Lol OK
So we need the voltages on abc. I'm surprised they are "large" devices but that's no problem.
Have to stay logical, so measure the voltages... we know the 30 volts is OK, and we know the negative rail to the opamps is not.
The worry now is that something has happened and there is an issue with something fed by that rail that's seeing off the regulator but we wont know untill we go through the process.
So we need the voltages on abc. I'm surprised they are "large" devices but that's no problem.
Have to stay logical, so measure the voltages... we know the 30 volts is OK, and we know the negative rail to the opamps is not.
The worry now is that something has happened and there is an issue with something fed by that rail that's seeing off the regulator but we wont know untill we go through the process.
Sounds promising... take the TIP32 PNP transistor out and see if -12 volts appears across zener. Does the zener read short on ohms range/diode check ?
Edit the possibilites now are that the zener is duff/and/or/the TIP32C. Don't switch on with the zener removed as that would put full supply on the opamps. The resistor feeding the zener should feel hot. The TIP32C is an old "standard" and easily substituted.
Edit the possibilites now are that the zener is duff/and/or/the TIP32C. Don't switch on with the zener removed as that would put full supply on the opamps. The resistor feeding the zener should feel hot. The TIP32C is an old "standard" and easily substituted.
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Hi guys, pulled the tranny (that sounds suss), anyway no charge at the zener or on the output of the resistor ( which was a little warm - possibly from the iron). No resistance on zener on 2000k ohm setting. diode check is showing zero both ways both tests done in circuit - have I done right? Resistor showing 19 on 2000k setting.
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With the TIP32 removed there will be -30 volts on both sides of the resistor feeding the zener. I think it's a 3K3 if I'm reading the photo OK "3301" Thats 3,3,0 and 1 nought.
Easiest quicky way is to swap the zener for a resistor that gives around 12 volts on the junction of the two components... and that voltage feeds the base of the TIP32. A 3K3 would give -15 volts.
So that's one option... resistors in place of zener as a temporary test.
The other involves using a reversed biased base emitter junction to give around 8 volts. The junction behaves as a zener in this condition. And you have spare transistors.
Do you want to try it ?... it should be OK as we check the voltage before fitting the TIP32 and it may prove if anything else faulty.
Easiest quicky way is to swap the zener for a resistor that gives around 12 volts on the junction of the two components... and that voltage feeds the base of the TIP32. A 3K3 would give -15 volts.
So that's one option... resistors in place of zener as a temporary test.
The other involves using a reversed biased base emitter junction to give around 8 volts. The junction behaves as a zener in this condition. And you have spare transistors.
Do you want to try it ?... it should be OK as we check the voltage before fitting the TIP32 and it may prove if anything else faulty.
OK 
Using the transistor is easy, two wires ... I'll draw it anyway and you can have a look.
Also it's worth looking closely at all the small IC's... just to make sure none looked physically "cracked" and damaged due to over volts. That's my main concern... trying to avoid you keep ordering odd bits one at a time.
Using the transistor is easy, two wires
... I'll draw it anyway and you can have a look.Also it's worth looking closely at all the small IC's... just to make sure none looked physically "cracked" and damaged due to over volts. That's my main concern... trying to avoid you keep ordering odd bits one at a time.
You can make a zener of around 8 volts with a base emitter junction of a transistor. You can use either an NPN or a PNP device.
You connect just the base and the emitter in place of the zener diode.
This applies whether using either a new zener or using the transistor.
1. Remove the TIP32
2. Remove the zener.
3. Either fit a new zener, then switch on WITHOUT the TIP32 fitted and confirm that -12 volts now across zener.
4. To use transistor... if using a TIP 32 as a zener connect the base to ground (that's the stripy end of where the zener was) and the emitter to the 3k3 resistor.
Now switch on (still without the main TIP 32) and confirm around -8 volts across our "new zener" only if this is correct do we proceed.
5. Whichever method was used we now have to fit the main TIP32 regulator (use a new one) and power up. When you power up I would keep hold of the main TIP32 regulator (not the zener) and make sure it doesn't overheat... it could if there's a fault... so be prepared to switch off instantly if so. Hopefully it will work.
If you only have one new TIP32 use that for the main reg and try the old as the zener. If by chance the old one is duff you can use a TIP31 as the zener, use the same legs, base and emitter but reverse them on the board. That only applies for the zener... not the main reg which must be PNP.
Good luck with it... as long as the voltage is -12 or less across the zener before fitting the main TIP32 then you won't have problems.
You connect just the base and the emitter in place of the zener diode.
This applies whether using either a new zener or using the transistor.
1. Remove the TIP32
2. Remove the zener.
3. Either fit a new zener, then switch on WITHOUT the TIP32 fitted and confirm that -12 volts now across zener.
4. To use transistor... if using a TIP 32 as a zener connect the base to ground (that's the stripy end of where the zener was) and the emitter to the 3k3 resistor.
Now switch on (still without the main TIP 32) and confirm around -8 volts across our "new zener" only if this is correct do we proceed.
5. Whichever method was used we now have to fit the main TIP32 regulator (use a new one) and power up. When you power up I would keep hold of the main TIP32 regulator (not the zener) and make sure it doesn't overheat... it could if there's a fault... so be prepared to switch off instantly if so. Hopefully it will work.
If you only have one new TIP32 use that for the main reg and try the old as the zener. If by chance the old one is duff you can use a TIP31 as the zener, use the same legs, base and emitter but reverse them on the board. That only applies for the zener... not the main reg which must be PNP.
Good luck with it... as long as the voltage is -12 or less across the zener before fitting the main TIP32 then you won't have problems.
Attachments
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Mooly,
You are the smartest cow I know, it works hooray!! sensational !! that tiny little zener was the culprit, replaced with a 12v from a local store, put it in sans regulator, test - 10 to 11 V, put in old regulator ( in case I did something wrong had the new one as backup), lo and behold music giver of life, food of love. Really appreciate all the time and effort you have put in, I got my boom back! Now supplemental question what are the potential pitfalls of seeing if this chip can be grounded? would be so much easier if I didn't have to isolate this chip, but obviously don't want to undo the good work done. Also do I have any options re those little fuses - will be about $22.00 aussie (30p or 0.5 Euro - i kid) in fuses, not the end of the world by any means but if there is an option??
Thanks again Mooly, I haven't learned as much as you have tried to teach, but I have definately learned. While I always knew a circuit meant electrons finishing where they started, I now think of a pcb as a little river system, with eddys, dams and flows, makes it a little less bewildering for me...
You are the smartest cow I know, it works hooray!! sensational !! that tiny little zener was the culprit, replaced with a 12v from a local store, put it in sans regulator, test - 10 to 11 V, put in old regulator ( in case I did something wrong had the new one as backup), lo and behold music giver of life, food of love. Really appreciate all the time and effort you have put in, I got my boom back! Now supplemental question what are the potential pitfalls of seeing if this chip can be grounded? would be so much easier if I didn't have to isolate this chip, but obviously don't want to undo the good work done. Also do I have any options re those little fuses - will be about $22.00 aussie (30p or 0.5 Euro - i kid) in fuses, not the end of the world by any means but if there is an option??
Thanks again Mooly, I haven't learned as much as you have tried to teach, but I have definately learned. While I always knew a circuit meant electrons finishing where they started, I now think of a pcb as a little river system, with eddys, dams and flows, makes it a little less bewildering for me...
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Thanks for the kind words it's great that you have it all working.
Those fuses are a real rip off I know... alternatives... what you can get really. They are a real safety feature though... never be tempted to leave them shorted. If a short occured on the PCB the transformer would overheat very quickly... and that's a real fire hazard.
These's nothing to stop fuseholders and 20mm glass fuses being used, or "wickman" fuses of correct rating (anti surge whatever type) like these,
Your Search Results | Farnell Australia
these types of fuse are widely used in commercial stuff, TV's etc so should be available but they aren't cheap (for what they are) as you can see.
If there's room on the PCB you might be able to drill holes and wire PCB mounted fuseholders in neatly like these,
BULGIN|FX0321|FUSE HOLDER, 20X5MM | Farnell Australia
The isolation thing on the chip ! Why not measure on the metal tab version which pin actually connects (reads short) to the tab. It may well be pin 4 (the negative supply) rather than pin 7 (the "ground pin"). Then see if that's the same as the heatsink or not. Obviously if the tab is connected to pin 4 internally in the chip and the heatsink is "ground" then it's no go.
The type of insulating pad you need is again the thing that's used in TV repair etc for insulating power transistors. Probably something like a TO3P outline would just fit,
BERGQUIST|3223-07FR-104NH|THERMAL PAD, TO-3P | Farnell Australia
any repair shops might have something suitable on a scrap chassis maybe or sell you a new one. I don't know how your chip is secured, it may be clamped or might use the hole in the tab... which means fitting an insulating "top hat" so the screw doesn't create a short. I'm guessing it's clamped though, hopefully.
These are the top hats, the T0220 mica washer though is too small, you need the T03P or larger. If needs be you can use two washers butted together.
MULTICOMP|MK3306|INSULATING KIT, MICA TO-220 | Farnell Australia
And you have done really well getting this far... excellent job.
it's great that you have it all working.Those fuses are a real rip off I know... alternatives... what you can get really. They are a real safety feature though... never be tempted to leave them shorted. If a short occured on the PCB the transformer would overheat very quickly... and that's a real fire hazard.
These's nothing to stop fuseholders and 20mm glass fuses being used, or "wickman" fuses of correct rating (anti surge whatever type) like these,
Your Search Results | Farnell Australia
these types of fuse are widely used in commercial stuff, TV's etc so should be available but they aren't cheap (for what they are) as you can see.
If there's room on the PCB you might be able to drill holes and wire PCB mounted fuseholders in neatly like these,
BULGIN|FX0321|FUSE HOLDER, 20X5MM | Farnell Australia
The isolation thing on the chip ! Why not measure on the metal tab version which pin actually connects (reads short) to the tab. It may well be pin 4 (the negative supply) rather than pin 7 (the "ground pin"). Then see if that's the same as the heatsink or not. Obviously if the tab is connected to pin 4 internally in the chip and the heatsink is "ground" then it's no go.
The type of insulating pad you need is again the thing that's used in TV repair etc for insulating power transistors. Probably something like a TO3P outline would just fit,
BERGQUIST|3223-07FR-104NH|THERMAL PAD, TO-3P | Farnell Australia
any repair shops might have something suitable on a scrap chassis maybe or sell you a new one. I don't know how your chip is secured, it may be clamped or might use the hole in the tab... which means fitting an insulating "top hat" so the screw doesn't create a short. I'm guessing it's clamped though, hopefully.
These are the top hats, the T0220 mica washer though is too small, you need the T03P or larger. If needs be you can use two washers butted together.
MULTICOMP|MK3306|INSULATING KIT, MICA TO-220 | Farnell Australia
And you have done really well getting this far... excellent job.
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Just to round out have ordered the wickman fuses, a new diode that will fit a little better than the leg mounted one I purchased locally and a mica insulating kit. I think I may have jumped the gun in replacing the chip - oh well. The tab of the chip is connected to pin 4, with a small resistance between pin 7 and the tab so isolated it will be. Once again thanks for all the input - I think I may find myself getting drawn more into this new world 
.
.
Tab to pin 4, I suspected as much... it's to do with the way IC's are made, the base or substrate of the chip is usually the most negative point, and that ends up being the metal tab.
Faultfinding is interesting (it was the day job and usually all the evidence is there...
When you have fitted the insulator check on ohms that the tab is isolated from the heatsink... it will read something if checked in circuit but not of course 0.00 ohms.
You think you might have jumped the gun replacing the chip ?
Well... I think this is what happened (don't shout)
An overload as you mentioned caused the fuse to pop, the IC could well be OK.
The zener as a standalone fault is possible, but it's not chip related or overload related... did you maybe possibly perhapsly just short or measure when the main caps were charged and put 30 volts momentarily across the zener. Or something metallic on the PCB. Have done that sort of thing many times over the years.
We'll never know. As long as you use a bulb, then fitting the old IC should be OK if you ever wanted to test it. Always power up with no speaker connected and check the DC volts across the speaker output is zero before connecting speakers... that applies to any amp when faultfinding.
A great result though, and all in under a 100 posts
(
Faultfinding is interesting (it was the day job
and usually all the evidence is there... When you have fitted the insulator check on ohms that the tab is isolated from the heatsink... it will read something if checked in circuit but not of course 0.00 ohms.
You think you might have jumped the gun replacing the chip ?
Well... I think this is what happened (don't shout
)An overload as you mentioned caused the fuse to pop, the IC could well be OK.
The zener as a standalone fault is possible, but it's not chip related or overload related... did you maybe possibly perhapsly just short or measure when the main caps were charged and put 30 volts momentarily across the zener. Or something metallic on the PCB. Have done that sort of thing many times over the years.
We'll never know. As long as you use a bulb, then fitting the old IC should be OK if you ever wanted to test it. Always power up with no speaker connected and check the DC volts across the speaker output is zero before connecting speakers... that applies to any amp when faultfinding.
A great result though, and all in under a 100 posts
(
I'm sure we can get this up to 100 posts! Well wickman fuses finally arrived and all is back together - those fuses were a little large so had to put a 90 degree angle in the legs to fit to the pcb. Back together and all working!!
Funny with that zener, in my ignorance and randomly testing things I checked all the diodes and this one had no reading well before Mooly diagnosed it as the fault, not knowing what it did or if being in circuit would affect the readings I didn't think much of it - my thought with such things is that it is always the obvious thing...(maybe not always). Was pretty careful with the board other than when I measured across the + and - of the regulator - test probe became arc welder. Any way let this be a lesson to anyone working with a software based active crossover - be very careful with how much input you give your expensive and sensitive equipment....I know I will be
Funny with that zener, in my ignorance and randomly testing things I checked all the diodes and this one had no reading well before Mooly diagnosed it as the fault, not knowing what it did or if being in circuit would affect the readings I didn't think much of it - my thought with such things is that it is always the obvious thing...(maybe not always). Was pretty careful with the board other than when I measured across the + and - of the regulator - test probe became arc welder
. Any way let this be a lesson to anyone working with a software based active crossover - be very careful with how much input you give your expensive and sensitive equipment....I know I will be- Status
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