PSU query

The regulated output on the left of that pic at TP1 is +4.9V the other output to the right labelled 6A is the switched battery voltage +5.3 to

piglet

Thanks, Erich. This design seems highly unusual to me and it's hard to work out what's going on here. I'm seeing minus 8V on the emitter of T8 which makes no sense to me. Es gibt keinen sinn! Does negative 8V WRT GND seem okay to you??

Yes that circuit does need careful analysis but what you see sounds correct. T7 and T8 keep dry battery separate from the rechargeable and do the switching in the negative rail so it may look strange at first glance.

Do you have dry cells installed as well or just the rechargeable? I am hoping that when switched ON (the switch between terminals 6A and 6B) you should see the voltage at T8 emitter to ground become a few tens mV instead as T8 conducts.

I worked a little on Uhers in Munich in the 1970s but always much preferred Nagras :)

piglet

piglet

Both Uhers and Nagras are becoming highly collectable now for some reason. There seems to be a renewed interest in tape. A used Uher Report Monitor in good working order can fetch over 500 euros currently. For Nagras - jeez - three or four times that price or more! You're obviously way better than I'll ever be when it comes to working out circuit diagrams, Piglet. I'll be for ever in your thrawl. I'm done today with the tonband but will take another look at it tomorrow. Thanks again.

It certainly did look very unusual indeed!

There are 3 options at least. You can put 7x D cells in the battery compartment. You can insert the monolithic NiCad battery into the same compartment. Or you can insert the PSU (which is the same dimensions as the NiCad block) into the battery compartment and run it from the mains supply, and that's what I've been doing for testing purposes. Despite there being power 'in' to the regulator board, there is nothing more than 0.7V to be found on any of the component leads. It should therefore be simple enough to trace the fault, which must obviously be very close to the 'power in' point.

Well, I have my doubts, as T8 is a prime suspect here. I'm very grateful for your expert advice here, Piglet. What a stroke of luck you worked for Uher back in the day.

CD.

Yup, turned out both T7 and T8 were blown O/C as expected. Strangely low spec choice of transistor for a position in the circuit like that. Must have been on the ragged edge a high percentage of the time....