Cadence ZRS8000D voltage regulators

[Dr Zeus]

Ive got this amp in for repair. It powers and produces rail voltage from the best that I can tell (+-82vDC) but none of the opAmps are getting regulated voltage.



Top left of this photo has 2 transistors KA7815 at L7815 and KA7915 at L7915. Referencing amp general ground measures less than +-0.020vDC on all three legs of both.

Bottom of the driver board on the left of the amp has KA7812 at L7812 and KA7912 at L7912. KA7812 measures -82vDC on all pins. KA7912 measures +82vDC on all three legs of both.

The amp also lacks LED illumination when powered, although both Power and Protection LEDs test out and light with the DVM.

Any clues to start? Where would I find secondary center tap if general ground is not the best?

[Dr Zeus]

I pulled KA7812, KA7912, KA7815, and KA7915 off the PCB and each are measuring oddly using the DVM, with KA7912 measuring the worst.

The pads where for these transistors measure the same voltages as post 1 referencing amp general ground.

KA7912 diode checks with a beep and 0.150 or less reading across all legs.
Leg 1-2: 203 ohms
Leg 1-3: 73 ohms
Leg 2-3: 166 ohms

If the regulators shorted, what are the chances the opAmps were also taken out?

[Perry Babin]

I think you'll have to replace the regulators to determine what was damaged. There may be resistors in series with the regulators. Check them if you have no input voltage to the regulators.

[Dr Zeus]

Alright. Of my parts-amp collection I found a busted PCB to a Maxxsonic branded amplifier which is ironically 90% similar to this Cadence. Fortunately it looks like the audio aide of the parts amp is still in-tact with opamps and components usable for testing. I've got work to do!

[Dr Zeus]

Well, with replacement regulators the amplifier experiences the same issue where voltages are as posted in the first post. The only main difference now is the KA7912 as stated in the second post was replaced with a good regulator. All regulators are now replaced from the parts amplifier.

On powerup, nothing gets hot but nothing on the audio side gets regulated voltage. The replacement regulators appear to be checking out OK by the dvm.

In compairing this amplifier to my spare one, the resistance of the regulator pads are different readings, where legs 2 & 3 of the KA7812 are measuring 4k ohms. The spare amp is measuring in the millions.

[Dr Zeus]

I just noticed there appears to be some heated/damaged small transistors close to the PS driver board of the amplifier. Four transistors between the two power supply coils have mild burn and de-solder marks under the board. Two are C3228 and the other two are A1275. You can barely see them in the first photo.

Q7: C3228
Q8: A1275

I cant read the board for the other two because glue from the coils are covering the letters.

Could these have anything to do with the regulators being out of order?

[Dr Zeus]

I just figured out something (Me=stupid!) This amp runs with two power supplies, and one of the power supplies is toast. All 6 PS fets (Q11 through Q14) are shot. IRFP064N. If I rebuild both supplies I'd need 12 of these fets, and they are 'dang' expensive and sold out in a lot of places. Pacparts wants $7.50 each.

In the meantime, I'm gonna pull one or two from the good supply and see if this amp will power up completely.

[Dr Zeus]

Q8A wich was a C3228 and PS driver dropped one of it's legs. I had a spare; C3227, which seems to be alright in place of the C3228 for now. I moved two fets from the good supply side to the previously blown side and now both Power Supplies power up the amp. As I was measuring the opAmps (+-15vDC now WOhoo!) several of the output transistors went up; Q13, Q14, Q15, Q16, Q17.

Theres a fair chance that I should have first tested the outputs. My bad; anyways the bank is now shorted legs 2&3 on Q13, Q14, Q15, Q16, Q17 which are all IRF9640 fets.

[Dr Zeus]

Clipped the above, and now Q201 through Q205 are getting warm as well; also IRF9640s. The gates for these outputs are leading to Q5 and Q23 on the driver board (Left rising board in first post) which are medium sized surface mound transistors with "AG QW" written on them which are SOT89 sized BCX52-10 PNP drivers.

I'll have to figure out if these or any other component on the driver board has failed...

Can I use anything as a sub for these such as MPSA06/56

[Dr Zeus]

This amp has the same output driver board as the Hifonics Brutus amp on the DVD; except whats strange is the orientation of the board on the main PCB is flipped 180 degrees. I'm guessing this driver board is either symetrical or the Brutus amp likely has the audio section reverse from this Cadence (Most likely because the TO-220 regulators are on the other side). The Brutus amp uses different PS Fets among many other things.

Which driver<s> would possibly be the best ones to check on this board?

I'm also trying to come up with a customer cost and replacement parts for this amp. Since I must replace the entire power supply, one option is to use IRFP064N fets, but they are about $7-$10 each most everywhere. Is there a better option that isnt as costly? Arrow has IRFP064PBF which are ~$2.38 each but they appear to be rated at 100V / 31A. The originals appear to be 60V / 110A.