Transistor Help

[Reddave101]

Sorry if I sound stupid but on my understanding from my diagram which shows I need a PNP transistor and on my understanding what a PNP is.

Emitter, Base, Collector 1,2,3

but diagram of a 2SA935Q shows Emitter, Collector,Base?

what am I missing? By chance do I have to swap leg 2 & 3 round? Basically put leg 3 in middle hole and 2nd leg in 3rd hole to get correct way round?

 

[73's de Edd]

Sir Reddave 101 . . . . .

OK . . .then . . . . now with your transistor to be tested . . . . placed on a surface for testing with its flattened side up.
You take DVM meter and set to its DIODE test function, vice its alternative OHMS test function.
Now in looking at your four sets of readings, the very first and very last are valid readings, with the two center readings only verifying that there is
no leakage or shorts between the other possible lead combinations . . .so all is good .

SIMPLIFICATION . . . . .for any future testing.

Now, on your PNP transistor, do take notice that " black 3rd leg " appears on both of your 1st and 4th tests so clarify and simplify testing in the future by initially finding the BASE lead of the transistor to be tested and and place . . . and keep . . . your BLACK meter test lead on the BASE and then swing your RED meter test lead to one and then the other of that transistors two other leads (COLLECTOR and EMITTER). If you have two good transistor junctions, your junction voltages will be read out, it being 736 and 784 millivolts in your case. Usually they are being within 75 millivolts difference.
As far as actual junction voltage range swings, that can be attributed to specific transistor semiconductor construction and chemical doping.
I have read possibly as low as 450 millivolts and as high as 700's in all of my past testing of silicon types of transistors.

Now if having / or / testing an NPN transistor, you would have had the meter RED lead on the transistor BASE and swung the BLACK lead between the transistors two other leads (COLLECTOR - EMITTTER). Expecting those two junction voltage readings to be present for a good unit.

A very final test is to test between COLLECTOR and EMITTER with both of the possible meter lead polarity connections . . . . . looking for any C-E short / leakage , but it not being expected, with it having PASSED the two earlier tests.

I wasn't expecting your parts acquisition being so quick . . . . as I wanted to tell you to initially have the main unit NOT being connected to the two offending units . . . particularly the tuner ? (I believe it was) . . . . . .that caused a main unit dimming . . . . upon its connection ?
With you initially confirming that with installed new transistors, that you are NOW having the proper presence of that NEGATIVE 30'ish voltage for the -VFL supply line to feed to those two other units VFD family of displays .

In my researching those units, they are somewhat isolated by 220 ohms of series resistance BUT there is being a NEGATIVE voltage electrolytic capacitor placed across the supply line earlier, which could cause your problem . . . . dimming on connection . . . . . if it has shorted down.

Fill me in . . . . .

73's de Edd . . . . .

Best file compression, to be found around, is being : . . . . " DEL *.* " . . . . . . wherein, you will then get a phenomenal 100% compression !

.

 

[Reddave101]

Thankyou for the detailed write up and your time to look at my issue. Please understand I only know basic.
I’ve gone through the transistor pics and info I have and the setup ECB is correct according to the parts list: have tested the new transistors and they are ECB aswell.

the new problem I have is that now I have put in the new transistors, I get no screen whatsoever on the amp let alone the tuner, so it doesn’t come on like before and then start dimming until cap C114 blows. Now it just doesn’t come on at all.

Also to clarify the amp is the main unit that dims when the tuner plugs into it and when the amp dims the tuner dims aswell until they both go off completely. If the tuner isn’t plugged in the amp will stay lit and bright and run perfect.

there is no issues at all with the other units,cd,tape or graphic.

the bit That confused me is that the schematics show Q111 and Q112 as being EBC but the parts list show ECB. That’s was I understand that is from diagrams I’ve found online as above. Really sorry I’m useless when it gets too technical I only know basic. Could I ask where abouts the 220ohm resistor is please to test?

just to also mention on the schematics it shows a couple of resistors that aren’t actually on the board, R101, R102 & R104 on that circuit

I have found a Japanese supplier who has the 2SA935Q transistors and has shipped them out to me but will be a while for delivery but still don’t understand why these compatible ones are not working. The other ones I bought aswell were the BC640

thanks again it’s really appreciated

 

[Reddave101]

EDiT , sorry meant which negative capacitor to check not resistor

thanks

 

[73's de Edd]

Sir Reddave101 . . . . .

the new problem I have is that now I have put in the new transistors, I get no screen whatsoever on the amp let alone the tuner, so it doesn’t come on like before and then start dimming until cap C114 blows. Now it just doesn’t come on at all.

Rgr Rgr on your two transistor types, in their having the same lead basing assignments.

Now . . . .

With all of the potential excess power drainage level that the main units VFL minus supply has been subjected to lately, lets see if possibly that (con) fusible resistor R122 has blown open and gone open circuit, thereby giving no AC input power to your following regulator circuit.
Here is its schema, moved to below.

Go with your DVM set to AC voltage and be expecting a 50'ish volt level when your meter probes are reading between pins 1 and 3 of that purported W102 . . .10 pin connector.
Power up and expect that AC voltage, if so then move the pin 1 connection over to the B side of R122, from its just measured A side.
If no voltage there you need a common 1 ohm at 1/2 watt carbon film resistor to replace with, for then being able to continuing testing.
If things are then back to normal, your main power supply filter of C113 should be giving you ~50 ish volts negative.
Then you might have immediately noticed that units VFD is lit up, so check down at the end of the supply at -VFL (H) markup and see if it is now -30ish.

On the tuner unit, that mentioned filter initially placed across the -VFL power supply line input is:
Adobe document page 42
Connector PIN902 . . . . pin 8
C911 47uf @ 35Vdc E-cap . . . . .is connected across and filtering incoming -VFL negative voltage supply line.
Other relevance . . . .
Of minor significance is that past that cap the -VFL line ties into R941 a 330 ohm resistor (vice my erroneously mentioned 220 ohm ) which could only pull down the supply a mere 10 ma if faulted on its other load side.
Intermediately two 2.2 K resistors tap off some of that -VFL supply, but with those being even higher resistances, they present minimulist loading.

Go-Dog-Go time . . . .

73's de Edd . . . . .

Any time things appear to be going better, you have likely overlooked some things.

.

 

[Reddave101]

Afternoon, your write up and explanation is fantastic easy for a novice like me to understand.

I’ve tested pins 1 & 3 and only getting 22.9 AC. I’ve checked pin 3 to B & A and no reading whatsoever

Thanks again really appreciated

 

[Reddave101]

Sorry just mention I’ve also checked the resistor on the board and the 2 on the power board aswell and getting 1.7ohm on all 3

 

[Reddave101]

I’m going to try explain my findings the best I can so please bare with me.

I have 3 of these amps all with the same problem(so is a generic problem with the system).

1st system. Wife bought me This system 2 years ago with the initial problem, no screen on amp or tuner. Opened the amp and saw C114 was blown, so replaced the cap and faded until went again. Not being electronically minded and don’t know anyone who is, I was on the lookout for a replacement amp, so found a complete system which was the Z9500m(MKII) but internals were identical. So swapped guts out of amp to put in the Z9400M.

was working perfect for past 16 month with all connected. Couple of month ago I powered it down and cleaned(polished it). Powered it back on and the system was dead. Unplugged and tried again and pop something blew inside the amp but still works(sound) but without screen on amp or tuner.

opened up amp and C114 had blown. Replaced the cap and all lit again for a couple of minutes then the 2 screens(Amp & Tuner ) faded out again.

was on look out again for another amp and luckily enough I found one which suffered from the problem if the tuner is plugged into it the screens will go and when the owner saw the screens fading a couple of years ago he unplugged everything and boxed it up and stored it away until I came along after one.

got it home and saw the C114 was swollen but hadn’t blown and amp was running bright and perfect but changed the cap anyway as it was on its way out. Tried plugging tuner into it and screen starting to fade slightly so unplugged straight away and all been good since..

so have 2 amps I can play with to get right so can repair what is wrong with the one I’m using(don’t want look for another amp as hard to find).

the two spare amps will illuminate when the cap is replaced but only for a couple of minutes, expect when I put a 100/50v cap in C114 instead of the 100/10v in one of the boards, that one stayed on for about 30 mins before screen going off which is better than the usual 2 mins.

I really looked at one of my spare boards and saw that at some time in its life the Q111 & Q112 transistors had been replaced(bad soldering). So read about transistors and how to check when they are bad and from what I concluded after testing is the transistors were bad which would explain why they would of been replaced at some point.

now 1 board and my main unit I’ve checked and those transistors have never been replaced but I’m getting the same bad reading on them ones aswell which is what started this post..

now I’ve replaced the transistors with bc640 and tried the 2SB647aswell but since doing so I have no screen coming on whatsoever. Whereas before it came on but faded out?

I have just tested all 3 boards at the points mentioned and all 3 boards are giving me the exact same reading. 22.9 pins 1&3 and no reading when I check R122. And when I check R122 ohm I’m getting 1.7ohms. I have dropped in a new cap at C113 with a 100/100v but still literally nothing on the screen

the only thing that has been changed in those 2 boards are the compatible transistors, so I’m thinking maybe not that compatible. As mentioned I have found the exact transistors 2SA935Q which have been shipped to me and fingers crossed will be landing this week at some point.

sorry for long post just wanted to try explain what I’ve done and tested(easier when got spare boards)

again Thankyou for your help

 

[Reddave101]

I don’t know if significant as forgot to mention, CAP C114 will still blow even if amp is in standby. Power plug turned on but amp in standby. It won’t go bang but will swell.

so basically as longs as power is going to it the cap will fail, turned on or in standby?


And also the main stereo I’m using, it doesn’t blow the cap either when on or in standby mode unless the tuner is plugged in

like I say I don’t know if relevant in diagnosis

thanks

 

[Reddave101]

Afterwards all I’m after trying something, as said before how the transistors had been replaced at some point in its life but done badly so thinking maybe the holes were damaged as like said one was slightly loose. So thinking soldering out of board may possibly help. The way I’m looking at the diagram I’m thinking of soldering =

Q111 E=R104 , C= -C114 , B=E Q112
Q112 C=? , B= -C113

E=emitter , C=collector , B=base

I’m hoping I’ve looked at the diagram correctly as I’m looking at it logically. I just don’t know where the C on Q112 should be as I do not have resistor R101 or R102? On the board so can’t solder it in between them.

sorry if being a pain I just really want this up and running perfect again

really appreciate the help

 

[Reddave101]

Just an update: I managed to source the original SA935Q transistors and have arrived and installed and 2 hrs later it’s still working perfect. The compatible ones I ordered didn’t work, I literally had no screens on the amp or tuner with them installed, so obviously weren’t that compatible. So again thanks all for all the advice and help and a massive thankyou to 73’s de Edd for extensive write ups and looking for me