Vintage Products

Re: Beogram 4004 Trouble

Step1 — Sat, 21 May 2011 14:54:12 GMT

Where did you get those hook test leads from? They look quite nice!

Re: Beogram 4004 Trouble

HarryPierce — Sat, 21 May 2011 12:49:42 GMT

Allright!! Life signs! I obtained a set of jump cords and jumped plug P4 (see pic below-what a beautiful mess...;-). Then I hooked my multimeter sequentially into each of the connection and measured the current, while operating the power supply under 0.5 Amp current limit. This quickly allowed me to identify pin #3 as the offending current sink.

The orange lead on pin #3 connects to board "8" and interacts with both the data link and the mute circuits. I first suspected the mute circuit to be bad, and removed the relay and 8IC1. This did not reduce the current, so I soldered them back in. On to the data link circuit. Here the burnt out 1N4148 diode gave me the clue to check 8C11 which connects to ground. Indeed it turned out that this capacitor had a short circuit. I replaced it with a 2.2uF elco (see pen tip in pic below) and also exchanged the temporarily inserted 1N4002 with a proper new 1N4148. Then I put

everything back together and fired it up, still using the regulated power supply. Voila-no more short circuit. Pressing "33" now draws a smooth 0.19Amp at 25V DC. The other functions also came to life. Pressing start launches the slide towards the table searching for a record. Stop sends it back etc...

Unfortunately, a new problem made itself apparent (see my next entry "BM 4004 Solenoid Problem?")

Re: Beogram 4004 Trouble

tournedos — Sat, 14 May 2011 14:32:45 GMT

You would need to cut the traces on the circuit board and later bridge them back. It was just an idea and maybe not worth the trouble, perhaps it would be more useful to just check the resistances on the supply lines of this board (P8 pin 9 = 30V, P8 pin 8 = 21V). If they don't seem much of a load, I can't see how plugging the board back in would harm anything.

The calculation on the mains side fuse will only give a rough upper limit to the constant current you can draw. You should rather think of the power consumption. Earlier you said you gave up at 0.8A @ 5.7V - that would be only 0.8*5.7 ~= 4.5W, which I think is still way less than the deck will need in full operation (I would guess closer to 20W, i.e almost one amp at the nominal supply voltages).

Re: Beogram 4004 Trouble

HarryPierce — Sat, 14 May 2011 13:59:59 GMT

Hi Mika,

Thanks much for your input! A possibly naive question: How do I disconnect the four traces? I can see how to do the two right ones by taking the jumpers out, but the ones on the left?

I do not think that I have shorts anymore...the three "serious voltage" carrying pins on P4 of the main board seem to lead now into "reasonable resistances". Can I assume based on the 250mA fuses that a current of about 120V/25V*0.25A=1.2A will be o.k. and not kill additional stuff? (well, actually, I guess I answered this question already by burning the fuse...aeverything that could get killed under such conditions probably did get killed...;-)

Thanks!

Rudy

Re: Beogram 4004 Trouble

tournedos — Sat, 14 May 2011 13:27:46 GMT

The possibly problematic part of your board 8 contains only the Datalink control circuitry for the deck. So, it might be possible to isolate it from the rest for testing (disconnect the four traces coming down from above the black plastic tower in your pic, and leave P10 disconnected).

The upper part with the relay is the muting circuit common to all these (two-channel) decks. R2 adjusts its delay and is in no way critical. Middle position would sound nicer than all the way to one end, though.

The service manual snippet containing 4004 specific stuff we have on site is next to illegible, so I'm not sure what the function of that diode is. 1N400x might work in place of a 1N4148 depending on application, but it is designed for rectification and will be worse in just about every other spec compared to a small signal diode. Order 50 pcs while you're at it, they cost next to nothing

Unfortunately I can't guess on the correct startup current, but it won't be too small as the motor starts up. Also, some circuits might not work properly when the supply voltage is too low.

EDIT: just realized there's a better scan in another service manual. D11 seems to be inline the supply to part of the control circuitry. If it had burned short circuit, there might be a problem around TR1-2-3-4.

Also, leaving P10 disconnected will disable some functions. The "33" start should still work.

Re: Beogram 4004 Trouble

HarryPierce — Sat, 14 May 2011 11:15:27 GMT

Hi There,

Thank you very much for all your great input!! I spent some more time with my 4004 baby, and made some progress (perhaps). First, I heeded Olly's advice and hooked the board up to my power supply. It turned out that the high current only occurs when P4 is connected (pen points to it in the picture-I apologize for the poor focus-forgot to turn on macro). When I disconnected it, I was able to run the motor when pressing 33 (~0.13 Amps at 25 V DC at P3-1) and the 33 light comes on under the rpm adjuster wheel. -text continues after the picture-

When connecting the plug, a high current occurred (~0.5 Amp/<2 V). I took the board under the key pad out (labelled "8") to check the components. What I found under the P8 on that board was the missing BC144 transistor (see pic). The previous owner-joker probably thought to better send me all the parts...;-). I decided to keep the NTE128 replacement in the H-bridge despite the fact that the found BC144 seems to be in working condition. I should point out that I also replaced all elcos on the main board, made sure that all potis actually work, and checked all semiconductor components with the component check function of my lovely new (old) Fluke 97, i.e. I think the board may be in working condition-text continues after pic-

This may well have caused a short on the plug since the solder points probably contacted the transistor housing. When examining the voltages on P4 on the main board when pressing "33" before taking board 8 out, it seemed that only pins 2,3 and 7 pulled up to significant voltages (24,24,5.9V). When checking the corresponding pins on the plug against ground, I found that 3 had a short to ground.

At that point I decided to check all diodes and transistors on board 8 and exchange the two elcos (see pic below). I found that 8D11 was burned through. Since I did not have the exact 1N4148 replacement, I scavenged a 1N4002 from some discarded board I had lying around. The data sheet seemed to suggest that the 1N4002 can take more than the 1N4148, but I am not sure if this is a good idea with regard to frequency response and all that-any input here would be appreciated. I will order the proper one with my next Newark shipment...-text continues after pic-

After putting the board back in and making all connections the short at pin 3 of P4 was gone (1.9MOhm now), I ramped the voltage on the main board back up to 25 V, and experimented with pressing "33" under slowly relaxing current limit. Unfortunately, the current is still fairly high. I went up to about .8 Amp, and reached a voltage of about 5.7V. At that point I got a bit nervous and decided to write this post hoping for some expert advice! ("A man's gotta know his limitations"-Clint Eastwood/Dirty Harry...;-).

It would be quite interesting to know what the current is in a properly working deck when pressing "33".

One more question remains: the 8R2 trimmer on board 8 was set all the way to zero Ohm when I took it out. That seemed strange, but after finding the BC144 I think nothing can be taken for granted in there...Any advice to adjust R2 would be appreciated.

Thanks much in advance!

Rudy

Re: Beogram 4004 Trouble

tournedos — Thu, 12 May 2011 12:49:16 GMT

HarryPierce:
If the motor seizes, does that typically damage the 8-pin IC that controls it? Do you know what IC that is? The cryptic labeling does not seem to lead anywhere in terms of replacement possibilities etc...

I believe it is exactly as it says on the top - a C1003 (or µPC1003) by NEC and looong discontinued. It was used a lot in the 1970's in various cassette decks etc.

Seems pretty robust though, I don't think I've seen any discussion about it failing.

Re: Beogram 4004 Trouble

HarryPierce — Thu, 12 May 2011 12:44:37 GMT

Ah yes!! I now remember transformers from my Physics classes...;-). I agree this must have been a full short somewhere. Maybe something mechanical in the key pad? It happened when I pressed down the 33 button...I cannot imagine it is the transformer, since I did not touch it when it happened. Also: after that event, I put in a new fuse, and I got the prescribed 21 V after the supply transistor, and the fuse stayed happy.

Rudy

Re: Beogram 4004 Trouble

Step1 — Thu, 12 May 2011 12:12:53 GMT

Just in case you have not realised please bear in mind that the 250mA rating is on the mains side which would equate to about 60W @ 240V on the primary before failure so this will mean it will take a couple of amps on the secondary side before the fuse fails! I think the solonoid draws a couple of ampsinitially but the circuit is designed to reduce current to a much lower holding level within a few milliseconds so should not pose a threat to the fuse.

Anyway, looking to measure a 'fault current' of 250mA is only going to lead you down the wrong path. I suspect you will be looking for a near dead short. Get what you know is broken right first and work from there! One bit at a time!

Maybe check some of the transistors? Also have you unplugged the transformer and tested alone although this does not sound the case I have had a duff unit which is still awaiting a donor!

Keep up the good work though!

Re: Beogram 4004 Trouble

HarryPierce — Thu, 12 May 2011 11:03:25 GMT

Hi Olly,

Thanks for your advice! Much appreciated! I think, I need to first check the H-bridge transistors and add the missing TR20 before I can start consistently measuring the board outputs etc...When I played with the motor yesterday, I tried many times to start/stop it to see if it would get stuck sometimes and draw a high enough current to blow the 250mA fuse, but it did not. But then, at the beginning I had that "bearing noise", and it seemed to run rough initially, and there was the belt putting tension on the bearings... So, there may have been a temporary "seizure" at the moment when I blew the fuse when pressing "33".

If the motor seizes, does that typically damage the 8-pin IC that controls it? Do you know what IC that is? The cryptic labeling does not seem to lead anywhere in terms of replacement possibilities etc...

Thanks!

Rudy

Re: Beogram 4004 Trouble

Step1 — Thu, 12 May 2011 10:16:48 GMT

I am guessing you have not managed to run the player without blowing a fuse yet? Not sure the spikes are normal or not but I would concentrate elsewhere tbh if the motor runs fine. You need to identify exactly which area / function is pulling too much current. Does the deck work without the motor connected? At what point does the fuse blow? Is it associated with with any particular function?

Re: Beogram 4004 Trouble

HarryPierce — Wed, 11 May 2011 23:16:18 GMT

O.k...last post before bed time! I ran the motor for some time while playing with the oscilloscope. The motor quieted down considerably and now is virtually silent. The current went down to ~15 mV at 4.4V. I guess some old lubricant...I hooked up the oscilloscope to the generator output (blue/white) and it shows 200mV peak to peak (see pic below). Question: Is it normal to have such spikes in the curves? Thanks!

Rudy

Re: Beogram 4004 Trouble

HarryPierce — Wed, 11 May 2011 22:41:01 GMT

That was quick! I received some very friendly (off line) advice, and ran the motor on its motor leads (red and blue), and at 4.5 V it draws 30 mA. It spins up nicely, but makes a bit of a ruckus, like it may need a bit of lubrication. Although with platter mounted I was not able to hear anything before the fuse blew. Is this noise normal when it runs w/o load, or do I need to take it apart? Thanks!

Rudy

Re: Beogram 4004 Trouble

HarryPierce — Wed, 11 May 2011 22:11:02 GMT

Thanks again for all your input! I had a bit of time and tested the slide motor. It seems to run well and the slide moves reasonably fast at about 4.5V while drawing about 60mA. That much for "why the H-bridge transistor died"....

I am a bit confused about testing the motor for the table. I think I have the "servo controlled DC motor" (see pic below). I was wondering how one can bench test such a motor? Any advice would be greatly appreciated! Are the three leads for supply voltage and control signal? Which of the red/blue/white leads is for what? Thanks!

Rudy

Re: Beogram 4004 Trouble

HarryPierce — Fri, 06 May 2011 15:18:27 GMT

Thanks much for your detailed input!! Much appreciated! I will test the motor and do the powersupply ramp-up you proposed and report back!

With regard to the cartridge, I do not have a cover at this point (a typical ebay trade, I guess...). There is also a dent in the aluminum top of the cartridge (the 33/45 speed adjust panel popped out during shipping and may have hit the cartridge, i.e. I will probably have to look for another one...live and learn...;-).

Rudy