BeoLab 8000: dead / no red LED, measurements attached

KolfMAKER

Bronze

569 posts

Posted March 28, 2023 at 05:11 GMT ? Edited March 29, 2023 at 03:22 GMT

I have a BeoLab 8000 that is dead with power attached: no red LED. It has serial number 14xx, and yes it had foam rot. I have cleaned all electronics, connectors, etc. Also I have done some checking & measuring: On the PSU PCB, I have done continuity measurements, and found no faults. Also I have measured all voltages, the result is visible in the picture attached.

AC in is fine, and voltages on both sides of T2/stand-by transformer are ok.
On the output side of the PSU PCB, the voltages are zero volts.

The Relay shows voltages that I think are not OK. What probably explaines why the voltages on the output side are zero. Question:

Is this just a matter of a broken Relay, or is something else going on?

Location: The Netherlands

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Keith Saunders

Bronze

186 posts

Posted March 29, 2023 at 16:01 GMT ? Edited March 29, 2023 at 16:01 GMT

#700238

You show in your diagram that T2 between pins 7 & 12 is at 231 volts. The T2 relay will NOT trigger if there is no AC voltage on Pins 1 & 3 of Plug 2 on the power supply. If there is really zero volts between pins 1 & 3 of plug 2 on the power supply, then either you have broken PCB track between the T2 transformer pin 7 and plug 1 pin 1 OR broken track between T2 pin 12 and plug 1 pin 3 OR pin 9 & 10 on T2 are not connected.

Location: Hampshire, England

KolfMAKER

Bronze

569 posts

Posted March 30, 2023 at 13:34 GMT

#700258

Thnx Keith! I measured the voltage between pin 1 & 3 of P2 = 44 volts AC Just to be sure, I also measured continuity:

T2 pin 7 > plug 1, pin 1 = OK
T2 pin 12 > plug 1, pin 3 = OK
T2 pins 9 & 10 = OK

Knowing this, what do you think is wrong?

Location: The Netherlands

My B&O Icons:

Keith Saunders

Bronze

186 posts

Posted March 30, 2023 at 19:12 GMT

#700266

Well, it is excellent that you have 44 volts between pins 1 & 3 of plug 2 So, the fault is either going to be one of the following:-

The 24 volt relay itself is faulty, less likely, but possible
The D1 diode across the relay coil is short circuit
The + 15 volts is missing from the emitter of Tr3
The - 15 volts is missing from the emitter of Tr4
The "auto start" circuit used when using phono socket is enabled has a fault.

Check points 3 & 4 first by measuring between a ground point such as Plug 2 pin2 and the emitter of Tr3 (+15 volts) and then Tr4 (-15 volts) Measure the voltage between pins 1 & 2 of plug 3 on the power supply module If +15 and -15 volts are correct, but there is zero or near to zero volts between pins 1 & 2 of plug 3 then the "auto start" circuit may the cause.

Location: Hampshire, England

KolfMAKER

Bronze

569 posts

Posted March 31, 2023 at 21:43 GMT ? Edited April 1, 2023 at 13:19 GMT

#700373

Thanks a lot Keith! Red LED is ON again First of all, after my last checks I put the PSU/AMP-block back into the speaker casing, and connected everything back to original. Surprisingly, the red LED went ON again! So that's good. Obviously I also checked if it would respond to an audio signal, but unfortunately it doesn't. (I checked, with RCA connection as I currently do not have equipment to connect via MasterLink) Next checks

TR3 Emitter <> Plug 2, pin 2 = + 15 volts
TR4 Emitter <> Plug 2, pin 2 = - 15 volts
Plug 3, pin 1 <> pin 2 = 24 volts

D1 check I set my multi-meter to continuity/diode check and measured twice: once with the black probe on the top of D1 and the red probe on the bottom, and once vice versa. See the measurements in the picture below. Interestingly, with the red probe on the top and the black on the bottom: the relay clicks, the Amp turns on and music can be heard coming from the speakers. I found that the D1 is a type 1N 4148 diode. So I probably need to look for this one as a SMD type. Like to hear what you think Keith. Could this be the cause and is it just a matter of replacing it? Or could there still be another underlying cause?

Location: The Netherlands

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Keith Saunders

Bronze

186 posts

Posted April 1, 2023 at 15:14 GMT

#700402

Powerlink" rather than "Masterlink"? Also you said "Plug 3, pin 1 <> pin 2 = 24 volts" which is excellent because that should have triggered the relay. Was the RED light on when you checked this? Next Steps As you are using the phono input and taking into account the information in your previous post it is most likely that the fault is in the "Auto Start" section or the D1 diode is not within tolerance or the relay itself. If you are able to replace the D1 diode with a suitable replacement I think it would be the next step. The negative end (plug 3 pin 1) of the D1 diode is directly driven from the "Auto Start" circuit which takes your source input on the RCA socket. You could therefore also test between plug 3 pin 1 and plug 1 pin 2
Location: Hampshire, England

KolfMAKER

Bronze

569 posts

Posted April 2, 2023 at 12:39 GMT

#700432

Clarification Points In your last post you said “I currently do not have equipment to connect via MasterLink” I am assuming you intended to say “Powerlink” rather than “Masterlink“? Also you said “Plug 3, pin 1 <> pin 2 = 24 volts” which is excellent because that should have triggered the relay. Was the RED light on when you checked this?

Ad. MasterLink > Yes, you are right. I meant of course PowerLink.
Ad. Red light > Yes, the Red LED light was on at that moment.

Concerning the D1 diode Keith, can I just order a '1N 4148 diode SMD type' ?

Location: The Netherlands

My B&O Icons:

Keith Saunders

Bronze

186 posts

Posted April 2, 2023 at 14:50 GMT

#700438

Location: Hampshire, England

Beobuddy

Bronze

4231 posts

Posted April 4, 2023 at 10:30 GMT ? Edited April 4, 2023 at 10:32 GMT

#700502

Leave the D1 as it is. They rarely fail and it seems that you're able to trigger the system with your multimeter, So Tr1 works. It's not clear what your figures are. I guess that these 584 and 726 are mV's? As your using the multimeter in the diode testing mode. I provides you the forward voltage from a diode. The first number 584 will probably 0.584V and the forward voltage of D1. The second 726 is probably 0.726V and the forward voltage of the internal diode of Tr1 (base-emitter). This is the result of in-circuit measuring of components. This explains why the BL8000 switches on when you put the probes over D1. The multimeter uses a small voltage (mostly around 2V) to test the forward voltage of a diode. I would start by measuring whether there is a voltage on the base of Tr1 when powering on and off. It should be 0V (in standby) or 0.7V (forward voltage) on the base of Tr1. Resulting in the collector of Tr1 going down to ground level. D1 is only used to protect Tr1 for negative voltages provided on pin4 on the powerlink plug.

Location: Utrecht

Quite a challenge to achieve "Less is More" while having the Beovirus.

KolfMAKER

Bronze

569 posts

Posted April 4, 2023 at 10:38 GMT ? Edited April 7, 2023 at 09:48 GMT

#700503

Thnx Beobuddy. FYI, the multimeter I am using is a Voltcraft VC130-1. So I measured between TR1 and GND/pin 2 on P2, while having power on the BeoLab 8000. So it's in standby mode, red LED on. Here's the results:

TR1 Base <> Pin 2, P2 = 0 volts
TR1 Collector <> Pin 2, P2 = 7,33 volts

What do you think BeoBuddy, what could be the underlying cause?

Location: The Netherlands

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