Pioneer qx-8000a broiled resistors

ca. = circa = approximately

The schematic 'centre' voltage is 26.2V, but it's not critical, just a good indicator that the amp is fairly well balanced in terms of DC voltage.

The idle current is much more important - that one I'd adjust accurately, and check / tweak it over about an hour or so, until it settles to about 25mV across R35 (23.5mV if your R35 is now 0.47R) - it'll vary as the temperature equilibrates.
 
Yes im going to do this measurement .what do you think for this contemporary semiconductor analyzer - Atlas DCA55. I have a chance to get it for $60. Is it worth the money?
 
I don't have any personal experience with them, but Peak generally have a good name. The UK price is $60-65 new, so $60's not that special.
Probably worth asking in the diy forum.
 
Goldie99, im doing the measure right now. Idk if im corect but i going to measure r35 with negative lead on frame(base board) and positive on the one leg of R33.
 
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Sorry !! it is 26.6 26.5 time to time go to 27.8???
And after 15 min on powered amp it is went down to 16.9
 
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After 1 hr playing with vr3 got 24.8v on r35. I will stop any adjustment and measure for now.
 
Goldie99, im doing the measure right now. Idk if im corect but i going to measure r35 with negative lead on frame(base board) and positive on the one leg of R33.
To measure voltage drop across R35, which is how you measure & calculate the idle current, you just put the negative DMM probe on chassis ground (pcb terminal number 1, or the amp chassis is fine), and the red probe on pcb terminal number 13 (I assume it's included on the pcb for exactly that - I can't see why else it would be there), or the Q11 end of R35. The DMM should be set for measuring DC millivolts.

"one leg of R33" I guess is a typo ?

THE R ON R35 IS 6
If you have changed R35 to a 0.6R resistor, the 'target' millivolt drop across R35 would be 30mV for the same idle current (you just calculate it from Ohms law)

Sorry !! it is 26.6 26.5 time to time go to 27.8???
And after 15 min on powered amp it is went down to 16.9

?? what is ??

After 1 hr playing with vr3 got 24.8v on r35. I will stop any adjustment and measure for now.

Provided you mean 24.8 mV, and not 24.8 V, then it looks good and you can leave it there. Please, always be sure to quote the correct measurement units, for all measurements - without the right units, the measurements are worthless, and may lead to (potentially expensive) mistakes....

You don't need to push it up to 30mV, especially if the rest of the amp is still in original unrestored condition, and it's sounding ok. The amp is at least 44 years old, so it would probably benefit from a full service, and probably a recap as well.... but that's a lot more work.
 
Provided you mean 24.8 mV, and not 24.8 V,
yes that is correct.
? what is ??
Yes this was very strange - the first measure was 26.6 mV, after a couple of minutes 27.8mV and after another 5 min it drops to 16 mV. Then i start to work with vr3 and adjust itto 24.8mV
The amp is at least 44 years old, so it would probably benefit from a full service, and probably a recap as well.... but that's a lot more work.
Well the all board are looking very fresh, obviously, no body had been touched them and I couldn't see any damaged cap. But this is just conclusion made with visual inspection... which probably mean nothing.
 
OK - when you measure the voltage drop across R35 (that's now 24.8 mV), it will be very 'sensitive' - it's highly dependent on the temperature of the output transistors / heatsinks, so even a 'draught' in the room can affect it (try blowing on the amp while measuring it...). The good news is that D1 & TH1 both appear to be working ok - they are responsible for automatically adjusting the idle current as temperatures change, but you have significant thermal mass there, so it takes time.... even the slightest adjustment to VR3 takes a while to 'settle down' again. I've taken up to 2-3 hours to set one before now, it just depends on the amp.

Unfortunately, you're correct - you can't judge at all how good or bad a capacitor is by looking at it, unless it's obviously leaking / bulging / etc., time will tell....... in the mean time, enjoy the new sounds !

Alan
 
Thank you, Alan! Yes I'm happy with this new gear.Plan to plug an equalizer using pre out and main in.There is one pair per amp - so two pre out and two main in and the switch is one( there is no jumpers as in Sansui amps) Im going to follow the connection on the schema. Yeah very happy and ready for a new project!!:) So thank you again and :beerchug:
Ivo.
 
Goldie99, Merry Christmas, Alan! I wish you all the for the New Year!!
Ivo.
:beerchug:
 
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Newbie here. Have followed the broiled resistors, but not seen any in the Pioneer QX-8000 as I seem to have a very weak right channel in 2 channel stereo or 4 channel stereo mode. Quadrilizer seems to have all 4 speakers working properly with slight adjustment of front balance to the right after some warm up period. Pre-out from another receiver to main in is o.k. in 2 channel mode was good. Tested pre out of QX-8000 to main in of another receiver and was o.k. also. I only had time for about a minute or two worth of testing, and when came back later and tried again right channel was almost no output or same as before. De-oxit mode selector, pots, and the pre out main in switch in back also. Even tried in seperated mode using rca's and same. Power supply voltages: B1 54.8, B2 23.41, B3 22.4, B4 22.5, B5 11.67, B6 32.7. Visual inspection nothing alarming. Any suggestions and help where to continue next would be appreciated. Nice sound with what have thus far. I think somewhere in pre-amp area so far, but why it worked for a minute or 2 in the right channel using pre out to another receiver?
 
There are two output boards - for 1 & 3 channels and 2 & 4, so your problem is before or after outputs if you have the same problem in the two modes. Download the Service manual from HIFI Engine and follow the schematic. Check the power supply. I'm not an expert its just my hobby, maybe somebody else will give you specifical help. Try also in Pioneer forum.
Regards!
 
Hello ivo, and if this sounds familiar to anyone else.
I have recently been able to test and probe a little more, and when first turn on it will work in 2 or 4 channel stereo mode, and after few minutes to 15 to 20 minutes it will go back to only the left speakers. What I can duplicate every time now is that if in aux or phono, and it occurs, all I have to do is switch to fm, and change off and on station with usual hiss in between off station and then right channels come back, and stay there when switching back to phono or aux. The 4 channel stereo does work correctly also when using aux 4 channel inputs with an SACD.
My next step is follow signals using schematic, and why the fm station changing enables the right speakers again. This fm station changing only corrects the right speakers when selector is in fm mode, and not just turning the station dial when in another mode like phono or aux. If all-ready in fm mode, it will still occur the same way, and only have to go off and on a tuned station to allow the right side to resume. Such a strange problem.
 
Tread the switch selector with pressure air and then with Deoxit D5, in an hour again with air.
 
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