[Mark-sf]

That problem is generally the speed selection relay and trimmers need replacement. You can find updated replacements from Beoparts-shop.com (now: Danish Sound Parts).

• This reply was modified 1 week, 4 days ago by Dillen.

[Mark-sf]

I’m afraid that reading does not make sense assuming you are measuring mAs. What you are looking for is not the steady-state reading but a current jump as you plug it in. I would use a second meter or Oscope to catch the drop in voltage at the time. At this point given your limits and these imperfect medium, I would replace the regulator just to rule it out as it’s very cheap.

[Mark-sf]

You measure current by putting your meter in series with the circuit. This means disconnecting the regulator output, soldering a jumper and using your probes in series. If you have alligator clip ends even better.

[Mark-sf]

The 7805 regulator can source more than 1A of current if working properly which is more than enough to blow the fuse before its short-circuit protection kicks in. I would confirm by measuring the output current when you plug the TT in and see if it exceeds 1A before dropping. If it doesn’t I would replace the regulator. If it does you are not going to have to start disconnecting 5v loads on the board and testing for 5v.

[Mark-sf]

This is where it gets tough as you may be hitting your original problem. I would check how much current you are drawing on P6-1 as you may have a bad regulator. Normally F1 (800ma) would blow if there was a large draw due to a shorted transistor such as the Lift driver TR9. Also is it at .5v just plugged in?

[Mark-sf]

Putting C24 in backwards would definitely take out the F1 transformer fuse but could have damaged part of the diode bridge or transformer secondary. Are you getting AC voltages across each transformer secondary? If so when you connect P7 back only, what voltage are you seeing across C24?

[Mark-sf]

marcham wrote:

Update: I retested the pins you suggested but left the other connectors plugged in. With this setup, pins P7-12 and P7-6 do have continuity. The schematic screenshot below shows where P7-12 leads; P7-6 goes to ground. The bottom-most path is from P-712, leading to D42 and a relay. Would you suggest following both paths and testing each component as I go, or is there a more efficient way to test? Thanks!

Yes, P7 is the only connector you should have removed. I would check for losing the short by selectively removing the gnd sides of D20, 0C1, 0C2 and 0IC1 to find the defect.

[Mark-sf]

I would start by leaving the supply disconnected and measuring resistance on the board side between each pair of windings pins looking for a short. Ex: P7 pins 2 and 4. Then you can desolder to find the shorted part.

[Mark-sf]

To add one advisory to the excellent advice already posted, if you have put in one or more of the electrolytic caps backwards and tried to turn it on, you’ll need to check the fuses, transistors and regulators prior to that as you have effectively shorted them. This is likely why you have not made progress.

[Mark-sf]

It’s likely a missing diamond or mis-calibrated tracking force. I doubt its a cueing mechanism issue.

[Mark-sf]

You can get that one to work by removing the top platter and belt.

[Mark-sf]

The proper fluids will not leave a residue especially if you dry them. Just keep the liquid off the labels.

[Mark-sf]

The sound issues you are describing are not likely due to a dirty stylus or record Bass distortion is more likely to be caused by improper stylus force or a failing stylus cantilever suspension. I would recalibrate your tracking force to 1.2g for your MMC4 and 1.5g for your MMC5 first and then evaluate. As to cleaning the stylus, I prefer the gel-based ones such as from DS Audio as they leave no residue. Finally, a Spin-Clean Record washer will be a significant step up from your brush cleaner

[Mark-sf]

Since, you found a shorted cap replaced all of them, it is likely the culprit for the burnt resistor. OpAmps usually work fine or simply fail by their nature.  If the sound is now clean without noise and distortion, I would just button it up and enjoy.

[Mark-sf]

If R121 burned, I would replace IC 10 & 11 as they are connected to the same resister. I would also change out C103 & 107 which I believe you are doing.

[Mark-sf]

There are actually 2 dual opamps IC10 and 11. You may be referring to the 100 μF caps on the 15v -/+ rails that help smooth the DC. However, their failure, assuming they opened versus shorted, would not cause white noise in my experience. It is also not likely that both channels would fail together since each has its own dual opamp.  If in fact both channels exhibit the same white noise your problem is likely in the 15v dual power supply section.  This regulation was done discretely back then and is where I would start.

[Mark-sf]

You haven’t mention what component/system it is connected to. If both channels have the same distortion you may be overdriving the input to your receiver as the diigital side sounds fine and once the signal leaves the DAC chip it flows in discrete L/R circuits which are unlikely to both distort unless you have problems with either the +15v or -15v supplies to their opamps.

[Mark-sf]

As far as the coils go those readings should be fine. Hope your restoration goes well.

[Mark-sf]

I don’t see the video; however, you should take a look at the service manual and follow the adjustments in Section 5.1. While doing that take note if it also needs cleaning and lubrication which is covered in 4-8.

[Mark-sf]

You need to use the 120v position AND need to ensure that the fuse in 500mA. If you are unsure of switch end positioning, use an ohm meter between the two AC pins and the 120v one will have about half the resistance of the 240v one.

[Author]

Posts