LANEY Chrome o Zone issue

[Palantine]

Hello there,
I just received from Germany an old and NOT WORKING Laney Chrome o Zone (see the attached schematic).
This amp comes to me with ONE lead of the speaker connection desoldered.
Plus it was fitted by TWO 8 ohm each speakers instead of the 16 ohm speakers that the schematic show.
Plus the sleeve of the speaker connector jack was complitely loose and floating.
That said, I assume the amp which run 8 ohm with the internal speaker(S) has the output transformer 'fried' (because it had to work with an overall speaker load of 4 ohm total....2x8 ohm connected in parallel).

The amp was in awful overall conditions....dust everywhere but ALL the fuse are ok.
I powered up the amp in stand by, connecting it to an external cab (8 ohm)....no fuse blow.....I switched to stand-by ON and ALL can I hear is a loud HUM and two power tubes (V9 and V10) were glowing blue. The other two (V7 and V8) looks normal. No sound comes out. I immediately turn OFF the stand-by and then the main power switch.

I'm not a repairman....so I ask you to help me troubleshooting the most likely causes of the malfunction.

Thanks in advance to everyone that would help me figure out what is going wrong with the amp.

Palantine

[Enzo]

Actually, the schematic shows a 4 ohm and an 8 ohm output, switch selectable. SO two 8 ohm in parallel makes 4 ohms, which would make the amp happy.

Who says your output transformer is "fried"? In any case, running the speakers at the wrong impedance is not likely to fry it.

V9 and V10 glow blue? Pull V9, power up. Does V10 still do this? Now return V9 and pull V10. Same test?

Pull all four power tubes and power on. Check voltages on V7 socket since those seems to be working. Now on sockets 9 and 10, see that you have good B+ voltage on both plate and screen, and good bias voltage on the control grids.

Missing bias voltage is my first suspect, either from circuit defect, or from one of those two tubes swamping it off.

[Palantine]

Who says your output transformer is "fried"? In any case, running the speakers at the wrong impedance is not likely to fry it.

Dear ENZO, first of all thanks for your reply.
Actually the amp works! Preatty loud (considering is a 30 watt).....so the OT 'should' be fine.
As I wrote in my post, I'm not a repairman.....so I guess the OT was bad.

I cleaned all the pots and contact; I resoldered some joints and cleaned all over the dust....pots were scratchy (I have to replace someone).
Actually ONLY the overdrive/lead channel works (killer lead!) with a background of white noise (but Laney is famous for building noisy amps)...in the triode mode the amp is almost quiet, but in pentode it makes a lot of hum and white noise.
I must check the BIAS for sure (but I don't know where to mesure....I mean the test points).

Damping also works. HI and LOW imputs works as they should.

Tubes glow in the right way; maybe power tubes runs a little hotter.

The clean channel is NOT working but this is another chapter.....almost dead silent except for a little hum (it seems not receiving current, as the crunch/clean function green led doesen't work).

I'll bring the amp to my friend who is a REAL repairman and I'll report the solution next week.

Again, thanks

[bsco]

Dear ENZO, first of all thanks for your reply.
Actually the amp works! Preatty loud (considering is a 30 watt).....so the OT 'should' be fine.
As I wrote in my post, I'm not a repairman.....so I guess the OT was bad.

I cleaned all the pots and contact; I resoldered some joints and cleaned all over the dust....pots were scratchy (I have to replace someone).
Actually ONLY the overdrive/lead channel works (killer lead!) with a background of white noise (but Laney is famous for building noisy amps)...in the triode mode the amp is almost quiet, but in pentode it makes a lot of hum and white noise.
I must check the BIAS for sure (but I don't know where to mesure....I mean the test points).

Damping also works. HI and LOW imputs works as they should.

Tubes glow in the right way; maybe power tubes runs a little hotter.

The clean channel is NOT working but this is another chapter.....almost dead silent except for a little hum (it seems not receiving current, as the crunch/clean function green led doesen't work).

I'll bring the amp to my friend who is a REAL repairman and I'll report the solution next week.

Again, thanks

If this is something like the Jet City amp I had to repair a while back, the overdrive channel was the default channel with no foot switch connected....in order for me to use the clean channel. I had to have the foot switch connected....this may or may not apply to your particular situation....

[Palantine]

If this is something like the Jet City amp I had to repair a while back, the overdrive channel was the default channel with no foot switch connected....in order for me to use the clean channel. I had to have the foot switch connected....this may or may not apply to your particular situation....

Not my friend; I have the Jet City JCA 22 H too and that's the way is designed. The Laney (I own four by now) are complitely switchable by the front panel; so everything you can do by the footswitch (that is a more advanced chapter coz I don't know actually if it works) you can do by the switches located in the front panel.

[bsco]

Not my friend; I have the Jet City JCA 22 H too and that's the way is designed. The Laney (I own four by now) are complitely switchable by the front panel; so everything you can do by the footswitch (that is a more advanced chapter coz I don't know actually if it works) you can do by the switches located in the front panel.

I wasn't sure about that as I haven't had the opportunity to work on any Laney gear.......it is not a big seller here and nobody carries that line....

[Enzo]

ALL can I hear is a loud HUM and two power tubes (V9 and V10) were glowing blue.

Actually the amp works! Preatty loud (considering is a 30 watt).....so the OT 'should' be fine.

This is a bit confusing to me. Either the amp works or it only makes a loud hum and lights up half the tubes. Can't have both ways.

[Palantine]

This is a bit confusing to me. Either the amp works or it only makes a loud hum and lights up half the tubes. Can't have both ways.

ENZO, I'll try to explain me better.
When I first turned on the Laney I heard only hum and no sound probably because I was playing in the clean channel (that doesen't work) and I wrote the post.
After that, I cleaned all the tube sockets, resoldered some crucial joints (in the power tube area) and sprayed all the pots.....then I turned on the Laney for the second time and I switched the front panel (from channel one to channel two)....the crunch/lead channel worked pretty fine...pots are not only scratchy, they are almost gone, but the amp works.

It still hum....there is always a background hum....in clean and in dirty mode, probably due to some preamp tube (likely V1 and V2, I don't know) and/or because is biased a little hot. The second time all the four power tubes were glowing nice orange with some blue fluorescence.

Anyway, as you told me in your previous post, the OT seems OK and that's a good start point.

Now, referring to the schematic, could you tell me what I have to check in order to troubleshooting the clean channel problem?
Seems that no current flow in this channel, dead silent (hum apart), leds off....V1 and V2 are glowing....wires coming from the two preamp tubes to the PCB seems ok (continuity test) but under the PCB there are some SMD and I really really hope they are not the cause, coz the tip of my soldering iron is bigger than these and I cannot even read the value.

[Enzo]

So start at the start. Got power supply to that board? I see +15v, got that? Got B+? They come in on a three-pin connector. Does B+ reach pins 1 and 6 or each 12AX7? If the tubes are conducting, each cathode will have some voltage on it, pins 3 and 8.