Hi! I've finally bought a SONY TC-D5M in excellent aesthetics conditions at a resealable price. I've changed its belts and everything is working great except the recording. When I record, the left channel is exactly where I've adjusted while setting the rec level on the VU meter, while the right channel is way lower, exactly as you can see on the picture (I've recorded on a type I tape a 333hz tone from a pc, I've set the record level at 0db using the VU meters of the TC-D5M. The difference in balance between the channels can also be heard through headphones or measured using a multimeter). - I've already sprayed a lot of deoxy on the rec/play switch on the motherboard and moved it up and down a lot without any major difference. - I've also tried to spray the deoxy on the rec potentiometers and move them around but I couldn't increase the rec of the right channel. - Playing a test tape at 400hz, the 2 channels are perfectly balanced. - in some rare occasions, the right channel is also quieter than the imposted rec level. it's very rare and it looks to happen when I record with the cassette recorder upside down but I'm not 100% certain. What can I do?
Fact that R channel sometimes also goes quiet does suggest a connection problem. You would need an oscilloscope or at least a multimeter than can measure AC voltage in audio range to see where exactly the signal is attenuated. Regarding the cleaning of rec level pots, you are reffering to the external ones or the internal calibration trimpots ? You say you couldn't increase the levels of the R channel. You mean no matter how much you rotate the pot, the recorded level doesn't get higher than -10dB on the VU meter ?
I have a multimeter TRMS, but honestly I don't know where to start looking on the circuit. I've cleaned the internal calibration trimpots (RV502 and RV402). The right one (RV502) is maxed out, the left one I cannot remember (it could also be almost at maximum). if I increase the rec level (using the external knobs) I can increase the level of the right channel higher than -10dB.
Here some photos, maybe they can help. (The switch have been sprayed again with deoxy after I took the photo)
Trimpot shouldn't need to be maxed out to obtain recorded levels at least close to the source. The important thing to determine is if this problem is regarding the audio level itself or bias/head. With a sinewave fed at the input, adjust the levels on the VU-meter at a fixed value and check the level at different points (pin 11, 7, 14, 6 of IC401/501). Also check the bias levels getting to the head are actually the same after the bias trap circuit (L401/C430) on both channels. If the levels of both audio and bias are equal, problem can be a worn head or incorrect head height.
Tomorrow I'll try to check the levels as you suggested. In the meantime I'll add some info: this morning I've opened and cleaned the PB/REC switch, it was kinda dirty, I used Svitol Electric and IPA to clean it. Unfortunately, it did not make any difference, but I've discovered that by recording with the recorder upside-down the R channel gets actually as loud or even louder than the L channel (both the REC trimpots are maxed out). Furthermore I've done a test recording at 400hz and 10.000hz to see if the bias was off (recording at -20db on a type I blank tape), I'm attaching a video of the result. There is a small trop between 400 and 10.000hz.-
That's very interesting working upside down and its the clue that needs to be investigated. Wonder if it's something mechanical or the tape path changes when upside down...
I've done some digging and: - the azimuth was off (the rec has not improved and the same behavior while recording upside-down is still present); -the head picks up a lot of ferric oxide from the tape (as you can see from the pictures, you can see the head clean and the head after about 5min of Pb/REC on a type I blank tape. I've demagnetize the head using a wand recently); - the erase head was a little crooked to the right. I could't notice any other problem. is the head done?
Head does have some wear, although I don't think the head is the problem given it works fine upside down. A head problem would manifest regardless of position and would also affect playback to some degree: even though it may not be audible, a difference in L/R frequency response could be measured in such scenario. The oxide residue is normal and not an indication of a head problem. What tape are we talking about ? Some of them tend to shed more oxide, especially on this pointy head (which puts more pressure). Regarding the problem, you need to figure out what is changing exactly when unit is sitting upside down. Measuring the levels and bias and see if those change when unit sits upside down can give some direction.
For the PB it is quite ok but, when I adjust the PB trimpots (using a test tape at 400hz and measuring the output with a resistance of 47kohm with my multimeter) every time the voltage is quite different. I always set it to 0.55v but the next time is somewhat different, and it is different between the 2 channels. I don't know if this is something to be expected, the V doesn't change drastically (I found it on 0.60 or 0-50V more or less). I'm using some blank type I tape ordered from tapeline. I'll try to study the circuit and do the measurements and I'll let you know!
The levels I would check at the output of CX174 also, the line out measurements can be unreliable. There is a thread on tapeheads that says what levels should be there. If the levels are also inconsistent at CX174 then you can draw the conclusion it's a problem. Some variation is normal, but in the order of +/-10-20mV, not 100mV.
I've done the measurements on IC401 and IC501 on all pins. I've obtained the same measurements on both of them. Here's the measurements: 1 -7,12V 2 0V 3 -2,64V 4 -1,32V 5 -0,02V 6 0V 7 0V 8 7,05 9 -0,02V 10 0V 11 0V 12 -1,94V 13 0V 14 -0,05V 15 -0,05V 16 -0,09V From what I understand they are both dead, I should have voltage on pin 16, correct?
So, I’ve done a little more research IC401/501 should not be dead. The problem is that I do not have voltate on pin 16, I’ve checked some resistors and transistors but I could’t find the culprit. I’ve already opened and cleaned the PB/REC switch but maybe i could have do e a better job, could be it be the problem? Here is a couple of pics of the opened switch before the cleaning
Those voltages are AC or DC ? We are only interested in the signal inputs and outputs (pins 11, 7, 14 and 16, in this order), can ignore the rest. Measurements are AC with a sinewave fed to the LINE IN and unit in record mode. ICs are not dead, nor are other components. Given it works upside down, it's more than likely not a component failure but something mechanical (like a connection becoming better when upside down). Yes it could be the REC/PB switch, but very unlikely given it was manually cleaned. Plus the initial spray cleaning wasn't changing anything, so based on that alone would be inclined to think the problem isn't there. What you need to do is isolate the problem, you need to know if the audio signal is actually attenuated or it's a bias/tape path problem instead. Guessing can take a lot of time and at the end if you change more than one variable at a time, you won't even know what actually fixed it.
The voltages I gave you earlier were DC. Now I've measured in AC, pin 7 (7mV), 11 (16mV) and 14 (18mv) were identical between IC401 and IC501, while pin 16 was a little different between IC401 (522mV) and IC501 (511mV). I've used a sinewave of 1kHZ and I've set the VUs at 0db. During the weekend I'll try to follow the audio signal path using the multimeter and see if I can find anything. In the meantime I truly want to thank you for the support! I'm a beginner in the electronic world and I must say it is giving me a little headache but it is also quite fascinating, I need to learn A LOT. Thanks!!
The levels at the output right before the bias trap (pin 16) are almost equal. The 11mV difference represents ~0.18dB, which is insignificant. A 9dB difference would mean one is 511mV, while the lower being 181mV. What you should check is if you get these levels at pins 16 both when upside down and when sitting normal. Imagine normally measurements are done when upside down.
I've done the measurements and at pin 16 in different positions and, every time, the mV is around 510mV both for IC401 and IC501 (11/12mV difference between the 2).
Means the audio part is fine, problem is either related to bias or the tape path somehow changes when upside down. Next thing to measure is the bias itself (after the trap), see if it's the same for both channels regardless of orientation. If bias signal is ok, problem is likely related to tape path changing when orientation changes.
I've followed the procedure for testing the bias as shown on the service manual (recorded at -5db 300Hz, 1kHz and 10kHz and then measure the AC voltage on the line out). For the R channel the measurements are: 0,250V (300Hz), 0,200V (1kHz) and 0,007V (10kHz). For the L channel: 0,330V (300Hz), 0,250V (1kHz) and 0,008V (10kHz). I tried measuring the kHz on the head while recording nothing but I was not able to do it.
To clarify: when is upside down, the R channel is not always correctly set on the REC level (it's almost always better than when I record normally, but not always at the rec level. Upside down the L channel is a weaker than the rec level at times), furthermore I have both the REC trimpots at max in order to achieve the correct REC level on the L channel (and on the R channel when it's somewhat working).
