250W amp - Mark Bass , Little Mark 250, of 2008, Italy

Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:4hk9r7h2t8o105tj2isub73tnsuiiu7rs2@4ax.com...
On Thu, 17 May 2012 08:13:30 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

When I get back to it I will try a 72V zener over one of the Brown-out?
zener chain of 220/200V zeners ...

I would think that 420VDC would be required to "turn on" the series
connected zener pair. A 240VAC source would produce 350VDC, so ISTM
that these zeners would be sensing an overvoltage rather than a
brownout. That said, the overvoltage would have to be an extremely
large one (+20%).

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
Click to expand...
That 47K must put the current into the uA regime
I doubt the Ebers-Moll sort of stuff applies in this sort of illegitimate
area of operation.
Tried a 6.2V 1W zener
Vz 6.22V (initially then rising) @ 78mA
96 percent of Vz @ 7.4mA
95% @ 810uA
92% @ 102uA
77% @ 9.6uA
66% @ 2.6uA (4.12V)
 
I'd forgotten to at least try the PA and its ok up to +/-25V dc on a bench
PS , 63V rated caps, so less than the 80V of that schematic.
The PA is certainly different to that schematic, pair of those 5 pin SAP
devices with intimate thermally connected sensing diodes
 
470K not 47K

I thought startup was a bit quiet, somewhere along the way I've managed to
short G-S on the high side IRF740. The other one changes state on DVM
"diode" test. Shorted turns on the switch mode transformer ? Change C68,
perhaps punch through ?
 
A dropper will go in with changed 1uF and new sacrificial IRF740 tomorrow
1KHz RLC testing of the Tx
feedback coil .039mH
240V tap 2.37mH to gnd
230V tap 2.22mH
100V 1.8mH looks reasonable

Along the way that Zener3 in the 200+220V zener chain is probably 6.2V (at
low uA level) and the 2N7002 (SMD topcode mark 782 R) functions as it should
 
On Thu, 17 May 2012 16:42:56 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

Along the way that Zener3 in the 200+220V zener chain is probably 6.2V (at
low uA level) and the 2N7002 (SMD topcode mark 782 R) functions as it should
Click to expand...
AISI, the 2N7002 FET should be off in normal operation, so I think
you're wasting your time in this area. If you're concerned about the
"Drive IC's" Enable pin, then disconnect D37.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:6o0br7l5o00sr2urjcet6rjmfoic8ehuer@4ax.com...
On Thu, 17 May 2012 16:42:56 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

Along the way that Zener3 in the 200+220V zener chain is probably 6.2V
(at
low uA level) and the 2N7002 (SMD topcode mark 782 R) functions as it
should

AISI, the 2N7002 FET should be off in normal operation, so I think
you're wasting your time in this area. If you're concerned about the
"Drive IC's" Enable pin, then disconnect D37.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
Click to expand...
I agree, there is another associted point. There is no jumper configuration
in that area for 100/120V countries so must be completely inoperative , in
mormal operation, in those countries
 
I suppose for this amp only used in 240V land, then replacement SMPS driver
powerFETs only need to be rated 600V/10A and for such an amp only in
100/110/120V land then 300V/20A rating
 
"Nut case Kook is off his rocker "


I suppose for this amp only used in 240V land, then replacement SMPS driver
powerFETs only need to be rated 600V/10A and for such an amp only in
100/110/120V land then 300V/20A rating
Click to expand...

** ROTFLMAO !!!!!!!!!!!!!!!!

Go look at the fucking CIRCUIT !!

Idiot !!!
 
I've acquired a new IR2153 and desoldered the original unkown driver and as
the Tx primaries are some distance from the driver IC, soldered in a turned
pin socket. The old one has Thailand and R3 mould marks on the underside and
perhaps the second line on the top starts with a 7 and the third line ends
with a 5 . I'm assuming there was a top line that is well ground out.
Will power up with a couple of droppers in there with 60 percent mains ,
still set on 240V jumper.
I can now compare old and putative replacement
 
A bit further forward I suppose. Exactly the same, for 2153 and original,
audible low level oscillator noise , 10 seconds or so after switch off
presumably coming down from ultrasonic and dropping in pitch over a couple
of minutes while there is HV in the main caps. And +/-0.5V on the main rail
caps transfered across the Tx from the startup pulses, instead of the +/-60V
or so . But no sustained drive. Next is some monitor of the Tx primary
feedback route to the driver and somehow monitor the osc f, perhaps change
the SM cap is easier, the SMRs measure ok. Any tricks for fooling the driver
into thinking there is more feedback than actual, a battery wired-in?
 
On Fri, 18 May 2012 08:49:52 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

I suppose for this amp only used in 240V land, then replacement SMPS driver
powerFETs only need to be rated 600V/10A and for such an amp only in
100/110/120V land then 300V/20A rating
Click to expand...
JP1 in the bridge rectifier area configures the unit for 240VAC
operation when open, and 120VAC when closed. In the latter case the
circuit becomes a voltage doubler.

Therefore Vdc = 350VDC in both configurations.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
On Fri, 18 May 2012 16:12:40 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

A bit further forward I suppose. Exactly the same, for 2153 and original
Click to expand...
I would have done a bit more testing before I opted for the 2153.

For example, I would have disabled the "Driver IC5" by shorting the
drain and source pins of T24 with a blob of solder (assuming a GDS
pinout). This would allow the Vcc capacitor (C52) to charge to the
IC's internal zener voltage. You could then compare this voltage
against the datasheet.

If the IC is oscillating, then this frequency may also provide a clue
to the chip's identity.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
On Fri, 18 May 2012 16:12:40 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

A bit further forward I suppose. Exactly the same, for 2153 and original,
audible low level oscillator noise , 10 seconds or so after switch off
presumably coming down from ultrasonic and dropping in pitch over a couple
of minutes while there is HV in the main caps. And +/-0.5V on the main rail
caps transfered across the Tx from the startup pulses, instead of the +/-60V
or so . But no sustained drive. Next is some monitor of the Tx primary
feedback route to the driver and somehow monitor the osc f, perhaps change
the SM cap is easier, the SMRs measure ok. Any tricks for fooling the driver
into thinking there is more feedback than actual, a battery wired-in?
Click to expand...
I'm having some difficulty understanding your plan, but first allow me
to explain how I think the circuit works. If I'm wrong, someone will
hopefully correct me.

Firstly, I would not attempt to substitute a battery for the
"feedback" voltage. This will defeat the IC's overload protection. If
you are going to do this, at least disconnect the 1uF capacitor (C68).
Also, instead of a battery, you could add several 270K feed resistors
between Vdc and Zener3. Then monitor the IC's Hi and Lo outputs. That
should at least give you some confidence in the IC.

As for how the IC works, I believe it would have a start mode and a
run mode. In the start mode it would draw a very small current,
probably less than 1mA. This would allow the Vcc capacitor (C52) to
charge. When Vcc exceeds the undervoltage lockout threshold, the IC
switches to run mode. It then attempts to kickstart the supply by
pulsing the MOSFETs. In run mode the IC would draw more current than
can be provided by R78, in which case C52 would begin to discharge. If
a regenerated supply cannot be developed from a secondary transformer
winding via D34, C69, D21, and C70, then C52 will discharge to below
the lockout threshold, causing the IC to revert to start mode. C52
then charges once again, and so on.

Therefore, if there is an overload on the secondaries, the regenerated
supply never eventuates, and the IC hiccups. Some IC's will count the
number of hiccups and shut down completely if there are too many
attempts.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:lkidr7lud934go47n39ao9oa079sm4mrik@4ax.com...
On Fri, 18 May 2012 16:12:40 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

A bit further forward I suppose. Exactly the same, for 2153 and original

I would have done a bit more testing before I opted for the 2153.

For example, I would have disabled the "Driver IC5" by shorting the
drain and source pins of T24 with a blob of solder (assuming a GDS
pinout). This would allow the Vcc capacitor (C52) to charge to the
IC's internal zener voltage. You could then compare this voltage
against the datasheet.

If the IC is oscillating, then this frequency may also provide a clue
to the chip's identity.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
Click to expand...

I am getting very inconsistent poor to bad ESR with electroC69 so will
change that and C70.
 
The 2153 has Thailand in a dimple on the rear of the package and an empty
dimple on the diagonal, this structure the same as the ground off one, minus
the R 3 .
I wonder how many IR 8pin , that pinning packages , were available in 2008
and a year or two before. Unfortunately I don't like using isolation
transformers and scopes on SMPS to narrow down a bit more, if I regularly
dealt with SMPS failures then perhaps it would be different. If this one
wasn't a lot of difficult to probe SM around the DIP8 SMPS driiver ,hemmed
in by heatsinks and large caps then may have been different
 
On Sat, 19 May 2012 09:10:14 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

I am getting very inconsistent poor to bad ESR with electroC69 so will
change that and C70.
Click to expand...
Those capacitors are a common reason for failure to start. Sorry, I
assumed you would have checked them.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:qeidr71te3214431fl2ptv7eie4mh3rq74@4ax.com...
On Fri, 18 May 2012 08:49:52 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

I suppose for this amp only used in 240V land, then replacement SMPS
driver
powerFETs only need to be rated 600V/10A and for such an amp only in
100/110/120V land then 300V/20A rating

JP1 in the bridge rectifier area configures the unit for 240VAC
operation when open, and 120VAC when closed. In the latter case the
circuit becomes a voltage doubler.

Therefore Vdc = 350VDC in both configurations.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
Click to expand...

So that 220/220V zener chain is perhaps more for the possibility of someone
jumpering JP1 to 100V and plugging in to 240V and instead of 350V dc trying
to get to 700V dc

Have got inundated with more normal stuff and this Mark will have to wait a
few days
 
I now see someone else has been here before and ground off IC5

music-electronics-forum.com/t10881/

What is the difference between IR2153 and IR21531?
The original has a diode between Vcc and VB so perhaps whether 2153 or 21531
or any other IR it should be the D variant or adding a high voltage diode
externally
 
On Sat, 19 May 2012 11:29:12 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

So that 220/220V zener chain is perhaps more for the possibility of someone
jumpering JP1 to 100V and plugging in to 240V and instead of 350V dc trying
to get to 700V dc
Click to expand...
Ah, that would make sense. I was wondering why there was a 275V MOV
across A-N, since that voltage would be below the overvoltage
threshold for the zener chain.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
On Sat, 19 May 2012 13:52:58 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

I now see someone else has been here before and ground off IC5

music-electronics-forum.com/t10881/
Click to expand...
Did you see the following post in that thread?

====================================================================
Have you noticed that pins 1 and 4 (Vcc and COM) of IC5 are reversed
on the schematic (if this is IR21531)?
====================================================================

I noticed on the one i'm working on. I was hoping it was an error in
the schematic but it is not.

I verifyed continuity to ground at pin 1.

So the IR21531 is not a drop in replacement as far as I can tell. I
have looked at just about every self oscilating half bridge drive they
sell and nothing that has pins 1 and 4 swapped.
====================================================================

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
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