So, I took out the capacitor and inserted a fresh fuse…
Powered it up and nothing happened… and the fuse blew.
Then I tried again with the capacitor and it lit up and then after a second it went out and the fuse blew.
Deffo the capacitor that’s stopping it from working.
I’ve got a new one coming today.
Powered it up and nothing happened… and the fuse blew.
Then I tried again with the capacitor and it lit up and then after a second it went out and the fuse blew.
Deffo the capacitor that’s stopping it from working.
I’ve got a new one coming today.
73's de Edd
- Aug 21, 2015
- 3,730
- Joined
- Aug 21, 2015
- Messages
- 3,730
I took out the capacitor and inserted a fresh fuse…
Powered it up and nothing happened… and the fuse blew.
Then I tried again with the capacitor and it lit up and then after a second it went out . . . . . . and the fuse blew.
What kind of CRAZY-AZzZz logic are you using ?
When you . . . .
I took out the capacitor and inserted a fresh fuse…… and the fuse blew.
Is telling you that X capacitor presence is not the fault . . . . . the trouble ACTUALLY lies within the units power supply components or the POWER HUNGRY audio output sections components
Use a standard 60-100 watt old style filament incandescent lamp in series with the AC power into that amplifier . . .to let you know if there is presently a serious failed components / overload condition STILL lurking within that unit.
A bright lighting of the bulb after power turn on should confirm a power overload presented by internal faulted component(s).
And save you additional fuses !
73's de Edd . . . . .
Powered it up and nothing happened… and the fuse blew.
Then I tried again with the capacitor and it lit up and then after a second it went out . . . . . . and the fuse blew.
What kind of CRAZY-AZzZz logic are you using ?
When you . . . .
I took out the capacitor and inserted a fresh fuse…… and the fuse blew.
Is telling you that X capacitor presence is not the fault . . . . . the trouble ACTUALLY lies within the units power supply components or the POWER HUNGRY audio output sections components
Use a standard 60-100 watt old style filament incandescent lamp in series with the AC power into that amplifier . . .to let you know if there is presently a serious failed components / overload condition STILL lurking within that unit.
A bright lighting of the bulb after power turn on should confirm a power overload presented by internal faulted component(s).
And save you additional fuses !
73's de Edd . . . . .
If there is another problem then how come the dodgy capacitor made a difference. As in allowing it to turn on???
But without dodgy capacitor it didn’t turn on but just blew the fuse.
To me that dodgy capacitor seems to be delaying the mains power a bit (1 second) before blasting through the fuse and blowing it. Therefore the dodgy capacitor isn’t doing its job properly???
I may be wrong.
But without dodgy capacitor it didn’t turn on but just blew the fuse.
To me that dodgy capacitor seems to be delaying the mains power a bit (1 second) before blasting through the fuse and blowing it. Therefore the dodgy capacitor isn’t doing its job properly???
I may be wrong.
The glass fuse is only one amp. So that shows that either the capacitor is giving it more that one amp or the unit is drawing more that one amp.
I think it’s the capacitor as that has blown and how it makes a huge difference when in circuit with a fresh fuse.
When a new capacitor is applied then it will not be giving the fuse too much amps…?
I think it’s the capacitor as that has blown and how it makes a huge difference when in circuit with a fresh fuse.
When a new capacitor is applied then it will not be giving the fuse too much amps…?
Delta Prime
- Jul 29, 2020
- 2,987
- Joined
- Jul 29, 2020
- Messages
- 2,987
Is it possible to upload it?
73's de Edd
- Aug 21, 2015
- 3,730
- Joined
- Aug 21, 2015
- Messages
- 3,730
Sir ZJS . . . . .
This snippet schema should suffice with most info that will initially be needed.
Your cap is the YELLOW mark up C813 and DEFINITELY not related to the amplifier not coming on, particularly if not installed, as was experienced as the the case in one of your tests, with the fuse STILL blowing..
Its principal function is to make life easier on the power switch contacts at switch power off . . . . IF . . . . the ac line cycle happens to be at either of its peak nodes.
That power transformers primary can generate one fierce back EMF burst , if switched off at that instant, arcing away a bit of switch metal. The cap takes away/absorbs the peak of it. This is akin to use of buffer caps in other electronics circuits
You might have experienced a like similarity, if you happened to have switched ON an incandescent room light . . . . . and it goes off like a flashbulb. No EMF is involved there, but just the random chance of power application at an AC peak node voltage instant.
An aged bulb further heightens the probability.
SO . . . .leave the C813 capacitor out . . . . . .and then replace it later, when one arrives . . . but its non circuit presence will not have one iota of interference with our further testing.
INITIAL POINTS OF INTEREST . . . . . of the . . . . .
Ferguson 3939 Power Supplies and Audio Output Circuitry
( Left mousie clickee-clickee makee pick-cha 'mo bigg-ee-bigg-ee . . . . . or FARRRR left, off pic clickee-clickee . . . restores forum text. )
In the above at the right bottom quadrant is the T801 power transformer with its primary winding lined up and down on its right half.
There is one option in changing between 220 and 240 VAC input, should you need use of that higher voltage level, whichever yours is closest to.
On the transformers left half are being 3 vertically arranged secondary windings. The very top one feeds your two backlight illumination lamps for your two power meters.
The next winding down is having a center tap and feeds two 20VAC sources to the BROWN rectifier cluster at the left.
This supply OR the audio output power transistors that it feed are our most suspect problem childs.
The very bottom winding is used for a minor power supply at the ORANGE rectifier cluster within Part PC970 which supplies power to another main pre amp section in the system. They just opted for snatching its 24AC raw power from this transformer, other than another one having to be placed in that unit.
You can isolate those BROWN and ORANGE power supplies for initial troubleshooting with push on-off wire connectors . Terminals 23 and 28 . . . are RED flagged for disconnect of the two 20VAC sources and only terminal 30 of the 24VAC is BLUE flagged and only it needs to be disconnected, in order to to disable its 24VAC power input.
I really don't suspect that ORANGE supply as being your fault / problem.
I suspect either the BROWN supply that is taking 20VAC inputs that then create + and -28VDC supplies for the power audio output stages . . . OR . . . the 2 sets of power output transistors. . . OR . . . their conglomerate of 13 transistors along with their ancillary support diodes and resistors.
Look at the schematics GREEN and VIOLET flagged Audio Output Power transistors They are labeled as being MJ2955-VT621 as the top PNP one and 2N3055-VT622 as the bottom NPN unit.
Now look at the photo below and zero in on the two large black E-caps at mid center and at both of their frontal ends. Each one is very close to alulillyumininny-yum-yum tabs, which I perceive as being tabs for 4 spread apart heat sinks for those 4 power transistors ALONG with the total bottom plate being used for spread out overall heat sinking.
Nowhere do I see the presence of my left quadrants bottom corner footprint of a diamond shaped metal 2N3055-2N2955 .
SO . . . .? . . . possibly, instead, they are using the plastic TO-3 cased versions . . . the MJ series.
If metal TO-3 cases are used, typically they are socketed and 2 transistor base and emitter pins plug in and two screws on top case mount them and completes the transistor collector connection..
It's as simple then as loosening two screws and lift out for transistor testing or making its removal from circuitry for troubleshooting.
BUT . . . . the MJ series can have their leads, right angle formed for plug in and then only one mount screw is being used for a collector connection to the power tab.
TO DO . . . . .***
Find and inspect those 4 transistors and fill me in on that sketchy situation of . . . . if they are plug in or have 3 soldered on wire leads coming to them.
While we are looking at that pic and those two larger black E-caps . . . you can see 4 twisted wires of two ORANGES and a BROWN and a GREEN wire that are plugged into the board between the E-caps centers and they then route over to the T801 power transformer .
Can't you just GUESS that the two ORANGES are being the 20VAC and that the BROWN and GREEN are the 24VAC . . . . . I'll bet 'cha !
PRELIMINARY TESTING . . . . . IN INITIAL FAULT EVALUATING OF ITS TWO POWER SUPPLIES
After confirming those last wiring connections unplug the two ORANGE ones and either the BROWN or GREEN and mark or keep up with their
exact replacement positions.
Then power up an confirm your power meters are lighting up and then staying on for 5x times the time that the unit ran before blowing the fuse the other times.
Then, if successful, power down and then plug in that BROWN or GREEN lead that you unplugged.
I'm expecting a repeat success on retesting.
Next look at the schematic and find those two R621 and R622 resistors ( I marked up with GREEN and VIOLET dumbells ) that are associated with the amps RIGHT audio channel and its POWER transistors.
Also locate the same resistors associated with the amps LEFT channel and their numbering is similar with them being R721 and R722 on the other half of the PC972 circuit board and their companion power transistors being VT721 and VT722.
We will be needing to find the common tie points of those two sets of resistors . . . . . and on the schematic snippet you can see that common junction is marked up as a pale Robins Egg BLUE with a white box reference of ZERO volts DC presence, if that parts cluster is operating normally, WITH SERIOUS IMBALANCING PROBLEMS . . . . that voltage point could shift to an almost full -28 or +28 volts.
That will be our test on the units audio power output stages just after confirming + and - 28 VDC presence.
In the interim, I will wait for your *** info request and get your voltmeter at the ready.
Solely Available Picture Found . . . . . of a 3939 Chassis Parts Layout . . . . .
I stand by awaiting your findings requested and . . . now, git yer poppylingcorn and cole drank reddy !
73's de Edd . . . . .
This snippet schema should suffice with most info that will initially be needed.
Your cap is the YELLOW mark up C813 and DEFINITELY not related to the amplifier not coming on, particularly if not installed, as was experienced as the the case in one of your tests, with the fuse STILL blowing..
Its principal function is to make life easier on the power switch contacts at switch power off . . . . IF . . . . the ac line cycle happens to be at either of its peak nodes.
That power transformers primary can generate one fierce back EMF burst , if switched off at that instant, arcing away a bit of switch metal. The cap takes away/absorbs the peak of it. This is akin to use of buffer caps in other electronics circuits
You might have experienced a like similarity, if you happened to have switched ON an incandescent room light . . . . . and it goes off like a flashbulb. No EMF is involved there, but just the random chance of power application at an AC peak node voltage instant.
An aged bulb further heightens the probability.
SO . . . .leave the C813 capacitor out . . . . . .and then replace it later, when one arrives . . . but its non circuit presence will not have one iota of interference with our further testing.
INITIAL POINTS OF INTEREST . . . . . of the . . . . .
Ferguson 3939 Power Supplies and Audio Output Circuitry
( Left mousie clickee-clickee makee pick-cha 'mo bigg-ee-bigg-ee . . . . . or FARRRR left, off pic clickee-clickee . . . restores forum text. )
In the above at the right bottom quadrant is the T801 power transformer with its primary winding lined up and down on its right half.
There is one option in changing between 220 and 240 VAC input, should you need use of that higher voltage level, whichever yours is closest to.
On the transformers left half are being 3 vertically arranged secondary windings. The very top one feeds your two backlight illumination lamps for your two power meters.
The next winding down is having a center tap and feeds two 20VAC sources to the BROWN rectifier cluster at the left.
This supply OR the audio output power transistors that it feed are our most suspect problem childs.
The very bottom winding is used for a minor power supply at the ORANGE rectifier cluster within Part PC970 which supplies power to another main pre amp section in the system. They just opted for snatching its 24AC raw power from this transformer, other than another one having to be placed in that unit.
You can isolate those BROWN and ORANGE power supplies for initial troubleshooting with push on-off wire connectors . Terminals 23 and 28 . . . are RED flagged for disconnect of the two 20VAC sources and only terminal 30 of the 24VAC is BLUE flagged and only it needs to be disconnected, in order to to disable its 24VAC power input.
I really don't suspect that ORANGE supply as being your fault / problem.
I suspect either the BROWN supply that is taking 20VAC inputs that then create + and -28VDC supplies for the power audio output stages . . . OR . . . the 2 sets of power output transistors. . . OR . . . their conglomerate of 13 transistors along with their ancillary support diodes and resistors.
Look at the schematics GREEN and VIOLET flagged Audio Output Power transistors They are labeled as being MJ2955-VT621 as the top PNP one and 2N3055-VT622 as the bottom NPN unit.
Now look at the photo below and zero in on the two large black E-caps at mid center and at both of their frontal ends. Each one is very close to alulillyumininny-yum-yum tabs, which I perceive as being tabs for 4 spread apart heat sinks for those 4 power transistors ALONG with the total bottom plate being used for spread out overall heat sinking.
Nowhere do I see the presence of my left quadrants bottom corner footprint of a diamond shaped metal 2N3055-2N2955 .
SO . . . .? . . . possibly, instead, they are using the plastic TO-3 cased versions . . . the MJ series.
If metal TO-3 cases are used, typically they are socketed and 2 transistor base and emitter pins plug in and two screws on top case mount them and completes the transistor collector connection..
It's as simple then as loosening two screws and lift out for transistor testing or making its removal from circuitry for troubleshooting.
BUT . . . . the MJ series can have their leads, right angle formed for plug in and then only one mount screw is being used for a collector connection to the power tab.
TO DO . . . . .***
Find and inspect those 4 transistors and fill me in on that sketchy situation of . . . . if they are plug in or have 3 soldered on wire leads coming to them.
While we are looking at that pic and those two larger black E-caps . . . you can see 4 twisted wires of two ORANGES and a BROWN and a GREEN wire that are plugged into the board between the E-caps centers and they then route over to the T801 power transformer .
Can't you just GUESS that the two ORANGES are being the 20VAC and that the BROWN and GREEN are the 24VAC . . . . . I'll bet 'cha !
PRELIMINARY TESTING . . . . . IN INITIAL FAULT EVALUATING OF ITS TWO POWER SUPPLIES
After confirming those last wiring connections unplug the two ORANGE ones and either the BROWN or GREEN and mark or keep up with their
exact replacement positions.
Then power up an confirm your power meters are lighting up and then staying on for 5x times the time that the unit ran before blowing the fuse the other times.
Then, if successful, power down and then plug in that BROWN or GREEN lead that you unplugged.
I'm expecting a repeat success on retesting.
Next look at the schematic and find those two R621 and R622 resistors ( I marked up with GREEN and VIOLET dumbells ) that are associated with the amps RIGHT audio channel and its POWER transistors.
Also locate the same resistors associated with the amps LEFT channel and their numbering is similar with them being R721 and R722 on the other half of the PC972 circuit board and their companion power transistors being VT721 and VT722.
We will be needing to find the common tie points of those two sets of resistors . . . . . and on the schematic snippet you can see that common junction is marked up as a pale Robins Egg BLUE with a white box reference of ZERO volts DC presence, if that parts cluster is operating normally, WITH SERIOUS IMBALANCING PROBLEMS . . . . that voltage point could shift to an almost full -28 or +28 volts.
That will be our test on the units audio power output stages just after confirming + and - 28 VDC presence.
In the interim, I will wait for your *** info request and get your voltmeter at the ready.
Solely Available Picture Found . . . . . of a 3939 Chassis Parts Layout . . . . .
I stand by awaiting your findings requested and . . . now, git yer poppylingcorn and cole drank reddy !
73's de Edd . . . . .
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