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I can’t offer any specific repair advice for the BL8000. However, I can provide some general advice based on a repair of a BL4000 with a similar issue.
Based on my initial inspection, I didn’t think that I had an issue with foam rot, but I was wrong. I found several places where there was either open circuits or higher than expected resistance in the traces. Some of the telltale signs were black spots like in the picture below. Other places had white(ish) colored spots or were at the edge of a solder pad. The most insidious corrosion was where a trace ran under another component. Some of the breaks were not apparent until the area was cleaned with a scratch pen. I narrowed down the spots to examine in detail by installing needle tips on my multimeter probes and setting the meter to measure resistance (as opposed to using the “continuity beep”).
This picture shows a few of the steps in the progression of the repair. Note that the traces under the black spots ranged from being OK, to being partially corroded, to being completely corroded.
Hope this helps some,
Glitch
Whilst I have not needed to look at a Beolab 8000 for a very long time, I took time to remind myself of the workings of the circuit.
To answer your last question first, the problem could be IC1 and I noted you have tested all parts of PCB5 by comparing with a working unit.
Given everything works perfectly with a Powerlink connection is helpful because that reduces the area for investigation considerably. The problem is almost certainly going to be prior to R85 on PCB2 where it feeds the base of TR9. The reason I say this is because where you use the Powerlink to switch on the speakers it forces the collector of TR16 which feeds the other end of R85.
If you have an oscilloscope I would look at the anode of D17 which is also the junction of R136 and the collector of TR17 with and without a signal at the phono input.
If you only have a multimeter, then the best way is comparing voltages between a good unit at the bases of TR14, TR16 and TR17 with and without a signal at the phono input.See attached circuit diagram of the area of concern
Let me know how you get on..
@Glitch: Thanks for your input and especially the visualization. This helps understand what to look for. So I will check again.
@Keith: Also thanks a lot!
TR14, TR16 & TR17
In the meantime I measured what you suggested. Since I do not have an oscilloscope, I used a multimeter (Voltcraft VC130-1), in diode/continuity mode. IO found out that the direction of TR16 on my PCB is 90 degrees different than the layout in the Service Manual. But I assumed the Base to still be the left leg of the two next to each other.
You can see the results below. In all measurements, no continuity signal but a value measured.
Measuring at TR16 with & without signal on RCA, the relay switched on. With audio signal on the RCA, music was also there.Additional
In the schematics of PCB02, I read that IC1 should measure +15v at leg 8, and -15v at leg 4.
- I measured 29v.
As IC should also measure +15v at leg 8, and -15v at leg 4, I checked that one too.
- Also 29v.
Question:
- What does this mean to you?
- In the meantime I have also received a new IC1. Do you suggest to execute the replacement, or do you have another suggestion?
@Keith: thanks, I guess I misunderstood.
So I re-measured with the multimeter in DC voltage.
Also, I did the same measurement with a speaker that switches correctly on the RCA/Line-in.
This is what you meant?
Here’s the results of measuring TR14 at Base, after removing R136.
Curious to learn what the results mean.
R136 removed.
Thanks for your patience with me Keith. I am still learning, but I get this one.
Here’s the new measurements with: the negative lead of the multimeter on Pin 2 of P2 for ground, and the positive lead to Leg 4 and Leg 8 of IC1.
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