ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Good evening all
as post in another trhead I recently bought a Beomaster 5000 and Beocord 5000 both dead.
Beocord has display with no sign of life, so thinking about a PSU problem
I've begin checking on this , following suggestions of Menahem and many others expert, I made total recap, I have already replaced the 10 ohm fusible resistor, replaced the 2 ribbon cables, changed all BC547/557 but nothing seems okay.
I got +29VDC, -29VDC, and +12VDC unloaded.
Checked all resistors and just R16 is actually 4,6K, instead of 6.81K on the circuit diagram, I'll replace during weekend.
If someone has some other suggestions I'll be glad to apply.
Thank you all.
MArco
You should have a red dot on the front of the machine,if the main processor is running at least.If not,you need to investigate the 5 volt supply there.Nothing else will function if the 5 v supply is missing.
Nick
Hi Nick
5 v supply is present on pin 1 of P7 connector so I'll reassemble PSU on deck and check again if there's a red dot on the front of the machine.
Many thanks
Hi
Display show sign of life and LM317 become warmer after few minutes, I must investigate and replace it also.
Have a nice weekend all.
The 10 ohm safety resistor that burns up in the power supply,is in the 14v supply line to the deck motor.It usually blows because the motor has seized due to the belts perishing and tangling up the mechanism.
There is a safety circuit that monitors the 14v supply,and if it's too low,eg due to jammed mech ,the main processor is inhibitied,so no functions are available.
Is your mech jammed?Disconnect the motor to see if the machine then fires up without it?Obviously the mech won't run,but there should be some activity when pressing buttons.
My mech isn't jammed, I've disconnect the motor before took the pic, although motor run well if I power up with a battery...
Have a nice day
Marco
Pin 16 of IC1,the processor,is the 5v supply there.
Check for dry joints where the ribbon cable from the keyboard connects to the main board too.
Check the reset network TR26/C33
Otherwise,I think you will have to check for activity on the various in/out ports of the processor,but it could be faulty.
I have a spare salvaged part for this if you need it?
Thank you for suggestions Nick
Good afternoon
check voltage on pin 16, 3,90 volts, but watching on schematic Vcc (5V) should be on pin 40, I'll check tomorrow.
Have a nice afternoon
Sorry,yes you are correct it is pin 40.I think I need new glasses?
Don’t sorry Nick I’ve use 300x magnify to see where find 5V..
have a nice evening
check on pin 40 and found 4.90V so think IC1 maybe still good, I must continue investigate on PSU in particular on transistors BD533/534..
I'll update in next days,
Check the connector to the front panel.Make sure the pins are clean.And check its solder joints.
Martin
Hello Martin
thanks a lot for this other suggestion.
check connector and flexible wire, cleans contacts but nothing new happened...
Hello all
make some progress during weekend, checked all resistors, all has correct values, checked the reset network TR26/C33 as suggested from Nick and change C33, TR26 seems good, asI haven't a Variac i've power up using a coupling trasfo so I've only 125 V instead 230 V, and finally something appear on display, "RECORDING POSSIBLE", so seems deck is in pause mode but no sign of life from keyboard.
Next text will be power up on 230V and see what happens, obviously any suggestions will be appreciate
Have a nice evening.
Eh.... are you using a 220-240V Beocord on 125V and wondering why it doesn't work?
After all replacements made on PSU as I haven't a Variac I've use coupling trasfo, Beocord when first plugged on 230V doesn't work at all.
And testing it on 125V would provide you with what info?
Was the present fault also present before you started?And in that case did you diagnose the fault before you started replacing components?If not, why did you replace them?And how much did you replace?
Check the supply voltages and signals around the large chip in the frontpanel with a scope (not just a multimeter - it won't tell you if there'stoo much ripple or noise).
I'm on this forum to learn more as I can, I've only a DMM and no scope so I'm trying to repair these two beautiful pieces using what I have and what someone can suggest me, I've replaced all transistors and some resitors because after desolder and measure found resistors out from specific value and transistors fried.
I've try with 125V because there are some voltages that not completely match what is show on service manual.
Have a nice evening
I understand your position - and I admire people wanting to have a go at fixing things themselves, but I amnot sure if I understand the working methods used here - or the advice you were given.My recommendation would always be to diagnose any present faults before eventually upgrading and replacing a lot of things that "could potentially make the thing even better".There's a huge risk that you will introduce new faults which could make it much more difficult to diagnose the original problem.Faults due to "natural" causes are always far easier to diagnose than it is to take as much as a qualified guess at what could possibly havegone wrong when somebody fiddled with everything and/or replaced a lot of things more or less on sight.
Repair first. Do upgrades later. And when doing upgrades, do only a few things at a time and then test. That'd make eventual fault-findingso much easier. Particularly for a "kitchen-table" repairer.
Beocord 5000 has a number of standard faults, all of which are fairly easy to remedy.I have lost count of the ones I have repaired - but it's a three-digit number.They are superb decks and they rarely need a lot of components replaced. I certainly never had to replace more than about a handful - and that being only in severe cases.
Voltage readings depend greatly upon the instrument you use and the circuit you measure in. Keep in mind, that the instrument takesplace as a part of the circuit when connected, so its internal impedance and capacitance etc. affects the circuit - and the reading. Resistors and voltages a bit out of spec will typically not cause a major malfunction, whereas shorted transistors definitely could.Voltages a bit off is quite common (ref. to the explanation above) - but shorted transistors are not common sights in Beocord 5000.They shorted for a reason. That reason will have to be found and corrected before replacing the shorted transistors and powering up again.
Anyway, I suggest you turn to the experts who gave you the initial advice and let them guide you on.And do let us know how it goes.
In the mean time, will you let us know what the initial problem was?
Thanks Martin for your reply, as wrote on first post my Beocord had display with no sign of life, so thought about a PSU problem
During these weeks checked and replaced BD533/534 and LM317, all shorted, 10 ohm fusible resistor, browning, and the 2 ribbon cables.
On connectors P6 and P7, power up on 230V , I've tensions that exceeded more or less of 30% as describe on SM, for this reason I try to power up on 125V.
Have a nice Friday.
Sounds like a severe case of overvoltage.Lightning strike perhaps.With all those components burned - also blackened cables! - I'm afraid that it's safe to say that this Beocord will neverrun again unless all internals are replaced (in one go).Too many semiconductors will be bad and many more will have internal scars that will show up sooner or later, so even if you findand replace all bad components now, you'll face problems again before long.If cables have blackened, some of the copper traces on the circuit boards will also have experienced overloads (that's where the cables come from and go to).In my opinion this Beocord has reached a dead end.I suggest you grab another one.They are plentyful, so choose one with "only" standard faults.That would also be the cheaper solution.Finding f.e. a replacement processor would not be easy and there's a good chance it could only come from a donor Beocord anyways.
If your cabinet is nice, you could find another with a bad cabinet to make it even cheaper.
yes you are probably right about lightning strike, I would just check copper traces on the circuit boards after all my cabinet is nice, so search another one with a bad cabinet.
Have a nice Monday
Now we know that your machine has suffered some sort of flashover or voltage surge,it seems pointless to struggle on trying to fault find.
As Martin suggests,there will be damage in all sorts of places,and although you are keen to fault find,it will be an interminable job!!!
As the machine is in good condition otherwise,and you have repaired the power supply,why not swap out the main board?
I have a spare one that I think is working.It will certainly be better then the one you have?
You are welcome to it gratis if you'd like to have it?
Just reimburse me for postage?
Regards,
And the Dolby board.And the display board.
Hello Nick
thank you for your offer, frankly think problem are still located in power supply board, let me time to check pcb another time and after I'll be glad to pay postage for motherboard.
Hello
I I want to publicly thank Nick for providing me spares pcb for my Beocord that now return to be a functioning deck, all function play well, still remain minor issues that may solve in next days.
Many thanks again Nick all the best