• 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

Yamaha A-1 JDM ( Silver face ) restoration .

Nashou66 said:
Decided to check the fusible resitors( 47ohm 70ma ) and one on the left channel measure in the kohms. So There is one issue.
Click to expand...
Was this FR403 in the phono stage? Can't see that causing measured voltages if AUX selected.
Or FR503? or...
 
mbz said:
Was this FR403 in the phono stage? Can't see that causing measured voltages if AUX selected.
Or FR503? or...
Click to expand...

It was FR402 I think , on the pre board . Now that you mention it I may not have had the amp set to AUX when I went to adjust the voltage at VR 401 and 402. Would that do any damage? I did not see anywhere where it says to set amp to Aux.

Athanasios
 
Last edited:
VR401,2 are for the EQ amp so yeah, happy to do it with phono selected, probably does not make a difference as the function selector just switches audio signal. My question was more about the FR being in the phono stage and it possibly contributing to the dc offset at the LI pin(drive). If this was the case then switching to AUX might affect the offset and possible confirm the FR was the source of the problem or...
 
Ok the 4 fusible resistor's on the Drive board all measure 47 ohm.

I decided to remove the front panel to access the Pre board. to get to it you need to remove the front face plate,
Remove the volume/head amp board and its connected daughter board that holds the Disc switch.
then remove the two screws on the side that holds the front chassis section and loosen the two screws in the sloted
holes.. Also on the Pre board are two screws that hold that to the main chassis. Remove those. now you can slide
out the front chassis and tilt it to access the bottom of the pre board.
Here I removed FR402(19 ohms) and FR 404 ( OL ).

Should I replace them and fire her up? They are 47 ohm 1/4 watt Metal film

51844108337_876098c569_b.jpg


Nashou
 
mbz said:
I'd power up with DBT to check for shorts, don't look at DBT voltages. Power up normal if DBT ok then check voltages...
Click to expand...


I don't have a DBT , I just fly by the seat of my pants!! :D

Yeah I know I should build one.

Well any how I installed 2 new resistors and I can adjust that channel , which is the right at TP2. It started at 18 vdc and I go it down to under 200mv but it danced around a lot.

The left channel still shows 32.xx VDC and adjusting VR 401 . Both fusible resistors measure ok.

Athanasios
 
mbz said:
Little too close to the +35V rails possibly pointing to TR415 or TR409 or TR411 c-e short or...
Click to expand...

Removed and tested TR409,411,413,415,and 417 . All measure ok .

the vd1212 diode is ok as is the Zener 6 volt diode . 6.35 vdc on the one side with 32 on the other.

Athanasios
 
R443, 330ohms, open?
EDIT:Scratch R433(typo) should only see low voltage.
C411 33P polystyrene would be a long shot.
 
Last edited:
One approach would be to track down the source/path of the high voltage, ie, starting at the TP (+32.xV) test at TR415base, expect +33.xV, if TR415b is lower then test R455, if that is also lower then got to be TR415c-e.
 
mbz said:
R443, 330ohms, open?
EDIT:Scratch R433(typo) should only see low voltage.
C411 33P polystyrene would be a long shot.
Click to expand...

Not low. over 32 vdc

mbz said:
One approach would be to track down the source/path of the high voltage, ie, starting at the TP (+32.xV) test at TR415base, expect +33.xV, if TR415b is lower then test R455, if that is also lower then got to be TR415c-e.
Click to expand...


TP1= 32,27
TR415 b= 33.24
I figured Id go to the next point
R455 right side of R = 29.80 Left side of R = 28.44

What next? All the legs of TR 415 read high from 33.24 at b, to 34 at c and 32.50 at e

EDIT: Fixed typo's, ( TP2 to TP1 and TR416 to TR415 )
 
Last edited:
Thought problem was with the left channel. I'll continue to reference left channel
TP is high, base of TR415 is "0.65V" higer, next would be TR409 and TR411 emitters, hopefully one emitter is at the same voltage as the collector (=TR415 base), this would indicate a c-e short under load. Failing that leaves C411, this is a polystrene, unlikely to fail, in this case check voltage at TR409b
 
mbz said:
Thought problem was with the left channel. I'll continue to reference left channel
TP is high, base of TR415 is "0.65V" higer, next would be TR409 and TR411 emitters, hopefully one emitter is at the same voltage as the collector (=TR415 base), this would indicate a c-e short under load. Failing that leaves C411, this is a polystrene, unlikely to fail, in this case check voltage at TR409b
Click to expand...

Oops !!! Typo for TP2 it should be TP1 . my bad.

I'll go check what you posted.

Nashou
 
Feeling motivated, I grabbed my A1 from the corner, replaced the blown 1AT fuses (F202,3, wtf?). Variac'd it up, set voltages/bias etc and it's been playing happily. Must have a bad solder connection or damaged track or... to explain the previous bad behaviour...
 
mbz said:
Thought problem was with the left channel. I'll continue to reference left channel
TP is high, base of TR415 is "0.65V" higer, next would be TR409 and TR411 emitters, hopefully one emitter is at the same voltage as the collector (=TR415 base), this would indicate a c-e short under load. Failing that leaves C411, this is a polystrene, unlikely to fail, in this case check voltage at TR409b
Click to expand...

EDIT: Schematic i was using has c411 labeled as C409

Ok some voltages.

TR409
b= 32.48
c= 33.19
e= 33.17

TR411
b= 33.20
c= 33.18
e= 33.17

Should I pull c411 and check?

mbz said:
Feeling motivated, I grabbed my A1 from the corner, replaced the blown 1AT fuses (F202,3, wtf?). Variac'd it up, set voltages/bias etc and it's been playing happily. Must have a bad solder connection or damaged track or... to explain the previous bad behaviour...
Click to expand...

Awesome!!

Nashou
 
Last edited:
C411 seems fine. My parts tester took a crap and the peak DCA doesnt measure caps.

The LCR meter I have shows it at .048nf

Nashou
 
Nashou66 said:
TR409
b= 32.48
c= 33.19
e= 33.17

TR411
b= 33.20
c= 33.18
e= 33.17
Click to expand...

c & e voltages the same generally make me feel uneasy. Also TR411e-b looks sick, look for sub for TR411 probably replace 409 at same time.
EDIT:
TR409 2SA872 maybe KSA992?
TR914 2SA914 maybe KSA1381?
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom