are saying are loose bolt to the main heat sink?
 
Last edited:
On the SR-2/3 models there is no power indicator that can flash.
If the speaker relay dosent kick in within 5 seconds there might be a DC offset fault or other problem.

The SR2/3/4 models do not, to my knowledge, get the burnt 22k resistor in the differential stage, only TA-2/3. (my guess is that they used carbon resistors there instead of metal film.)

Bad solders on the +/-18V regulation trannies can blow the rail fuses on SR-2 (probably on the SR-3 too, since they are almost identical.)
But as there is just one fuse gone I guess it's the one that is by the 30V circuit for the tuner. (If AM/FM and Mhz dosn't shows on the display, it's a good bet.)

Service manuals can be found on HIFI Engine.
 
SImple but oft overlooked question.....

Does this unit have Pre-out/Amp-in jumpers? And are they present?
 
dogwan said:
SImple but oft overlooked question.....

Does this unit have Pre-out/Amp-in jumpers? And are they present?
Click to expand...

No pre out/in jumpers on the SR models.

SR-4 has jumpers on the back, but that is for a signal processor or such.
Could easily be mistaken for pre out/in jumpers but are before volume/tone control.
 
I'm getting a little lost here in what sort of tests I should be doing. Is this unit worth my time since I have a setup I'm happy with:
Carver m-4.0t amp
Carver c-6 preamp
I would love to have it working for a separate setup elsewhere In my home thought!
 
You must log in or register to reply here.
Back
Top Bottom