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Old 23rd Jul 2021, 11:02 am   #69
Uncle Bulgaria
Join Date: May 2016
Location: Cornwall, UK.
Posts: 1,241
Default Re: Uher CR 210 Cassette Recorder Check Out

I hope my travails make your check-out rather easier! I'll make all the mistakes first. I was rushing as I hoped to give it back during an event my friend's running today, so there's a lesson in there somewhere.

Originally Posted by DMcMahon View Post
Really unfortunate the motherboard crack and annoying the overheating R67, I cannot easily see R67, is this on the motherboard ?
Yes, it's in square G7 on the 1-99 board diagram, just under the large capacitors directly to the rear of the loudspeaker DIN socket. It's top left of the Drive Assembly diagram (164241000 version), and seems to exist for this purpose - burn out in case of a drive short as it is on the 9.5V rail supplying the motor and drive electronics.

It's now burned out three times, and I've worked out that it's because the pad where the wire link to 905 is soldered (+ side of C28, H4 on board 1-99 on the 164241000 diagram) has a bizarre fault. Metering this pad shows high resistance to ground, but applying slight pressure reduces this to only a few ohms. This also occurs when manipulating the wire to 905 when it's soldered to the pad, as if the slight twisting is shorting something out. As I have the bottom cover off, no doubt in some orientations on the desk this pad is slightly compressed by the wires beneath the board, causing the intermittent short.

The motor stops, and all the current is dumped through R67 and it burns out.

The crack is nowhere near as bad as my CR 240, where it arrived with a break across about a third of the motherboard and I had to jumper a few dozen tracks. It's just across T1, the HF bias area, so when I sort the short I'll have to see if Record works or if I need to jumper the couple of connections around there.

Originally Posted by DMcMahon View Post
Sorry was getting boards 600 and 700 mixed up, 700 has 10 transistors. Is the 700 layout in the PDF manual different to your board, I think the PDF layout is the same as my service sheet.
My error - some BCE connections are inline rather than in the triangle I've got used to seeing on these diagrams, so there are more transistors on the 700 diagram than I realised. I have two diodes soldered across the back which are different from their positions in the diagram. I think they're D713 and D714. Their marked positions on the component side are taken up with a large tantalum capacitor. I had to replace D713 as it was behaving as a resistor, and D714 had broken away from one contact. D713 is marked as BA181, which appears to be an obsolete normal diode so I used a 1N4148.

Originally Posted by DMcMahon View Post
Yes know about the Accessory socket options but not sure about the centre pin connection for track 4 ?
My F111 attachment has no pin 6, and the CR 240 circuit diagram has no pin 6 connection on the socket, so I'm at a loss here. I haven't got a CR 210 user manual which might describe possible specific accessories, alas.

Originally Posted by DMcMahon View Post
A lot of work testing those small electrolytics, how are you proving that they are leaky, does your reformer box do low voltage so can measure the leakage current ?
I'm testing them with a homebrew ESR meter, checking them against one of those bought LCR testers, and reformed/leakage tested in my Everyday Practical Electronics tester which goes down to 10V. It takes a little while to build up if there's leakage, so if it's hanging at 4V on the 10V range with 0.6mA of leakage on a 6V capacitor, there's probably an issue!
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