Blockbuster deck

[docs]

Hi All,

I know this is a long shot but...
Does anyone know the Blockbuster deck REALLY well ?!
I'm basically helping out Retro Addict to try and fix his Blockbuster which has an FM stere issue and also has 2 springs that I am not sure where should be.

When the power is on the deck will not stop when FF/REW is pressed. When the power is off the stop works when FF/REW is pressed.

The radio on FM works the same when on FM and when on FM stereo and the stereo led does not light up when moved to FM stereo but the audio remains the same.

Any help/advice/photos etc would be hugely appreciated.

 

[blu_fuz]

skippy

 

[Gluecifer]

This EXACT problem happened with my C-126!
I'd have to turn the power off to get it to stop FFDing, or REWing.

The ridiculous thing is that I took that deck out and put it in another radio and now the controls all work fine!! Inssane!

All I can suggest is to check the leaf switches to make sure they're all working as I'd imagine this is what the issue was.

Probably not much help, but good luck!



Rock On.

 

[docs]

Thanks guys, I think the problem actually relates to the backplate either being too loose or too tight.
It looks like it needs to be perfectly tightened since it has a spring retention to it too.

I have got it working perfectly but it does seem fitting the deck affects it too.

Thanks for the suggestion Glue appreciate it.
I even checked my SCR-8 deck which is more or less identical and those springs are nowhere to be found so I don't think they are from the deck.

 

[MR.GROOVE]

The FM stereo problem seems to be an MPX problem. I solved this once by turning the potentio meter from the mpx on the tuner-board a bit..try it..maybe this will help!

 

[docs]

The FM stereo problem seems to be an MPX problem. I solved this once by turning the potentio meter from the mpx on the tuner-board a bit..try it..maybe this will help!

Is this the VR1 you refer to ?
What is odd is that FM sowkrs exactly the same on FM and on FM Stereo just no difference in audio output.
Changing anything on the VR1 at all has zero affect on FM.
VR1 looks like it should have 10k (max) resistance across it but it has 3.6k.

I think something is blown, I'm trying to follow the SCR8 schemtic for it.

 

[Superduper]

The FM stereo problem seems to be an MPX problem. I solved this once by turning the potentio meter from the mpx on the tuner-board a bit..try it..maybe this will help!

Is this the VR1 you refer to ?
What is odd is that FM sowkrs exactly the same on FM and on FM Stereo just no difference in audio output.
Changing anything on the VR1 at all has zero affect on FM.
VR1 looks like it should have 10k (max) resistance across it but it has 3.6k.

I think something is blown, I'm trying to follow the SCR8 schemtic for it.

On the SCR-8, VR1 adjusts the stereo pilot setting, which is performed by connecting a probe from frequency counter to TP7 (pin 12 of mpx decoder IC2) to ground. Adjust VR1 at a quiet point in tuner dial to 19khz +-50hz, as mearured on the frequency counter. This MPX decoding design does not have a separate stereo separation adjustment so if the stereo indicator is lit, and there is no separation, then the IC is suspect. The non-prescribed and less accurate way of adjusting VR1 is to turn the control, while the tuner is tuned to a stereo station, to the midpoint (adjusted from both directions) where the stereo indicator lights.

 

[docs]

Thanks Norm, the Stereo FM light never lights regardless of VR1 adjustment and the techy guy who had this before me supposedly replaced the UPC1197C though my voltage readouts on pin 12 and across VR1 seem low.

Not sure I can sort this one out.

 

[Superduper]

Thanks Norm, the Stereo FM light never lights regardless of VR1 adjustment and the techy guy who had this before me supposedly replaced the UPC1197C though my voltage readouts on pin 12 and across VR1 seem low.

Well, not sure what you are comparing against but pin 12 of IC2 is only supposed to be .11 volts, and pin 16 feeding VR1 is only .04 volts. Obviously with voltages this low, even the resistance in the probes and surface oxidation can affect the readings. Don't know why you would be reading voltage across VR1 though. I also don't think VR1 should be suspect if it adjusts smoothly across the 3.6k range you speak of. That's because if you remember, anything tested in circuit will read it's spec'd value (never more) and frequently tests lower due to parallel resistance introduced when in circuit. The only way to test and confirm any suspected low resistance reading is to take it out of circuit by lifting at least 1 leg. If you suspect IC2 is ok, then you should do a voltage test of all the pins of IC2 and go from there.

Does the tuner pull in stations fine and strong? Because the MPX decoder needs a reasonably strong signal in order to do it's job. If the signal passed on to it by the tuner is weak, then you won't get stereo even if the decoder is doing it's job properly.

 

[docs]

Hi Norm, yes stations come in nice and strong whether on FM or FM Stereo.

I will check voltages across IC2.

 

[docs]

Hmm I seem to be getting lower than expected voltages on IC2 than expected from the schematic.

For eg: pin should be 2.64v but I read 1.37v and pin 6 should read 2.06v and I read 1.01v.

Furthermore, output from IC1 pin 9 is 0.83v which should be 2.08v which is also reflected on the inward pin 2 on IC2.

 

[Superduper]

What are you reading on pin 3 of IC1?

 

[docs]

Reading at pin 3 is 1.65v

 

[Superduper]

Reading at pin 3 is 1.65v

Ok. We are making some presumptions here, which is that the SCR-8 schematic applies or significantly so, to your blockbuster.

If that is the case, remember how I walked you through the low voltage issue with your blockbuster? Well, you need to check if the #9 voltage rail is 3.46v, because it sounds like the voltage to that rail is too low. All the points you mentioned are common to supply rail #9. Check it, and maybe replace that regulator if necessary. The regulator is comprised of Q104, D108, and a leaky or shorting C158 could cause issues, as well as R165 and R166.

 

[docs]

Ok Norm thanks a bunch will check those out.
I did notice that R2 is giving 0 output though and it should be a 220k resisitor.

 

[docs]

Checking Q104.
The pin from R164 is reading 0.06v when it should be 3.47v

Checking the resistance of R164 gives peculiar results, it basically counts to zero so I'm going to lift one leg and retest.

 

[Superduper]

I did notice that R2 is giving 0 output though and it should be a 220k resisitor.

Why would you be measuring output at R2? That is the RF input to the FET. The FET is expecting current that is virtually undetectable with a voltmeter. Put it this way. Whatever voltage a short piece of wire can pick up out of thin air, would be what the FET would be expecting. Let's not get sidetracked here. You are getting a strong signal to IC1 or else you wouldn't be hearing stations. So figure out why your IC's are not getting the voltages they need first since low voltage to those IC's will hamper their performance. THAT is a fact. The datasheet shows that this IC requires 4 - 16 volts operation. As implemented, the voltage supplied to it is already below recommended amounts since it's being powered by a 3.46 volt rail and through a resistor at that. Anything below will almost surely cause it to NOT work.

 

[Superduper]

Checking Q104.
The pin from R164 is reading 0.06v when it should be 3.47v

Checking the resistance of R164 gives peculiar results, it basically counts to zero so I'm going to lift one leg and retest.

zero or infinity regarding resistance? That is different.

Also, when you checked the voltage is .06v at the collector of Q104, did you also check voltage at the other side of R164? If you did, and get good voltage at the other leg, then there is likely a short somewhere on the other side or the resistor is opening up (and not counting to zero, but rather to infinity).

 

[docs]

R164 was counting to zero not to infinity.

 

[docs]

With R164 out of the board I can not get any reading out of it at all.