GK 1001RB II output

[nevetslab]

R14 182ohms R18 43kohms , just kept going can't find an open resistor. Can't thank you enough Nevetslab for all your support, sorry it's been a pita. On a side note, I did acquire a scope, Tektronix 465 ,may be another thread learning how to use it

If R18 is 43k, is R9 also 43k? Those two resistors are the base bias resistors for Q2 & Q2A. Though R18 being almost 4 times higher than the schematic value shouldn't prevent Q2 from conducting. I'd now look for continuity thru the Q2 current path, starting with where R18 connects to the +101VDC rail (common to R15, R24, R31, R33 and source resistor R39. With R18 connecting there, the next node is the Q2 collector side, where the circuit node is R18/Q2 Collector/Q10 base/D7 cathode. Then, verify the circuit node being base of Q2 connects to R18, R19 & C12. Then verify next circuit node being emitter of Q2, connecting to R14. If all those connections are there, Q2 has to conduct, with balancing the current from Q4, feeding both emitter resistors R14 & R11.

With 0V across R31, and +30V at D7 Anode/D1 Cathode, the positive half of the output stage is pulling the output buss high. D7 anode and C1 cathode are separated by two zener diodes D9 & D5, with the bias circuit between them (q12/Q13).

Q16 is at the Anode of zener D9. Hmmmm......if emitter resistor R26 of Q11 is open, that would allow this voltage gain stage to shift high, and no current flowing thru Q14, and Q10 and Q2. Also verify that the two zeners D9 and D5 are ok.

Oh......a Tektronix 465 scope. Great.....nice scope. Did you get one or two X10 probes with it (in the pouch)? That will allow you to work at elevated voltages, giving you as much as 50V/Div down to 50mV/Div. Sure, we can assist in the basic tutorial on that.

[shortcircuit]

no R9 , that's a difference in the schematics using 2sc3381 vs 2x 2sc2240BL they eliminated R9

[nevetslab]

no R9 , that's a difference in the schematics using 2sc3381 vs 2x 2sc2240BL they eliminated R9

Neither differences here are significant, as these are, after all, bass amps. I've never noticed anyone using a complimentary bias resistor on the feedback side where R9 was used. And, 43k in place of the lower 12k value makes little difference....not the reason for Q2 to NOT be conducting.

Did you find the negative side emitter resistor R26 open?

Or, any open traces in the Q2 circuit?

[shortcircuit]

R26 is reading 1.24M ohms , voltage across R26 is 4.47vdc , I haven't traced the current path yet etc. , it will be late tomorrow before I can get back to this ,then I will follow through with instructions from post #46 and get back with you, sorry for the delay .

PS I traced the circuit path nodes , I have continuity through all the node test points , diodes ok , across R31 .129vdc

[nevetslab]

R26 is reading 1.24M ohms , voltage across R26 is 4.47vdc , I haven't traced the current path yet etc. , it will be late tomorrow before I can get back to this ,then I will follow through with instructions from post #46 and get back with you, sorry for the delay .

PS I traced the circuit path nodes , I have continuity through all the node test points , diodes ok , across R31 .129vdc

I think you've found the culprit. R26 needing to be 47.5 ohms (1% part), instead 1.24M! The voltage across it would be set by Q8, set by Q9 via D4/R22. Verify those parts just ahead of Q11. This all may come back together by replacing R26. Good findings on the current path for Q2!

[shortcircuit]

I think you've found the culprit. R26 needing to be 47.5 ohms (1% part), instead 1.24M! The voltage across it would be set by Q8, set by Q9 via D4/R22. Verify those parts just ahead of Q11. This all may come back together by replacing R26. Good findings on the current path for Q2!

Hopefully you found the culprit post #48, I just tried to follow instructions , unfortunately I don't have a replacement here ,have a few places to check tomorrow . I pulled R26 out, just to make sure , DEFINITELY BAD ,will double check other components. I will get back with you asap with (positive results)
You are impressive , can't thank you enough

[shortcircuit]

I think you've found the culprit. R26 needing to be 47.5 ohms (1% part), instead 1.24M! The voltage across it would be set by Q8, set by Q9 via D4/R22. Verify those parts just ahead of Q11. This all may come back together by replacing R26. Good findings on the current path for Q2!

I found some 1/2w 47ohm 1% , they measure 46.5ohms on my meter, do I dare try one ?? If R26 was a 47.5ohm 5%/10% tolerance I wouldn't hesitate, but at 1% I'd rather ask first.

[nevetslab]

I found some 1/2w 47ohm 1% , they measure 46.5ohms on my meter, do I dare try one ?? If R26 was a 47.5ohm 5%/10% tolerance I wouldn't hesitate, but at 1% I'd rather ask first.

Yes....pop it in. We can always change that out later to be clinical.....now we're just trying to get the amp up and running.

[shortcircuit]

One step forward 3 steps back, not good, replaced R26 got a puff of smoke(not sure from where Q11 I think) , it took out R26 , Q11, D5 that I know of so far. And yet it will still come on and the circuit protect will go red to blue, it just smells a bit worse.

Paper weight or boat anchor ?? Just a thought

[nevetslab]

One step forward 3 steps back, not good, replaced R26 got a puff of smoke(not sure from where Q11 I think) , it took out R26 , Q11, D5 that I know of so far. And yet it will still come on and the circuit protect will go red to blue, it just smells a bit worse.

Paper weight or boat anchor ?? Just a thought

NO, DEFINITELY NOT a paper weight. We JUST arrived at the first solid evidence of WHY its not behaving. And, showing us that what the DMM tells us checking for semiconductor junctions is NOT the same as the device IN-CIRCUIT, where it may have been stressed from other factors in what took it down in the first place.

Obviously Q11, R26 & D1 will need to be replaced. Don't power it up yet! Now, looking at the schematic a bit. Audience participation welcome here. From the previous measurements, where you had several volts between Q11 emitter and the neg supply, that suggests Q8 is ok, though it was pulling Q11's base up higher than normal. Q8 is the negative side voltage driver to Q11, which drives the neg side of the output stage. It's base is set by D4 and R22, current supplied via Q9, as well as it's drive signal. Now, D1 failed. Why?

I'd look at the negative side of the output stage at this point. Starting with Q3 & R13, the emitter resistors R52, R53, R55, R56, R58 & R59, as well as the lowest set of xstrs Q28, Q29, Q31, lower middle xstrs Q22, Q23, Q24, their driver Q7. And, the three 475ohm resistors from D18-D20, which set the bases at the mid-supply point of -43.5VDC.

Earlier, finding you had 30VDC on both Q11 collector AND Q14 collector, not quite sure how you get around the two zener diodes D9 & D5, as they're above the bias string Q12 & Q13. The bias is set to place base voltages at Q16/Q7 at 4.9V - the zener voltage of 3.6V, or +/- 1.3VDC at the bases. That's our target goal. You did indicated checking the zeners as far as their junction. They may no longer be 3.6V zeners. They're relatively easy to test, out of circuit. A 10k resistor in series with the cathode, anode grounded, and say 10-15VDC applied to the other side of the 10k, and measure the voltage across the zener. Something like that. A 9VDC wall wart will work as a DC source for the test.

If all checks out on the neg side, do likewise on the positive side. I know it's a mental challenge, but, we can lick it, if you're willing. Good hunting!

If al

[shortcircuit]

I think D1 survived , D5 is open , this will take a while to sort out, I dread pulling the heat sink , I have no parts supply, so I have to order almost everything, so I need a complete list to save on $$$hipping cost, and I'm 2 weeks from everywhere . I will continue on with this, but it's going to have to take a back seat to a few other projects that I can complete. I will keep you informed , and still can't give thanks enough to all on the forum.

[nevetslab]

I think D1 survived , D5 is open , this will take a while to sort out, I dread pulling the heat sink , I have no parts supply, so I have to order almost everything, so I need a complete list to save on $$$hipping cost, and I'm 2 weeks from everywhere . I will continue on with this, but it's going to have to take a back seat to a few other projects that I can complete. I will keep you informed , and still can't give thanks enough to all on the forum.

I wouldn't pull the heat sinks unless it's found we have open or shorted power xstrs. As GK uses Bergquist K6 insulator sheets (or equiv), they wouldn't be re-usable, and new ones would have be ordered from GK. I've so far NOT had to pull heat sinks off, finding valid measurements on the component leads. Hopefully all the damage is NOT under the heat sink, since the emitter resistors are tucked in there as well. I know what you mean with the shipping costs. I cringe every time I submit an order, knowing that the next repair may just burn me for another shipping fee, since ordered placed on line with Mouser and Digi-Key can't be added to (at least not with Mouser....think Digi-Key has the same policy).

As GK owns a lot of the GK gear in our Rental pool, it hasn't cost us (CenterStaging) to replace items that go missing or have failed hard. I'll give them a call next week just to see what a replacement Power Amp assembly would cost for the 1001RB.

[shortcircuit]

I wouldn't pull the heat sinks unless it's found we have open or shorted power xstrs. As GK uses Bergquist K6 insulator sheets (or equiv), they wouldn't be re-usable, and new ones would have be ordered from GK. I've so far NOT had to pull heat sinks off, finding valid measurements on the component leads. Hopefully all the damage is NOT under the heat sink, since the emitter resistors are tucked in there as well. I know what you mean with the shipping costs. I cringe every time I submit an order, knowing that the next repair may just burn me for another shipping fee, since ordered placed on line with Mouser and Digi-Key can't be added to (at least not with Mouser....think Digi-Key has the same policy).

As GK owns a lot of the GK gear in our Rental pool, it hasn't cost us (CenterStaging) to replace items that go missing or have failed hard. I'll give them a call next week just to see what a replacement Power Amp assembly would cost for the 1001RB.

I can replace both the pre and power boards for $235(for both together)+ free shipping from Full Compass , would have total new guts (- xformer) . If it were mine that's what I'd do at this point. I've made the offer to the owner ,but this was supposed to be a simple input jack replace (his diagnosis,his work order) so I don't think he was prepared for major work.

[nevetslab]

I can replace both the pre and power boards for $235(for both together)+ free shipping from Full Compass , would have total new guts (- xformer) . If it were mine that's what I'd do at this point. I've made the offer to the owner ,but this was supposed to be a simple input jack replace (his diagnosis,his work order) so I don't think he was prepared for major work.

I had forgotten that's where this repair began. Yup....HIS DIAGNOSIS, HIS WORK ORDER! We may still get lucky and find nothing major has failed. Not sure how you'll have to bill for the time spent, this being done via internet servicing.

[shortcircuit]

I had forgotten that's where this repair began. Yup....HIS DIAGNOSIS, HIS WORK ORDER! We may still get lucky and find nothing major has failed. Not sure how you'll have to bill for the time spent, this being done via internet servicing.

I'm not feeling lucky on this one Q11 is shorted and under the sink , R22 , R26 , R27 , D5 all toast, R29(3.92k) is reading 1095 ohm in circuit , getting high readings on some of the emitter resistors under the sink . I'm here for the knowledge,education(if I remember anything) a nod to Enzo's quote , and to gain Logic (: if I was in it for $$$ I'd be much better off collecting returnable bottles. Added a pic , note R26 is not soldered in.