UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players

Notices

Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

Reply
 
Thread Tools
Old 22nd May 2020, 11:15 pm   #1
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Telefunken M204 TS E2 Commenced

Made a start tonight checking out my Telefunken M204 TS E2, which arrived a few days ago. Unlike its rebadged sibling the Senator TT 494, it arrived with no shipping damage and good condition Perspex lid.

Condition wise looks reasonable from the front, quite tatty from the rear and inside.

3 of its 4 drive belts are missing with remaining belt (flywheel) possibly well stretched and like the Senator the capstan shaft is well off centre (to the left of) of the hole in the heads mounting plate. Heads look good condition and pinch roller is quite cracked and stiff to rotate.

When I removed the chassis from the case I found 2 springs inside, hopefully will find a home for these later. All 4 springy plastic bars to reset the tape counter segments are broken/missing, I found 2 remnants in the case.

The Mode selector switch is very stiff on its first 5 positions and will not switch to the last 2 positions including "Stereo".

Noticed that one of the internal fuses (315mA) has blown, hopefully that is not ominous.

Will fit a 3 core mains cable and plug and power up to see if motor runs and DC supplies come up, before doing anything else.
Attached Thumbnails
Click image for larger version

Name:	Telefunken 204 #1.jpg
Views:	70
Size:	70.9 KB
ID:	206492   Click image for larger version

Name:	Springs.jpg
Views:	34
Size:	30.6 KB
ID:	206493  
DMcMahon is offline   Reply With Quote
Old 23rd May 2020, 9:38 am   #2
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

Continental 2 core mains cable and 2 pin plug replaced by 3 core and 3 pin. Mains voltage selection changed from 220 to 240. Replaced blown 315mA fuse.

Powered up OK (so fuse OK) and motor runs. +21.5 volt DC supply good. Because had to disconnect from internal speakers to get it out of its box, presently the two fuses for the output of the two power amps are removed, will refit these later when reconnected to the speakers.

Next to install 3 new belts, am hoping that the fitted flywheel belt may be OK (a bigger job to replace that belt) and hopefully get the tape transport all working. Will do some general cleaning as I go.
DMcMahon is offline   Reply With Quote
Old 23rd May 2020, 8:38 pm   #3
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

3 new drive belts installed and the tape transport appears to be working fine and all 3 speeds work. The original flywheel drive belt looks to be holding up (thought originally it looked a bit loose). Did quite a bit of cleaning, lubing various stiff parts and glue repairs.

Next to check out the very stiff (and some positions not switching into at all) Mode select switch. Very unlikely to be the associated electrical switch, which is multi position slide switch on the main board, assume problem to be a mechanical problem with one of the connecting actuating mechanisms.
DMcMahon is offline   Reply With Quote
Old 24th May 2020, 10:18 am   #4
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

Stripped, cleaned and lubricated several mechanical parts of the Mode Selector switch mechanisms, all of which were gummed up. Now operation not stiff but not as smooth as one might expect, I think just due to the design (how the teeth on a pawl ratchet segment engage with a little roller pin).

However during the above I realised that it was impossible for the mechanics to switch to the 6 positions marked on the switch control knob, it only can switch to 4 positions.

Comparing the switch operation to my Senator, I then realised that I had mixed up the 2 knobs between the 2 machines. Both knobs had been in the same component storage box and by mistake I picked up the Senator knob and fitted to the Telefunken.

The Senator is 4 track with 6 positions on the knob and the Telefunken is 2 track with 4 positions on the knob. Seems a stupid thing to do but I think at the time had not really released that the Telefunken was 2 track and therefore automatically assumed that the 2 control knobs were the same.

Next to test playback and record.
DMcMahon is offline   Reply With Quote
Old 25th May 2020, 9:14 am   #5
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

Refitted the two 1.25A output fuses in the power amp and reconnected the loudspeakers in readiness for testing playback and record.

While doing this got side tracked for quite a while, when I noticed that one side of the main board was somewhat bowing out due to the tape speed switch actuation hardware that operates a slide switch on the board, not being correctly aligned and as a result the slide switch was not switching properly if at all.

Did several things to fix this, no single one worked reliably on its own.

1. Top corner plastic fixing of the board was broken and the fixing screw head was smaller than the hole in the board. Used a longer self tapping screw (original machine screw being too short when used with the washer) and large washer to fix down, this reduced the bowing but not enough.

2. Loosened and adjusted a fraction inwards metal actuator on the slide switch.

3. Tweaked (slightly twisted over) the main metal actuator so that the slide switch actuator sat on the horizontal top edge of the main actuator, rather than sitting on the sloped edge as before adjustments.

4. Combination of 1, 2 & 3 got it working OK wth no bowing but quite stiff operation, which somewhat surprisingly was due to the slide switch itself, a spray of contact cleaner got the switch loosened up.

Interestingly while comparing the switch operation to my Senator, saw that on the Senator all the components on the board are identified but on the Telefunken none of the components are identified.
Attached Thumbnails
Click image for larger version

Name:	Bowed side of board.jpg
Views:	33
Size:	46.7 KB
ID:	206709   Click image for larger version

Name:	Resecured top corner.jpg
Views:	30
Size:	54.8 KB
ID:	206710   Click image for larger version

Name:	Senator components identified.jpg
Views:	33
Size:	150.8 KB
ID:	206711   Click image for larger version

Name:	Telefunken components not identified.jpg
Views:	31
Size:	128.9 KB
ID:	206712  
DMcMahon is offline   Reply With Quote
Old 2nd Jun 2020, 12:09 am   #6
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

Playback tests on both channels give zero sound, so some diagnostics required.
DMcMahon is offline   Reply With Quote
Old 2nd Jun 2020, 10:12 am   #7
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

Record also dead, fuses and power supplies are OK.
DMcMahon is offline   Reply With Quote
Old 2nd Jun 2020, 11:02 am   #8
Ted Kendall
Nonode
 
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 2,157
Default Re: Telefunken M204 TS E2 Commenced

Does it erase?
Ted Kendall is offline   Reply With Quote
Old 2nd Jun 2020, 1:11 pm   #9
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

No it does not erase existing recordings, so the electronics generally seems dead everywhere.
DMcMahon is offline   Reply With Quote
Old 2nd Jun 2020, 3:04 pm   #10
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

From some tests proved that there is nothing coming out of the power amps to the speakers in Play mode because there is no signal coming out of the Playback pre-amps.

Now starting to look at the shared Playback and Record pre-amps circuitry by injecting a test signal from Sig Gen into the Radio DIN input in Record mode. Using my Senator as a reference which responds well to the test signal.

So far the later stages of the PB/Record pre-amps look dead.

I have a suspicion that there has been some work done before on the main board because at least 6 of its transistors look totally different to the same transistors on the Senator (have not yet identified their type # on either unit). Also at Post # 5 I noticed that the board was not being held by a couple of its plastic retainer clips as if the board had been previously removed at some stage and not fitted back properly into the clips.
To access the solder side of the board for component changes would require the board to be removed (which looks difficult).

Not easy to identify/locate relevant components so slow work.
DMcMahon is offline   Reply With Quote
Old 2nd Jun 2020, 9:37 pm   #11
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

Slow progress, finding it very difficult to find my way around the board identifying/locating correct components, have found some differences in component values between the Senator and the Telefunken and some differences with both to the schematic external connections.

Bias Oscillator is not working at all in Record.

The left Record amp and I think right also (have mainly been looking at the left channel) is partially working (both with Signal Gen inject signal and microphone signal) but the output signal to the power amp at 100uF signal capacitor C124 (left channel) is bad, good signal on input to C124 but nothing out.

By touching C124 then get a good signal out (while capacitor touched) looks like a bad connection, but not 100% convinced. Even with a good signal (by touching C124) there is still no signal out to power amp via volume control and/or to VU meter, so suggesting a second fault maybe through the Record/Play slide switch.

Seems strange that both channels are bad maybe indicating a common problem but so far looks like several separate problems ?

Will have to remove the board (which does not look easy) to investigate the C124 connection issue but first want to check more the right channel and the left channel signal apparently not switching through the Record/Play switch.
Attached Thumbnails
Click image for larger version

Name:	IMG_20200602_213003776.jpg
Views:	17
Size:	100.1 KB
ID:	207501  
DMcMahon is offline   Reply With Quote
Old 3rd Jun 2020, 2:40 pm   #12
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

Checked out the right channel, very surprised that it had the same symptom as the left channel. i.e. good pre-amp output at C224 input but no signal at C224 output and as before by moving C224 could get good signal out.

Could not believe that had 2 faults with same symptoms of bad connections around the capacitors so looked elsewhere and found could induce exactly the same by touching other components such as the 2 Record/Play slide switches (S101 Mono Stereo & S201 Stereo). Used contact cleaner on the switches but no change.

Checked out why no VU indications. By pressing the capacitors to get good signal could monitor signal getting to both VU meters, but zero indications on the meters. Found that the 2 meters common connection was not connecting to 0V/ground as they should.

Checked the VU meters common connection back to the board OK but no sign of it connecting to 0V by measurement.

Partially removed main board to investigate further.

Soldering around the slide switches and the suspect capacitors looks OK, maybe a couple could do with resoldering.

Found the cause of the missing 0V connection back to the VU meters. There is 6mm long crack on one side of the board that has broken right through the board and has severed 3 artwork tracks including the track that provides 0V back to the meters (and other circuitry).

I will repair the 3 tracks with solder bridges strengthened with wire and will check out what other parts of the circuit these 3 broken tracks connect to.
Attached Thumbnails
Click image for larger version

Name:	Cracked board.jpg
Views:	17
Size:	52.9 KB
ID:	207543   Click image for larger version

Name:	IMG_20200603_143134815.jpg
Views:	17
Size:	106.2 KB
ID:	207544   Click image for larger version

Name:	IMG_20200603_123108652.jpg
Views:	18
Size:	101.9 KB
ID:	207545  
DMcMahon is offline   Reply With Quote
Old 3rd Jun 2020, 9:00 pm   #13
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

After repairing the 3 tracks now have good left and right pre-amp outputs, but still no VU meter indications.

Checked out some of the connections that the severed tracks went to, one of which was a leg of the Bias Oscillator transistor, so was hoping that the Bias Oscillator would now work but it is still dead. Will investigate this once I have sorted the Playback and Record amps.

Found that the left channel VU meter not working was due to another crack in the board breaking a track that carries the VU meter calibration/gain pot (R154) wiper out to the VU meter. This crack was close to the other crack previously found (actually a continuation of original crack). For some unknown reason had problem getting good continuity across the latest repair to this track so ended up bypassing the track with a wire.

Now have good left channel VU meter operation.

The right channel VU meter not working is due to the pre-amp signal not reaching the VU meter, which only leaves the connections through the relevant switch section of the Record/Play switch, so will check that out next.
Attached Thumbnails
Click image for larger version

Name:	Latest crack.jpg
Views:	10
Size:	66.6 KB
ID:	207580  
DMcMahon is offline   Reply With Quote
Old 4th Jun 2020, 2:11 pm   #14
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

While checking out why no VU meter signal on the right channel, the good left channel has stopped working and now there is a constant -3dB signal on the left VU meter with no signal input.

Some good news the Bias Oscillator has started working.
DMcMahon is offline   Reply With Quote
Old 4th Jun 2020, 4:25 pm   #15
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

While previously doing the investigation work leading up to Post 14, I replaced the 100uF C124 on the left channel that had previously appeared to have given problems when moved. So I rechecked that area and found the connection between C124 and R151 was open circuit.

By measuring, it was down to 1 piece of artwork track and I thought it was the solder pad at C124 so I scrapped back the lacquer to resolder the C124 pad to further along the track. But with lacquer removed I could see a tiny break across the track about 5mm from C124 pad.

After repairing the track break, the left channel is working fine again and strangely now the right channel VU is also working. Did not notice it at the time but looking at the photo (near middle) there may be a crack fault line either side of the track break (at 315 degrees) and a definite crack nearer the bottom of the photo.

Even though the right channel is working, comparing it to the left channel, the signal level is a lot lower, can compensate for this by winding the right channel record level up but this results in the signal clipping.

So there maybe a problem with the right channel signal gain.

But before I get too bogged down investigating it, I will reconnect the speakers to see if any Playback sound and if so check out recording.
Attached Thumbnails
Click image for larger version

Name:	IMG_20200604_142457346.jpg
Views:	12
Size:	71.0 KB
ID:	207657  
DMcMahon is offline   Reply With Quote
Old 4th Jun 2020, 6:51 pm   #16
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

Its not giving up. After fully fixing back down the board to get ready for Playback and Record tests have lost the right channel VU meter signal again !!

Also the flywheel belt has come off, this is the first time this has happened on this machine and is a right nuisance as quite a strip down to get belt back on. The belt coming off the flywheel is one of the issues with the Senator.
DMcMahon is offline   Reply With Quote
Old 4th Jun 2020, 10:45 pm   #17
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

Traced and fixed the problem with right channel VU meter not working, it was another broken through track, in fact caused by a continuation of the same crack in board at Post 15.

Note to myself - even though the right channel VU meter is working its response/decay time compared to the left channel VU meter is very slow. by a factor of around 5. Should first check out smoothing capacitor C227 (50uF/10 volt) connected to the D201 diode rectifier for the meter.
DMcMahon is offline   Reply With Quote
Old 4th Jun 2020, 10:54 pm   #18
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

Quote:
Originally Posted by DMcMahon View Post

When I removed the chassis from the case I found 2 springs inside, hopefully will find a home for these later.
No obvious sign of a home for the 2 springs ?
DMcMahon is offline   Reply With Quote
Old 5th Jun 2020, 2:20 am   #19
Reelman
Octode
 
Reelman's Avatar
 
Join Date: Aug 2008
Location: Rotherham, South Yorkshire, UK.
Posts: 1,022
Default Re: Telefunken M204 TS E2 Commenced

If they are springs without a hook/loop at the end they may be used to connect an electrical coating on the case to “earth” when assembled. The other end would be probably soldered to the PCB. Grundig certainly did this on some models.

Sounds like you have a machine that has been assessed for repair and deemed uneconomic or the owner would not pay. The engineer then put it back together quickly and roughly to save spending anymore unremunerative time on it.

When you have it working again you will certainly feel pride in a job well done! Good luck.

Peter
Reelman is offline   Reply With Quote
Old 5th Jun 2020, 10:10 am   #20
DMcMahon
Octode
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 1,474
Default Re: Telefunken M204 TS E2 Commenced

Peter, the springs have end hooks as per photo in Post #1.

While hoovering the floor area this morning, I found another very similar spring on the floor ?

David
DMcMahon is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 1:56 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.