Help: Sansui 881 tuner section not working after 5 minutes

mycity33

New Member
881 works OK for perhaps 5 minutes. It seems that both AM/FM on tuner section is affected. AUX and phono inputs work fine and drives speakers. Below are voltages listed on 1507 board (Tuner board)

When powered up.....After 5 min when AM/FM dies
Point 14 = 1.1..........0.5 v.
Point 15 = 0.1..........1.9 v
Point 16 = 0.1..........0.8 v
Point 17 =12.7.........2.5 v
Point 18 =12,6.........2.5 v

Diode D02 was shorted blowing fuse F03. Replaced D02, same problem.
Sansui service manual states that I should have 12,6 volt on points 15, 16, 17. Somehow it was working fine without 12 volt for 5 minutes. If someone have experienced same scenario let me know which components you replaced, tks
 
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Just a thought here /// B2 which is the 13.5 volt feed from the PS
(F-2437) is probably your issue..
Off DO-01 & 02 YOU HAVE ABOUT 44 VOLTS DC
THis goes through R-01 ( 150 ohm 5 watt ??)
and hits collector of TR-03.. the EMITTER SHOULD HAVE ~ 13.6 volts as well as the base….. Based on ZD-01 and TR-02 & 02 for regulation…

So if I were a betting man.. I would FIRST LOOK at cold solder, fractured solder connections @ R-01… Next I would look at TR-03's (2SD313 ) connections….

I would unscrew it ( and I'll bet it's LOOSE ) put some heatsink goo on the back , tighten it back up, reflow all the connections… THEN using a GOOD DC volt meter…

Hang it on pin 13 of the PS board.. and watch to see if the 13.5 volts FADES AWAY or just GOES AWAY…

If it just GOES away verify that you still have 44 ( ish ) volts on both sides of R-01

This should be a good starting point~!

Mike
 
Oh and pin 14 has 34 volts on it … IF the 13.5 Goes away.. see if you still have this voltage as well
 
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Thanks for detailed troubleshooting instructions vigman.
At times when cold tuner section does not get 13,5 volt. Other times emitter drops voltage after few minutes on TR03. Voltages are then E=2,3 C=43,2 B=13,4
Resoldered TR03, no change. Could not get screw out of heatsink, its stuck. Would you suspect that TR03 stops working ?? Should I replace TR03 or ??

Could not find Pin 14 on power board

ZD01=13,4 and 0.0
TR02= E=13,4 B=36.1 C=14.0

Hang it on pin 13 of the PS board.. and watch to see if the 13.5 volts FADES AWAY or just GOES AWAY…>>>>>> Exactly as you wrote, voltage dropping to 2,8
If it just GOES away verify that you still have 44 ( ish ) volts on both sides of R-01….>>>>>> I have 42,1 and 29, 1 volt

Here are other transistor numbers, TR04 & TR05 seem low:
TR02 E=13,4 B=36 C=14.0
TR04 E=0,3 B=2,6 C=1.0
TR05 E=0.3 B=0,9 C= 0,0
 
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Ok seems like the FEED is failing

Hang your meter on
Off DO-01 & 02 YOU HAVE ABOUT 44 VOLTS DC

Tell me if this 44 V is still there when you loose the 13 .5 volts.
 
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Off DO-01 & 02 YOU HAVE ABOUT 44 VOLTS DC >>> D02=43,6 V D01=25,4 V

Voltages on DO-01 & 02 do not change after tuner section dies.
D02 vas replaced earlier due to shorted diode. Fuse F03 was blowing. Could there be a connection?
 
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I made an OOPS DO 2 & 3 are the 44 volts
So you say the voltage is the same on the Diode side of DO 2 & 3
IS R105 getting HOT?
Tell me what the voltage is on the collector of TR-03
( working & not working )
 
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So you say the voltage is the same on the Diode side of DO 2 & 3 >>> Yes, cathode side of D02=43,6 Cathode of D03=43,4 Anode of D02 and D03 is 0,1 volt


IS R105 getting HOT? >>> I do not see R105. If you mean the R01 (150 OHM 5W) that one is hot to the touch after 1/2 minute and burns my finger after 10 minutes. I still have 45 and 43 volt on R01 after tuner dies.

Tell me what the voltage is on the collector of TR-03 >>> 22,3 V
 
TO be clear… the voltage on the collector 22.3 working or not ?

Now tell me the voltage on the BASE of 03 working / not
 
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TO be clear… the voltage on the collector 22.3 working or not ? >>>When tuner working TR03 collector is 22.3 When tuner dies it jumps to 43,1

Now tell me the voltage on the BASE of 03 working / not >>> Tuner working TR03 base is 13.4 When tuner dies its 13.4

Today i did push firmly on R01 and TR03 after tuner died. It started working again and did work for 6 hours. I suspected broken solder on power board and continued pushing gently on both sides to flex board slightly but tuner continued working.

44v feed to R01 gets reduced to 22v on other side of resistor and goes to collector of TR03. Tuner works fine at that time. Then tuner dies and I have 43v (between R01 and TR03 collector). Is it possible to have resistor that instead of open is shorted? Where would the 43v appear from? What do you make of it??

Before today I did clean leads of R01 and resoldered. Not sure what changed by pushing on R01 and TR03.
 
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Can you take a pix of the solder side of the board @ R-01 & TO-3
Something is OPENING UP under load & heat
 
reply and pictures

Pictures attached TR03 on left and R01 right (wide lead spacing)
I resoldered twice both TR03 and R01
 

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There are a bunch of really marginal solder connections around that area...
I would touch up MORE on that board...Is it still working?
 
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It' s working since this morning, about 2 hours. I will resolder again and keep you posted how it performs long term, thanks a lot Vigman
 
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