{"id":1246,"date":"2015-07-17T23:50:45","date_gmt":"2015-07-17T21:50:45","guid":{"rendered":"http:\/\/dc2wk.schwab-intra.net\/?page_id=1246"},"modified":"2015-07-28T23:26:01","modified_gmt":"2015-07-28T21:26:01","slug":"repair-of-a-sommerkamp-ts-788dx-coffee-warmer-3","status":"publish","type":"page","link":"https:\/\/dc2wk.schwab-intra.net\/?page_id=1246","title":{"rendered":"Repair of a Sommerkamp TS-788DX (Coffee-warmer 3)"},"content":{"rendered":"

Its unbelievable, I got one \ud83d\ude42
\nI have a Sommerkamp TS-788DX. The third Coffee-warmer.\u00a0That was a long dream from me \ud83d\ude00
\nAnd I payed not so much for it.\u00a0But it was sold as part broken.
\nThis is the TS788DX without cc. That means without the 10m repeater function.
\nhttp:\/\/www.sommerkamp-sprechfunk.de\/TS-788DX.html<\/a><\/p>\n

This sommerkamp has the problem, that you can’t change the frequency any more, when the radio is warm. If you wait leave it some hours off and you switch it on, it works again.
\nSomething like this is hard to find !<\/p>\n

\"IMG_4125\"<\/a>
\nSo I open it and see what it can be.<\/p>\n

\"IMG_4118_mark\"
\n<\/a>If I take Ice-spray and use it on that marked IC, it works again for some minutes.
\nTHis tree ICs in this area are NAND Gates for the Channel Selector and the up and down buttons.<\/p>\n

\"IMG_4107\"<\/a>
\nAt first I checked the Channel selector. It have a little bit bad contacts, but it works with contact spray. I checked also the four diodes at that switch.
\nThe problem is still here!<\/p>\n

\"IMG_4109\"<\/a>
\nThe I checked over 50 solder pins in more then one week work.
\nThe problem is still here!<\/p>\n

I use washers, under the board, that the circuit board is not braced
\nThe problem is still here!<\/p>\n

\"IMG_4121\"<\/a>
\n<\/a>Then I changed the other two ICs from that circuit.
\n<\/a>
\n\"IMG_4123\"<\/a>
\nI install sockets<\/p>\n

\"IMG_4124\"<\/a>
\nAnd checked the IC with a test board before I plug it in again.
\nAnd I change a lot of diodes around this ICs.
\nI re-solder all contacts at the upper side of this board.
\nThe problem is still here!<\/p>\n

I checked the schematic and the datasheet from the NAND gate and I think, I know now why !
\n\"IMG_4118_messung\"<\/a>
\nThe channel selector is wired with some pins of that IC. And they are comes together at the red marked pin. If you change the frequency, this pin is high and has near 7V.
\nThis is a NAND (not and) gate.
\nSo If the yellow marked pin has no volts and the red one has 7V, the green marked pin has always 7V volts and is high. If you change the frequency or not!<\/p>\n

We know now that the channel selector the switch the red marked pin high. But The yellow one must have volts too, to get the green one low!
\nOnly then its possible to change the frequency!
\nI try this out, give the yellow one 7V and the frequency is changed.<\/p>\n

I checked every part in this line. But I does not find whats broken. The voltage at this yellow pin is fluctuate from 0.30V to 6V! Alone! That not normally.
\nIf this voltage at the yellow pin is near so high as the red one, it works.<\/p>\n

I checked the blue marked IC too and I adjust the voltages (they are in the manual).
\nThat’s important for the step size and the frequency differences at 26.000 and 29.999 MHz.
\nThe problem is still here! But its better. I can work now with for many hours \ud83d\ude42<\/p>\n

After that and 3 weeks of work, I need a break. I clean everything with air.<\/p>\n

\"IMG_4131\"<\/a>
\nEverything looks clean now<\/p>\n

\"IMG_4132\"<\/a>
\nLooks nice and clean from the other side too.<\/p>\n

And build it together.
\n\"IMG_4137\"
\n<\/a>In that state I can work with for some QSOs. \u00a0Later I will continue with this project.<\/p>\n

Update 1:<\/strong><\/span>
\nI had try to give the pin with the missing voltage, the power what he need. I made a bridge from IC32 Pin 8 to IC31 Pin 9. Now the radio is working and i can use for change the frequency the UP and DOWN on the mike. But the Scanner is without function then.
\nEverything fine so far and I can life with. Maybe I have a better Idea later.<\/p>\n

I made some tests and a alignment
\n\"IMG_4142\"<\/a>
\nTwo tone test on USB. Not bad so far.<\/p>\n

\"IMG_4143\"<\/a>
\nThe clearness of SSB.<\/p>\n

\"IMG_4148\"<\/a>
\nThe USB frequency with 1 KHZ modulation<\/p>\n

\"IMG_4147\"<\/a>
\nThe LSB frequency with 1 KHZ modulation<\/p>\n

\"IMG_4145\"<\/a>
\nThe AM modulation. I be not sure what I see here \ud83d\ude41 \u00a0But it sounds not bad.<\/p>\n

\"IMG_4157\"<\/a>
\nTh FM deviration is about 1.65 KHZ min. and 1.78 KHZ max.
\nIts clear but not so loud. More is not possible!<\/p>\n

\"IMG_4149\"<\/a>:
\nThe frequency on FM and AM.
\nThe frequency drifts from cold state to warm state over 1 KHZ! After 1 hours it is stable<\/p>\n

Update 2:<\/strong><\/span><\/p>\n

I have done a modification with the FM-Mod. I replaced the C166 from 0.033uF to 0.1uF and I add to the resistor R287 a second one from 47kOhm.
\n\"IMG_4166\"<\/a>
\nNow are 2.6KHZ derivation not a problem.
\nThe power is via a 40db attentuator. So 0.69mW are 69Watts on FM \ud83d\ude42
\nThe FM mod is a little bit better now. The USB Mod is still not so fine, but it works.<\/p>\n

Update 3:<\/span><\/strong><\/p>\n

After some Weeks of fun with this radio, I leave it yesterday run with receiving a frequency the hole day. I did not transmit yesterday. In the late evening, I see that the red light (SWR protection) is on. I switch the radio off and on again, but the light goes not off. \ud83d\ude41<\/p>\n

So I check the schematic, how this SWR protection is working.
\nThe D89 is a Thyristor. The gate of this become a positive voltage from the reflecting of the SWR bridge. Then the D89 is switching and the red light bulb become minus.
\nThis circuit blocks also the working of the TR16 over the TR17, and no output is come out of the transceiver. \u00a0If the transceiver is switched off and on, the\u00a0Thyristor is a sort time powerless, he blogs the minus of the light bulb, and the red light is off.
\nSo if this problem happend, it can be that the D89 or the TR17 is broken. In my case was it a bad solder pad in the area of TR17.
\nIt cost me over 4 hours, to find this. Now it’s working again.<\/p>\n

lets see how long \ud83d\ude42
\nSee the Videos of this radio:<\/span><\/p>\n