swr workingman 15 trouble

[zairec14]

Its 7 measured across the resisitor. one has - and the other has +_ both around 7. Yes we did have 4.3 at output. But i did not change transistor nor check them yet.
HV rail and 15-/+ i have yet to confirm as well. Im spending time thoroughly reading the schematics i have to familiarize myself with the orientation of things and i have seen somewhere the location of HV -/+ rails and 15 -/+ rails refering to where i can measure.
What might of changed the output reading is when going through the power supply schematic and checking that i didnt connect something backwards or rather that it follows the schematic as best as my little experience can convince i realized that the middle yellow wire of the secondary of xfmr showed connection to the board on the schematics. Thats the only thing i can think of that is different.
I still owe you the measurements you asked for. Ill get to that A.S.A.P

[zairec14]

reporting back on Q12 its a pnp and base to collector has a forward drop of 0.667 and base to emitter a drop of 0.672 . resistance base to emitter a whopping 7.60 M. and base to collector ol or rather it reads -3.45 M with the - probe at the base and + probe at collector and reads OL if you swap the probes around to + at base and -probe at collector.
is this what we needed to know?

[zairec14]

also the schematic gives a reference to 15-/+ rails in a few locations along the board. I can only confirm at this time that at the top of r1/r2 resistors it indeed reads just over 15v , more around 16+. is that still within good function?

[zairec14]

one more thing i feel is imoerative to add . I have noticed a bit of a pop top on the filter caps its not very visible but i was leaning a finger atop of one while measuring or doing a visual inspection of the board when i felt one. and the other is around the same . its just not as flat as caps tend to be. im not to worried about it though ill keep an eye on them though if it does continue ill be taking the board out and removing them. tHE LESS I MESS WITH THE BOARD THE BETTER I FEEL ITLL BE STICKY BIZ ONCE ITS OFF THE MOUNTS

[Enzo]

Testing transistors:
other than to detect shorted or extremely leaky transistors, resistance readings are not very useful. The forward junction drop is useful. As you know the thing should read like two diodes. However, the most common failure mode for a bipolar transistor is emitter to collector shorts. Once a part checks OK from base to the other two terminals you also must check for E-C shorts. If you measure a transistor with E shorted to C, the two base junctions can still test OK.

[zairec14]

Enzo sir, Im honored thank you for that bit of knowledge. As soon as i get a chance i'll research what im looking for as far as readings on E to C. Im assuming theres some reverse biased method of reading the drop from P to P in a transistor. If not an easier logic to it.

[Enzo]

E-C should read as open, just as it would with two diodes.

[zairec14]

OK. JUST SO I CAN CLARIFY THIS FOR MYSELF AND ANYONE ELSE that might be unsure. Enzo, so if a diode gives a reading with the probes on either side its a goner, correct? It should only read with probes in their respective polarities. Then when your reading for e to c shorts it should read open when measured for resisitance.?? In diode mode if it were to give a reading with probes on either side that would mean the e to c has shorted and its a goner.
Did i capture this lesson on the edge of an ice berg or am i slipping somewhere ?

[DrGonz78]

Only reason I included using resistance method for checking a transistor was in case multimeter was cheapo and did not have a diode check mode. "Then when your reading for e to c shorts it should read open when measured for resisitance.??" So resistance between E and C should be OL (infinite) on a healthy reading. Any low resistance reading between E and C will show that it is leaking (e.g. 500k resistance) or completely dead short (0 ohms). Sounds like your understanding it very clearly.

So back to the amp... Q12 is obviously just fine and the only reason we tested it to such extremes was you had said "q12 was not giving me a read any which way." So from the start you replaced R31 and R43 (in the Zobel Network) since they looked burnt or cooked. At that point you replace Q10 as per "found that one of the power transistors 2sc3264 @ q10 was not reading from the emitter with the dmm while power was on." (<<<<That reading could have been caused by shorted trace or bad solder connection where voltage was not reaching the Emitter leg of Q10) Since they come in pairs you started with fresh new set and replaced Q10 and Q4. At that point we built a light bulb limiter before powering it on for the first time to make sure that we would not blow anything up, as a precaution (amp was never blowing any fuses). The amp's limiter detection LED was engaging too and that is still a problem correct?

Things I was confused by in the thread so far...
----You mentioned center tap (yellow wire of secondary)... "What might of changed the output reading is when going through the power supply schematic and checking that i didnt connect something backwards or rather that it follows the schematic as best as my little experience can convince i realized that the middle yellow wire of the secondary of xfmr showed connection to the board on the schematics. Thats the only thing i can think of that is different. " What did you mean exactly? What was different? Just not sure what you meant here...

---You measure 4vDC on the output and now it is reading 30mv DC.

---Measured -/+16vDC for low voltage rails. Was this with light bulb limiter connected? Seems to be the normal working voltages but I would expect lower if testing voltages with light bulb limiter connected.

--- Did the light bulb limiter ever shine bright when powered up?

[Enzo]

A diode conducts in one direction only. I don't use resistance for that because the voltage in some meters is not enough to turn on the diode junction. The diode test works on most any diode. Yes, on diode test, it should conduct (as in show some voltage drop, like 0.6v) one direction and show open the other. Red probe on the anode (triangle or arrow end), and black probe on the cathode (the line end on drawing and on part), and a good diode will read a typical voltage drop. Reverse probe positions and it should read open - same as probes not touching anything.

Bipolar transistors test like two diodes joined at one end. SO you test those two as diodes as you would real diodes. If either shows shorted, the part is bad. Once the two "diode" junctions are tested, then test Emitter to COllector. That should test open both directions. If it looks open on diode test, it probably will on resistance as well.

Now often times you can do these tests while the part is still in the circuit, but sometimes other parts in the circuit become parallel current paths. Like say the driver transistor before the output transistor in a power amp. Those two transistors are partially in parallel, so your readings may be confused. SO I always start by testing them in circuit, and if any APPEAR to be bad, I remove them and retest. If they seem OK, they probably are. There is nothing you can put parallel to a shorted transistor that will make it appear good.

[DrGonz78]

A common problem with amps with heavy vibration is cracked solder joints or even cracked legs at the joint. Not only that but the pad can crack right near the where it connects to the trace leaving an open connection even soldered up, hard to find those ones. That is why I mentioned the part about Q10 not having voltage at the Emitter leg, as that it is how I understood it from your post. When you removed Q10 did the leg have a crack through it and how did the solder joint seem? Also, is there a headphone jack on this amp?

We need to understand what was meant by saying "The built in limiter light was on consistantly though." Does this mean light was on constantly without signal applied or as you applied signal it triggered the limiter LED to activate. The latter of the two would be good and it would show that signal is being passed to the limiter section which is usually right before the power amp section. So you might need to trace the signal through the preamp section towards the power amp to check where the signal is dying out.

[zairec14]

wow, illl try to keep to each question in order. forgive me if i omit one accidently.
ok initial test of the top of this thread was carried under load. yes limiter LED at that time was lit without pulsing or modulation the way aclipping light would and if i remember correctly this feature worked when i took past that point it that it had to limit the output.
(center tap ) and my reference to that was posed more as a questioning of my ability to understan the schematic. the schematic of the power supply i felt showed 3 wires at primary connections to fuse and mains. That is a past observation but still questionable to me but may or may not be of importance now. xfrmr has two actual wires at primary both black. At secondary has two read and a center yellow that was tied off and i dint recall if and where it was making connection. Later i observed on a better copy of power supply that far right shows rectifier connection and the words (connect to board ct connection) labeled for the yellow wire at CENTER of secondary coil.
Prior to me connecting the limiter bulb and making the yellow wire connection to board we did have 4.3 at output. now we have 30 mv.
So bulb has been used since it was suggested so all testing had underwent applied. Note: for switch to light up while bulb was lit at same time i jumpered from conn.3 on switch to the hot side of mains in before fuse.
What exactly changed the voltage of output is unclear to me as well. ONLy two things different. center tap of secondary coil is now connected at unstuffed bridge also shown in one of the schematics to be on board before filter caps.
now q10 im questioning the diagnosis now b ut good thing i kept them . ill pull them out and confirm now im more confident in my ability

[zairec14]

the board was a little tricky to work on and i inspected as best i could with a big look through lamp with magnifier and i did not see pad or wire break but i could of missed it but not really

[DrGonz78]

Later i observed on a better copy of power supply that far right shows rectifier connection and the words (connect to board ct connection) labeled for the yellow wire at CENTER of secondary coil.
Prior to me connecting the limiter bulb and making the yellow wire connection to board we did have 4.3 at output. now we have 30 mv.

That makes more sense to me now and now I see how this was changed by reconnecting the center tap. Since you had this on the back burner is it possible that you had disconnected the center tap and left it off by accident?

So bulb has been used since it was suggested so all testing had underwent applied. Note: for switch to light up while bulb was lit at same time i jumpered from conn.3 on switch to the hot side of mains in before fuse.
What exactly changed the voltage of output is unclear to me as well. ONLy two things different. center tap of secondary coil is now connected at unstuffed bridge also shown in one of the schematics to be on board before filter caps.
now q10 im questioning the diagnosis now b ut good thing i kept them . ill pull them out and confirm now im more confident in my ability.

My only worry here is that the light bulb should be in series through hot wire connection of AC mains before it ever reaches the amp. Conn. 3 from what I see on the schematic is the white wire... Neutral?? There is a coupling cap and a thermistor(I think) parallel between hot and neutral. Is the light bright as can be?? This also might explain why your voltages are not being lowered by the light bulb limiter. If my thinking is correct you just connected a light bulb in parallel to AC mains, and it will just light up. If that is what has been done here then we are not using the light bulb limiter correctly. In fact, we just want to turn the amp on and see the bulb goes dim, which indicates the amp is not pulling a bunch of current. The light bulb limiter is there to light bright and limit current if there is a short in the amp thus saving fuses from popping. Please check this over carefully.

I would personally prefer to just make something like this that you can plug the amp into, with or without a switch. Add a ground connection to the the diagram below too.

[zairec14]

yes it almost positivley what happened , I really just overlooked the center wire . now im not positive its still where it needs to be but it seemed to help. more of that later
back to the bulb limiter. Im going to make one like the diagram then so that we can both be sure of the testing here.
what i did is i hooked up the bulb in series to what i believe is the hot , which resembles the schematic as its seen from inside the amp facing. hot on the right nuetral on left. Now to be clearer if i was behind the amp looking at the plug and connecting it the hot would be on the left and nuetral on the right . In a position as if i were plugging it in . Does that give the right picture??
The only difference is that i put the bulb right before the fuse on the inside after the mains connection. In series of course minus the seperate switch for bulb.
Also this amp never had a thermistor i put one in a while back but when we began testing it took a minute to reach 110/115VAC and it was in my way. Now as far as the coupling cap i believe it didnt have one either. there is a grounded rail where all the grounds meet and has one green wire that connects to the cabinet combo ring output . That rail has a big cap looking cylinder of 335k 250v and a ceramic resisitor of 10w 8.2k . But aside from that it never had a coupling cap in between the hot and nuetral. Im pretty sure of that . It did occur to me to put one in in the past but my logic was if it didnt have one to begin with it was fine.