Technics SU-V9 adjusment procedure questions

Hello Fernando,
Thank you
I can not find the KSC940 anywhere, at the online stores i buy from, so i believe I got KSA940.


edit comfirmed i can see a 40 in Q612. Q611 i remember now i had cut the legs too short, possible there is not much contact?

v9 transistors.jpg
 
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Check everything you don't trust. Works for me. Every time I think "mmm I don't trust this", the problem is there.

Also check the replacement transistors pinout. It's normal that some replacements need to be installed facing back (EBC instead of CBE). (Not in TO 220, more common in small to-92 parts)
 
I found the old2SD381 NEC part? should i use it?

I think the transistors KSA940 is the same direciton, KSC if that part is fried, have to go to mouser or elemet14. RS is free shipping so i can just get another KSA if its faulty

go over that area first, might be something amiss
 
let's check the schematic and proceed step by step, please post where did you measure the missing voltage.

Q611 must have +48V at the collector, 17.6V at the base, +17 V at the emitter

Q612 must have -49V at the collector, -17.6V at the base, -17 V at the emitter

Please check all those 3 points. We need to see if the voltage is reaching Q611 and Q612, if they are biased (voltage at the base) and if they are feeding the +17 and -17V

Pay attention to transistor insulation, if any. Collectors are at + and - 48V, and the transistor metal tab is the collector, so if you short the body to ground, you are shorting the 48 V rails
 
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[/QUOTE] This shows power lines coming in form transformer. I was careful with power supply wiring to get it correct, i guess if wrong it would not work. New Film capacitors 0.01uf near transformer plus 4 new thyristors. Power board new 0.047uf films
View attachment 1252991
? possible a resistor or dry joint is letting more power in?
View attachment 1253003

check on board break ( black line is where the break was). I might check it again[/QUOTE]

Hi, sorry if this is an incorrect question: is there no problem putting all those non polar film caps where polar electrolytics were used by the factory?
Good luck with your V9!
 
Hi Fernando, Baily and Guillaume
Thank you :)
There is no + 0r -. All negative (-) and very low values.
Q612 ( on 20mv setting, and 200mv setting for C
C = -01.0
B = -1.70
E = -1.07

Q611
C = -0.00
B = -0.04
E = -0.37


I checked over power board before putting back - wiring transformer to mains is as per manual and colour of wire. Possible to check again to see if any issues there

broken boarad appears to be good in that area, i checked before doing adjustments.

I found a few green electro caps. Polar as in Elecros, only 2 have been replaced with film on the main board. Power board i broke a leg on one, and decided to change for other film caps. They were ceramic blue type. Also the 0.01uf near the relay - changed those ceramics to film caps.

I get 55v + and 55+? on TP503 and Resistor ( Q327)
 
Voltage is not reaching the transistors, check R627 and R628 (resistance and voltages), and check the transistors are not shorting the voltage to ground (check the collector -transistor tab- is not connected to ground).

Something had cut the path from the rectifier (d601-602) to the transistor Q611 (and the same at the negative rail), Check continuity from the diode D601 to R627, an them to Q611. R627 is 120 ohm. There must be 120 ohm between diode 602 and Q611 collector.

A shorted Q611 + shorted Zener D620 would drop the voltage to ground, but R627 should be too hot and burn.
 
Collector for Q612/11 no continuity to ground
Thyristors D601-4 C continuity to ground ?

R 627 continuity to D601/2
R 628 continuity to D603/4

R627 to Q611 continuity to C

R 628 to Q612 no continity to C?
v9chk.jpg

ohm rating for both in circuit without power on
R327 1 at 200 setting and 2000 1340 etc, at 200 , quickly at first 122.1 then back to 1
R 328 at 200 148 ohm?

maybe take voltages on the Resistor side ( going towards D601-604)
 
There must be 120 ohm between diode 602 and Q611 collector.

Please check this again just in case, and the same between D603 and Q612, but if you don't have continuity from R628 to Q612 Collector, something is not OK there, fix first the passive components before measuring voltages again. The fact it measured 122ohm for a brief second could mean a broken connection or bad solder, not an open resistor, but if in doubt, replace the resistor, or measure it desoldering one lead from teh PCB. Try to fix those 2 voltage rails until you trust 100% those PCB traces.
 
thanks Fernando,

Using the continuity and earth in earth terminal (Thyristors) D601/2 C continuity
D603/4 continuity K not C(A)

I will locate those. and remove one resistor leg to test and get a better reading.

I cant see a break on the board but for sure i can see the trace going to Q612 C

Good idea fix any issue before turning on power.

123.1 very briefly, another attempt 176, all quickly going back to 1

Q612 collector, scrap the board and put fine wire to try to connect it. I have very fine wire 32awg 600v 200c wire, cant see any break but these must be
 
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I’d be lookin at R627 / R628

After the thyristor based rectifier blew, I’m sure ripples would have ensued

What voltage over main (18,000uf) caps? - should be on 55v/rail
If no voltage at collectors of Q611/612 those resistors have gone open...... if they have check for shorts in transistors 611/612 and mosfets Q610 Q611 (zener diodes too)

This surely is a Pepsi challenge
 
Thanks Baily
I totally fear the thyristors, it was a real bang, if i were a cat i wouldve lost a life. Yes for sure something else couldve got done, why the cap near them i replaced 0.01 x 2 near the relay.

How do I test the main 18000 caps? earth to a pin on the cap, I kind of forget where hook up. +55 and +55 for Q327 and TP503. The big old cappies will be needing a charge

Very low voltage at 20 setting on member and plus no continuity with Q612 C and R 628. Voltages were very low -01.0 for C 612 and -0.00 for C 611. Q610 and Q611 i can go over those tomorrow.

The V9 is at the dinner table lol and has been her new home for a bit

The V9 is sure a Pepsi challenge.


Baily, found an old post with V9, ( the 18000uf caps)
K of 601/2
A of 603/4

This will be same as caps... yeah... use 200Vdc
 
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Yeah Sam...

Nearly all amp voltage measurements are from component to ground- Unless testing volt drop across specific components (like bias setting etc)

So yeah there should be 55v at main caps, when that is known good, then check Q611/612
 
Cool Baily, I was concerned as there is continuity with the Thyristors D601/2 A and D603/4 with K
This time they will not blew i hope. Hope to see 55v,not like last times low values. Then we can move on to Q611/12 ( resistor or part no suited though is on the AK transistor list)


The old Q611 part i found it and checked with diode reverse to see if its okay. Hopefully the transistors in place are fine, save the trouble of pulling out


R627/8 are 120ohm 2% tolerance in service manaul 1/4 watt, schemtic is 2w
 
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1/4 watt is too small for those resistors.

They have near 7V across them, so you have 7V / 120ohm = 0.058A current in that resistor. That means 0.058A*7V=0.41Watt dissipation. I'd use at least 1 Watt resistor, and not much more than that, since those resistors act as fuses. Under a short at the regulator, or any abnormal current draw, they should blow. Carbon resistors can burn in flames, I've seen that, a small 1/4 watt burning like a match, I'd use a metal film, not too large (metal film resistors can take some more power before burning, so not fast fuses, but they don't catch fire)

1% is not relevant in this application, regular 5% is OK.

I'd use something similar to the original part you see in the unit.
 
Thanks Fernando, yes the service manual says 1/4 watt, but on the printed schematic it has 2 W.

Baily and Fernando

Went over V9 front end seems fine, apart from continuity with L E and R, which might be normal anyway. Wiring appears to be in right position, Broken link with Q612 fixed continuity to R628
Double check?
earth to pins A D601/2 has continuity and D603/4 K, but test points have no continuity with earth

K 601/2 and A 603/4
safe to proceed and test big cappies
 
I'd plug it with a DBT and check the + and - voltages are OK (they will be a bit lower, but they should match).

You can check the voltages reaching R627 and R628 (even if the resistors are not in place)

Try to find a point electrically connected to the main caps, so you can attach your probes without slipping or shorting anything.
 
Hi Fernando,
Yes i covered them with pvc tape so no slippage - not sure what DBT is, i am sure i did check i got the wiring right for left and right channel. IF from memory there was continuity with all 3 for the turntable and it worked.


Hiya Baily
V9 readings this time NO transistor went bang, my brothers did it for me, since they had steady hands.

601 K +54.8
602 K +54.8
603 A - 53.4
604 A -53.4

not - 55v but might be good still not sure

IF that is all good, then issues is that dead transitor and possible damage to transitors Q61/12 or the mosfet ones 609/10?
 
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