Help needed, Lanzar opti 2500

[Leif]

Hello everyone,
I have now an broken old Lanzar opti 2500 on my workbench and it seems like the preamp is broken. The amp section in it self works.
All inputs and gain&bassboost works, but when i increase volume distorssion accrue. In mono mode a very week and highly distorssion signal comes out from the amp.
I measured that the op-amps (U1-U4) gets a voltage of 28V.
So i wonder where the problem could be.

thanks!

-Leif-

 

[Perry Babin]

Does the rail voltage remain constant when you try to drive it to high power?

With no RCAs plugged in, do you read ~0 ohms between the RCA shield and the non-bridging speaker terminals?

Do you have an oscilloscope?

 

[Leif]

Hi,
The rail voltage is in idle about 92V and when i push it higher rail voltage variate between 70 - 110V.

With no RCA connected there is about ~0 ohms between rca gnd and non-bridging speaker terminals.

I have not got a oscilloscope at home right now, but tomorrow i can borrow one from work.

 

[Perry Babin]

Assuming that this is essentially the same as the 50c, Q1 and Q3 are the muting transistors. With the black meter probe on the RCA shield, what DC voltage do you read on the 3rd leg of Q1 and Q3?

 

[Leif]

Both Q1 and Q3 has -14.5VDC on leg 3

 

[Perry Babin]

That's OK.

Transistors Q4 and Q5 are the input to the power amplifier's differential amp. If the signal is clean there, the problem is in the power amplifier. If it's not clean there, the problem is before the power amp. Check the signal at the output pins of each of the op-amps to see where it becomes distorted.

 

[Leif]

ok, thanks for now.
I have to borrow a oscilloscope from work to check that, but it has to wait to tomorrow.

 

[Leif]

ok, a new problem after bending Q4... DC in speaker outputs...

Q4 and the other transistors do not have any short circuits, but in the speaker right channel output is -13VDC and in the left +13VDC.
Rail voltage is now about 107V

My DC power supply is set to 12.2VDC

So wtf just happend?

 

[PQatPIT]

Ha! Another Finland guy with broken Opti2500.

I have a similar one, with power supply down. Some resistors burned black and just wanted to know their values, otherwise it seems to be ok. Those resistors route power supply fets their pwm signal. Bought it like that as a project, just haven't had time to repair.

When I was young I drooled for one and I just couldn't keep my hands of of it . Maybe we should join forces here? Email pq (at) pitsop.fi.

 

[Leif]

Alright,
I´d just e-mail you PQ, but your e-mail address seems to bee wrong... even with the @

I wonder how many of those amps is sold here in finland? They were quite expensive...

What components are you interested to know?

 

[PQatPIT]

It is pq (at) pitstop.fi. One "t" missing...

 

[Perry Babin]

Leif:
Do you have any DC offset on the output pins of any of the op-amps?

Are the power supply voltages still ±14v on the op-amp power supply pins?

 

[Leif]

If you mean U1 - U4, Yes. If i measure between op-amps output and common speaker terminals, there is about 13VDC.
In some of them there are 13VDC in the inputs *** well...

 

[Perry Babin]

With no RCA cables connected, confirm that you still have 0 ohms between the RCA shields and the non-bridging speaker terminals.

If that's still 0 ohms, post the voltage on the pins of each of the 4 op-amps. Copy and past the following:

Ux
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:

 

[Leif]

Hi Perry
There is still 0 ohm between rca gnd and non-bridging speaker terminals.
Measured between Ux pin and rca shields:
U1
Pin 1:13,73
Pin 2:4,67
Pin 3:0
Pin 4:0,67
Pin 5:1,37
Pin 6:13,73
Pin 7:13,8
Pin 8:14,57

U2
Pin 1:13,95
Pin 2:13,95
Pin 3:13,98
Pin 4:0,66
Pin 5:0,37
Pin 6:14,15
Pin 7:14,15
Pin 8:14,70

U3
Pin 1:14,10
Pin 2:1,40
Pin 3:0,19
Pin 4:0,64
Pin 5:1,39
Pin 6:1,55
Pin 7:1,56
Pin 8:14,80

U4
Pin 1:14,02
Pin 2:14,04
Pin 3:14,05
Pin 4:0,66
Pin 5:0,32
Pin 6:14,22
Pin 7:14,24
Pin 8:14,78

 

[Perry Babin]

You lost your negative regulated supply to the ICs (on pin 4). In the 50c, Q85 (a TIP117) and ZD8 are the negative regulator. They are near U1. Yours should be similar but the circuit board designations may be different. Check the transistor and the Zener diode.

 

[Leif]

Hi again,
It seems that the problem is near Q82 in the DC-DC section. The TIP117 do not get any voltage at all... about -2V... not near -50V as the rail is.
When I follow the folios and try to find where the missing voltage but as far as i measured I did not find it.

 

[Perry Babin]

In the 50c, D15 provides rectified negative voltage to R151 which feeds the collector of Q82.

 

[Leif]

Ok, when i measured R151 from the IFRZ side there is -57V and on the other -2V to the Q82. When i removed the R151 and measured it was about 3.3k as it should be.
But now i did find that R152 was not 10ohm, but endless. Outside was ok, not burned or nothing.
Can the problem be there why I cant get negative voltage?
I don`t have 10ohm resistors at home so I cant test it right now, it has to wait to tomorrow.

 

[Perry Babin]

Right. R152 is 10 ohms. I had it wrong in my notes.

If possible, buy flameproof resistors. Buy a few extras in case there is a problem that's causing them to fail. The problem would be excessive current draw from something being fed from Q82 (filter capacitor, something being fed from the 15v regulator...). .