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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 16th Jun 2017, 1:26 am   #1
otronics
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Default HMV Radiogram Model 2342 Broken Radio

Hello.

The radio (FM, MW and LW) does not work on my unit.

No signs of bulging caps, tin-whiskers transistors etc.

Where else should I start looking?

Many thanks.

Oliver.
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Old 16th Jun 2017, 7:59 am   #2
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Default Re: HMV Radiogram Model 2342 Broken Radio

I assume it works as a record player?

You could try cleaning the wave change switches. If that doesn't work you'll have to take voltage readings.
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Old 16th Jun 2017, 11:14 am   #3
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Default Re: HMV Radiogram Model 2342 Broken Radio

Hi.

Yes, the record player works.

I will try some contact cleaner on the wave change switches although as all bands are dead, I expect a component has blown.

Any idea where I should take voltage readings from?

Many thanks.
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Old 16th Jun 2017, 11:19 am   #4
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Default Re: HMV Radiogram Model 2342 Broken Radio

Readings should be taken with respect to the chassis. the expected results are shown in the service sheet.
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Old 16th Jun 2017, 11:21 am   #5
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Default Re: HMV Radiogram Model 2342 Broken Radio

Tin whisker AF117 ETC I expect as per your previous request on this forum.
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Old 16th Jun 2017, 11:40 am   #6
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Default Re: HMV Radiogram Model 2342 Broken Radio

The service sheet for this model is available http://www.service-data.com/section.php/3824/1/2342.

You dismissed the tin whisker transistor problem in your first post but the early version is fitted with AF11x transistors in the AM front-end and the AM/FM IF amplifier; the later version is fitted with AF12x transistors in those positions and don't suffer from tin whiskers. So double check which transistors are fitted in your set.


Quote:
Originally Posted by otronics View Post
Any idea where I should take voltage readings from?
As the gram works and the radio (both AM and FM?) does not, suspicion falls on the IF amplifier. Measure the collector, emitter and base voltages (with respect to chassis as Graham says) on VT4, VT5 and VT6.
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Old 16th Jun 2017, 9:21 pm   #7
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Default Re: HMV Radiogram Model 2342 Broken Radio

* I have the service manual.

* I have cleaned the switch contacts - no change.

* Both AM and FM are not working.

* I have AF116 transistors - some of the pins are covered in insulation.
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Old 16th Jun 2017, 9:33 pm   #8
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Default Re: HMV Radiogram Model 2342 Broken Radio

AF116's suffer from the 'tin whisker' problem, as do all AF11x and OC17x series transistors
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Old 16th Jun 2017, 9:50 pm   #9
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Default Re: HMV Radiogram Model 2342 Broken Radio

Time for new transistors then?

I am getting voltage on one or two pins at best per transistor...
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Old 16th Jun 2017, 9:52 pm   #10
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Default Re: HMV Radiogram Model 2342 Broken Radio

Quote:
Originally Posted by otronics View Post

* I have AF116 transistors - some of the pins are covered in insulation.
The tin whiskers are inside the transistor, nothing to do with insulation on the leads.

Frank
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Old 16th Jun 2017, 9:56 pm   #11
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Default Re: HMV Radiogram Model 2342 Broken Radio

Ah ha. Thanks.
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Old 16th Jun 2017, 10:05 pm   #12
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Default Re: HMV Radiogram Model 2342 Broken Radio

I would still suggest that you take some voltage readings and check the results before you start changing transistors. At least they'd show which transistors were at fault.
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Old 16th Jun 2017, 10:07 pm   #13
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Default Re: HMV Radiogram Model 2342 Broken Radio

Should I be getting some voltage on all transistor pins?
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Old 16th Jun 2017, 10:18 pm   #14
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Default Re: HMV Radiogram Model 2342 Broken Radio

As Station X said in post 4 the expected voltages are shown on the service sheet.

The Base and Emitter voltages in the main will tend to be quite low.

See example in the snip.

Cheers

Mike T
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Old 16th Jun 2017, 10:19 pm   #15
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Default Re: HMV Radiogram Model 2342 Broken Radio

Quote:
Originally Posted by otronics View Post
Should I be getting some voltage on all transistor pins?
The voltages you should expect are shown in your manual.

An example is shown below with pinout details.

EDIT: post crossed with Mike, interestingly showing exactly the same example.
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Old 16th Jun 2017, 10:27 pm   #16
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Default Re: HMV Radiogram Model 2342 Broken Radio

I would add that switch S1A disconnects power from the radio section of the circuit when GRAM mode is selected, so checking for voltage there could be a good starting point.
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Old 16th Jun 2017, 10:32 pm   #17
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Default Re: HMV Radiogram Model 2342 Broken Radio

Quote:
Originally Posted by ukcol View Post

EDIT: post crossed with Mike, interestingly showing exactly the same example.
Great Minds Colin

Actually I chose that one as it was a less cluttered than VT6 and VT4 half is on another page so I guess yours was the same sort of thinking

Cheers

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Old 17th Jun 2017, 8:01 am   #18
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Default Re: HMV Radiogram Model 2342 Broken Radio

As a starting point, give all the AF1xx transistors a good tap, sometimes it gets them working for a while. You then know what the problem is.
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Old 17th Jun 2017, 9:16 am   #19
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Default Re: HMV Radiogram Model 2342 Broken Radio

Quote:
Originally Posted by Cobaltblue View Post
Actually I chose that one as it was a less cluttered than VT6 and VT4 half is on another page so I guess yours was the same sort of thinking
It was exactly.
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Old 17th Jun 2017, 11:08 am   #20
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Default Re: HMV Radiogram Model 2342 Broken Radio

Quote:
Originally Posted by Station X View Post
I would add that switch S1A disconnects power from the radio section of the circuit when GRAM mode is selected, so checking for voltage there could be a good starting point.
Thanks - that works fine as voltage is there.
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