Yes it is a cap, apparently a tantalum capacitor. they popped and smoked when it turned on. They may have been cracked before and I just didn't notice but they're real cracked now. I have sent a message into steve at stargate electronics to see what can be done. Also have an email into Rick's home theater repair here in St Petersburg who said they too can take a look at it for 35 bucks to assess the damage. Mostly worried about mosfet outputs being damaged, which apparently are no longer available or difficult to get the exact replacement. I have had some good responses and solid information given to me here and on another audio forum and I've learned a lot in the little time I've been dealing with this. I admit that I am very new to this kind of equipment and do understand that I've already made a fair share of mistakes here.
Going to get some quotes but if it seems like an amp I just wont ever be able to trust not to cause damage, it will be sold as broken / for parts or repair only.
You have a difficult problem as there is a grave issue here.
Tantalum caps are known for this when not used properly. They have low internal resistance and small form factor. However if their rated voltage is exceeded by a small amount they explode spectacularly and have set fires. If voltage is not exceeded they have long life.
So something likely occurred to cause an over voltage.
So the best solution to make the amp even safe to use in your home is to replace all those tantalum capacitors with solid aluminum ones. There may be a problem fitting them in. This is a must for safety.
Now a big problem is that I can not find a schematic or service manual. I have got close and run into no longer available when other B &K manuals are available. It is certainly possible they have been pulled for safety reasons.
One thing has been clear to me is that you have to be an expert on these amps to work on them. This is another red flag as it is a strong hint there are stability problems with it.
I have come across people who have had problems not being able to keep the DC offset stable. This seems a particular problem with B & K amps. The service procedure seems the same across the range.
These procedures should be performed by a qualified technician.
1. Plug the amplifier into a variac.
2. Connect an 8 Ω RMS @ 20 Khz.
3. Slowly turn the variac up to operating voltage while monitoring the rails for excessive
current draw. The meters should not read more than 400 mA DC. If one or both read
more than 400 mA, turn the bias pots (P2) to minimum and retry.
4. Set bias of the amplifier by adjusting the bias pot (P2) mounted on the solder side of the
board to achieve a reading of 200 mA on each channel for models ST 140, ST 140M,
ST 202, and ST 202+. The bias for the Pro 600, EX 442 and M 200 amplifiers is 250 mA.
Setting the bias higher than stated only causes the amplifier to run hotter and burn out
faster. It does nothing for the sound quality of the amplifier.
5. Set the DC out of the amplifier by monitoring across the outputs. Adjust the DC pot (P1)
for 0 VDC ± 5 mVDC.
Thank You,
B&K Components, Ltd.
Now you still have the problem of the output devices being NLA. I did ascertain that these need to be closely matched. So if there already is trouble here or it develops later the chances of finding a closely matched pair is close to none.
Certainly this amp is not now safe to use as a five channel amp.
To me there seem far too many issues to make this a sensible and worthwhile project.
I never like touchy products and these seem it. I like amps stable as rocks, and have really zero tolerance for gear with these types of issues. Probably good they are extinct.
Basically what I'm trying to tell you is that pursuing restoration of this unit is probably not a wise use of funds.
I have a strong suspicion these units were not that good from day 1.
