Ok, I'm preparing my shopping list but can't find high temp LEDs anywhere...
And I'm getting confused with this led search, gone to Maplin but that was a waist of time (the guys there don't know nothing about nothing) so I'm looking at Farnell/RS and Conrad.
Found Leds from 1.9V to 12V forward voltage and from 2mA to 50mA forward current and intensity raging from 1 to 34000mcd...
My question is witch one(s) ?
Ric
And I'm getting confused with this led search, gone to Maplin but that was a waist of time (the guys there don't know nothing about nothing) so I'm looking at Farnell/RS and Conrad.
Found Leds from 1.9V to 12V forward voltage and from 2mA to 50mA forward current and intensity raging from 1 to 34000mcd...
My question is witch one(s) ?
Ric
Just use any cheap 5mm green standard LED.
The temperature is no problem if you change the resistor,
see post 90. I use what I have on top of my toolbox, can
send you a few, but the local supplier can surely help.
Voltage is a little bit less than 2 volts at these currents.
A.
Just to say that the amp is on standby waiting for the parts to arrive.
Got 2 (new to me) used cd players to play with 1 Marantz CD80 and 1 Philips CD371
Thanks everybody
Ric
Got 2 (new to me) used cd players to play with 1 Marantz CD80 and 1 Philips CD371
Thanks everybody
Ric
Cambridge Audio Amp A75 schematic
My first foray into diyAudio, I notice a mention of the A75 schematic I am
looking for. Does anybody still have one of these?
My first foray into diyAudio, I notice a mention of the A75 schematic I am
looking for. Does anybody still have one of these?
Hello all. Just got hold of one of these, I think the relay needs replacing and I'll be doing the upgrades recommended in this thread. My supplier has not got the MJE243 / MJE253, the nearest seem to be BD680 / BD679 will these do? thanks
No. BD679/BD680 are darlingtons.
Perhaps Toshiba's 2SC2238 / 2SA968 are a good choice, but please note the much more higher ft of arround 100MHz instead only 40 MHz by the MJE 243/253.
http://www.onsemi.com/pub_link/Collateral/MJE243-D.PDF
Download | Datasheet Archive
The BD379/380 could also use from the electrical parameter, unfortunately no ft is mentioned.
http://pdf1.alldatasheet.com/datasheet-pdf/view/50783/FAIRCHILD/BD379.html
BTW - I am looking to a cover pic from the Toshiba databook with BjT for low-, medium- and power applications. Perhaps one of the member can post this.
Last edited:
I've had a good look at the power amp board and the most visably damaged resistor seems to be R13 (470R) and R222 is somewhat toasty !
For me the question always arises, how can happen such design errors, even by currently released home hifi amplifier models.
by managers who think they can be engineers and push specs too far - like X-pro says, the original A3i was designed to be a 40W amplifier, pushed to 60W by managers increasing the supply rails and allowing no safety margin.
In the meantime I received a diagram for Cambridge A70 type power amp and will send it to everybody who is in need for repair.
HELP
I,m back to the bench to repair one of mine A3i but...
What the hell...
Everything measures fine, no shorts even replaced transistors that were fine and it still wont work
As soon I power it up the 4amp fuses blow up (2 to 3 seconds)
Yes I tested the output power transistors and they are fine (new ones) if I power the board up without them everything is fine
All 4 leds light up and all voltages measure correct.
I'm starting to think that I was sold FAKE 2SC2922/2SA1216
I didn't made any changes to the Amp yet i want to have it running and then do the changes that Alex (X-PRO) indicates in one of the previous posts
Any Ideas ?
Ric
I,m back to the bench to repair one of mine A3i but...
What the hell...
Everything measures fine, no shorts even replaced transistors that were fine and it still wont work
As soon I power it up the 4amp fuses blow up (2 to 3 seconds)
Yes I tested the output power transistors and they are fine (new ones) if I power the board up without them everything is fine
All 4 leds light up and all voltages measure correct.
I'm starting to think that I was sold FAKE 2SC2922/2SA1216
I didn't made any changes to the Amp yet i want to have it running and then do the changes that Alex (X-PRO) indicates in one of the previous posts
Any Ideas ?
Ric
First - check the voltage between emitters of the drivers (BD139/BD140) without power transistors. It should be about 1V and adjustable by the bias pot. If it is considerably more and/or not adjustable then check the Vbe multiplier transistor Q9.
There are some fake output "Sanken" devices around - possibly you've got these.
Cheers
Alex
Where did you get the transistors ?If the answer is eBay, you got fakes. They're probably making it oscillate and blow up.
No luck...
Fryed Q8 and Q108 (smoking)
Did not had the time/chance to measure voltage on BD139/140 emitter before the magic smoke decided to come out. 🙁
Replaced Q8/108
Checked Q11/12/111/112 all OK
Q7 and Q107 OK but replaced.
Vbe multiplier Q9 and 109 are OK but replaced anyway
Protection diodes D2/3/102/103 checked and OK
New leds (4)
Resistors around the transistors checked and replaced were needed.
I'm running out of ideas with this one...
In one of the previous post someone mention the replacement of R16 or R18 from 3k3 to 10K with normal (cheap) leds can that be the cause of all this trouble ?
Ric
Fryed Q8 and Q108 (smoking)
Did not had the time/chance to measure voltage on BD139/140 emitter before the magic smoke decided to come out. 🙁
Replaced Q8/108
Checked Q11/12/111/112 all OK
Q7 and Q107 OK but replaced.
Vbe multiplier Q9 and 109 are OK but replaced anyway
Protection diodes D2/3/102/103 checked and OK
New leds (4)
Resistors around the transistors checked and replaced were needed.
I'm running out of ideas with this one...
In one of the previous post someone mention the replacement of R16 or R18 from 3k3 to 10K with normal (cheap) leds can that be the cause of all this trouble ?
Ric
Power up safely with Variac or resistors in place of the fuses,
see post 90
http://www.diyaudio.com/forums/soli...dge-audio-a3i-repairs-mods-9.html#post2450679
see post 90
http://www.diyaudio.com/forums/soli...dge-audio-a3i-repairs-mods-9.html#post2450679
Morning everybody
If I run the board for more then 5 seconds without the power transistors Q10/110 and R11/111 go up in smoke.
Need to ask my brother for the camera ( I'm on holiday in sunny Portugal).
Trimpots are set to half way (center position)
Don't have a variac but will try the resistors (as soon I can get my hands on a couple of them)
Ric
If I run the board for more then 5 seconds without the power transistors Q10/110 and R11/111 go up in smoke.
Need to ask my brother for the camera ( I'm on holiday in sunny Portugal).
Trimpots are set to half way (center position)
Don't have a variac but will try the resistors (as soon I can get my hands on a couple of them)
Ric