Mitsubishi DA-R25 receiver with no output

[manuel weiss]

I'm the only owner since 1981. Used all the time through perhaps 1996 or so. Remained plugged in, but off , and not used much at all in last 20 yrs. Last time I listened to it, must've been 2-3 years ago. I Noted about a year ago that there was no sound output, although tuner comes on with power-up, and appears to be latching onto local FM and AM stations .

I have had some lightning storms over the years, but never checked this unit specifically after one of them.It wasn't on a surge control, but was never in use during a storm.


I began troubleshooting recently:
Internal inline fuse is good, with continuity
AC power is present at transformer terminals. VOM reads 106 volts.
No hum from unit, and zero heat generation by transformer or at IC power amp heat sink ( two SKI1066ii units in line).

No burn or visually suspect spots on any of the PCB boards. It all looks pristine.
I have a service manl, wiring and schematics for the unit.

Can I troubleshoot the power Amp IC units ( SKI1066ii without sophisticated equipment , and only a VOM and LCR meter, and without desoldering and removing them? I'd like to have some idea that they are both bad before potentially doing more damage to the unit.

 

[duncan]

Let me ask the dumb questions up front: you mention the tuner, but have you tried phono or aux sources? Also is there any output at the headphone jack? Finally, any chance this is one of those amps where the speaker switching is implemented in series, so you won't get sound out of set A if both A and B are selected and there's nothing hooked to B?

 

[manuel weiss]

thanks for reply; the tuner doesnt produce sound, it just is obviously searching appropriately for, and latching to local stations w a strong signal, by visualizing the LEDs on the front, which demo the information. The unit is not producing any sound. No hiss, etc. The alternative input sources of course are inoperative. This is an output issue, i believe.
I neglected to mention there is no output thru headphone jack( I tried this first thing) and the A and B switch for speaker output will work with a, b, or a and b simultaneously,(when correctly working). There is no output when the A and B spkr switches are moved thru all the permutations. Its not the switch.

 

[SVI2004A]

On STK, What voltages are at pins 2 And 5 (output) and pins 10 and 12 (input)

Should be
0v at pin 2
0v at pin 5

And I’d expect to see approx
1.8v at pin 12
-1.8v pin 10

 

[manuel weiss]

Thanks so much.
The Left SKI has 46 or -46 V on every pin. When I shut power off, there is residual +/-26 V on these pins

Right one has voltages as you suggested. 0.01 V on pin2, pin5

Schematic shows +44V on pin #1, -44V on pin 6 on these ICs. Its IC #502, #602 on the schematic, I believe.
It appeared to my inexperienced eye that 1, 6 were input, 2 and 4 the outputs
I attached the schematic

I would think right channel would work, left not, based on this data. What am I missing? I assume L SKI unit is bad.

I really appreciate your comments- thanks- mrw

 

[SVI2004A]

Ok looks like they’re using internal Emitter resistors- so pins 3&4 are your outputs

Ignore the symbology on the IC - pins 10 and 12 are inputs.

Here is STK1060II schematic

 

[SVI2004A]

It could be drive circuit

Pins 3&4 you say has 46V... is that +46 or -46v

Pin 12 - is that at 46V if so + or - and pin 10 voltage is?


———

If +46V was at pin 12, I’d expect +46V at pins 2,3,4,5
And would expect to see 42v or so at pin 10

This would mean fault if in driver stage.

——-

If +46V at pins 3&4 and -46V at pin 10 and similar at pin 12 there would be issue with power amp.

 

[leesonic]

Could be the output packs and/or the driver chip. The following thread might be useful for the voltage measurements :

http://audiokarma.org/forums/index.php?threads/mitsubishi-da-r25-receiver-restoration.776307/

Lee.

 

[manuel weiss]

ok, thank you; svc manual schematic for the 1060 is attached, transistor 4 and 5 are swapped but I assume this is just their numerology at the time. I didnt see any other difference.
LEFT: I have a pos or neg 46 volts at every pin on the left SKI.(neg 46 on 2-6, 8 and 10, pos 46 on 7, 11, 12, and 0 on 9. I couldn't get #1 without shorting it w alligator clip, the case is in the way, --as it was I briefly shorted pins w alligator clip on 1 and 2 with power off, there is residual 20 volts or soon on all these pins when power is off. Hope that didnt fry it, although it looks like seein voltage on all the mins is not good (?)

Voltages on right unit are:
Right: 1= +45V
2 0
3 0
4 0
5 0
6 -45
7 0.6
8 -0.6
9 0
10 -1.8
11 -0.6
12 +1.8

So. What does all this mean? Are they both bad? if right is ok, still no sound out of r channel either.....
Thanks!

 

[manuel weiss]

sorry:Lee: I saw the link you referenced before,last week, it just was a bit over my head; is driver chip(= voltage amp?), and is power supply reference to the large transformer only? or are you referring to a whole pc board as a power supply , because you replaced some electrolytic capacitors in the power supply, apparently, as well. how did you spot those?

thanks

 

[Drugolf]

Just had to replace one of the STK3076 in mine, but it wasn't completely shutting down output.
There is nothing plugged into the pre-out or main-in RCA jacks on the rear is there?

 

[manuel weiss]

thanks-
I have all the inputs unplugged. I have the covers off the unit and have been merely visually inspecting it, and checking the voltage at pins of SKI ICs, there are two of them. I noted them above. Similar finding on at least one of them to the data Lee posted June 2017, linked above.

 

[SVI2004A]

Replace the Lch STK 1060

 

[manuel weiss]

thanks synchro bias; replacing left ski Iunderstand, right channel is out also, so I assume there is another component at fault.

 

[leesonic]

Try pulling both the output modules and measuring the voltages on the pads, referenced to the power supply ground. If you have voltages similar to mine, then your driver chip is bad also.

I wouldn't bother replacing just one or two, change both the outputs and the driver chip. Send a PM to @Tom B and see if he has the outputs, and get the driver from Littlediode over in England.

@srs735 is the owner of the DA-R25 featured in my thread, he says it's working fine now.

Lee.

 

[manuel weiss]

thanks so very much lee;
this is what I reckoned also. I'll do all that. I am assuming the diode and capacitor you pulled from circuitry around the left IC op amp checked out ok, but led you to deduce that the drive was bad. Did you replace the electrolytic caps because they were specifically bad, or because it was a thorough, appropriate thing to do while you were there?

 

[srs735]

@srs735 is the owner of the DA-R25 featured in my thread, he says it's working fine now.

Lee.

I'm happy to say that mine sounds incredible and hasn't skipped a beat since Lee worked on it for me

Hopefully this will take care of yours

Stuart

 

[Drugolf]

It's a heck of a receiver. Some manufacturers were producing some good stuff those years before all the plastic and production cost cuts snuk in.

 

[leesonic]

Did you replace the electrolytic caps because they were specifically bad, or because it was a thorough, appropriate thing to do while you were there?

I did a full restoration on this for Stuart, so I replaced everything that could go bad, which electrolytics frequently do.

Lee.

 

[chazix]

thanks synchro bias; replacing left ski Iunderstand, right channel is out also, so I assume there is another component at fault.

Wot, it's not until the 20th entry in the thread that someone points out:

This receiver has a protection circuit that will disable both channels if there is substantial DC voltage at either of the power amplifiers' outputs. This applies to all speaker and headphone outputs. (There's actually a separate relay for the headphones, something I can't recall seeing elsewhere.)

HTH,

chazix