Discussion in 'Pioneer Audio' started by r887661, Sep 10, 2017.
Got them...in construction mode...
You can pull the molex plugs for the outputs from the amp board. (I was thinking of the 1250)
Best to start checking the outputs.
Where was my head.
I have a few things in Barter Town listed
I must visit Barter Town...
Outputs (two or more) are shorted, the driver circuit could be turning them each on HARD but that will short them right damn quickly.
On initial power up, C1 is in a discharged state, thus AC from the wall socket flows into the transformer through the R1 3.3 ohm 20w resistor and the microtemp thermal fuse. The microtemp is INTENDED to be in contact with the 20 watt resistor!!
This 3.3 ohms slows the charging of the big power capacitors, because the Toroidal power transformer will let through FAR MORE current than the wall can deliver to these thirsty BIG capacitors (an E-I square transformer saturates at a particular level and CANNOT pass more power - but a toroid CAN!!) . R1 3.3 ohms 20 watts is NOT intended to be in circuit long - it would get too damn hot - a fire hazard really, so the microtemp will open up if it gets too hot - and being in contact with the resistor means the resistor's heat is quickly transferred.
ok, so the transformer is now passing strangled AC through, as the big caps charge their voltage goes up and their current drain through R1 drops and the strangling decreases (kind of like a dim bulb), eventually rising to 76v DC from a particular FU1 secondary, which is fed to R2 (1.8k, 1w) and C1 (10uf 63v) to charge C1 over a certain amount of time. Some of the OTHER units just monitor the voltage on the big caps and allow the relay to pull in when there's enough juice, but this one has it's own special capacitor. In 18 milliseconds or so (one cycle of 60 hz ac) the cap is charged enough to pull in the relay, which closes it's contacts, passing FULL current to the transformer. If the relay doesn't pull in, or the relay contacts are burned, R1 stays in circuit and heats up BADLY, thus popping the microtemp.
The second half of the problem is the shorted outputs pulling huge amounts of current which keeps the 76v DC secondary voltage low and the 3.3 ohm resistor strangling the unit and heating itself up.
It doesn't matter that the relay COULD operate, and take the 3.3 ohms out of circuit, so because of the strangling (caused by the shorted outputs) this doesn't happen.
I had more eloquence entered, then between the editor, my browser and my mouse, it was eaten and lost and I am too tired to retype it.
If you look at post #3 of this thread I said to check the output transistors, most of the time when the micro temp blows up it is the outputs. After the outputs blow up there could be many more components down the line fried also. I had the same issue with a 1250 a few years ago.
Quality advice and explanation. I thoroughly appreciate it. I am moving house this weekend so will have to relocate my workshop and get set up. I pledge to get back to everybody buy the end of next week. This is such a great challenge and an opportunity to learn. Thanks to you all....
How are the output transistors identified? which board are they on please? I have Markthe fixer indicating board AWR-104 and this was the one that was flapping loose in the unit when I prurchased it.
Mark, this board was hanging loose when I picked up the unit...logic says this is where the problem is. I also have a spare 3.3ohm resistor board with the microtemp attached. Also have a spare relay S2...we will get there....thanks for your stellar advice...
Just managed to snag an AWR-104 from a working unit being torn down for spares...includes some other boards too.
As I have a spare AWX-098 and Relay S2 should I go ahead and change out all three at the same time?
If not, what order do you recommend?
Maybe you should have someone look at it for you.
I had no idea that filthy receiver like that could be hosed down with a garden hose and then rinsed with distilled water and not see any damage to the pots or the ICs especially in the tuner section. I gather that it isn't typically the norm to clean like this but wow did your receiver come out clean!
The outputs are located behind the long main amp board, they are screwed into the big black heatsink. Going out and buying used boards from breakdowns means cutting wires and soldering them back on the pins, wouldn't it be easier to just rebuild each board? There are plenty of tutorials on the 1050 on this forum with parts replacements and methods on how to do it.
Used boards from parting out are NO guarantee that the board even works. In fact they are probably LESS likely.
If you google cleaning methods this is not an unusual recommndation, I have been doing it for years and have never had a failure. A final thorough dousing in distilled water then at least seven days with a fan heater no less than 3ft away will dry it out perfectly.
I have considered that but I picked this up for $180 and figured maybe I could learn something...I'll give itmy best shot, subject to all of AK memeber's advice and see where it goes....
I totally agree with you, however, having a spare board in hands means I can test the individual components a lot more easily and it will give me a heads up on repairing the installed piece...
Everybody...I completed moving house this weekend and I am setting up my work area. I should be back into repair mode by Wednesday so please be patient as I am going ahead with the repairs...
As I posted to Markthefixer, I totally agree with you, however, having a spare board in hands means I can test the individual components a lot more easily and it will give me a heads up on repairing the installed piece...
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