Roberts Revival 250 PCB query

[martinhog]

Hi, just acquired a very clean but dead Revival 250. A good read through these posts show that it can be damaged easily by applying the wrong polarity voltage. As the battery connector has been played with, I think this is the case .
I dismantled it, however I could not see the audio output ic that often fails. I am wondering if several PCB versions were used ? The radio’s serial no. Is 4586 and the PCB is marked R717 1610890. I can hear a faint crackling through headphones if plugged in. No other tests have been carried out yet .All comments very welcome ,thanks .

[martinhog]

A quick update. Had a good look at the PCB, it features 78LO5, TA7358AP and TA8117N ic’s (totally different to my garage Revival).
The 78LO5 was dead so I replaced that. When connected to a good battery, the set draws 24mA. When connected to earphones, it will tune the FM band, however the sound is very distorted with noise on top of the audio. With the volume at minimum, the noise (oscillation ? ) is still present . With the headphones unplugged, the only sound is a barely audible crackle from the speaker. The speaker is OK.
Any comments/opinions welcome. I am thinking the TA8117N but it is working , sort of.
Many Thanks

[Paul_RK]

I think your serial number will mean the set is one of the relatively few with a case covering of genuine leather - tan, blue and yellow were the options I'm aware of. We've 50 "standard" R250 numbers on file at the Roberts group and the lowest of them is 200041, suggesting a likely start at 200001. Yours then would be among the earlier R250s, but I've no detail on the changes made in the course of production.

Paul

[David G4EBT]

Don't know if this thread is any use:

https://www.vintage-radio.net/forum/...oberts+Revival

There's a picture of where the audio IC was. Afer removing the fried one, I fitted a turned pin DIL socket for the new one.

It was a radio that belonged to my son, on which he inadvertently plugged in the wrong power connector and reversed the polarity. I had to replace the (long since obsolete) audio chip, an electrolytic cap and fried resistor. All for the sake of a penny diode which Roberts could/should have incorporated to prevent revers polarity. When I opened the radio up, I was shocked at what a heap of tat it was, with its SRBP PCB, tiny little speaker, and inaccurately machined MDF. (Style over substance. 'Lipstick on a pig' comes to mind).

Replacing the audio chip capacitor and resistor it restored the FM function, but restored but not AM. I assumed that was due to the SIL AM chip, but another forum member sad that switching from AM to FM a few times might clean the switch contacts, given that such radios are little used on AM. I'd meant to give that a try when I next visited my son, but never got round to it.

Maybe, as you say, your PCB is a different design. (I don't have the serial number of my son's radio or even if he still has it. Most likely gone to a charity shop by now).

If nothing else, many find their styling appealing. The Revival in all its iterations will have been quite a money-spinner for Glynwed, or whoever owns Roberts these days.

Every good wish in sorting yours Martin.

[martinhog]

Originally Posted by Paul_RK

I think your serial number will mean the set is one of the relatively few with a case covering of genuine leather - tan, blue and yellow were the options I'm aware of. We've 50 "standard" R250 numbers on file at the Roberts group and the lowest of them is 200041, suggesting a likely start at 200001. Yours then would be among the earlier R250s, but I've no detail on the changes made in the course of production.

Paul

Hi, the casing on mine is a shiny red covering and it does feel like leather. The serial number comprises of 4 digits only with no leading zeros. Thankyou .

[martinhog]

Originally Posted by David G4EBT

Don't know if this thread is any use:

https://www.vintage-radio.net/forum/...oberts+Revival

There's a picture of where the audio IC was. Afer removing the fried one, I fitted a turned pin DIL socket for the new one.

It was a radio that belonged to my son, on which he inadvertently plugged in the wrong power connector and reversed the polarity. I had to replace the (long since obsolete) audio chip, an electrolytic cap and fried resistor. All for the sake of a penny diode which Roberts could/should have incorporated to prevent revers polarity. When I opened the radio up, I was shocked at what a heap of tat it was, with its SRBP PCB, tiny little speaker, and inaccurately machined MDF. (Style over substance. 'Lipstick on a pig' comes to mind).

Replacing the audio chip capacitor and resistor it restored the FM function, but restored but not AM. I assumed that was due to the SIL AM chip, but another forum member sad that switching from AM to FM a few times might clean the switch contacts, given that such radios are little used on AM. I'd meant to give that a try when I next visited my son, but never got round to it.

Maybe, as you say, your PCB is a different design. (I don't have the serial number of my son's radio or even if he still has it. Most likely gone to a charity shop by now).

If nothing else, many find their styling appealing. The Revival in all its iterations will have been quite a money-spinner for Glynwed, or whoever owns Roberts these days.

Every good wish in sorting yours Martin.

Thank you David, a good read ! The article describes the “Revival” that is my garage radio perfectly. I think mine is in early version using another PCB ? It has R717 on the silk screen.
I am going to add a picture of the PCB if that assists anyone. .

Many Thanks again.

[SiriusHardware]

If you have some sort of audio tracer such as a scope or a small amplifier try 'listening' to each of the pins on the audio amplifier IC - if using an amplifier as the tracer it would be wise to have a DC blocking capacitor in series with the audio signal pickup probe because many if not most of the IC pins will have significant DC voltages on them.

If you can find small, but undistorted audio signals on at least some of the audio amp IC pins that will probably mean that you have good audio up to the audio amp IC, but not afterwards, suggesting that the audio amp itself is faulty.

Also look for something like a very low value, low wattage 'fuse' resistor in the +ve power feed to the audio amp IC - if there is one it may have burned higher-value without going open-circuit, in which case it will be causing power starvation to the audio amp so it can (sort of) function when producing low output to a medium impedance load, but not when asked to supply high output to a low impedance load, ie, speaker.

[martinhog]

Good morning, thanks for your reply, I will check that next. I am convinced the radio has been a victim to a reverse polarity connection. The previous owner has also killed the Roberts mains adaptor that came with it !

[Radiocruncher]

Hi Martin

It will almost certainly be the TA8117N. I’ve done a few sets similar to this and reverse polarity takes the voltage regulator and IC out. It could have damaged the audio IC as well but usually that survives.

Regards

Graham

[Hybrid tellies]

Just a useful note.
I have repaired two earlier versions of the R250 both of which use a 9v supply from a PP9 battery. Later versions used a 6v supply from either four C or D cell batteries.

Simon

[martinhog]

Good morning, thanks for all your replies.
Following advice from SiriusHardware, I can get clear audio at pin 19 of the TA8117N, but nothing if I feed a signal into pin 18. Pin 12 is at VCC. Like others have said, I think its the TA8117N (this chip also includes the audio stage of the radio) ?. Time to find one, they are scarce now, and put a diode inline with the positive feed. Thanks for all your help.

[martinhog]

Quick update: Managed to get a TA8117N from eBay, fitted this and the radio worked a treat. Added a schottky diode inline with the positive supply "just in case".
Many thanks for all your replies.

[Boulevardier]

Originally Posted by martinhog

Added a schottky diode inline with the positive supply "just in case".

Well done! The diode is an excellent precaution - I always fit one. Don't know why it isn't recommended standard practice - the small voltage drop rarely matters too much.

Mike

Don't know why it isn't recommended standard practice

It is in my book but mass manufacture saves every 0.01p it can though.

[David G4EBT]

Originally Posted by merlinmaxwell

It is in my book but mass manufacture saves every 0.01p it can though.

And boy, does that show in the Roberts Revival.

A masterstroke in cost minimisation, price maximisation (charging what the market will stand), and style over substance.

Still with the Royal Warrant too.

[Squipper]

I know I'm a bit late to this thread, and I'm pleased you got it sorted.

The Revival in this instance isn't an R250. It is a Revival 200.
Back in 1989, Martini ran an advert including an RT1, and their phones rang off the hook from people wanting to buy one. Obviously, they didn't make them anymore, and things were financially tight for the company. Richard Roberts commissioned a cabinet build to resemble the radio, and used the existing R717 model (which had sold relatively poorly), changing only the speaker and cosmetics. This worked particularly well for them, having just made 500 sets, they (very) quickly sold out. Richard then had 1000 more made (this time calling it 'Roberts Revival), which also sold out in a week, and there story of the Roberts Revival was born. That one set pretty much bailed them out of the mess they were in.
The earliest Revival 200 (I have one) had an HDF rotating base, (later models had rubber feet), and shiny aluminium control knobs / wave change (later ones plastic or painted aluminium)

In short, it's an R717 in a Revival 200 case. In any case, nice find, and glad it lives on.

[Graham G3ZVT]

Is that your 200 Paul?
The serial number suggests it was the second one off the line!

[Squipper]

Originally Posted by rambo1152

Is that your 200 Paul?
The serial number suggests it was the second one off the line!

Yes...

I have plenty of 'early' Roberts models

[Radiocruncher]

Great bit of history Paul and thanks for sharing the pictures of your set