audio-talk

Hi all, will try again to attach the spreadsheet. if someone can have a look and make some suggestions on which transistors look to be faulty. I have an idea which are not right but would appreciate another set of eyes.regards Wolfgang

Well, I didn;t actually say check the transistors, I said the test points, and most of those need a scope to see what he waveform looks like.

Sorry Nick, my mistake, all those test results are from the boxes on the service manual, I tested them to see if there was a deviation from what was stated and I noticed there were a few that were completely different. I dont know if those results mean anything. I will try and use the scope try get those wave forms. Like I said before, I am a plumber and I am learning how to use all the test gear, please bear with me.

Just a question to all, I used 74LS73AP JK Flip Flops when I replaced the IC's in the SP10MK2. I have read that there are negative and positive flip flops, if I use the wrong ones, will that affect the result?

-ve like the 7473 should be correct.

Hi all, it has been a while since my last post, good news is I managed to get the SP10Mk2 running at all speeds, the problem was a broken wire on the coil in the motor, I re-soldered it and away she went at normal speed. I still have a problem though, it doesnt seem to lock onto the speed, it runs a bit slow or a bit fast but doesnt lock hard on any of the speeds. I tried to get the wave forms on the scope that are specified in the service manual but I just cant get a good clean wave form. it is very dirty. I will post a photo of the wave form I get. By replacing all of the chips, will that affect the wave form?

Regards Wolfgang

Sounds like the phase lock isn't working, check as described in the manual. If you have changed the IC's the most likely cause is the transistor tr220 in the start of the div network that provides the pulse to the phase lock circuit double clocking into the flip flop. Again, try a smaller resistor instead of the 47k one.

At least that's the problem I had and the solution. Checking the waveforms on the logic board against the manual is the place to start.

Hi Nick, will try that tonight, something I did notice last night wast that when set to 33 or 45 the strobe was flickering slightly but when set on 78, no flickering, weird.I also noticed that when the power supply voltage is raised to 32.5 volts the platter slows down and when the voltage goes lower it start to speed up. Could this be from the double switching that you are talking about?

No idea.

Just to be clear, I am looking at the logic circuit Schematic and it it resistor R261 47k which is connected to TR220. Correct.

Regards Wolfgang

Yes. If you have the problem I had, if you look at the signal that transistor feeds into the flip flop and the output of the flip flop it will oddly seem to be the same rather than half the frequency, its because there is double triggering going on on the FF input so the signal that feeds the phase detector happens twice as often as it should so it can't lock.

Hi Nick, tried a 1.1K resistor in parallel with the 4.7k, unfortunately it didnt make any difference. I dont know if I mentioned it before but I am a Plumber not an electronics engineer. I have been struggling to get some of these waveforms that are in the service manual. I have a pretty good knowledge but not to the level of people like yourself. I am happy that I managed to get this far. I will go back to the beginnning, everything else works fine, it is just the speed thing is doing my head in.

Ok, well, show us the waveforms you do get.

Hi nic thank you for taking pity on an old fool. I would like to send you an image but every time I drag the image accross , it tells me the file size is too large, I tried zipping but that didnt work either. Can you tell me what size file I can send

Regards
Wolfgang

Hi Nick, will try sending a couple of photos.