Marshall tsl 602 problem

[Rod]

Hello!

I have a Marshall tsl602 combo wich the power valves and cathode follower ligth up, the other preamp tubes dont light up and theres no sound.

Im going to measeure some voltages in the screens and HT, i also removed the power tubes and put the amp on, and theres no ligth also in the preamp tubes, what should ive check for here? the schematic is very confusing.

[Helmholtz]

Please do post the schematic.

[Rod]

Hello Helmholtz!

Here you have it, im going to check also the voltage of the fiilaments

TL60-60-02 (2003) iss7.pdf (drtube.com)

[Helmholtz]

Ok, V1/V2/V3 heaters are supplied by DCV. Check DCV across the output (FILA/FILB) of the rectifier bridge BR1.

[Rod]

Helmhotz, ive got 4.78V in all filaments.

In standby mode i should have voltage in all the anodes Pin 1 and 6 of every premp tube rigth? because in every anode of the preamp ive got 0.2 volts and in the R59,R60,R62, R64 it gives 0.15volts.

[Helmholtz]

Helmhotz, ive got 4.78V in all filaments.

In standby mode i should have voltage in all the anodes Pin 1 and 6 of every premp tube rigth? because in every anode of the preamp ive got 0.2 volts and in the R59,R60,R62, R64 it gives 0.15volts.

You should have around 6 VDC measured between pins 4 and 5 to pin 9 of preamp tubes.
If lower, check rectifier BR1 and C51/52/59/66.

In standby all HT1/2/3 voltages should be zero (after discharge time). Standby is sleep mode.

[Dave H]

In standby mode i should have voltage in all the anodes Pin 1 and 6 of every premp tube rigth?

Standby switch labeling often causes confusion. When the Standby switch is in the "off" position (top pushed in) it's in "standby" mode (no anode voltage). When the Standby switch is in the "on" position (bottom pushed in) it's in "play" mode and you should have anode voltage.

[Rod]

Helmhotz , how do i check the BR1? its a closed plastic box.

And to check the capacitors do i have to desolder them from the pcb? and check them one by one ?

[The Dude]

BR1 is a known issue with these amps. You can try resoldering it- often it's just cracked joints from heat. I usually just replace it and stand the new rectifier off the board further to keep heat away from the solder joints. I've also had them test good, but fail under load.

[Rod]

Is it normal for the preamp tubes to have 4,8 v in pins 4 and 5 and in the cathode follower tube pins 4 and 5 have almost 0 volts?

[g1]

Probably the ones lit up are AC heater, and the ones not working are DC heater.

[Helmholtz]

Is it normal for the preamp tubes to have 4,8 v in pins 4 and 5 and in the cathode follower tube pins 4 and 5 have almost 0 volts?

As said, you should have about 6VDC between pins 4 and 5 (not wrt ground!) on all preamp tubes. PI and power tubes are AC heated.

Again, what is the voltage between FILA and FILB?

[Mick Bailey]

I've lost count of the times I've replaced the bridge rectifier in these amps so that's the first thing I check.

[Rod]

Helmholtz

Are the test points for the bridge rectifier the ones marked with the red arrow in the picture bellow? im not sure, because if they are not to test the BR i've got to take the pcb out and desolder the BR and test it.

https://drive.google.com/file/d/1snS...ew?usp=sharing

[Jon Snell]

Check between FILA and FILB, these can be easily measured between pins 5 and 9 of V2 NOT pins 4 and 5!
The bridge BR1 fails as a matter of course to keep us engineers busy and always replace it 1/2 inch proud of the PCB to keep it cool.
4 x 1n400* can suffice if that is all you have to hand but not very aesthetic.
Check for bulging capacitors; part schematic attached.