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This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Greetings all,
Almost completed the restoration of my really old 4002 - have changed all tin-can transistors in the hope I can revive the record-cleaning function......but, no, it did not work !
Changed all BC142 and BC143 types but then 4R1= 8.2ohm went up in smoke ?????
I suspected the 0TR4 which is a TIP41A but it checked out ok !
The sad thing is the rest was working fine before and I simply can not understand
What possibly could have gone wrong ?????????
Far too nice a table to wreck.......can anyone assist with clues ?
And before you ask, some of the old tin-cans measured very suspicious before, hence the change !!
Cheers, ALF
When this sort of thing happens to me (and it has), I step away from the problem for a little bit to recharge and get some fresh thoughts going. Return to the scene and go back through all of the components you replaced. Make sure something didn't get put in backwards and make sure everything you unsoldered got soldered back in again. It is easy to miss something or wire something wrong when changing a lot of components.
I have attached a diagram of what I think the circuit area you are describing is. 4R1 and 0TR4 operate the 0RL1 solenoid. Check the voltages on that circuit. Something allowed too much voltage on that resistor to smoke it. Either a component failed or something is wired incorrectly.sonavor
Hi sonavor,
Thank you for your encouraging words:-)
The question is: how can I possibly measure those voltages without turning on the table
And most certainly roast 4R1 - 8.2 Ohm resistor again ? Perhaps damage some other parts on board# ?!
I did not even touch board #4 when I changed all those tin-can transistors.
I unsoldered 0TR4 and it checked out ok ! Also double-checked all changed tin-cans
For correct positioning and soldering - all fine !!
In the 'off' status I could measure about 45V on the solenoid which is down to slightly
Higher mains voltage.
So, in other words I feel pretty unsure about the next steps ??
Even checked 0TR1 but checked out fine ?!
Anything else I could do or check ???
Cheers, ALf
Why did you replace all the transistors?Were they all bad or ?
Martin
Reason was that some of those tin-can trans measured suspicious and may have had
An impact on the still not working 'record cleaning' function !!
So I decided to play it 'safe' and replace all of those tin-cans !
Big mistake as the 'new ones' caused big problems, being either wrongly labelled
Or simply dead ?!
Anyway, I started to re-fit the old BC142 trans and can report so far the smoking resistor seems to go ok.
All trouble has not subsided as the drive motor now refuses to spin - I will continue to refit the old 1TR7 and 1TR8 and shall report back !
Not a good day in the 'office'
Hello again,
As said earlier - bad day in the office !
The table starts ok, carriage moves over......all fine as long as the solanoid is not lowering
The arm, however if engaged....then after a couple of sec 4R1 starts to get really hot and eventually dies.
I can only suspect 0TR4 to let too much current through to 4R1 or am I wrong here ??
By looking at the solanoid circuit i can not identify any other component being directly in contact with that resistor.
Any further advice would be fantatstic :-):-)
PS: motor stopped spinning because of a detached wire on TIP31
Alf,
Don't get me wrong;Most common faults in Beogram 4002 are known and documented, and pretty muchevery possible fault is easy to diagnose for an experienced repairer.We have many skilled tech guys here and we are eager to help, but your workingmethods makes it more or less impossible to predict and diagnose anything, let alonesuggesting the next step.
You replaced a bunch of transistors because they measured "bad". How?After that you realized that by doing so you had introduced more faults.Then you refitted the old transistors - how many and which ones?Only to realize that there is now a new fault, seemingly unrelated to the original.
It's my experience, that replacing components on sight is not the way to repair things.A simple diagnose and repair to each present fault is the way to go.Only after this you can consider improving/renewing fault-prone components.
Again, please don't get me wrong; I don't know the level of your electronic skills, I can only judge fromyour methods, broken wires, smoking resistors and the terms you use (tin-can transistors etc.) andI don't know how experienced you are with tangential Beograms.(They are usually not suitable for beginners).
I admire people who wants to have a go at DIY-jobs but I have an even larger respect forowners, who realize when they are in too deep.
To repair something you will first need to know how it's supposed to work.Do you understand how the solenoid lowering circuit works?
Thanks for that Rune,
I will definitely follow up that link !!
Martin,
You didn't get me wrong but it is perhaps a good opportunity to clarify a couple of points.
I certainly appreciate the experience and advice from everybody trying to help - no exception !
The work on this 4002 wreck was quite intense so far and that it was actually playing
Records again is wonderful. I should have done a pictured run of steps I have done to get it to that point.
What wasn't working was the 'record cleaning' function - ok, after reading on one forums post about changing those old T-39 type transistors I started checking.
No harm doing that - I am not a certified & qualified repairer running a business, meaning
I can spend as much time as I want. It is also common knowledge, published numerous times how tricky and sometimes unreliable some testing methods for transistors are !
With that in mind what damage can you possibly do in replacing all of those BC142 and BC143 caps ??
To be specific, I replaced TR1, 7, 8, 16, 30, 28, 27 - do I care about $3.20 ? NO!!
And yes, I can read their pins and put them in the correct way - not rocket science !
For some unrelated reason and due to twisting and turning of board1 one wire of TIP32
broke and that is now fixed after some searching :-)
I never claimed to be a trained electronic technician but am proud of what I have done so
Far as I don't have an expert or workshop around the corner who would even look at a 35-Year old BG4002 !!
That is the reality - acknowledging the fact that some problems are just outside my expertise doesn't help nor is it very satisfying to dump such a nice machine in the bin.
My methods may not be technician-textbook style but get some things-problems done
Btw, the expression tin-can caps comes from an electronic technician because of their looks !
It should of course read 'tin-can' transistors and not caps !!
ALF
I verified some of the voltages but most are about 4V higher - that can not be responsible
To put 4R1 into smoke - but what is not quite clear is which is limiting the current ?
I believe the higher voltage would be consistant with a sligthly higher mains voltage output of the step-down transformer ?!!
I also noticed in your diagram 1TR13 and 1TR14 are 1TR15 and 1TR16 in my circuit diagram - that may only look like a difference in numbers but checking the parts-list they are different transistor types.
But that said, the table was running without a glowing 4R1 before and what exactly causes the high current appearance all of a sudden puzzles me.
I know the BG4000 has a current-limitter switch, so is there an equivalent in this model.
The SM for the type 5503 does not contain a more detailed description of the solanoid circuit like I found in later BG4002 SM's.
Any comments from your end ???
Hi ALF,We are pretty much flying blind here without pictures and diagrams of what you actually have. Regarding the voltage problem at 4R1, I thought you said backing out to the original state of your transistors eliminated the problem there. Anyway, continuing on....Because 4R1 is what pulls down the voltage to activate the solenoid, I suspect OTR4 and maybe 3D1. Just because a transistor passes a transistor tester check off-board doesn't mean it can't fail under load. You might first try disconnecting the OTR4 emitter connection to 4R1 and monitor the voltage across the resistor with that configuration. It should be pretty close to zero volts DC. With that setup also measure what the voltage is at the collector to ground, the emitter to ground and the base to ground. When everything is connected back per the schematic, the voltage across the 4R1 resistor should be less than 4 volts DC I believe (3.5 VDC according to the schematic).
What is the state of the 1N4004 diode 3D1? Does it test out okay?
-sonavor
As John said above, this is very difficult because the way you work and what you tell seems to be inconsistent.
Please let me ask you this again;Do you know, how the soleniod circuit is supposed to work?I take it, you are aware of the two different current levels for activate and hold and you already checkedthe function and mechanical activation of the associated switch?
Is the serial number of your Beogram higher or lower than 260028 ?Assuming that it is higher (most are):Check the solenoidCheck (or replace):3D1 1N40014R1 8,2 Ohm 0TR4 TIP41A1TR15 BC547B1TR16 BC1421R56 47 Ohm 5W ceramic1R57 150 Ohm 1WThe way 1D2 (a zener) is mounted tells you that this is a stabilized power supply, - right?This means, that a slight raise in mains is not cause for a higher voltage on the DC rail in the Beogram, the reason forthis will have to be found elsewhere.Martin
hi sonavor + martin
may I shed some light into the darkness ? the not working 'record wiping' function triggered all of this - do you remember ?
I was working with the BG4002 Type 5503 circuit diagram and its partslist from the appropriate service manual.
I backed out of the new BC-142/143 series of transistors as it seemed to have caused damage, which seemed unrelated !?
went back to the old BC ones and thought for a moment 'problem solved' ..... NO, smoke was coming out of 4R1 again after only a few seconds after the solanoid was activated ....... that is why my earlier message may have caused confusion ?!
.......exactly what I said previously about testing transistors off-board !
4R1 showed just under 8Ohm with activated solanoid, which wasn't right.
I did go through your suggested procedure without any positive outcome, apart from a good-testing 3D1 !
what I previously checked and replaced was 0TR4, the mechanical solanoid switch worked fine and so did the solanoid !
checked and replaced 1TR16 as well as the 1R56 and naturally 4R1.
Martin added 1TR15 on its list of components to check...........that one I DID NOT CHECK and it seems after replacing that one
with a BC547B - fitted was actually a BC237B - the smoke has subsided and it works :-))
I know, I said this before but after playing 2 records 'smoke-free' I consider it DONE.
on another note:
top left corner of the circuit diagram you find OFF 41V, ON 35V, v 31V
I measured OFF 44.6V, ON 39.6V, v 30.2V
on the main DC rail I have 24.2V instead of 22.8V !!
What still doesn't work is the "Record Wiping' function which is precisely what sparked all of this.
still very happy to listen to good ideas in that regard - until then
A BIG THANK YOU for your patience and expert advice
cheers ALF