Philips reel to reel

[suebutcher]

The record-replay head of my EL3586 measures 41 ohms, so 30 ohms isn't too far out assuming that both EL3586 and EL3587 used similar heads.

[Copey84]

Hi sue thanks for reply.
Tried the tea spoon handle, no thump on speaker, did make a slight scratching sound though.
I take it no thump is bad?
Also remeasured the coil and its 36ohms, had forgotten the exact resistance thought it was around 30.
Probably should mention I resoldered one of the wires going into tape head that had broken off, that's when I first measured the resistance of coil.
Repair seems fine, did have to remove head from casing think it all went back together ok, just thought I'd mention it.
Would you expect to just get distortion on speaker when running tape through a bad head?
Might try and get a replacement head, is there anything else you can think of that I could try?
Thanks again for reply, much appreciated.

[suebutcher]

If you heard anything at all when you moved the metal over the head, the head is probably OK. (In my experience heads either work or they don't, though magnetization can cause distortion, and wear loss of high frequency response.) The only thing I can suggest is try running a known good recorded tape through the machine, and check that the tape is in close contact with the record-play head. There should be a felt pressure pad on a small lever that presses the tape against the head when the play button is pushed.

[Copey84]

Thanks sue, will have a look through my grandads collection of tapes see if there's anything that will play.
If not I'll try knew tape see if it makes a difference. Think tape makes good contact with head will check again though.
Thanks for help, I'll let you know if there's any success.

[Copey84]

Hi all, think I may have found the fault.
There is a resistor grounding the two emitter legs from the germanium transistors that has overheated so much that I can't read the colour code.
Disconnected the resistor and measured the resistance which is around 20Mohms, way off the value stated in wiring diagram of 4700ohms.
What would be the more likely value of resistor needed to ground the emitters?
The solder joints were fine so think there was a failure somewhere else, possible the transistors trying to draw too much current, not sure appreciate any help.

[suebutcher]

I assume you're talking about the AC128 output transistors? If so, the burnt out resistor should be 4.7 ohm, not 4700 ohm. You're right, a failure somewhere else could have caused the burnout. I'd check the two AC128's, they might also be damaged, and the transformer that drives them in case there's a short from the primary to the secondary. If that's all OK, replace the burnt resistor with a 1W 4.7 ohm, and give it another try. With no signal, the current drain measured at the output transformer should be 10mA.

[Copey84]

Thanks sue will remember it's a 4.7ohm resistor not 4700, my mistake.
Yes transistors are the AC128, is there any way I can test without having to de-solder them and the transformer?
Also, can I measure the current drain at the secondary of the transformer, with no signal meaning play record open circuit?

[Copey84]

Hello again, spent some time this afternoon testing transistors and transformers and all seemed fit for use. Replaced the burned out resistor and turned on, still no music coming through but there is a definite improvement. Although I can't hear any of the words of old recordings you can tell there's something there now trying to come through, if that makes sense. The speaker is much more active and you can notice the change in volume now.
As the machine was running I kept checking the components to make sure nothing was over heating and all seemed fine, apart from no music coming out of speaker.
However after about 15min the speaker started to make a strange rumbling noise, didn't sound good so I turned it off and left it for tonight, getting sick of it if I'm honest, but don't want to give up on it just yet.
Only thing else I can think of is changing the caps and maybe even the transistors I tested today as the tests were borderline.
Anyway if anyone's got any suggestions that they think might help let me know, thanks.

[suebutcher]

You really need to locate the fault. To do that you will need, at the least, a simple two-transistor signal injector, a cheap multimeter, and a copy of the circuit diagram. Blindly replacing components is going to be time-consuming, and expensive unless you have a big junk box of spares to draw on. And it won't do any good if the problem is dirty switch contacts - there's something like a dozen of these along the chain between the playback head and the loudspeaker.

[Copey84]

Hi sue, have got a decent multimeter and circuit diagram no signal injector though.
Checked functional switches like play record and other links that are open closed through record button and all ok.
Have tested germanium transistors and will test the other transistors with same method in circuit.
I included a few photos maybe you could help me identify some of the components.
There's a coil in between the two transformers not sure what it's for, and two other components that look a bit like diodes.
Also traced some of the wires on PCB and came across this grey wire from casing to one side of speaker, any ideas what it's for?

[TonyDuell]

The little glass components are diodes, probably the ones in the recording level meter circuit.

I would guess that coil is part of the bias/erase oscillator circuit (only used when recording), which may well use the same transistors as the audio amplifier output stage (which is only needed on playback). Unfortunately the circuit has not appeared in a high enough resolution for me to be able to read it.

[TonyDuell]

Looking at it again, and looking at the EL3586 diagram (which is similar, but has some differrences) I think the coil is shown just above the level meter on the diagram and is pat of the 'bias trap' circuit (to prevent the recording bias signal ending up in the amplifier or meter circuits). It is not important for playback.

[Copey84]

Hi Tony think there is also something wrong with recording circuit. Have tried setting the record level but no change in dial, will check diodes.
Do you know what purpose the grey wire serves? see 2nd photo.
It comes from one side of speaker and terminates on side of casing, but doesn't seem to connect to anything else.

[suebutcher]

One of the wires from the speaker connects to the chassis and to one terminal of the output transformer secondary. The other wire from the speaker goes via a switch to the other terminal of the output transformer secondary. The switch should conduct during playback, and disconnect the speaker during recording, otherwise you'd get a howl if you were recording with the mike. It's possible that the grey wire termination is a test point, but it's not shown on the diagram. Anyway, check that the circuit from speaker to secondary and back is intact, and confirm that the speaker works.

[TonyDuell]

Going back to post 33, the same amplifier (essentially) is used for both recording (input from the microphone, output to the head) and playback (input from the head, output to the power output stages). So a fault in that section could cause both poor playback and no deflection on the level meter.

As others have said, rather than check components, I think you need to (a) check the DC voltages on the transistor connections and (b) start tracing signals.

[Copey84]

Thanks for replys guys, will check voltage levels and post how I get on.

[Copey84]

Tony, sue here are the voltages taken from all 6 transistors with play button activated.
T1@ base=7.93v @ collector=4.25v @ emitter=7.86v
T2. 7.68v. 4.74v. 7.77v
T3. 7.95v. 4.22v. 8.58v
T4. 5.57v. 1.29v. 5.44v
T5. 8.61v. 0.02v. 8.73v
T6. 8.60v. 0.05v. 8.72v
All voltages referenced to negative battery terminal on recorder.
Have included photo of wiring diagram with transistors numbers.
Think the problem is T5 and T6 collectors not turning on, or could it be something else?

[suebutcher]

I think you're measuring from the 9V power rail to the transistors - you should measure from the chassis to the transistors. If that's what you've done, then correcting your readings for this the output transistors are about 0.4V base, 8.9V collector, and 0.3V emitter. That's what they should be. I can't comment on the other transistors, you'll have to take more readings using the chassis as the reference point.

When voltages are given in a circuit diagram, unless otherwise noted, these voltage are measured from the chassis.

[suebutcher]

OK, assuming that connecting the meter to the negative 9V supply rail hasn't upset the readings, the voltages on the other transistors are OK, except the T1 emitter is a bit high at 1.2V, and the T3 emitter is low at 0.4V. Test the resistors around these transistors. Have you also confirmed that the speaker is working properly? (You can disconnect it and test it by touching a 1.5v battery across the terminals.)

[Copey84]

Hi sue, I measured all the transistors to the negative battery terminal which is connected to the chassis.
In your last post you stated T1 and T3 emitters are high and low but they don't match my recorded values in post 37.
Also thought the speaker was working with all the noise and distortion, seems even more active since I replaced the 4.7ohm resistor. How does 1.5 battery connected test it?