Grundig Hit Boy 310 - UK Vintage Radio Repair and Restoration Discussion Forum

poppydog · 17th May 2016, 10:53 pm

I wasn't going to bother posting this on here but I thought somebody might gain a little help from it.

In the beginning this radio had an intermittent on/off switch, sometimes it would turn on, sometimes it wouldn't but the switch side was underneath the pcb. Once opened I found the pcb had heavy blobs of black sealant all round the mounts, even the retaining screw for the board had some sort of thread lock sealant on it. I had to cut the black sealant away before the board even moved and then once it did move it didn't move much as the speaker wires (wire wrapped) gave very little movement. Once the speaker wires were removed the board came out. The switch was covered in black fluff as there is no cover over it. Once that was cleaned it worked for a few seconds then stopped, it was then I found that the earphone socket was faulty so that was quickly de-soldered, a piece of folded wet and dry rubbed between the contacts a couple of times sorted that out. It worked for a little while then the speaker decided to give up the ghost, so another was pinched from another Hit Boy. A couple of electrolytic caps were replaced and so was the fuse and I then had power on mains and battery (I did think someone had replaced a couple of the caps but that was not so).

All was ok apart from I didn't have any AM, servisol down the wave change switch didn't seem to work, and this is where I did have to have some help from a very kind gentleman who pointed me in the right direction and told me exactly what to do and look for. I carried out continuity tests on the wave change switch - that was ok. I bridged a couple of suspected diodes with a known good and that didn't make any difference. Next on the list was the AM oscillator transistor, this tested ok with the ohms meter so I tested the voltages and these were not good. However, when I put my probe onto the base of the transistor it burst into life. The solder joints were checked and resistor values were checked only to find the schematic had an incorrect value on one of them, it read 820ohm when it should have been 820kohm. I quickly whipped another transistor out of my other 310, soldered it in and it was perfect. BF241s were ordered and as the lead orientation was different I had to bend and twist to fit (which I hated doing), after these were sleeved, voltages were checked again and all was ok. The radio receives all stations on all wavebands LW, MW and FM loud and clear (admittedly I am very high where I live), however, it does perform very well

Everything was cleaned and reassembled, I even resealed the board as it was originally. The way this radio was put together and 'sealed' I don't think it was ever meant to be serviced/repaired.

I know this radio probably isn't to everybody's taste, but being made in the late '70s its about 38 years old so I would say its 'vintage' and its my first 'proper' repair using, I guess, proper diagnosis but I did say I had a little online outside help.

One notch on the bedpost for the no knowledge brigade.

Regards
Poppydog

GeoffK · 18th May 2016, 10:03 am

These Grundigs are very smart radios, a bit of a shame that Grundig had to have them made in the far east to be competitive. Well done on getting this repaired Poppydog, it had a variety of faults, the on/off switch is usually the first thing to fail on an otherwise working radio, then the earphone socket. It is unusual for the speaker to go faulty so it would be interesting to know just what was the fault with this. Curious that the speaker connections where wire wrapped, unusual for a small far east made radio when all the other connections where soldered. The electrolytic capacitors in low voltage transistor radios usually last without giving fault, so seldom need changing though if it has a built in mains power supply the capacitors here might be more vulnerable. And finally finding the fault with the AM stage was the mixer transistor, worth checking with the meter, the lower base bias with the additional meter resistance in parallel to the base resistor must have been enough to make the transistor conduct. It certainly doesn't help when the schematic has such a mistake with the resistor value. A very good comprehensive write up, and useful information on what could be a stock fault with this model. Congratulations on your first repair, now it's on to the next one!

poppydog · 23rd May 2016, 10:30 pm

Good grief Hetrodyne, you have stolen my thunder with that reply. I couldn't have put it better myself. I don't seem to get many replies to my posts but that one is worth a thousand.

Yes I am pleased with the outcome (no cock-ups).

Quote:

Originally Posted by Hetrodyne

and useful information on what could be a stock fault with this model. Congratulations on your first repair, now it's on to the next one!

There maybe a stock fault with this model so I may post a question on my original Hit Boy 310 posts in the domestic radio section.

Regards
Poppydog

17th May 2016, 10:53 pm	#1
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Grundig Hit Boy 310 I wasn't going to bother posting this on here but I thought somebody might gain a little help from it. In the beginning this radio had an intermittent on/off switch, sometimes it would turn on, sometimes it wouldn't but the switch side was underneath the pcb. Once opened I found the pcb had heavy blobs of black sealant all round the mounts, even the retaining screw for the board had some sort of thread lock sealant on it. I had to cut the black sealant away before the board even moved and then once it did move it didn't move much as the speaker wires (wire wrapped) gave very little movement. Once the speaker wires were removed the board came out. The switch was covered in black fluff as there is no cover over it. Once that was cleaned it worked for a few seconds then stopped, it was then I found that the earphone socket was faulty so that was quickly de-soldered, a piece of folded wet and dry rubbed between the contacts a couple of times sorted that out. It worked for a little while then the speaker decided to give up the ghost, so another was pinched from another Hit Boy. A couple of electrolytic caps were replaced and so was the fuse and I then had power on mains and battery (I did think someone had replaced a couple of the caps but that was not so). All was ok apart from I didn't have any AM, servisol down the wave change switch didn't seem to work, and this is where I did have to have some help from a very kind gentleman who pointed me in the right direction and told me exactly what to do and look for. I carried out continuity tests on the wave change switch - that was ok. I bridged a couple of suspected diodes with a known good and that didn't make any difference. Next on the list was the AM oscillator transistor, this tested ok with the ohms meter so I tested the voltages and these were not good. However, when I put my probe onto the base of the transistor it burst into life. The solder joints were checked and resistor values were checked only to find the schematic had an incorrect value on one of them, it read 820ohm when it should have been 820kohm. I quickly whipped another transistor out of my other 310, soldered it in and it was perfect. BF241s were ordered and as the lead orientation was different I had to bend and twist to fit (which I hated doing), after these were sleeved, voltages were checked again and all was ok. The radio receives all stations on all wavebands LW, MW and FM loud and clear (admittedly I am very high where I live), however, it does perform very well Everything was cleaned and reassembled, I even resealed the board as it was originally. The way this radio was put together and 'sealed' I don't think it was ever meant to be serviced/repaired. I know this radio probably isn't to everybody's taste, but being made in the late '70s its about 38 years old so I would say its 'vintage' and its my first 'proper' repair using, I guess, proper diagnosis but I did say I had a little online outside help. One notch on the bedpost for the no knowledge brigade. Regards Poppydog Attached Thumbnails Last edited by poppydog; 17th May 2016 at 11:03 pm.

18th May 2016, 10:03 am	#2
GeoffK Heptode Join Date: Mar 2016 Location: Essex, UK. Posts: 602	Re: Grundig Hit Boy 310 These Grundigs are very smart radios, a bit of a shame that Grundig had to have them made in the far east to be competitive. Well done on getting this repaired Poppydog, it had a variety of faults, the on/off switch is usually the first thing to fail on an otherwise working radio, then the earphone socket. It is unusual for the speaker to go faulty so it would be interesting to know just what was the fault with this. Curious that the speaker connections where wire wrapped, unusual for a small far east made radio when all the other connections where soldered. The electrolytic capacitors in low voltage transistor radios usually last without giving fault, so seldom need changing though if it has a built in mains power supply the capacitors here might be more vulnerable. And finally finding the fault with the AM stage was the mixer transistor, worth checking with the meter, the lower base bias with the additional meter resistance in parallel to the base resistor must have been enough to make the transistor conduct. It certainly doesn't help when the schematic has such a mistake with the resistor value. A very good comprehensive write up, and useful information on what could be a stock fault with this model. Congratulations on your first repair, now it's on to the next one!