QRV08 Setup Instructions

[BMF]

AD825     IC2           IC6          IC11          IC15

Pin 2       6.9V        635mV         6.9V         611mV

Pin 3       6.9V        240mV         6.9V         231mV

Pin 4       0.0V        920mV         0.0V         902mV

Pin 5       5.5V        601mV         7.0V         415mV

Pin 6       7.6V        265mV         7.1V         321mV

Pin 7      14.3V        0.0V           13.5V         0.0V

All 4 LEDs light up for 1 second at Power On, then go dark. Within 10 seconds H1 and H3 light up but H2 and H4 remain dark. Powering down, H2 and H4 Flash On.

While I was preparing to make these measurements, I saw H1 and H2 once again alternately switch On and Off. In other words, H1 was On and H2 was Off; a few seconds later H1 was Off and H2 was On; then they reverted back to H1 On and H2 Off. H4 remains Off and H3 remains On...???

The pads for the C/G 10, 11, 33-36, 39, 40, and 47-50 are the same size as the tabs on the caps. This makes it very difficult to solder the caps in place. I pre-tinned the pads and the cap tabs, off-set the tabs on the pads so a little bit of each pad was exposed, and re-flowed them in place. I checked continuity of each cap tab with its connection to other components using the schematic and all are continuous. Considering that the solder mask should prevent shorting from one PCB pad to the other (under each cap) from the reflow, it's not likely but I suppose it's possible there are some shorts I cannot see. Would circuit connections to other components confound results from testing for shorts across each cap's pair of tabs using my DMM set to ohms?

I re-flowed all joints. Upon Powering On, all 4 LEDs light up for about 1.5 seconds, blink off, then H1 and H3 light up within 7 seconds. I noticed the resettable fuses associated with H2 and H4 were hot for a few seconds when Powering On...this happened before and after reflowing al the joints. I removed them and installed new ones....same result.  A short somewhere? I don't see any solder bridges. Where / what are the most likely shorted components given my description of odd behaviors and measurements?



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[BMF]

After Power On, all 4 LEDs go dark. About 7 seconds later, 2 LEDs light up.

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[peranders]

You have high power consumption on the negative side and the same problem in both channels. when the opamps has exactly the same voltage on pin 2 and 3 then regulator works. Pin 6 should also be within the linear range of the opamp. You have 7.6 volts which is as expected.

A brutal way to confirm the power supply is to cut the copper to the amp but you may find the fault avoiding cutting.

I recommend you to lift R3/E3 then the consumption would be the DC-servo opamps only. Have you put any tin on the jumpers on the solderside? Only one, not both if so you have a short circuit (see the schematics).

[BMF]

I tried a blob of solder on the negative bias jumpers (solder side), only. This had no effect so I removed the blobs.

All measurements posted, above, are without any Jumper connections.

The resettable fuses for the Negative Rails get HOT.

What should I expect to find / measure after removing R3/E3?

How do I get any readings on Pin 5 since the data sheet shows it's NC (Not Connected)?

What could explain random On/Off of LEDs at H1 and H2?

[peranders]

When the LED is on then the regulator _might_ work. Do you get -14 V at some point?

The R3 is shutting of the whole amp as I write in earlier posts.

Pin 5 of the opamp is not interesting...

[BMF]

All PNP and NPN transistors at the output and power supply measure 0.6 to .7 V.

E3 and R3 have been removed. Not sure what/where to measure for the next step.

[peranders]

The whole amp (as I write) shall be completely shut off. You are sure you don't have mixed up PNP/NPN? If the current consumption will drop you will end up in a stable supply voltage.

[BMF]

P-A,

I reconfirmed that all PNP and NPN transistors are properly placed across the entire board.
I reconfirmed that all ICs are correctly positioned.
I have no Jumpered connections.
I checked continuity between all connections...all are good....including transistors, ICs, resistors, and caps.
I replaced all ICs and transistors on the bad sides of the regulators.
I can find no solder bridges or other shorts.
All measurements previously posted were almost identical when retested.
All LEDs blink on at Power Up, go out, and the positive LEDs light up; negative LEDs stay dark.
The negative resettable fuses get Very hot for a few seconds and then cool down. Positive fuses do not get hot.
I removed R3 and E3. The amp transistors heat up to 100 F and 135 F at the PNP And NPN sides of both channels. Shouldn't removing R3 and E3 cut off power to the amps; if so, why are they heating up?

I'm stumped!    :?

[peranders]

I assume that R3 is removed.

Measure the voltage across all resistors starting from R4.

Which is your output voltage?

Voltage across C12?

[BMF]

R3/E3 Removed for these measurements:

R4 0v       R5 0v        R6 358mv        R7 10mv        R8 4.6v        R9 0.85v        R10 148mv        R11 16mv        R12 4.5v

R13 0.85v        R14 6.7v        R15 2.2v        R16 4.6v        R17 0.87v        R18 0v        R19 40mv        R20 16mv

R21 0v        R22 16mv        R23 0v       R24 0v        R25 0v        R26 3.3v        R27 3.3v        R28 0v        R29 3.8v       R30 3.6v

R31 3.6v        R32 25.3v        R33 19.7v        R34 1.3v        R35 1.3v        R36 1.3v        R37 1.3v        R38 6.5v

R39 15.7v        R40 0v        R41 1.1v        R42 2.7v        R43 290mv        R44 3.1v        R45 7.9v        R46 305mv

R47 4.5v        R48 170mv        R49 2.5v        R50 230mv        R51 0v        R52 2.9v        R53 7v        R54 629mv

R55 7v        R56 Jumpered        R57 Jumpered        C12 9.3v        G12 9.1v

Thank you!

[peranders]

You have a problem already at R6.

Could you tell me the marking of the transistor and what type and brand you have?

R4 has no current but still you have current through R6.

Could you also measure the base-emitter voltages on all transistors?

[BMF]

I have looked at this board and components for many hours over many days. I just found a problem. T/V 13 and T/V 14  are the exceptions to the Odd - Even numbering of these components. I misread and installed BC850 on T/V 13 and BC860 on T/V 14. I assumed these were correct so each time I looked at them under magnification, I could see the symmetry and assumed "all transistors are correct and properly placed."

Could this be my problem and solution? If so, why do the Positive rails work?? 

I will change them out after work and see what happens.

Anyway, here are the measurements you requested?

Parts from mouser.com

771-BC860C235
771-BC850C235
771-BCP53-16115

T1 3.1v     T3 5mv     T5 3v    T7 2.8v     T9 2.5v     T11 565mv     T14 ???     T15 0.64v     T17 0.64v     

T19 0.62v     T21 0.62v     T23 0.61v     T25 0.61v       T29 2v     T31 0.93v

T27 27mv     T33 555mv
 

[peranders]

is this measurements with corrected transistors? My basic theory was (if you remember) that you have some parts in the wrong positions. when you lift the R3 ALL transistors should be shut off. You can easily check that with measuring the voltage across all emitter resistors.

[BMF]

P-A,

I apologize for my last confusing post.

The measurements listed were made Before changing out T/V 13 and T/V 14.

All 4 LEDs are now ON! Voltages appear to be within spec.

Next up, biasing and then trying it out.

Thank you for all your support!

I would like to emphasize the importance of making sure T/V 13 and T/V 14 are reversed from the rest of the "odd" and "even" numbered transistors... for newbies like me!

Keith

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[peranders]

Good news. Now calibrate the amp!