Hi Alf,

Don't try to tackle too many issues at once. Right now it appears your issues are related to the power supply circuits. You need to troubleshoot the relays and see why they are acting the way they are. Determine if the relays are good or if the circuit controlling them is faulty. If you think the voltage regulators are running hotter than expected then check what their incoming voltage levels are. I would go through the power coming in from the transformers through the rectifiers and the power up circuit. Getting the power supplies in order first will make troubleshooting other issues a lot easier. Plus power supply problems will cause other things to fail so there is no sense hunting those things down until the power is fixed. You said the Beomaster has had a lot of restoration done on it already. You don't know if it was done correctly though. Someone might have made a mistake like an incorrect value or polarity. You will need to double-check everything that was done.

John

Hi Alf,

No time to delve into that tonight but I’ll certainly be around!

I have two working ones.

Try switching it on with both amp modules disconnected. I’d do that first. Then plug back each amp separately and see what happens.

The left side cooler does get quite warm, that’s normal. So to me this is a rather good sign, if anything.

Hi ALF,

I agree with a previous post of John's about faulty relays, I've also had to replace RL2 on a BM8000 I recapped a couple of years ago.

I'd measure the collector voltage of 6TR18 after you  plug the unit in and it's gone into Standby. It should be around -24v. When you try to power the unit on the collector voltage should increase to around -0.2v. If this happens and if you measure 0v at 7R1 then then I'd replace RL2. If the voltage doesn't change at the collector then I'd look for a fault in the relay circuit (6TR11/12/18).

Once you've resolved the issue with RL2 you can see if there is also an issue with RL1 or not.

Regards

Lonnie

Thanks John,

indeed, checking someone else’ work is worth doing:

first finding were on the tone/filter board with 2 caps in the wrong way (🙄) and a cracked IC2 chip.

Off to the power supply board 6: all caps are fine and put in the correct way, good news....

with P76 unplugged I have all voltage regulators IC4/5/6 delivering with

IC4 (5V) gets 11.3V supply, IC5(+15V) gets 24.4V supply and IC6(-15V) gets -25.2V and  P48 pin2/3 delivers 5V.

 

so far so good but, I am loosing the 5V the  moment I plug in P76 to the processor board - still scratching my head WHY ??

the processor board should get the 5V supply via P76 pin8/9. Unless I crack that 5V supply voltage issue I won’t even progress to further check RL1/2!

something must shorten out the 5V supply in the processor board ?? Damaged uProcessor ??.

btw, it is the same scenario with unplugged output boards 5, as thing Jacques suggested.

sorry Lonnie, I could not even get to your suggestions - many thanks for getting on board!

ALF

If you probe at P76 before plugging it in and there is 5V then lose it on plugging it in then there must be a short there. You said earlier you changed out the microcomputer IC oscillators. Did you remove the microcomputer ICS when you did that?  If so, did you make sure the oscillators were shorted while doing the procedure?  It is too late to worry about now but in the future one shouldn't really mess with the oscillators unless there are symptoms there is a problem related to it. I do change them out on restorations that involve expensive shipping just as extra insurance the unit won't develop a fault and have to be shipped back.

For now you need to verify the board is causing the short then see what component or trace is doing it. Since someone else previously worked on the board perhaps a bad solder attempt shorted a trace.  

John

thanks for your getting back John, I guess ‘guilty as charged!’

no, I did not shorten the crystals 😢 but I carefully removed the two uPs before I caried out the operation and reset both on new machined tulip-style sockets. Quite possible that I may have damaged the main processor ??

too late now to worry about - i do remember now when I studied how to do that.

there are definitely 5V present at the loose end of female P76, meaning the connecting cable is fine. 

As I understand the 5V come in to board 9 via P76 pin 8/9 !.....9C86, 9L4, 9D6, 9C85 as first ports on entry ?!

time to re-check the soldering again, ....done that twice, but perhaps I missed a accidental bridge ?

ALF

Ok,

solder-bridge at 9L7 !!!

the 5V supply has been restored 🙄😁

the uP test came out as ‘TP’ 🤙🙏

now I get a chance to follow uo on Lonnie’s suggestion about a possibly faulty 7RL1 or 2...

I’ll be back

ALF

Hi Lonnie,

just measured through your suggestions:

6TR18-C showed

about +430mV in STBY

about 17.imV in ON

and at 7R1 fluctuating voltages somewhere between -100mV to - 1.1V

shouldn’t I see about -25V at the kathode of 7D2 ?? I get basically 0V

ALF