General Forum

Re: New member, new (to me) Beomaster/gram 8000

Jeff Hoyt — Sat, 16 Jan 2010 23:13:29 GMT

I started a new thread about the Delayed Relay circuit.

Re: New member, new (to me) Beomaster/gram 8000

Jeff Hoyt — Sat, 16 Jan 2010 18:25:08 GMT

Probing around, here's what I'm getting:

Power resistors: ~115VAC across each

Large transformer: 0V in, 0V out

Small transformer: 115VAC in, 18.5VAC & 5VAC out

Re: New member, new (to me) Beomaster/gram 8000

Dillen — Sat, 16 Jan 2010 17:33:58 GMT

No, I'm talking about the +/- 55V secondary voltages.
You can also measure if any mains AC arrives at the (large) transformer primary at all.

The FM presets are stored in a chip on the processor board. The BM8000 should be able
to remember preset stations even if mains was disconnected for a long time (days or more).

Make sure you have everything connected properly and there are no broken solder joints
or PCB tracks, especially at the processor and display boards.
Signals essential to the general functionality of the Beomaster passes through the
display board to- and from the processor board, like f.e. strobe signals for the buttons
on the tonecontrol board (FM store etc.).

Normal is:
Tune in to a station, press "Store" and the "P" will start flashing on the display,
then press the preset button (1-9) you would like to store this station at.

The transistors I will have to look up.

Not a Muppet fan in particular but I do like Stattler, Waldorf, the Swedish Chef
and of course Muppet Lab.

Martin

Re: New member, new (to me) Beomaster/gram 8000

Jeff Hoyt — Sat, 16 Jan 2010 15:57:29 GMT

The startup resistors have been replaced with 5.6 ohm 5W wirewounds, but the output transistors have not been replaced yet. Now, are you talking about the smaller transformer secondary windings? I didn't check them for proper voltage. I will dig in there. But I do want a quote on those transistors.

Also, the tuner is not remembering my presets...even with the unit powered on! Is there a special memory cap somewhere, or something else?

Thanks for appreciating my avatar. If you're a Muppets fan, there's a whole section of new Muppets videos on YouTube. I highly recommend their "performance" of Bohemian Rhapsody.

Re: New member, new (to me) Beomaster/gram 8000

Dillen — Sat, 16 Jan 2010 15:31:10 GMT

Sounds like there still is a problem with the startup resistors or their circuit board.
RL2 closes, that's fine but RL1 is supposed to close shortly after the "soft" voltage is present on
the transformer secondary.
If the secondary shows no voltage at all, RL1 will never close and the amplifiers will not get any power.
Maybe a burned PCB track ?

If you already replaced the output stage transistors, there's no reason to replace them again, unless
proved faulty.

PS: Wonderful avatar !

Martin

Re: New member, new (to me) Beomaster/gram 8000

Jeff Hoyt — Sat, 16 Jan 2010 13:50:24 GMT

Here's what's happening:

At startup, RL2 instantly closes. However, RL1 never does. So I have full preamp/control functionality, but there is NO 55V voltage in the system. RL1 never energizes, there is 0V across its terminals, traceable back to the "delayed start" circuitry on Module 6. I get lost there, though. The capacitor is new, and all else looks visually OK.

Is this circuitry part of the "protection" system? (The "clipping" light never comes on at all.) I did pull and test the output transistors; B-C and B-E were OK, but C-E were shorted. Would this cause the +/-55V rail to shut off?

How much would it cost to get those transistors (TIP141/146 x3) from you?

I read, in another thread, you guessed (correctly) that a trimmer pot shorted, and took out the emitter resistors and output transistors. This appears to be exactly what happened in my unit. I have replaced the trim pots (on both output boards) with 10-turn Bourns type, but I am very frustrated that I can't get the 55V to the board to properly set the bias voltage!

Thanks for sharing your knowledge!

Jeff

Re: New member, new (to me) Beomaster/gram 8000

Dillen — Sat, 16 Jan 2010 04:05:12 GMT

No,

If the relays click one after the other with a few tenths of a second between, that part is working.
If they release again soon after, something is wrong in the amplifier(s). Could be a too high
idle current or badly adjusted DC offset (or something else).
Try measuring the +/- 55V and see if it is supplied to the amplifiers at all.
If so, then try putting a voltmeter to the amplifiers center rail (speaker output) and check for DC.
Does the "clipping" light flash on the front panel at startup ?

Martin

Re: New member, new (to me) Beomaster/gram 8000

Jeff Hoyt — Fri, 15 Jan 2010 17:24:11 GMT

Update: this morning I replaced the bad power resistors on the startup board. But the problem is continuing. I've traced it back to the "delayed relay" section of the power supply board (6). Could the receiver be refusing to come out of a "protect" mode?

Re: New member, new (to me) Beomaster/gram 8000

Jeff Hoyt — Thu, 14 Jan 2010 21:53:26 GMT

I discovered something: the two diodes on the startup board test OK (out of circuit, of course). However, the two big power resistors, 5.6 ohm, measure at ~200K! That would certainly explain the lack of power to the transformer, as those are the first components the AC sees as it comes in from the mains. Time to look through my junk and see what I've got...

Re: New member, new (to me) Beomaster/gram 8000

Jeff Hoyt — Thu, 14 Jan 2010 15:53:05 GMT

Thanks, Martin. I already have the SM, but didn't see the error code matrix before. I just found it. I will definitely check 9IC3, especially in the vicinity of pin 31. The unit works for a while, so I imagine the issue is heat related. Possibly a bad solder joint, or debris, or something. Thanks for the direction.

I will check over the startup board (7) tonight, I have replacement diodes if needed. It seems like the startup circuit is not powering the 55V system up at all.

Thanks again,

Jeff

Re: New member, new (to me) Beomaster/gram 8000

Dillen — Thu, 14 Jan 2010 09:51:34 GMT

The Beomaster 8000 is a wonderful machine but not the easiest to repair. Even experienced tech guys
develop grey hairs occasionally.
The service manual is download'able from our main site at a small fee - well worth it for all the info
kept in there and this site will be happy to see some support.
That manual would tell you that TE3 is a defect around 9IC3. Pin 31 in particular may be shorted.

Martin

Re: New member, new (to me) Beomaster/gram 8000

Jeff Hoyt — Thu, 14 Jan 2010 09:05:38 GMT

There are two distinct relay "clicks". I'm not sure how many there are onboard, though. I believe the fuses are good, also. One I visibly checked, the other ohmed at a dead short. I'm thinking something happened on that board, but what? Other than the relays, fuses, wires, and two big resistors, there are two small diodes. They "look" OK, but my next move is to test them, and replace if necessary. It's weird that even the big rectifiers have virtually no voltage across them.

And, the computer is acting up now. I left the unit on all night, and this morning it was on the fritz. I was able to run the self-test, and it came back with TE 3...what does that mean?

Re: New member, new (to me) Beomaster/gram 8000

Dillen — Thu, 14 Jan 2010 03:11:00 GMT

If the "startup"-board is the one at the back with the fuses etc. then I suggest you take a good look at the board and the fuses.

If the relay(s) does not click, check that you got all the cables and connectors back on correctly. Eventully, check
for cracked solder joints at the connectors.

Martin

Re: New member, new (to me) Beomaster/gram 8000

Jeff Hoyt — Thu, 14 Jan 2010 00:55:37 GMT

Well, good news and bad news. I got all the suspect components swapped out, and all the wiring harnesses put back where they go. The receiver powers up, and tests (Monitor + Standby) fine.

However, the power amp section does not power up. There is no voltage across the main filter caps (should be 55V), and there is no delayed relay clicking on. Upon the first turn-on, there was a wisp of smoke from...something. Something around the "Startup" board. However, nothing looks bad. So...

What do I look at now?

Re: New member, new (to me) Beomaster/gram 8000

Jeff Hoyt — Fri, 01 Jan 2010 14:20:06 GMT

I have my orders placed, and will receive them in a few days. I found the BF859* transistors at MCM, the rest at Digikey. I decided to shotgun all the electrolytics, since I have heard the RDE's are ticking timebombs.

* BF859 shares a datasheet with BF857, and appears to be a higher-voltage version of the original, Vce/Vcb is 300V, vs. 160V.