GK 1001RB II output

[nevetslab]

Plugging into input patching send was much stronger and clean , plugging into return to amp out yielded same low distorted output . Had 0vdc at pin 3 of LM3886

OK, sounds like the preamp is working ok (and your input connector is ok). Having 0VDC at Pin 3 on the tweeter amp is good. If you've re-soldered any/all of the questionable solder joints on the power supply area I pointed out, and elsewhere while in that mode of service, might be worth putting the PCB back into place, re-connecting everything (and make sure the 7-pin secondary AC wire connector is in correctly....they fail HARD if you're off by one pin, as I can attest to with 41 hrs of repair from being off).

With the amp all back together, we need to check the supply voltages. One thing that GK did NOT provide was a convenient Ground terminal to hang a probe onto. As long as the output connector's ground protrusion pins are making contact with the dead unpainted metal of the rear panel, you can connect you neg voltmeter probe to the Grn AC Mains Ground lead where it attaches to the chassis.....in the corner between the IEC connector and the Toroid...you had to remove it to get the chassis out. Getting the supply voltages (V++, V+, V-, V--) can be had at the outside terminals of the three bridge rectifiers. The LV supply's (V+, V-) are found on the outside terminals of the bridge rectifier just forward of the 7-pin secondary wire connector. The V++ and V-- will be on the ends, as will the V+ and V-, since the supplies are stacked.

They are a ways down from the surface. I use long EZ Hook probes when I go after those, so I can clip on and not risk having exposed probe tip slip off and short between the inside AC terminals of the bridges...so Please Be Careful here. As I recall, your supply voltages will be about +103V, +44V, -44V, -103V.

As you don't have a scope, the best we can do is use your music source, and with a patch cord connecting from the Send jack to another amp, adjust the Volume to where that sounds clean. From that point, you have the Boost Control and the Woofer & Tweeter controls to get your output to a speaker. The Tweeter output ONLY appears on the NL-4 connector Pins 2+ and 2-. Only the Woofer (full range or limited by push-button next to that control) comes out the speaker phone jacks. You can overload the signal if you turn the Boost control up too high. That stage (Q4 JFET) is the weak link in headroom on this amp.

The LV power supply regulators are on the main PCB. If you were reading +/- 15V on the preamp, as well as +/- 35V, then your supplies are fine. If not, the LV regulators are mounted in a somewhat inaccessible area...you can find them on the PCB layout drawings. Hopefully all that is ok.

[shortcircuit]

Bridge rectifiers BR1 -46vdc -107vdc BR2 -46vdc +46vdc BR3 +46vdc +107vdc Using music source test , regardless if boost is up or down the signal to output is low and distorted. I have to commend you on your length and attention to details in your replies. My apologies to you and to The Dude for not reporting power supply voltages back on post #4
a scope is in the near future

[nevetslab]

Bridge rectifiers BR1 -46vdc -107vdc BR2 -46vdc +46vdc BR3 +46vdc +107vdc Using music source test , regardless if boost is up or down the signal to output is low and distorted. I have to commend you on your length and attention to details in your replies. My apologies to you and to The Dude for not reporting power supply voltages back on post #4
a scope is in the near future

Do you have the schematics (multiple revisions) that include the PCB top/bottom foil pattern, with the parts/sch numbers printed over them as a guide to work from? Looking at Rev A2 of the 1001 RB II Schematic and PCB layout, the schematic gives you all the critical voltages from input circuit thru output. The only real way to look at it is with the PCB out of the chassis, and I think you'd have to also have the transformer removed from the chassis, so you could turn it upside down. Might even have to remove the front panel assy so the preamp can be positioned to interface with the power amp board. I've only had to do that on the 2001RB, but, you CAN find everything from the bottom foil pattern. It is a PITA, but, unless you find by probing with chopsticks on the main power supply components that the distortion changes when you find the culprit........

Actually, do that first. Probe with a suitable non-conductive tool....chop sticks work fine, long wooden handle from your kitchen drawer....something that you can do tapping of components from the parts side of the amp, and see if you can find the culprit. It may well be bad solder joints, since I presume this amp isn't drawing abnormal current. Are you using a light bulb limiter between the amp and the AC mains? While I have one here, I'm normally running with a power analyzer following my variac at the bench, when I'm first bringing something up, and can see high current problems right off. SMPS's not withstanding, as that technique doesn't work with them.

So, it's brute force time for the moment, and maybe you'll get lucky. If not, then the cause will be present in the voltages being vastly different from what they should be on the schematic. Be careful and safe, as it's lethal voltage exposed. That area (AC mains/secondary power supply section) could be covered over with insulation to keep you safe while probing the amp circuit. We'll be there to aide you.

[shortcircuit]

I have applied chop stick search several times and will again slowly and methodically. Not running a limiter , will give that a run also . I do have the schematics you mention , and will give it my best . I appreciate all your input,can't thank you and others on the forum enough.

[shortcircuit]

using light bulb limiter with 100w bulb , light bright at power up for an instance, then nothing on the bulb , but signal to output is louder (still low output louder) and consistent. Have yet to see the fan kick on (tested fan it's good) . would rather ask ?? before I try and dissect . still have fun with dissection ??

[The Dude]

All might be due to running the amp on the limiter. If there's no DC on the output, take it off the limiter and try it. Low supply voltage could cause low output and fan not running due to not enough voltage.

[shortcircuit]

Today is was the first time with the limiter , and audio input to output increased and consistent ,no surge at shut down , but still minimal .I have never seen the fan run except for with an isolation test , the heat sink never gets hot enough (or thermo) to kick it on. And I have left it on for hours, without limiter.

[nevetslab]

Today is was the first time with the limiter , and audio input to output increased and consistent ,no surge at shut down , but still minimal .I have never seen the fan run except for with an isolation test , the heat sink never gets hot enough (or thermo) to kick it on. And I have left it on for hours, without limiter.

......but still minimal? Uh.........meaning your output is still low and distorted? Or that you found the cause of that and corrected it?

The Fan doesn't kick in until the heat sink temperature is around 45 deg C (never actually measured it, but sitting at idle, it will never come on. I have to run these into a load or 4 ohm Ampeg speaker for a while (in the shop, I use pink nose, often 40, 50 or 63Hz 1/3 Oct Pink noise which is LF rumble), and the fan WILL come on after a while.

[shortcircuit]

Still have low and distorted output. Ran music source into the input while I choppped sticked around for the complete CD , that's why I questioned the fan issue. So I'm back to point to point voltage checks, I haven't thrown in the towel ,or raised the white flag.

[nevetslab]

Still have low and distorted output. Ran music source into the input while I choppped sticked around for the complete CD , that's why I questioned the fan issue. So I'm back to point to point voltage checks, I haven't thrown in the towel ,or raised the white flag.

I was afraid you'd say that. Sometimes I think what working on this particular series of GK amps does more than anything else is teach you patience. Or rage, when you find it again being mfgr / design defects. Think good thoughts. At my end, doing this as a daily adventure.....most everything has something to teach me, even if I'm not conscience of it at the time. Good hunting!

[shortcircuit]

I was afraid you'd say that. Sometimes I think what working on this particular series of GK amps does more than anything else is teach you patience. Or rage, when you find it again being mfgr / design defects. Think good thoughts. At my end, doing this as a daily adventure.....most everything has something to teach me, even if I'm not conscience of it at the time. Good hunting!

I finally had time to get back to this , I don't have the foil schematic for this board . So I'm still working from above , and still failing . On the schm D7 anode 4.9v AC? if so I have 25vac , D1 cathode -4.9v AC? I have 25vac . Across these resistors R16 0vdc , R15 5.48vdc , R24 4.92vdc ,R31 0vdc , R33 .1vdc does any of this make any sense to you, as you all know I'm in over my head on this one .

[nevetslab]

GK1001RB Power Amp Troubleshooting

I finally had time to get back to this , I don't have the foil schematic for this board . So I'm still working from above , and still failing . On the schm D7 anode 4.9v AC? if so I have 25vac , D1 cathode -4.9v AC? I have 25vac . Across these resistors R16 0vdc , R15 5.48vdc , R24 4.92vdc ,R31 0vdc , R33 .1vdc does any of this make any sense to you, as you all know I'm in over my head on this one .

Those two nodes (D7 Anode/Q14 Collector/D9 Cathode & D6 Cathode/Q11 Collector/D5 Anode are DC voltages....+4.9V & -4.9V. I'm attaching this GK 1001RBII Power Amp Schematic file, which has the PCB foil pattern/Schematic on several revisions.

1001RB-II_POWER_AMP_PN_206-0260.pdf

With 0V across Q2 Input side xstr (pins 1, 2 & 3) Collector resistor R16, there's no current flowing on the input side of the diff pair Q2, while too much current is flowing on the feedback side of Q2's collector resistor R15. That's why there's no voltage across R31 and too much across R24. R33 emitter resistor of Q14 isn't conducting current either due to Q2 input side of the 2SC3381 Diff Pair.

With the power off, supplies discharged, measure Q2's xstr junctions. It's a seven-pin matched pair NPN part. Here's the data sheet for that:

2SC3381 Dual NPN.pdf

The outside pins are the base, 2nd pins in are the collectors, 3rd pins in are the emitters. Middle pin is the substrate, which may be ground (I haven't looked, unimportant for now). If the input side of Q2 is bad, it needs to be replaced. I may still have a few 2SC3381's left. Toshiba discontinued it and it's PNP compliment, to the dismay and anger of the Audio Industry. I haven't checked on the internet for that part, so I don't know what the going $$ is on them nowadays. Since you do have current flowing on the feedback side, it seems like the constant current source Q4 & Q5, with their mute controllers Q1 & Q6 are working.

Q2 working is paramount for the amp to work. Without it, nothing that follows this input stage will be right, so you did land on the main culprit.

Make sure the collector resistors R16 & R15 are 2.00k, as well as R24, and R31 is 1.00k. Also check Q9, Q10 & Q14, as well as Q8 & Q11 with the Diode Test mode (no power applied, always).

Good hunting!

[shortcircuit]

I don't have Q2 2sc3381 , I have Q2 and Q2a both 2sc2240BL , checkout schematic attached to post #41 , still doing the same job as the dual. I pulled out and tested Q2,Q2a, Q9, Q10, Q8, Q5 all tested good. Q11 and Q14 test good . The only Q I find suspect is Q16 , I have continuity between the collector and the emitter. I have 30+vdc on D1 cath & D7 anode ,just to correct previous info. All resistors R15,R16,R24,R31 are good. I was hoping for a Q2 Q2a failure

[nevetslab]

Then check the emitter resistor for Q2--R14. When you don't have voltage drop across R16, and more than twice that flowing thru Q2A, something is robbing the current. Normal collector current on Q2/Q2A is 1.3mA. You're must slightly above that on Q2A, so I wonder if R14 is open? Or, if base bias resistor R18 is open? With this side of the diff pair not conducting, you won't have a working amp circuit.

[shortcircuit]

Then check the emitter resistor for Q2--R14. When you don't have voltage drop across R16, and more than twice that flowing thru Q2A, something is robbing the current. Normal collector current on Q2/Q2A is 1.3mA. You're must slightly above that on Q2A, so I wonder if R14 is open? Or, if base bias resistor R18 is open? With this side of the diff pair not conducting, you won't have a working amp circuit.

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