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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 29th Jul 2020, 9:53 pm   #41
crackle
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Default Re: Midland 77-810UK "Ready Rescue"

I have extracted the detail from the PDF at 600dpi I can then view it easier in PSP than using an adobe viewer.

Adjusting t2 was not very successful, I could not get the voltage anywhere near 3.5v.
The voltage was initially 2.196 and I could not increase it much more but I found if I wound the slug out the pulsing stopped, at 2.192v.
On tx the voltage was initially 1.310v at 1.308 the pulsing stopped.

Mike
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Old 29th Jul 2020, 9:55 pm   #42
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Default Re: Midland 77-810UK "Ready Rescue"

I hope you mean T1, not T2?
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Old 29th Jul 2020, 10:45 pm   #43
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Default Re: Midland 77-810UK "Ready Rescue"

S##T I wish I had the service information with layout drawing I am making mistake after mistake.
Hopefully Restoration73 is posting it to me.

What does T2 do then?
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Old 29th Jul 2020, 10:59 pm   #44
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Default Re: Midland 77-810UK "Ready Rescue"

No need to panic.

You measured the control voltage on pin 17 before you adjusted T2, so just adjust it back until the voltage is exactly the same as it was before... this only applies if you still have NOT adjusted T1, because adjusting T1 will have a much more dramatic effect on the control voltage on PLL pin 17.

If T1 is still exactly as it was you should be able to recover the original position of T2, or something pretty close, by adjusting it for the same VCO control voltage you originally had on pin 17, presumably on channel 20 RX mode.

Then (and only then) try adjusting T1 as advised.
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Old 30th Jul 2020, 8:16 am   #45
crackle
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Default Re: Midland 77-810UK "Ready Rescue"

Panic over, the radio is working again, about 5 watts on the output.
I have to appologise for not picking up on this comment and assuming my old Farnell L30/2 bench supply would be OK.
Quote:
Originally Posted by G6Tanuki View Post
Are you running it into a decently-shielded RF dummy-load? And is your power-supply known to be RF-immune?
I switched to using the Farnell supply because it had low current limiting (200mA or 2A), I thought it would be more suitable for when I was prodding around the board testing for the dry joint. At this point I had not fitted an inline fuse in the power cable and I was worried about the full 30 amps of my other supply being shorted.

I have just re-set T2 to give 2.867v on pin 17 (ch40 RX).
Then set the volts to 3.5 by adjusting T1. The slug was very deep in the former and it took a while to dig out the wax. I thought it would be better to dig it out cold rather than heat it and risk more wax running into the threads.

The problem was still there, then I thought I would try the idea of plugging into my Diamond GSV3000 Linear PSU. This showed the problem with the pulsing was not there.

So thanks to everyone especially SiriusHardware for his patience and excellent well explained methodical tests.

I will have a go at tweaking CT1 now to set the frequency.
R73 is sending me the manual, when it turns up I will update the thread with a copy.

Its horrible when you think you have been the cause of a fault, but luckily it was only the driver transistor that was damaged. The rest of the problem was me trusting in my old faithful Farnell PSU.

In the meantime here is a layout drawing I made.
Click image for larger version

Name:	IMG_5374 pale.jpg
Views:	58
Size:	80.3 KB
ID:	212195

Thanks again guys.
Mike

Last edited by crackle; 30th Jul 2020 at 8:21 am.
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Old 30th Jul 2020, 9:02 am   #46
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Default Re: Midland 77-810UK "Ready Rescue"

Good call by G6Tanuki, glad you got there by whatever means.
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Old 30th Jul 2020, 9:33 am   #47
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Default Re: Midland 77-810UK "Ready Rescue"

I managed to chat to my friend in Rochester, about 14 miles from Basildon.
Mind you that was on my 5/8 wave Imax 2000 antenna.

Mike
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Old 30th Jul 2020, 11:24 am   #48
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Default Re: Midland 77-810UK "Ready Rescue"

It's obviously alive and well. Just one question, when the transmitter was originally working, which PSU were you running it on then, your 30A one?
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Old 30th Jul 2020, 11:37 am   #49
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Default Re: Midland 77-810UK "Ready Rescue"

Yes, the 30 amp Diamond one, but I changed to the 2 amp one switched to 200mA for when I was poking around looking for the dry joint, as I felt that was a safer bet.
The radio draws just over 0.5A on TX. So the Farnell supply should have powered it. Must be the RF getting in to the PSU and upsetting it, though I am surprised there cant be much "intelligence/data" involved with the Farnell PSU.
Mike


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Old 30th Jul 2020, 11:41 am   #50
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Default Re: Midland 77-810UK "Ready Rescue"

You could try putting a 0.1uF capacitor between the +ve and -ve terminals on the Farnell PSU and give it another go.

It certainly was (and is) sensible to use a current limited supply when working on a suspected faulty item. That big PSU of yours could quite easily vapourise a track or two in the time it would take you to switch it off.
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Old 30th Jul 2020, 4:37 pm   #51
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Default Re: Midland 77-810UK "Ready Rescue"

Here is a PDF file of the service information pages of the Maxcom 7E Alert Mobile Transceiver. maxcom_7e_service.pdf
The file is compressed to 40% to fit the 4M limit.
The full user manual including schematic and layout drawings in higher resolution (10Mb file) is available here. http://www.kbmuseum.org.uk/other_ser...COM_7E_AMT.pdf

Thanks to Restoration 73 for making this available for all.

Mike
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Old 30th Jul 2020, 5:00 pm   #52
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Default Re: Midland 77-810UK "Ready Rescue"

Ah, that's lovely, thanks to both of you for that. I'll save and also print it and put a copy in my box file.

Maxon could almost always be relied on to put a layout diagram in their manuals, it's a pity the other manufacturers didn't follow suit.
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Old 30th Jul 2020, 5:18 pm   #53
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Default Re: Midland 77-810UK "Ready Rescue"

Yes it came out really well for such a small document, the print was small but very good quality.
The whole document was scanned at 300DPI.
The important layout drawings were re-scanned at 600DPI, and the schematic at 1200dpi then reduced to 70%.
The document is will soon be on its way back to Restoration73.
Its now deposited here, in the Radio Museum and the whole document is on my website.
Mike
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Old 30th Jul 2020, 5:55 pm   #54
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Default Re: Midland 77-810UK "Ready Rescue"

Thanks for doing that Mike. These radios tend to get little use and survive well. Unlike
a handy, they might have been a bit big with the front panel microphone.

The main two CB makers Maxon and Cybernet made radios of quite good quality which had to meet FCC requirements as their main market.
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Old 30th Jul 2020, 7:02 pm   #55
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Default Re: Midland 77-810UK "Ready Rescue"

Not forgetting the other major Japanese manufacturer, Uniden (they made most of the Cobras, Superstars, etc). Maxon were Korean, as a glance at the rear plate on any Maxon-built mobile CB radio will show.
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Old 30th Jul 2020, 7:44 pm   #56
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Default Re: Midland 77-810UK "Ready Rescue"

Yes, Uniden, think they used TC9119 PLL. Whilst some US ham radio manufacturers
made some CB equipment, I only remember Yaesu devising official conversions to 11m
for some of their amateur sets. In Japan there was CB around 900MHz that was very
popular, unlike our former 934 UK allocation.
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