Beocord 8004 stuck in 'STANDBY', help please.

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Hi,

 

I am hoping that somebody is able and willing to help me with a problem on a Beocord 8004 cassette deck (stuck in ‘standby’).

I have recently bought a Beocord 8004 (European 240volts with a drive motor date marking of February 1982) in generally excellent condition which initially worked apart from a few small faults (3 or 4 PPM led's intermittent operation and REC OPEN and MEMORY bulbs broken leads) but after a few days it failed in the following way, I left the unit playing one side of the cassette allowing it to switch itself off as it should after 30 minutes or so, the morning after that it was stuck in standby with the small red indicator light showing. It would not switch on again as before. The problem is the same with the 'amplifier' DIN plug connected or disconnected.

I have made some investigations using the correct schematics but before describing my findings I will tell you how the unit would switch on when it was working.

Note that I am not using this unit with other B&O equipment so it is not switched via DATALINK at pin 7 (amplifier DIN socket at rear).  The only way it would ever power ON was to plug it in at the mains supply after being unplugged, NONE of the control buttons would switch it on from standby when already plugged in at the mains, however the standby button would switch it back into standby. Is this correct or should some of the function buttons such as PLAY etc. switch the unit on from standby even when not connected to a B&0 receiver?

. My electronics knowledge is basic relative to what seems to be necessary but here goes:

I started my checks at the power transformer and supply board including an overall visual check of all components and connections etc. on all boards throughout the unit ( no apparent breaks, 'dry' solder joints, burn marks or odd smells etc. All 3 conventional type fuses (power transformer internal, power supply/motor control board and microprocessor/display board) are correct and have continuity. I checked, carefully removed and replaced every single pin connector in the whole unit as well as performing relevant continuity checks around them before and after, they seem OK. The supply into the transformer was approx 237 volts AC.

Checks on boards shown on Diagram D : I have attached a copy of the schematic with my markings, GREEN ok, RED not ok or a question.

The power transformer(9) seems to basically function with all voltages at the rectifier board(6) outputs correct apart from 19/26 (diagram numbers here are confused on my diagram) which should have 32volts( my reading here was 25/26 volts. This supply goes to the control board and is firstly split off to R30 and a Darlington BD678 on board(4). So this is not correct according to the diagram but would it stop the unit switching on? It must be added that the transformer outputs at P15-7 and P15-11 that supply the bridge rectifier at D5,6,7,8 were only 30volts AC both connected/disconnected from the rectifier board, would an eventual 32Vdc be possible after the rectifier with only 30 volts AC available? There is a capacitor across this primary marked 0.47u.

At C84 there is a reading of 4.8/5 volts which it seems is the OFF condition, 0 volts for on ( for on would this be 0volts or a switched earth?) . ( I don't know if this ON/OFF means the unit as a whole as I am looking for)

At the three voltage regulators (5) at heatsink I have no voltages at what I think are the  inputs P4 (pin 3), P4(pin 1) and what I think are the outputs P3(pin 7 should be +15volts), P4(pin 4 should be -15volts) and P3 (pins 3 and 4 should be 6.2volts). For these voltages I am not sure whether they should be present in 'standby' or not.

Other voltage readings on the schematic and ground points for this board seem to be good.

With my limited understanding I can not be sure which part of the circuit actually switches the unit from 'standby' to 'on' to allow power to all points of the unit, this also is not helped by my uncertainty in how many ways the unit can be actually switched on if from the function buttons. I would have thought that a signal from some of the function buttons when pressed would eventually switch the 0volts ON/5 volts OFF signal at pin 37 of IC8 and so on ( maybe I'm seeing this the wrong way). The user manual only describes the unit being switched on by selecting the 'tape' function on an attached B&O receiver.

There is a 4.8/5volts AC 50/60Hz feed at P21 (3) that feeds pin 1 of IC8, on the diagram it says 5.5Vp, is this critical at 5.5v or would 4.8 be ok?

I have checked that there is no short circuit at the 'standby' button on the control pad which may also have kept the unit off, it is functioning OK.

I have checked all the connections and tracks around the transistors leading to the voltage regulator units at the heatsink where there are no voltage outputs but they look OK and the continuity checks I have made there also seem OK. I also checked many of the voltages at the transistor legs where indicated on the diagram before the voltage regulators i.e + and - 24volts and 13 volts etc.

The components at the voltage regulator heat sinks and attached board look visually OK.

Diagram C :

Most of the (what I think) relevant voltages and ground points at board 1 (switching/processing/display) check out as per diagram C except for the aforementioned differences that come from boards on Diagram D.

I have not pursued checks on the boards of diagram A and diagram B believing them largely to be concerned with sound etc. (I may well be wrong!).

 

So at this point I am out of ideas and talent. I hope that somebody will be willing to help because I really want to go all the way with the deck as it was running well with great sound before this. It is also in great cosmetic condition.

I am sorry to have been so long winded in my description but I wanted  the relevant information to be available.

 

Thanks in advance to anybody for your kind help.

 

Best regards,

 

Duncan Hall.

 

 

 

 

 

 

 

 

Hi, I'm not familiar with a 8004, but I owned a 6000 and 9000 some years ago. Generally said the standby mode is always left, when any button is pressed. You should even be able to program the timer in standby.

Hi,

 

Thanks for the info.It will be useful when pursuing my checks!

I have a Beocord 8002 which is much closer to your model in production.  I bought it in 1981.  I can confirm that any button pressed, or cassette inserted will take the unit out of standby mode.  From what you describe as the manner in which it came "on" you already had a problem with the unit in addition to the ones you mentioned.  I am sure you have resolved the problem by now though.