Happy saga of a successful repair:
Infinity Intermezzo 2.6 10-1-16
Open circuit with ohmmeter. No power on.
There is no output, and
The LED on the volume control does not light, red or green”, check the items listed below:
Check the 3A line fuse to make sure it’s not open. If open, replace with a 3A MDL (.25 x 1.25) slo-blo fuse,
Infinity part# 80126 fuse is good
R22 can be checked in-circuit and should be:
100k ohms _5%. It measures 46.6k ohm and should be replaced.
Warming up the soldering iron and trying to find 100k ohm resistor. But there are two other smoked resistors, never the less, lets try the factory specified repair
Soldered in a 100k ohm resistor and connections verified for sure at the inner aspect the outer aspect is questionable.
We still do not have turn on, why? Switch is good. At least four outputs have no gain, before I realized how to test MOSFETS.
Outputs IRF9540 NTE2371 2.79 ebay
IRF530 NTE66 3.99 for 5 from ebay
Drivers
2N5551 NTE194 1.39 available
2n5401 NTE288 0.99 available Cracked a diode measuring the fourth mosfet.
OK we checked the Sencore TF26 and standardized such. The Sencore works on NPN and NPN mosfets if single gated. Let’s check the drivers now. All drivers have good gain.
Components around Q5 main board are charred. What is Q5? IRF740 Mosfet
IRF740 NTE2397 5.19 available.
Q5 is shattered.
Two resistors below it are unintelligible. Likely 475 ohm and 22 ohm.
OK the transformer winding connecting to IRF740 is good, all transformer windings were checked for open windings and they check good. C9 is shorted at 611ohms! So we need two 4700pf caps. OK I cut C9 and we are still at 613 ohms; is the short at IRF740 or the zener diodes
I cannot access Z4, and Z5 to test, same is true of R19, but they visually look good.
Shopping list
IRF9540 x 2 2.79 ebay purchased
IRF530 x 2 3.99/5ebay purchased
IRF740 x 1 4.75/5 ebay purchased
4700pf x 2 3.60/4 ebay purchased
Total 15.13 + 5 service manual 20.13, which is reasonable.
IRF740 is here. Wow heat sink assembly just unscrews from the main board and then just slides off of Q4 and Q5. Q5 re-identified and double-checked. Q5 will be desoldered and replaced. OK the Sencore did not verify that the IRF740 worked, but the you tube how to test mosfets with a dmm verified it did work out of circuit. Soldered in and connections verified.
To test mosfet connect – lead to source
+ Lead to drain
+ Lead to gate momentarily,
With known good mosfet this test does NOT work in circuit.
Z4 and Z5 test as diodes with fluke dmm.
22-ohm resistor (highly likely, difficult to tell because two bands are burnt) I have on the workbench.
I assume the other resistor is 475 ohms and we can hookup 390 and 82 ohms in series to get 472, close enough; on the workbench; measured it is 462 ohms.
The four power mosfets are NOT shorted drain to source, so just fix power supply, resolder diode, then power on.
I can clearly see that one of the resistors was R20 at 22 ohms and the other resistor was directly connected to it; likely R19 at 472 ohms for spec. Resistors soldered in and connections verified! Soldered in the C9 capacitor and connections verified.
Reconnected the power supply, and applied new silicon grease to the heatsink.
1N4148 is the diode I fractured. NTE519 is the cross-reference 100 volt 2 amp diode ultra fast! 1.49 at fry’s; soldered in and connections verified!
2N5401 is Q6, which cross references to NTE288. Traditional EBC pinout. R22 should be continuous with the collector. Connections verified!
I put enclosure back together with ¼ of the screws to test the amp. The woofer is not connected, but has a 3.5-ohm resistor in place of it. The tweeter connections have infinite resistance so that is connected. Will power on with eye protection and the variac.
No power on! On off switch works but we have infinite resistance across the circuit!
I found the schematic for the 250-watt power supply that powers the power supply board!
Check the bridge rectifier. Apparently the 250-watt power supply works, based upon diode tests without removing the board. R26, which is a surgistor measures 10 ohms at room temp, but goes down to 3 ohms with heat.
J4, which is the hot lead, makes it to the IRF740 that was smoked. So, CT- is similar to ground, whereas CT+ is similar to 120 volts positive. Pri+ is 120 volts positive. J2 and J1 CD+ and CD- respectively.
We may need the infinity hybrid bash controller IC chip.
OK the infinity service manual says replace all the fets and the bash controller chip
1) Q5 IRF740 replaced already
2) Q4 IRF740 tests well and good
3) Q1 IRF540 27N10E tests well and good
4) D1 MUR1540 NTE6248 highly questionable replaced!
5) D3 MUR1620 FEP16DT NTE6240 shorted all leads 3.49 in stock at Fry’s
Replacement NTE6240 checks well and good.
C6 has zero uf and a dead short! Is this the culprit or is it the rectifier. Removed from circuit and the cap measures over 1000uf, so it is good.
Removed the FEDP16DT, and it was definitely shorted. No wonder the BASH supply did not work. However we need to insulate the tab and also maintain good thermal conductivity! Done but needed electrical tape.
IRF9540 x 2 2.79 ebay purchased
D6 and C3 mounted and connections verified!
D1 is 324 ohms to ground. New NTE6248 measures as a diode. Actually D1 measures well and good out of circuit.
We are nearing the point where all that is possible has been done already!
Reverified that nothing is shorted to the heatsink and the black screws do conduct well!
OK I hooked up 3 Flukes to the woofer, tweeter, and CD- and CD+ and no voltage on
any of the 3 Flukes. However now we are burning 0.1 amps at 120 volts or 12 watts and the green LED is illuminated.
OK I disconnected the fluke connected to CD- and CD+, and reconnected the wires to CD- and CD+ and cautiously powered up on the variac, so far so good, 12 watts and I think I heard oscillation. Now let’s put a signal into the speaker and power up.
Same readings now connect scrap speaker and evaluate. However the above was carried out with no power to advent 400 receiver as a source. Powered up advent 400 and we get 12 watts input and have no dc across scrap speaker but have AC, which varies according to Advent 400 volume control. Let’s go straight to the speaker now. OK we have some output to the speaker and it is intelligible but low in volume. OK J1 and J2 are CD- and CD+. OK we have 144 volts DC at J4 and J5, which are marked primary positive and primary negative. Could this also be DC++ and ground? We have DC++ and ground across C6, which is 1000uf at 100 volts. No voltage at C6! Primary + is continuous to Q5. Q5 goes to ground appropriately. OK if we scope the gate of the IC chip assembly and measure Vcc we can determine whether or not the bash controller is up and running. OK J2 was already measured and it is V++ also, so likely the chip is not getting Vcc. Check transformer winding. OK windings are good. Q4 pin 3 is 9 ohms to ground, should this be 0 ohms? Pin 2 gets CT+, so there are appropriate resistances to Q4. CT+ makes it to Q6. Sencore TF26 would not be able to connect anywhere as there are no long leads. 6 and 13 should be ground and they are not on the HC1011 chip. J2(V++) should make it to the chip and it does not. Does J2 conduct to D3, no it does not! Legs one and three of D3 conduct, so likely the transformer winding is good. J2 does not make it to C6! J2 is continuous with C10. J2 does not make it to D1. Is C6 positive continuous with D1 top hat, yes! C6 is also continous with pin one of the U1 bash chip. Are C10 and D1 continuous? C10 and C6 are DISCONTINOUS! There is a wide berth copper foil connector that is also discontinous from C10 to top hat of D1. Jumper wire soldered and connections verified. Now let’s disconnect the J1 and J2 from the power amp and measure the voltage! OK essentially we still have zero volts.Back to the drawing board, R6, 5.11kohm should be grounded to the PWM ground and it is. Pin 6, 13, and R6 are connected together. There are 3 different gounds; ground, PWM ground, and audio ground.C6 negative should be continous with pins 6 and 13; and it is continuous.
Time to taste the soup. We have output but the same thing super low volume. J1 and J2 have no voltage. Hooked up J1 and J2 and we have more output but super low volume.Time to scope pins 13 and 14 on the BASH controller. OK there is no waveform at the gate. Furthermore there is no voltage at V++ on the scope, referenced to ground. This was double checked with the Fluke DVM. PWM ground is continuous with the C6 minus as appropriate.
D4 diac appears open, which may be OK. Q6, 2N5401 shows that the EB junction is questionable, but checks good on the Sencore TF26 Cricket analysis.
Q2, 2N4401, NPN checks well and good on the Sencore TF26 Cricket Analysis. Pin 11 and 13 should be negligible resistance; and it is as expected zero ohms. Check Q3, 2N5551, tests well and good on the Sencore TF26. 15v positive and negative feed the Output of LM324 which is LED control goes to J3G goes to on/off
J4D goes to LED Feature Mezzanine
OK what feeds the 15v positive and 15 volt negative? The 25 volt positive and negative feed the 15v positive and 15 volt negative.
Check outputs of D6 and D7 on power supply for 25 volt positive and negative.
U2 and U3 15 volt regulators are on the power amp board
I cannot trace this based upon the schematic, but I have a wild hunch that it is from the power supply board. Yes following the actual J14 cable it does go to the power supply board, it then changes its name to J6. J6A and J6C connect to the diodes D6 and D7 so the core supplying D6 and D7 should be energized. J2/J8 should be grounded!
Is the transformer winding hooked up to D3 smoked; transformer winding checks well and good. The D3 diode is indeed continuous with C6 negative. Is pin 2 of the D3 diode continuous with pin 1 of the chip? NO IT IS DISCONTINUOUS! Is pin 1 of the chip continuous with C6 positive; yes! Pin 2 of D3 is DISCONTINUOUS with C6 positive! Need to repair trace! Soldered the repair trace and connections verified. Now the D3 diode is continuous with pin 1 of the BASH amp. Ok powered up on variac and there is .05 volts DC at the speaker, so we have a basically good offset voltage. Let’s connect the speaker now. Wow it now works in the test speaker and the actual speaker! If anyone wants the service manual PM me.
