don't change the caps yet. Repair the PCB fault first and getting good voltages on the supply rails before you complicate it any further.
Doing multiple and random changes just adds to the risk of the mods going wrong.
Doing multiple and random changes just adds to the risk of the mods going wrong.
is the bulb glowing dim or bright or completely OFF?
If the bulb is dropping 10Vac, then the transformer see only 230Vac and the secondaries will be a bit low.
If the bulb is dropping 150Vac, then the primary now has 90Vac and the secondaries will be very low.
If the bulb is dropping 10Vac, then the transformer see only 230Vac and the secondaries will be a bit low.
If the bulb is dropping 150Vac, then the primary now has 90Vac and the secondaries will be very low.
It's a 60W bulb. When turning on the amp the bulb flashes bright and goes completely off.
I had tested it with a 40W LED, I know that won't work as a safety switch. But that bulb lights faintly even with the amp turned off.. but the power cable plugged in
I had tested it with a 40W LED, I know that won't work as a safety switch. But that bulb lights faintly even with the amp turned off.. but the power cable plugged in
No, LED lights or CFL bulbs will not work at all. it has to be a filament type lamp. The bulb filament is effectively working as a high power PTC resistor.
The transformers in these things arent terribly brilliant, so it could be with your mains low and the bulb in series, 33v is right. If it's symmetric (ie +33v and -33v) i wouldnt worry.
The transformers in these things arent terribly brilliant, so it could be with your mains low and the bulb in series, 33v is right. If it's symmetric (ie +33v and -33v) i wouldnt worry.
On the transformer itself it says 30 0 -30V
So I guess 33 is close enough?
If there are failed components would the voltage be largely different?
So I guess 33 is close enough?
If there are failed components would the voltage be largely different?
30V AC will give about 42V DC when rectified and smoothed - but this depends on the mains voltage in as well. The transformer will be wound for 240VAC at the primaries, but its normal for mains voltage to be as low as 230VAC or as high as 250VAC. You will also have some drop due to the bulb limiter.
If you are really concerned, pull the two fuses on the amp board, and measure the AC voltage coming from the transformer windings. You'll probably find it's slightly lower than specified on the label.
If you are really concerned, pull the two fuses on the amp board, and measure the AC voltage coming from the transformer windings. You'll probably find it's slightly lower than specified on the label.
I have measured the voltage across the red and yellow wires off the transformer and that is 67.7V.
Then on each side is 33.6V.
Voltage across each capacitor is 44.25v DC
There's 0V AC across caps.
Then on each side is 33.6V.
Voltage across each capacitor is 44.25v DC
There's 0V AC across caps.
OK, so where was your 33V reading coming from ? Which points were you measuring ?
Anyway, the power supply sounds fine
Anyway, the power supply sounds fine
I think it was from one of the two fuses to the black terminal. I checked around and that was consistent on the other side and also from a few other places.
So what would you suggest as my next step? Should I still replace the trim pots and the small transistors?
So what would you suggest as my next step? Should I still replace the trim pots and the small transistors?
Replace the trimpots and the SAP transistors.
The transistors I would test next are Q207-208, Q215-216. These are the VI limiting transistors which may have tried to turn on hard when the SAPs failed. In doing this they often burn because they cannot control the fault (because clamping the base drive to the SAPs does nothing, as the SAPs have shorted)
If these parts test OK, then everything else should be fine. If they are damaged, you will want to replace them, and additionally replace the MJE340/350 transistors.
In this case, as there were no spectacular burn marks, I think they will test fine - I suspect what has happened here is that the emitter resistor in the SAP transistors has failed open.
The transistors I would test next are Q207-208, Q215-216. These are the VI limiting transistors which may have tried to turn on hard when the SAPs failed. In doing this they often burn because they cannot control the fault (because clamping the base drive to the SAPs does nothing, as the SAPs have shorted)
If these parts test OK, then everything else should be fine. If they are damaged, you will want to replace them, and additionally replace the MJE340/350 transistors.
In this case, as there were no spectacular burn marks, I think they will test fine - I suspect what has happened here is that the emitter resistor in the SAP transistors has failed open.
The small Q2.. transistors closest to the sap15's beep continuity both directions from the middle leg to one of the outer legs. The others show no complete circuit between any legs.
you cannot use any bulb. It must be a tungsten filament bulb. It can be the old fashioned and mostly unavailable incandescent bulb, or the newer halogen incandescent with a slightly lower wattage rating for allegedly the same light output.
Buy or obtain a range of bulbs from very low (~20W) to very high (150W) to allow different equipment to start up. You can even use multiple paralleled bulbs to enable start up of very big amplifiers that are already biased to draw high quiescent current.
But it is better to start with a low wattage and test in stages as one proves that each stage is correctly wired.
Sorry, test them out of circuit... with the diode test. Google for how to diode test a transistor.
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