swr workingmans 15

[kip[py]

Hi dear

i have here a workingmans 15 the have a defect noise
the pre amp clip works no bad and the gain works bad the give bad noise
and the speaker give a 50 hz noise

what the problem maybe someone my can tell

[Chuck H]

Please post a schematic. You mention 50Hz si I'll assume your in a country that uses 50Hz mains frequency?!? I don't know that amp. A schem is paramount for diagnosis.

[kip[py]

Hi Chuck

yes the mans here a 50 hz
and here the link for the schematic SWR WORKINGMANS 12 15 SCH Service Manual free download, schematics, eeprom, repair info for electronics
i have see with a scope from connected PGND and R 25 and see no clean voltage
but the c1 and c2 are this clean

[Chuck H]

Here's the schem you'll need. The problem is going to be in the power supply. The linked schem is for the preamp only. Check along the power supply past the rectifier to isolate the problem. Could be a bad component or a burned pcb trace causing a ground fault, etc. First you need to find out where the hum is getting in. Since the rectified power shouldn't be at 50Hz, my money is on a bad rectifier.


http://music-electronics-forum.com/t26757/

[kip[py]

Ok thanks for your info

but if the rectifler bad are works the voltage still good ?
i see no bad voltage on the c1 and c2

[Chuck H]

Any 50Hz on the + end of C12?

[kip[py]

hi
i have test with a other trafo 2x 15 and gnd voltage and connect this to +15 volt -15 volt and gnd
and disconnect R1 and R2 but the tl072 drivers works bad no good sound from output TL072 c13 disconnect from the amplifier
i have see not bad TL072 ic
i have see only from r25 bad voltage

[Chuck H]

Maybe check D7, D8 and C7.

[J M Fahey]

i have test with a other trafo 2x 15 and gnd voltage and connect this to +15 volt -15 volt and gnd

So you took a 15+15V transformer, connected the center tap to ground and the 2 other wires to + and - 15V rails? (pins4/8 of TL072)
Please confirm.

Note: we seem to have a slight language barrier here.
Please *also* post your questions in your original language, might help.
And tell us where you are

[kip[py]

Hi Chuck

the parts D7 D8 C7 are good

and JM Fahey

yes i have connected with pin 4/8 TL072 from all ic the preamplifier give peeps with more gain
i come from the netherlands

ja ik heb de 15 voltage + _ gnd met de trafo aan gesloten
en de voorversterker geeft een slecht geluid (piepen) bij gain open zetten

[J M Fahey]

Dear kippy, there are a few things I don't understand.

yes I have the 15 + _ gnd voltage with the transformer closed (connected?)
and the preamp gives a bad sound (beep/squeal) when gain open up

1) I do not understand how you can connect 15 volts alternating current to +/- 15 Volts rails which are direct current
2) I do not understand how you can hear a pip/squeak "coming from the preamp" if your power amp is muted
3) please measure and tell us what voltages you read on pins/legs 4/8 at the TL072 integrated circuits
4) I *think* I understand your power amp is muted.
D7 rectifies transformer voltage and turns on Q1/Q2 after a small delay and feeds R25/R23 from the positive rail.
This seems to be failing.
Please confirm that you do not have Direct Current Voltage (positive or negative) at the speaker terminals.
Does the speaker cone move forwards or backwards and stay there, with *strong* hum?

Please repost #1 and #7 in Dutch, I still have some doubts.
I do not speak Dutch but between Google Translate and my very rusty German I can understand your posts a little better.
And please avoid abbreviations if possible, Translators can work with "ground" and "integrated circuit" but not with "gnd" or "IC".

[kip[py]

HI JM Fahey

als ik de ingang gebruik van de voorversterker en sluit een hoofdtelefoon (headphones) aan op c13
dan hoor ik vervormd geluid uit piepen
ik heb de eindversterker helemaal uitstaan geen high voltage R29 R42 geen verbinding met uitgang
als de versterker wel helemaal aanstaat ( turned on ) dan hoor je alleen maar een harde brom
met de gain open dan is de versterker van slag piepen brom(peep hum)
weerstand 2.7k wordt erg warm klopt dat ?

[J M Fahey]

HI JM Fahey

als ik de ingang gebruik van de voorversterker en sluit een hoofdtelefoon (headphones) aan op c13
dan hoor ik vervormd geluid uit piepen
ik heb de eindversterker helemaal uitstaan geen high voltage R29 R42 geen verbinding met uitgang
als de versterker wel helemaal aanstaat ( turned on ) dan hoor je alleen maar een harde brom
met de gain open dan is de versterker van slag piepen brom(peep hum)
weerstand 2.7k wordt erg warm klopt dat ?

Roughly:

if I use the input of the preamplifier and connect a headset (headphones) to c13
I hear distorted sound beep

Well, that signal level and impedance will not drive headphones, so that is not a conclusive test.
I suggest you make an improvised signal tracer, with a guitar cable which on an end has a plug, and on the other free end you solder the shield braid to ground and with the "hot" wire you touch different points you want to hear.
For example, test the preamp output, lifting 1 leg of C13 to separate preamp out from power amp in.
To listen, you plug the guitar cable into any working amplifier you have available.

I have the amp completely turned off no high voltage

I do not understand: you have the amplifier turned off so no high voltage rails, but you feed the preamp with an external voltage source? Is that so?
You should build a lamp bulb limiter and plug your amplifier there.
Turn it on, tell us if the lamp glows bright or dim and what high voltage do you measure on rails.
Also *disconnect* the speaker and tell us what voltage you measure at the amplifier "speaker out" terminals.
I still suspect you have DC voltage there.

R29 R42 not connected to output

Did you pull/take out/remove R29/R42? Please explain.

if the amplifier is fully turned (turned on), you hear nothing but a hard hum

It reinforces my suspicion that you have DC on the output, meaning burnt power transistors.
Disconnect that speaker and use the light bulb current limiter.

with the gain of the amplifier's open stroke beeping noise (hum Peep)

You say that with the gain full on, you hear a loud hum? And with gain off?
Or you hear a loud hum *always*, at any gain level?
I do not understand:
your amplifier *seems* to be muted, but you hear a loud hum "coming from the preamp"? How?

2.7k resistor is very hot right?

I do not know, you tell me.
Please answer what voltage do you measure on each end of 2.7K (always identify it by part number, in this case R23.

So far we have apparently contradicting information .
Thanks.

[kip[py]

de preamplifier de piept alleen bij hoge gain
op de uitgang van de eindversterker heb ik geen spanning de transitor Q10 and Q4 zijn niet defect 0.20 mv
ik hoor de brom ook als de eindversterker aan staat met gain dicht
r29 r42 geen verbinding met masa maken
en de voorversterker heb ik hier nog op 15 volt staan
geluid input voorversterker geluid erg slecht c13 en deze is van de eindversterker los gemaakt

[kip[py]

i have new test
i have disconnted the premaplifier and can hear a brum
the amplifier works well only with brum