So assuming the afore-mentioned current sources are still in shutdown, what are voltages at Q100C and Q102E? And at D133 anode, D134 cathode? Junction of R183, R185?
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Thank you @pitbul , I checked n101-2 resistor networks and values appear to have drifted 5%, 13% till 17% compared to the schematic.. "similar values" however could be spot from the working channel, would you suggest to proceed updating all of these with 1% 1/4w resistors anyway?
Assuming metal film 1/4w will do, as these networks are kind of weird components to me, shall the ends of two resistors be filed and inserted in the same pcb hole?
Not sure how this might affect the amp function though, care to describe which symptom you were having on your amp/what is the function/need of those networks? (I reckon your reply would be more useful to other experienced members who are graciously helping me) Thanks a lot!
@BSST I have measured and added the voltages in the picture, should be clearer than words - hopefully, thanks a lot so far!
Sorry for this, actually I am not able to spot Junction of R183, R185 (nor q121/q122) in MT2400 schematic, maybe these are from MA2400 schematic? mine is a MT2400 (Micro-tech) see following (red are measured values on non working channel, green are values from good amp channel when present):
The initially measured values at startup are indicated, after a 2/3 seconds these values change according to above.
Hoping I replied to all questions.. In the meanwhile I came slowly around to ordering the magic smoked 2SC2837 Q1 for the other channel, hoping it will be up and running soon, fingers crossed..
Assuming metal film 1/4w will do, as these networks are kind of weird components to me, shall the ends of two resistors be filed and inserted in the same pcb hole?
Not sure how this might affect the amp function though, care to describe which symptom you were having on your amp/what is the function/need of those networks? (I reckon your reply would be more useful to other experienced members who are graciously helping me) Thanks a lot!
@BSST I have measured and added the voltages in the picture, should be clearer than words - hopefully, thanks a lot so far!
Sorry for this, actually I am not able to spot Junction of R183, R185 (nor q121/q122) in MT2400 schematic, maybe these are from MA2400 schematic? mine is a MT2400 (Micro-tech) see following (red are measured values on non working channel, green are values from good amp channel when present):
The initially measured values at startup are indicated, after a 2/3 seconds these values change according to above.
Hoping I replied to all questions.. In the meanwhile I came slowly around to ordering the magic smoked 2SC2837 Q1 for the other channel, hoping it will be up and running soon, fingers crossed..
Would you report emitter voltages at Q105 and Q109 after turn-on transients have settled? What is status of E100, E101, ODEP LEDs?
For q105 Ve is 55.7Vdc at startup, turning into 57.2Vdc after few seconds, for q109 Ve is 5Vdc at startup, while slowly rising to about 7Vdc in 10 seconds or so.
The e100 and e101 are off all the time (I tested the leds with diode function and they seem operational).
The e100 and e101 are off all the time (I tested the leds with diode function and they seem operational).
I believe my eyes and schematic have inadequate resolution. 🙁
I intended to ask about Q106 emitter (junction with R141), not Q105.
Do our schematics agree? Seeking confirmation.
I meant to ask earlier: Do active LEDs indicate the failed state?
Thanks.
I intended to ask about Q106 emitter (junction with R141), not Q105.
Do our schematics agree? Seeking confirmation.
I meant to ask earlier: Do active LEDs indicate the failed state?
Thanks.
e100 and e101 are always off in standard working operation, assuming they turn on to signal the presence of a problem.
In my amp they are off anyway.
In my amp they are off anyway.
Sorry I'm so slow to arrive at focus on the problem. Am I correct in understanding that you can achieve the -ODEP voltages, but not the +ODEP? What voltage variation are you able to achieve via R132? Also, observe behavior of Q109 emitter re TP-110. How does it compare to the same points in the working channel?
I believe insufficient difference between the OPED voltages eventually leads to inadequate voltage across Q318.
I don't think you mentioned the direction of drift. If they shrank toward lower resistance, that might be problematic re reducing voltage difference.
I believe insufficient difference between the OPED voltages eventually leads to inadequate voltage across Q318.
I don't think you mentioned the direction of drift. If they shrank toward lower resistance, that might be problematic re reducing voltage difference.
geoturbo, I suggest that you replace network resistors with 1% tolerance, you will avoid unnecessary trouble. With correct values amp will be correctly aligned and you will be able to adjust idle current.
Crown amp are designed with single supply and you have to have half voltage on speaker terminals, your reference for measuring this is one of the power supply polarities. Measuring with gnd reference will lead you to a false conclusion. With corected resistor network you are able to have mid voltage, if not try to slightly deviate from the resistance value (put trimer and adjust) until V/2 is on the speaker terminals.
Crown amps are good sounding amps and you will enjoy after repair is done correctly.
Crown amp are designed with single supply and you have to have half voltage on speaker terminals, your reference for measuring this is one of the power supply polarities. Measuring with gnd reference will lead you to a false conclusion. With corected resistor network you are able to have mid voltage, if not try to slightly deviate from the resistance value (put trimer and adjust) until V/2 is on the speaker terminals.
Crown amps are good sounding amps and you will enjoy after repair is done correctly.
Thank you @pitbul , I have remeasured values of network resistors n101 and n102 (in circuit though) and values appear to have drifted towards lower resistance values (same behaviour could be spot in n201 and n202 networks from the other channel). The history of this amp is unknown, it could well have heavily worked in a very hot and sustained environment (cannot be sure this is the reason though).. I will definitely get the resistors in the next PO to Mouser.
@BSST no need to apologize, please. Even if slowly we're hopefully getting there/I am learning in the process.. the patient is on the kitchen table, as long as wife is allowing to keep him alive (and not throwing it out of the window) everything's going to be fine.
I'll try to speed up getting parts/fixing the network thing but cannot be done promptly I am afraid.. values of resistors shrank in value for all networks plus mid point is not at mid point anylonger (I think putting values here would not be any more relevant than this).
-ODEP is close enough to indicated table value per °C degrees (values could be found in service manual around page 13), while I cannot set the +ODEP voltage properly on its trimmer. I recall I needed to substitute r134 because its value had drifted considerably, substituting r134 resistor voltages on u103 appeared to be back to normal values (same as those of the good channel).
Before observing q109 emitter/tp110 voltages I'll need to fix the good channel, I'll report back when good channel will be back working correctly (or dig out the second MT2400 but don't tell my wife)..
@BSST no need to apologize, please. Even if slowly we're hopefully getting there/I am learning in the process.. the patient is on the kitchen table, as long as wife is allowing to keep him alive (and not throwing it out of the window) everything's going to be fine.
I'll try to speed up getting parts/fixing the network thing but cannot be done promptly I am afraid.. values of resistors shrank in value for all networks plus mid point is not at mid point anylonger (I think putting values here would not be any more relevant than this).
-ODEP is close enough to indicated table value per °C degrees (values could be found in service manual around page 13), while I cannot set the +ODEP voltage properly on its trimmer. I recall I needed to substitute r134 because its value had drifted considerably, substituting r134 resistor voltages on u103 appeared to be back to normal values (same as those of the good channel).
Before observing q109 emitter/tp110 voltages I'll need to fix the good channel, I'll report back when good channel will be back working correctly (or dig out the second MT2400 but don't tell my wife)..
As pitbul suggests, maybe rebuilding resistor network will resolve the problem.
I'm guessing the resistor network is a 7-pin SIP (single inline package). I'm imagining a small perfboard module, but sounds like pitbul has firsthand experience.
Good luck.
I'm guessing the resistor network is a 7-pin SIP (single inline package). I'm imagining a small perfboard module, but sounds like pitbul has firsthand experience.
Good luck.
Your odep (J500-9 to J600-9) is about a volt low. That is about the missing voltage of a shorted transistor.
Replacing 1% resistors that are 13% off (N101A to F) may make the odep model the heat put in the output transistors by excessive current better. I doubt if that is going to get you a volt back.
I would go through the odep stack from plus 15 to minus 15, looking for transistors with a Vce of zero or thereabouts. If that doesn't work I'd look at transistors b to e to make sure it is in the range 0.7 to -6 (for npn). Opposite for pnp. Either of those cases the transistor is likely bad. Even if it checks good with the diode test of the dvm - which is done at 2 v, not at 30 the real transistors have to stand off. Also check for diodes not .7 forwards to -anything backwards.
And don't go probing around with two hands in an amp with >+-40 rails. That is a good way to kill yourself. Voltage over 25 across your heart can stop it. Get a couple of pamona grabber to banana plug cables or queballs (the original) for your DVM. Those are a lot less likely to short across 2 things and blow them up, too.
Replacing 1% resistors that are 13% off (N101A to F) may make the odep model the heat put in the output transistors by excessive current better. I doubt if that is going to get you a volt back.
I would go through the odep stack from plus 15 to minus 15, looking for transistors with a Vce of zero or thereabouts. If that doesn't work I'd look at transistors b to e to make sure it is in the range 0.7 to -6 (for npn). Opposite for pnp. Either of those cases the transistor is likely bad. Even if it checks good with the diode test of the dvm - which is done at 2 v, not at 30 the real transistors have to stand off. Also check for diodes not .7 forwards to -anything backwards.
And don't go probing around with two hands in an amp with >+-40 rails. That is a good way to kill yourself. Voltage over 25 across your heart can stop it. Get a couple of pamona grabber to banana plug cables or queballs (the original) for your DVM. Those are a lot less likely to short across 2 things and blow them up, too.
Thanks a lot guys, made some googling and could not find anything on these resistor ladders actually.. but it will be worth me thinks @pitbul , parts are on their way..
Thank you @indianajo, thanks for the safety tips, I am a diyer and not in the business so any word on safety tips is appreciated.
Before going back on the "faulty" channel (Channel A) which was discussed till now and not yet resolved, I would like to gently draw your attention on the "formerly" good one (the one where I shorted collector&emitter on q301). I actually substituted q301 with a new one, but the channel is not working still. Should I check q317 pre-driver next? I reckon 2SC3298B is out of production and could be substituted with MJE15032G (?).
Thank you @indianajo, thanks for the safety tips, I am a diyer and not in the business so any word on safety tips is appreciated.
Before going back on the "faulty" channel (Channel A) which was discussed till now and not yet resolved, I would like to gently draw your attention on the "formerly" good one (the one where I shorted collector&emitter on q301). I actually substituted q301 with a new one, but the channel is not working still. Should I check q317 pre-driver next? I reckon 2SC3298B is out of production and could be substituted with MJE15032G (?).
For sure yes, check, it is good to replace with complementary on negative side, what I mean is to have transistor on probably good (negative) side of the same series.
It is also good to check Q318 which is also part of the current regulation in the amp, don't see what is on other part of the schematics and I don't have much time now to look at the schematics, and also probably negative transistor below Q318.
It is also good to check Q318 which is also part of the current regulation in the amp, don't see what is on other part of the schematics and I don't have much time now to look at the schematics, and also probably negative transistor below Q318.
If you shorted q317 c to e check r318 r300 d301 to d304 etc.
MJE15031/32 could work but you might get more slew rate out of MJE15028/29 with lower base capacitance. These are driven by TO92 parts, right? not a lot of drive current. MJE15031/32 are super high Vce. I would install a small heat sink on q317 q319. Manufacturers tend to leave these out because the sink is $.25 and hand assembly costs $.50, but they can extend the life of a marginal predriver.
MJE15031/32 could work but you might get more slew rate out of MJE15028/29 with lower base capacitance. These are driven by TO92 parts, right? not a lot of drive current. MJE15031/32 are super high Vce. I would install a small heat sink on q317 q319. Manufacturers tend to leave these out because the sink is $.25 and hand assembly costs $.50, but they can extend the life of a marginal predriver.
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I had been a bit too fast and had already ordered MJE15031/32s, they are now travelling I will substitute both on each channel.. their cooling is luckily aided already, not sure whether it will make a difference to substitute them with MJE15028/29s later on..
I don’t see other shot components around, r324 is measuring 1k in the circuit but 13k correctly out of it.. so hoping to fix it with new predrivers.. fingers crossed..
I don’t see other shot components around, r324 is measuring 1k in the circuit but 13k correctly out of it.. so hoping to fix it with new predrivers.. fingers crossed..